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What is the difference between a foot valve and a check valve?

In short, a foot valve and a check valve are very similar in that they automatically open or close depending on system pressure, allowing flow in only one direction and preventing backflow. Figure 1 shows a check valve on the right and a foot valve on the left, with the main visual difference being that the foot valve has a strainer on it. Given the similarities between the two valves, there are important differences. Foot and check valves have different installation locations in a system, different material requirements, and different designs. This article will focus on these key differences. Read our comprehensive articles about check valves and foot valves to learn more about each type of valve.

Operation principle

Understanding how check and foot valves work is helpful before discussing their differences. Both valve types open when the inlet pressure is above the valve’s cracking pressure. The cracking pressure is the minimum amount of pressure required to open the valve and overcome the force keeping the valve closed (spring or gravity). When the inlet pressure reduces below this limit, or there is backpressure, the valve closes shut.

Differences between check valves and foot valves

Design

Foot and check valves have a variety of design types, for example, ball check valves and ball foot valves. This section, though, focuses on the design differences that exist between all check and foot valves.

  • Screen: The first visual difference is the screen attached to the foot valve’s inlet end, which is often called a strainer or filter. Foot valves typically sit submerged in water in a well. The screen prevents larger debris from entering the foot valve and sticking the valve’s disc open and damaging other components within the system. A check valve does not have this protection and therefore is not applicable for media that has large solids in the flow.
  • Threading: A check valve has threading on both sides. So, a check valve fits into any part of the piping deemed appropriate. Removing a section of the pipe and installing a check valve is a straightforward process. Foot valves, however, have threading only on one side. Therefore, foot valves are only suitable for the end of a pipe, which is the end of a pump’s suction line.

Material

The key material difference between foot and check valves is that foot valves are in water for the duration of their use. Therefore, whichever material selected must be corrosion resistant. Materials often chosen are PVC, heavy-duty cast iron, bronze, and stainless steel.

Check valves have a wider range of material options because they operate in a wider range of environments. When selecting a check valve material, first understand the system’s pressure, temperature, and operating environment. Read our chemical resistance guide to learn more.

Installation

Because foot valves work on pump systems, this section will only cover the installation locations of check and foot valves on these systems. Both valves stop media from flowing back into the well when the pump turns off, thus keeping the pump primed.

A jet pump uses a foot valve at the very end of its suction line. In contrast, a submersible pump has a foot valve directly installed on its inlet. Both pump systems can use check valves in the same locations. However, this is not suitable for any wells that may contain solids large enough to get stuck in the valve and hinder its operation.

Deep well systems use one or more extra check valves along the suction line to protect the submersible pump and foot valve from the water column’s pressure. Shallow well systems may have a check valve on the suction line. Also, check valves can install directly at the jet pump’s inlet or between the jet pump and pressure tank. Beyond stopping backflow into the well, check valves are applicable anywhere where backflow may damage an upstream component or contaminate upstream media.

Foot valve and check valve P&ID symbols

Figure 2 depicts a check valve symbol (left) and a foot valve symbol (right).

Check valve symbol (left) and foot valve symbol (right).Figure 2: Check valve symbol (left) and foot valve symbol (right).

Summary

Table 1: Comparison between foot valve and check valve

Foot valve Check valve
Design A foot valve has a strainer on the inlet side. A check valve does not have a strainer.
Material Foot valves have a limited selection of materials: stainless steel, heavy-duty cast iron, PVC, and bronze. Check valves have more material options because they do not rest in water.
Application Foot valves are used for suction lift applications, like a well pump. Check valves are applicable for pump systems and any system that requires backflow prevention.
Installation Foot valves only go at the end of a pump’s suction line. Check valves can go at the end of a suction line, in the middle of the suction line, and anywhere else in the system where necessary.
Threading Foot valves have threading on the outlet side only. Check valves have threading on both sides.

FAQs

What is the difference between a foot valve and a check valve?

A foot valve has a screen on its inlet side to prevent large solids from entering the valve. Also, it fits at the end of a suction line in a pump system. A check valve is suitable for any system, including pump systems, that require media to flow in only one direction.

Can a check valve be used in place of a foot valve?

Yes, a check valve can be used in place of a foot valve. However, check valves do not have a protective screen and any large solids in the media can stick them in the open position.

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How to Select the material for Gate Valve

Selecting the right gate valve material is crucial in the gate valve selection process. Various materials are used for the gate valve’s body and seal. The material selection depends primarily on the media type and design temperature. This article discusses the common materials used in gate valves and how to find the right one for each application.

Gate valve material selection

Gate valves are used in a wide range of applications, and they come in contact with diverse media. It is critical to consider the material used for valve construction to prevent premature valve failure and system delays during valve operation. Consider the following criteria to select the proper materials for a gate valve:

  1. Media composition (whether clear or filled with particles)
  2. Material compatibility with the media used
  3. How long the valve gets exposed to the media
  4. Operating pressure
  5. Service temperatures
  6. Effectiveness of coating on materials
  7. Material availability and cost

Gate valves are available in various materials, as discussed in the next section. Various organizations are committed to developing and maintaining standards for valves and materials in specific environments. For example, gate valves are specified by the American Petroleum Institute (API) and the National Association For Corrosion Engineers (NACE) for their suitability to work with heavy corrosive media.

Gate valve body materials

The various materials used to construct gate valve body are discussed below.

PVC gate valve

PVC gate valve gate-valve-pvc.jpegFigure 2: PVC gate valve

In a PVC gate valve, the valve’s three main components, namely, the handle, housing, and gate, are made of PVC.

PVC gate valve features

  • PVC gate valves are not damaged by freezing temperatures, and these valves can also withstand temperatures up to 60°C.
  • Resistant to corrosion, making these valves ideal for chemical processing applications involving highly corrosive substances.
  • PVC valves are affordable compared to metal valves.
  • Excellent durability offering many years of reliable use.
  • Available in a wide range of sizes.

PVC gate valve applications

PVC gate valves are a good low-cost solution for most flow control needs at home. These valves are durable and corrosion-resistant, hence widely used in aquatic environments. A few common applications are:

  • Aquatics and aquaculture
  • Landscaping and irrigation
  • Tank drain valves and septic systems
  • Indoor plumbing
  • Spas

Brass gate valve

In applications where PVC gate valves would burst, it is a viable option to use gate valves made of metals or their alloys.

Brass gate valve features

  • Brass gate valves work on 0-16 bar pressure range with media temperatures from -20°C to 120°C. Hence, they can withstand higher temperatures and pressure than PVC gate valves.
  • Brass is stronger than PVC, but stainless steel is the strongest.
  • Brass gate valves are costly compared to PVC gate valves, but less costly than stainless steel gate valves.

Brass gate valve applications

Brass can withstand more heat than PVC, making them an ideal choice for residential plumbing applications. Brass is extremely corrosion resistant, and the gate valves made of brass are ideal for manufacturing industries involving natural gas or potable water.

Stainless steel gate valve

Stainless steel gate valveFigure 3: Stainless steel gate valve

Stainless steel gate valve features

  • Stainless steel is the most durable, heat-resistant, and corrosion-resistant material when compared to brass and PVC.
  • Withstands very high temperature (up to 800°C) and pressure. Stainless steel can withstand a wide range of temperatures (low to high) and pressure compared to brass and PVC.
  • Used to manufacture gate valve body and internal parts
  • Stainless steel gate valves have a simple body design enabling ease of repair, cleaning, and maintenance
  • Used in applications involving liquid, gas, and steam
  • Expensive compared to PVC, brass, and bronze gate valves
  • Needs a large area for installation compared to brass or PVC

Stainless steel gate valve applications

Stainless steel is extremely durable and corrosion-resistant, hence used in marine and industrial applications. Some common applications are:

  • Industrial applications like transporting natural gas and crude oil
  • Slurry applications
  • Drinking water applications at home as the material doesn’t leach into the water

Bronze gate valve

Bronze gate valveFigure 4: Bronze gate valve

Bronze gate valve features

  • Excellent machinability, strength, and corrosion resistance
  • Used to manufacture relatively small gate valves in low-pressure applications
  • Bronze gate valves are typically used for water pipes and equipment pipelines of about 300 psi (20 bar) or less, and temperatures in the range -20° C -150° C.
  • Higher cost compared to PVC, but less than brass and stainless steel
  • Bronze has higher corrosion resistance than cast iron, but less than PVC or brass.
  • Costlier than PVC but the cost is lower than brass or stainless steel.

Bronze gate valve applications

Bronze has high lead content; hence the material is not used frequently for drinking water applications. Bronze is commonly used for fluid control in low-pressure manufacturing industries and works well with steam, air, and gas. The material is also used in HVAC and marine applications.

Cast iron gate valve

Cast iron gate valveFigure 5: Cast iron gate valve

Cast iron gate valve features

  • Cast iron has strength lying in between bronze and stainless steel
  • Used to manufacture gate valve body
  • Very low tensile strength and elongation properties, but good casting qualities
  • Cast iron gets corroded over time.
  • Less costly compared to all other valve materials.

Cast iron gate valve applications

Cast iron is used for constructing gate valves in low-pressure and low-temperature applications. The material is a popular choice for gate valves in water, wastewater, heating, ventilation, and air-conditioning (HVAC) units. Cast iron gate valves are extremely cheap, yet sturdy; hence these valves are more suitable for underground applications than steel valves.

Cast steel gate valve

Cast steel gate valve feature

  • Casted carbon steel is a tough material, and the material is hard with excellent tensile strength and impact value.

Cast steel gate valve application

  • Gate valves made of cast steel are commonly used in industrial plants for high temperature and pressure applications.
Cast steel gate valves used in industrial plantsFigure 5: Cast steel gate valves used in industrial plants

Gate valve seal materials

Gate valve seats are available in two forms:

  • Integrated-type: The gate valve seal is made of the same material as the valve body and it is integrated into the valve body.
  • Ring type: In this type, the gate valve seal is in the form of a ring that can be either pressed in or threaded which favors more variation. The seat can be coated with polytetrafluoroethylene (PTFE) to aid high-integrity shutoff. The ring-type seal is again classified into resilient-seated and metal-seated gate valves:
    • Resilient seated gate valves: The gate is mostly composed of ductile iron and enclosed in a resilient elastomer material like ethylene propylene diene monomer (EPDM) forming a tight seal. These valves are preferred in water distribution systems because of the tight shut-off.
    • Metal-seated gate valves: Ductile iron is commonly used as the gate material, and rings are made of bronze to ensure a watertight seal.
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What is the difference between standard port and full port ball valves?

A ball valve is a type of valve that controls the flow of fluids through piping systems. Depending on the intended application, ball valves have a variety of designs. Based on the port size, a ball valve can be classified as either a full port, standard port, or reduced bore ball valve. This article compares the various advantages and disadvantages of each ball valve type. Read our ball valve overview article for more details on the working and design of ball valves.

Ball valves based on port size

Full port ball valve

A full port or full bore ball valve is a type of ball valve where the inlet and outlet pipes have the same diameter as the bore in the valve. In simple terms, the valve port is the same size as the pipe resulting in a full flow ball valve. For a full port ball valve, there is little or no resistance to the flow of fluids, and the flow path is straight.

Standard port ball valve

In a standard port ball valve, the size of the bore in the ball is smaller than the size of the inlet and outlet pipes. The diameter of the flow path through the ball valve is narrower on the interior. The standard port ball valve creates resistance to flow, increasing its fluid pressure. The flow path is usually straight.

Reduced port ball valve

In reduced bore ball valves, the port in the ball valve is one pipe size narrower than the inlet and outlet pipes. In other words, the diameter of the bore is one specification smaller than the pipes’ diameter specification. The fluid flowing through a reduced port valve has a higher velocity.

Full port (left) and reduced port (right) ball valvesFigure 2: Full port (left) and reduced port (right) ball valves

Comparison between full port, standard port, and reduced port ball valves

As the features of reduced port and standard port ball valves are identical in all aspects both valve types are grouped into one throughout the comparison process as seen below.

Port size

  • Reduced/standard port ball valves: The valve port is smaller than the pipe diameter.
  • Full port ball valves: The size of the valve port is the same as that of the pipe diameter.

Media

Media is the fluid flowing through the pipes and the ball valve. The media can be solids, liquids, or gases.

  • Reduced/standard port ball valves: Reduced or standard port ball valves are helpful to convey plain fluids like gasses or water. These valves transport light media in general.
  • Full port ball valves: The full-bore ball valves are suitable forviscous fluids because it offers little or no flow resistance. Examples of viscous fluid include paraffin, glycerin, etc.

Pipeline and flow control

  • Reduced/standard port ball valvesReduced and standard port ball valves offer a flow resistance, thus producing a pressure drop. The flow path through the valve becomes narrower on the valve’s inside. Reduced or standard port ball valves are ideal for relaxed working conditions where pressure drop does not affect pipe performance. This is because these valves reduce the velocity of the medium and hence suitable for applications where flow resistance is acceptable.
  • Full port ball valves: A full port ball valve has a straight flow path and offers little or no resistance to the media flow. The flow path through a full port ball valve does not become narrower on the inside. Full-bore ball valves are the only option for piping systems under strict working conditions. Underground pipes, regardless of the medium, must only use full port ball valves. When it comes to pipeline control, full port valves are ideal.

Pigging applications

Pigging is the process of cleaning a gas pipeline where a device known as a pig travels through the pipeline. This process is not supported by certain valve types that do not allow the free travel of pig through the connected valve.

  • Reduced/standard port ball valves: Reduced port ball valves have different diameters for the bore and connecting pipe; hence the pigging device cannot travel freely through a reduced bore ball valve for cleaning purposes.
  • Full port ball valves: In an open state, the bore of a full-port ball valve is parallel to the inlet and outlet ports; hence, there is no visual difference between the valve and pipe bores. In this way, a pig can have an unrestricted flow through the valve, thereby cleaning the bore of the valve along with the entire pipeline.

Cost

  • Reduced/standard port ball valves: A reduced or standard port ball valve has a compact body and thus lower costs.
  • Full port ball valves: Purchasing a full port ball valve requires a larger initial investment than purchasing a reduced port ball valve. The full port is more expensive because many materials are used in its construction. Because of its effective performance, a full-port ball valve is cost-effective in the long run.

Fitting space

Fitting space is the amount of space the ball valve will occupy when installed.

  • Reduced/standard port ball valves: A reduced/standard port ball valve has a small volume and thus requires little space.
  • Full port ball valves: A full-port ball valve has a large volume necessitating more space.

Transportation

  • Reduced/standard port ball valves: The small volume and lightweight properties of a reduced port ball valve make it easy to transport.
  • Full port ball valves: The full-port ball valve is heavy and has a large volume. This makes its transportation difficult and costly.

Full port ball valve with a drain

A full port ball valve with a drain is essential for preventing fluid or condensation buildup inside the valve. Failure to drain the valve can damage the valve. Draining is done to replace contaminated and stale fluids within the valve. Draining relieves any pressure that has built up within the valve. To drain a ball valve, first, allow fluid to flow into the drain by opening the valve. Then, close the valve to prevent fluid from flowing through it. Finally, open the valve and allow the fluid to drain. Read our article on condensate drain valve for more information.

3-way full port ball valve

A 3-way full port ball valve has three ports. These valves are available with either an L or T-port design. The L and T designation refers to the internal bore design, determining the media’s flow direction. A 3-way ball valve with a T or L port allows for mixing, distribution, or diverting the flow direction for different applications. To open a 3-way, rotate the ball until the ports are aligned with the corresponding ports, allowing fluids to flow through. To close, rotate the ball back to the closed position. When the ports are closed, they are out of place and not aligned with one another.

Comparison chart

Table 1: Comparison between standard/reduced and full port ball valve port designs

Standard/reduced port ball valve Full port ball valve
Pipeline control Not ideal Ideal
Cost Low initial cost High initial most
Fitting space Less More
Transportation Easy Difficult
Pigging applications Not ideal Ideal

FAQs

What is the difference between standard port and full port ball valves?

In a full port ball valve, the ports of the valve have the same diameter as the connecting pipes. The valve port size is smaller than the pipe diameter in a standard port ball valve.

Why is the standard port more common than the other types of ball valves?

The design of a standard port ball valve is convenient for most applications. It is compact, relatively light, and less expensive.

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Which valve is better between globe valves and ball valves?

Globe valves and ball valves are both shut-off valves typically used in piping systems. However, it is usually not immediately obvious which valve is most suitable for an application. System design should be finished before valve selection in order to select the best valve for the job in terms of cost, installation space, flow control, and more. Keep reading to learn more about how a globe valve may be more suitable than a ball valve and vice versa.

Working principles

Globe valve working principle

A globe valve in the open position (left) and the closed position (right) with the valve stem (A), stem (B), plug (C), and body (D).Figure 2: A globe valve in the open position (left) and the closed position (right) with the valve stem (A), bonnet (B), plug (C), and body (D).

A globe valve is a multi-turn valve, meaning that the handwheel needs to be turned more than 360° to fully open or close the valve. The main components of a globe valve are the valve body, bonnet, handwheel, stem, and plug. Media flows into the valve body (Figure 2 labeled D) through an inlet and exits the valve body through an outlet. The bonnet (Figure 2 labeled B) protects the threaded components of the valve and attaches to the valve body. As the user turns the handwheel, it turns the threaded stem (Figure 2 labeled A), which raises or lowers the plug (Figure 2 labeled C). Raising the plug opens the orifice, thereby allowing media flow. Lowering the plug into the valve seat seals the orifice, preventing the flow. Raising the disc, on the other hand, increases the flow rate. The flow rate is maximum when the disc is raised to its maximum position. The fluid flow rate is controlled by moving the disc proportionally through the stem.

Ball valve working principle

Ball valve parts; Stem (A), o-rings (B), body (C), ball (D), and seat (E)Figure 3: Ball valve parts; Stem (A), o-rings (B), body (C), ball (D), and seat (E)

A ball valve is a quarter-turn valve, meaning that the handle only needs a 90° turn to fully open or close the valve. The main components of a ball valve are shown in Figure 3. The stem (Figure 3 labeled A) connects to the ball (Figure 3 labeled D). The ball sits on the ball valve seat (Figure 3 labeled E), creating the seal. O-ring stem seals (Figure 3 labeled B) are used to prevent leakage. All of these components are within the valve housing (Figure 3 labeled C). As seen in Figure 3, the ball has a bore running through it. Under normal operation, the bore is either aligned with the valve ports to allow flow, or perpendicular to the ports to block flow. Read our article on ball valves for more details on how they work.

Flow control

Globe and ball valves are both used to turn on or off the flow. Globe valves, though, can also function in a partially open or closed state to modulate the flow. This flow regulation is achievable due to the globe valve’s disc sitting parallel to the flow. The linear flow rate achieved by globe valves is higher than that achieved by ball valves, and reduces the effects of water hammer.

Head loss

Globe valves have significantly higher pressure loss (head loss) in the fully open position than ball valves. This is because the fluid has to change direction multiple times as it passes through a globe valve.

Valve design

Globe valve design

Globe valves are available in three basic configurations: T- or Z globe valve, Y-globe valve, and angle globe valve. Read our article on globe valves for more information on each type.

Ball valve design

The ball valve can be classified into different categories depending on its housing structure, ball design, and port size. Depending on the housing structure, we can have 1, 2, or 3-piece ball valves. Depending on the port size, ball valves are categorized as full port ball valves, standard port ball valves, or reduced port ball valves. And depending on the number of ports, ball valves are classified into 2-way and multiport valves.

Symbols

  • Figure 4 shows the symbols for various globe valve configurations.
Globe valve symbols: globe (A), hand operated (B), pneumatic (C), motor operated (D), hydraulic operated (E).Figure 4: Globe valve symbols: globe (A), hand operated (B), pneumatic (C), motor operated (D), hydraulic operated (E).

The symbols for a ball valve are shown in Figure 5. For more details on the symbols of various ball valve configurations, read our article on ball valve symbols.

Actuated ball valve symbols; manually operated ball valve (A), pneumatically actuated ball valve (diaphragm type) symbol (B), pneumatically actuated ball valve (rotary piston type) symbol (C), electrically actuated ball valve symbol, and a hydraulic actuator ball valve symbol (D).Figure 5: Actuated ball valve symbols; manually operated ball valve (A), pneumatically actuated ball valve (diaphragm type) symbol (B), pneumatically actuated ball valve (rotary piston type) symbol (C), electrically actuated ball valve symbol (D), and a hydraulic actuator ball valve symbol (E).

Applications

Globe valves are used to control fluid flow. Furthermore, globe valves are advantageous in applications requiring precise throttling. Ball valves, on the other hand, are commonly used for plumbing system shut-off and isolation. Industrial applications for globe valves include fuel oil systems and cooling water systems, while those of ball valves include chemical storage and natural gas industries.

Globe valve and ball valve similarities

Globe valves and ball valves share some similarities. Both valves are used in piping systems to control the flow of liquids and gasses. Both are shut-off valves designed to allow or block the fluid flow within a pipe. Globe valves and ball valves can be operated manually or automatically.

Pros and cons of ball valves and globe valves

  1. Operation: Ball valves are simple and easier to operate than globe valves.
  2. Throttling: Globe valves are suitable for throttling operations, whereas ball valves should be either fully shut or fully open.
  3. Handle: Ball valves are quarter-turn valves which means the ball valve handle must be turned by 90° to go from fully open to a fully closed state or vice versa. The handwheel of globe valves must be turned multiple times from entirely closed to fully opened.
  4. Cost: Due to their simple structure, ball valves are cheaper than globe valves.
  5. Space: Globe valves occupy more space compared to ball valves.
  6. Pressure rating: Ball valves can handle higher pressure than globe valves.
  7. Durability: Ball valves are longer-lasting than globe valves.
  8. Leakages: Globe valves are more prone to leakages than ball valves.
  9. Media flow resistance: A globe valve offers more resistance to media flow compared to ball valves.
  10. Head loss: Globe valves have a higher head loss than ball valves.

Globe valve and ball valve selection

The selection between a ball valve and a globe valve depends on the intended purpose. The main factors to consider during the selection process are discussed below:

  1. Flow rate: Ball valves are desirable in applications where a high flow rate is necessary due to their full-bore design.
  2. Pressure drops: Ball valves have lower pressure drops because flow moves straight through them.
  3. Maintenance: Ball valves are simple to maintain because the valve only needs a little lubrication to stay clean. Further maintenance is necessary upon debris buildup.
  4. Temperature: Ball valves function better under high-temperature conditions due to their durable construction.

FAQs

What are the typical applications of a globe valve?

Globe valves are used commonly to control water flow in irrigation systems, regulate airflow in AC systems, and control oil flow in pipelines.

What is the main difference between a ball valve and a globe valve?

The ball valve has a hollow ball that rotates inside the valve, whereas the globe valve has a disc that moves vertically through the valve stem.

Which valve is better between globe valves and ball valves?

This depends on the intended application. Globe valves are better for throttling applications, while ball valves offer better performance as shutoff valves.

View our online selection of globe and ball valves!

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What is the advantage of gate valves over globe valves?

Despite their similarities at first inspection, globe and gate valves have significant differences that make each suitable for their applications. When choosing between these two valves for an application, understanding the application’s pressure, sealing, and flow requirements can ensure the correct valve is selected. This article discusses the differences between globe and gate valves to allow an educated decision before choosing between the two valves.

Globe valve vs gate valve comparison

Globe valves and gate valves are multi-turn, linear motion valves, meaning both valves require multiple turns to open or close. The closing mechanism moves up and down in a straight line to turn open or close the valve. At this point, similarities between the valves begin to diminish.

The globe valve differs from most valves because its name derives from its body shape (rounded) rather than its disc, which is the gate valve’s convention. Its disc moves up and down to allow or block the flow, similar to a gate. Read more on globe valves and gate valves to get a comprehensive understanding of both.

Flow properties

As seen in Figure 2, a gate valve is a straight-through, bi-directional valve, meaning its design permits flow directly through it in both directions. The only change to the flow occurs when the gate valve is closed, and the flow stops.

A gate valve flow properties when it is closed (left) and open (right).Figure 2: A gate valve flow properties when it is closed (left) and open (right).

A globe valve, on the other hand, has more turns for the flow path. As seen in Figure 3, the flow can take a z-shaped path (T- or Z-valve), an oblique path (Y-valve), or a 90° turn path (angle valve).

Because a globe valve diverts flow in a specific way, it has an inlet and an outlet port. Typically, an arrow on the outside of the valve’s body will indicate the valve’s flow direction. Also, the flow diversion causes a significant pressure drop through the globe valve. In contrast, a gate valve’s pressure drop is nearly non-existent.

Globe valves' flow paths: T- or Z-valve (left), angle valve (center), and Y-valve (right)Figure 3: Globe valves’ flow paths: T- or Z-valve (left), angle valve (center), and Y-valve (right)

Valve functions

Both gate valves and globe valves can operate as on/off valves. A gate valve is not meant to bused to throttle flow, but a globe valve can. Flow diverts within the globe valve and becomes parallel to the valve seat. This design makes globe valves efficient flow throttlers. Globe valves become unsuitable for throttling flow at larger diameters (above DN 150). Gate and globe valves can be operated mechanically, pneumatically, or electrically.

Note: With other factors equal, Y-valves are the least efficient at throttling flow because the valve seat is not parallel to the flow direction. However, this also means that Y-valves have the smallest pressure drop.

Visual differences

At a quick glance, gate valves and globe valves are not easy to tell apart. The following traits are what to look for to tell the difference:

  • Body: Gate valves usually have a rectangular or wedge-shaped body. Whereas the body of a globe valve is rounder, especially at its bottom.
  • Maximum height: Gate valves usually are higher when opened than globe valves.
  • Flow direction indicator: Gate valves are bi-directional, whereas globe valves are unidirectional. A marker on the valve, such as an arrow, indicates the flow direction and that it’s a globe valve.

Advantages and disadvantages chart

Globe and gate valves may have similar or different materials for their housing and seals. Read our chemical resistance guide to learn more about the advantages and disadvantages of the various materials. See the following chart to learn about more advantages and disadvantages.

Table 1: Globe valve and gate valve advantages and disadvantages chart

Globe valve Gate valve
Application Used for flow regulation (e.g., cooling water systems and fuel oil systems) More suitable for slurry due to less space in the valve’s body for sediment to get stuck and build up
Flow control Can be used or on/off control and can throttle flow Can be used for on/off control and cannot regulate the flow
Flow capacity Lower Higher
Flow direction Unidirectional Bi-directional
Flow restriction/pressure drop Flow diversion within the valve’s body creates significant pressure drop Full-bore valve, meaning there is no reduction to flow and pressure drop is insignificant
Power requirement Needs a large amount of force or an actuator to close under high pressure Needs less power to close under high pressure
Operating conditions Can operate at higher temperatures Can operate at higher pressures
Cost More expensive than a gate valve due to its complicated structure Cheaper
Leakage More effective sealing because force is applied to the disc when closed Good sealing properties
Installation space Takes up less vertical space, but requires more horizontal space If a rising-stem style, needs more vertical space, but less horizontal space
Weight Heavier Lighter
Ports Can have a 3-port configuration for straight-through flow Two ports

Selecting between globe valves and gate valves

Gate valves and globe valves are both excellent shut-off valves. However, when choosing between them, neither valve will outperform the other in every single application. Consider the following factors:

  • Flow control: Select a globe valve if an application requires flow modulation.
  • Flow capacity: Choose a gate valve if an application demands high flow.
  • Flow direction: Choose a gate valve if an application requires bi-directional flow.
  • Pressure drop: Select a gate valve if a minimal pressure drop is necessary.
  • Sealing: If an application demands excellent sealing, select a globe valve.
  • Contaminated media: Choose a gate valve if an application has slurry or other contaminated media.

The above variables are typically the most important when selecting a shut-off valve. Refer to Table 1 for further information.

Example applications

Globe valves

  • Cooling water systems: Globe valves operate in cooling water systems by controlling the water flow to maintain a desired temperature.
  • Chemical injection systems: Globe valves work well in industrial systems that need control over chemicals into reaction vessels or process streams.

Gate valves

  • Bulk material handling systems: Heavy-duty processes (e.g., mining, agriculture, and construction) use gate valves to control the flow of bulk materials such as grains, coal, and aggregate.
  • Water distribution systems: Many components of a water distribution system do not require precise flow control. Therefore, gate valves are suitable because they either block or allow flow.

FAQs

Which is better? A gate valve or a globe valve?

Globe valves have better sealing than gate valves and last longer. However, gate valves have significantly lower pressure drop.

What is the advantage of gate valves over globe valves?

One significant advantage of gate valves over globe valves is that they require significantly less power to close since they close perpendicular to flow rather than parallel as globe valves do.

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What is the difference between a gate valve and a plug valve

Plug and gate valves are both stop-valves suitable for a wide array of applications and media types. For example, they can both be used for clean media and media containing solids or stringy material. Therefore, it may be difficult to determine which is more suitable for a specific application. This article looks closer at the similarities and differences between gate valves and plug valves to help ensure the correct valve is chosen and used for varying applications.

Before deciding between the two valves, it is important to consider the following:

  • The number of ports needed
  • How fast the valve needs to operate
  • The pressure and temperature of the planned system
  • Installation space available

  • Plug vs gate valve comparison

    Plug and gate valves are named after the method that each uses to allow or block flow. A plug valve uses a plug with an opening running through it. When a gate valve is closed, its disc sits perpendicular to and blocks the flow, operating much like a gate.

    Operating principles

    Plug valves are quarter-turn valves, meaning the valve stem needs to turn only 90° for the valve to fully open or close. With mechanical lever actuation (pneumatic and electrical actuation are also possible), the valve’s lever is turned 90° to accomplish this. When turned on, the opening in the plug is in line with the ports, and media can flow through the valve. Closing the valve rotates the plug, so the opening is no longer aligned with the ports, and the plug’s body blocks the flow.

    Gate valves are multi-turn valves, meaning the valve stem needs to turn more than 360° for the valve to fully open or close. Therefore, a gate valve closes significantly slower than a plug valve. Turning the valve’s handwheel (mechanical actuation) can raise or lower the disc within the valve’s body. Fully raising the disc allows media to flow unobstructed, and fully lowering the disc blocks the media. Discover more by reading our gate valve and plug valve articles!

    Plug valve design

    Plug valveFigure 2: Plug valve

    The four distinguishing design characteristics of a plug valve are the plug shape, plug opening, whether the valve is lubricated or non-lubricated, and the number of ports.

    Plug shape

    • Cylindrical: This shape allows for a larger opening but has a shorter life span.
    • Tapered: This shape has a restricted opening but typically lasts longer.

    Plug opening

    • Rectangular: This opening is the most common; the size of the opening is at least 70% of the connecting pipe’s inner diameter.
    • Round: This opening can be full-bore or reduced-bore design.
    • Diamond: This opening has a venturi restricted flow type and is designed for throttling flow.

    Lubricated vs non-lubricated

    • Lubricated: The valve’s parts are entirely metal. Lubrication reduces friction between the plug and valve body, acts as a seal, and prevents corrosion.
      • Before lubricating a plug valve, consult the plug valve’s manufacturer to determine the correct lubricant to use.
    • Non-lubricated: A Teflon or plastic sleeve fits around a tapered plug, which presses the sleeve against the valve body for better sealing. Non-lubricated plug valves require minimal maintenance and are unsuitable for high-temperature applications.

    Ports

    • Double-port: A standard, bidirectional design used as a full-bore or reduced-bore valve.
    • Multiport: 3-way plug valves are common, but 4-way and 5-way are also possible. Multiport plug valves are used in transfer lines and diverting services. A single multiport plug valve can take the place of multiple gate valves.

    Gate valve design

    Beyond how to actuate a gate valve (mechanically, pneumatically, or electrically), the primary distinguishing design characteristics are the valve’s disc, how the bonnet connects to the valve body, and whether the stem is rising or non-rising.

    Disc types

    • Wedge: This type has a high wedging force which assists with sealing due to its wedge shape that sits on two inclined seats.
    • Knife: This type can cut through thick fluids and dry solids that build up using its beveled edge.
    • Double-disc: This type uses two discs that expand from one another to give a tight seal.
    • Slab: This type is one piece with a hole bored through it. The hole aligns with the ports, allowing flow, when the gate is fully open and the disc body blocks flow through the ports when the gate is fully closed.

    Bonnet types

    • Welded: This type is less likely to leak because it is threaded into the valve body and the body-bonnet joint is welded.
    • Bolted: This type is suitable for high-pressure and large valve size applications.
    • Screwed: Normally used in small size valves, this is the simplest type of bonnet construction.
    • Pressure sealed: As pressure within the valve increases, the body-bonnet joint seal increases. This type is used typically for high-pressure applications above 100 bar.

    Rising vs non-rising stem

    • Rising stem: The stem moves up or down as the valve opens or closes.
    • Non-rising stem: The stem remains within the valve as the valve opens or closes.

    Advantages vs disadvantages chart

    There are many materials available for plug and gate valves, so finding the right material for an application is possible. Learn more by reading our chemical resistance guide!

    Tbale 1: Plug valve vs gate valve

    Plug valve Gate valve
    Installation space Requires less space but has a long handle relative to valve size that must be considered Requires more space, particularly space above for rising stem valves
    Response time Quarter-turn valve, faster Multi-turn valve, slower
    Operation frequency Designed for more cycles Designed for infrequent cycles
    Leakage Can provide a bubble-tight shutoff Strong sealing capabilities except for low-pressure systems
    Corrosion/Wear Less corrosion and wear on the stem because it doesn’t sit in the flow path. May cause water hammer if incorrectly operated. The stem sits in the flow path and will experience more corrosion and wear
    Pressure Excellent design for low-pressure systems More suitable for high-pressure systems and may leak if used in low-pressure systems
    Temperature Lubricated plug valves are more suitable for high-temperature applications than non-lubricated plug valves Suitable for higher temperature systems but check with the manufacturer as too high of temperatures may warp the valve body, which will cause the disc and seats to become unaligned
    Flow control Provides on/off functionality and diamond opening plug valves can throttle flow Can only provide on/off functionality. Throttling flow will damage the valve.
    Flow restriction/Pressure drop Plug valves with restricted openings cause some pressure drop, full-bore plug valves are available Full-bore valve, pressure drop is insignificant
    Flow capacity Lower Higher
    Flow direction Bidirectional and multiport Bidirectional
    Power requirement Higher under high pressure Lower under high pressure
    Torque High, especially under high pressure Low

    FAQs

    Is a plug valve full bore?

    A plug valve’s plug opening can be full bore but is also available in reduced flow for applications where pressure drop is not a large concern.

    What is the difference between a gate valve and a plug valve?

    A big difference between a gate and plug valve is that a gate valve is multiturn, and a plug valve is quarter-turn. So a plug valve can be opened or closed faster than a gate valve.

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Gate Valve vs Butterfly Valve

Gate and butterfly valves are both used to turn on and off the flow, but butterfly valves can also regulate flow via partial disc closure. Butterfly valves are part of the quarter-turn family of valves and can be shut off much faster than gate valves, which are multi-turn valves. Gate valves are preferable for high-pressure systems whereas butterfly valves are preferable for larger port sizes.

Gate valves

How does a gate valve work?

A gate valve is named after its disc, which behaves like a gate by either stopping or allowing media flow. It has a simple operation compared to other control valves, which makes it one of the most commonly used valves. Because a gate valve is a full-port valve, which means that the valve’s ports are the same size as the inner diameter of the connecting pipes, there is very little resistance to liquid or gas media that flows directly through it. Therefore, the pressure drop through the valve is quite low. For a more extensive understanding, read our article on gate valves.

Operating a gate valve

Gate valves are multi-turn valves, meaning the handwheel must turn more than 360° to fully open or close the valve. Turning the handwheel in one direction or the other moves the gate up or down via the stem. When the gate is completely up, the passageway is unobstructed, and media can flow. When the gate is down, media is blocked and cannot flow. Gate valves cannot modulate or throttle flow because there is a nonlinear relationship between the gate’s travel and flow rate. If the gate is partially open, the flow will crash into it while traveling through the valve, causing the flow to move at a higher velocity and create turbulence, both of which lead to increased wear on the disc and seats.

The three common means for actuating a gate valve are manually, pneumatically, or electrically. The manual method requires an on-site user to spin the handwheel to open or close the valve. This method is the most cost-effective since gate valves are not typically opened or closed often. The pneumatic and electric solutions allow for remote operation of a gate valve. Pneumatic actuation requires a pneumatic system on-site and electrical actuation requires electrical power on-site.

Gate valve types

As mentioned above, there exist different styles of gate valves. Three factors typically determine a gate valve’s style: the gate type, the bonnet type, and the stem type.

Gate type refers to the disc that blocks the flow when the valve is closed, for example:

  • Wedge disc: The gate is shaped like a wedge and it sits on two inclined seats. This provides a high wedging force which assists with sealing.
  • Knife disc: The gate is a piece of metal with a beveled edge like a knife. It can be used to cut through thick fluids and dry solids.
  • Double disc: The gate is two discs which sit on two seats. The discs expand away from each other to provide a tight seal.

Bonnet type refers to how the bonnet is attached to the valve body. It can be:

  • Screwed: This is the simplest type of bonnet construction and is normally used in small size valves.
  • Bolted: These bonnets are used in larger valves and high-pressure applications.
  • Welded: The bonnet is threaded in and the body-bonnet joint is welded. This offers extra protection against leaking.
  • Pressure sealed: The body-bonnet joint seal enhances as pressure within the valve increases. Used typically for high-pressure applications above 100 bar.

Stem type refers to the position and action of the stem

  • Rising vs non-rising: Rising stem gate valves require more space above the valve than non-rising.
  • Remains within the valve vs rises out of the valve upon opening: Rising out of the valve makes the stem easier to lubricate.

Materials

The correct material depends on the application’s fluid service and temperature. Common materials used for a gate valve are:

  • Body and bonnet: cast steel, stainless stell, cast iron, gunmetal, bronze, brass, and PVC
  • Disc: stainless steel, polypropylene, Teflon, rubber lined (e.g., wedge disc)
  • Seal: EPDM, NBR, Teflon

These materials allow for a range of applications, so gate valves apply to relatively mild applications like household plumbing to more corrosive applications such as use in saltwater environments. For more information, read our chemical resistance guide.

Butterfly valves

How does a butterfly valve work?

The essential operation of a butterfly valve is achieved by turning its handle 90° or using a pneumatic or electric actuator. This turns the valve’s stem, which rotates the disc. In the fully closed position, the disc is perpendicular to the flow, and in the fully open position, the disc is parallel to the flow. Partial opening or closing of the disc can achieve proportional or throttled flow rates. In cases of a large butterfly valve or a valve used in a liquid application for which fast closure could produce water hammer, a butterfly valve can be gear operated via a gearbox (Figure 2, right). The gearbox’s handwheel must be turned more than 90°, though, which eliminates the butterfly valve’s relatively fast closing speed. For a more comprehensive understanding, read our article on butterfly valves.

A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the rightFigure 2: A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the right

Butterfly valve types

There are two key topics when discussing types of butterfly valves: body and stem offset. Body refers to how the valve’s body connects with piping, and stem offset refers to whether the stem passes through the center of the disc or is offset.

The butterfly valve body types are:

  • Double-flanged: This design is typically used for larger butterfly valves.
  • Wafer: Most cost-effective design; sandwiched between two pipe flanges.
  • Single flange: This design uses bolts and nuts passed through the valve’s holes to connect to both sides of the piping.
  • Lug type: This design has threaded inserts, and bolts are used to connect pipe flanges to each side. Suitable for removing piping from one side without affecting the other.
  • Flangeless: Like the wafer style, this design is sandwiched between two pipe flanges.
  • Butt-welding ends: Prepared for welding directly to piping.
  • U-section: Also clamped between pipe flanges and suitable for end-of-line service.

The stem can pass through the centerline of the disc (concentric) or be offset behind the centerline (eccentric). Offset, which can be single-, double-, or triple-offset, is used to reduce how much the disc rubs against the seating while closing. The higher the offset, the more the disc moves towards fully closed before contacting the seal. Any rubbing against the seal can reduce the service life of the valve. High-performance butterfly valves are specifically designed to withstand more demanding applications in terms of pressure and temperature.

The following compares a high-performance butterfly valve with a standard butterfly valve:

  • Maximum shutoff pressure: Approximately 50 bar (725 psi) vs approximately 14 bar (203 psi)
  • Tight shutoff: Below 260°C (500°F ) vs below 120°C (248°F)
  • Shutoff with allowable seat leakage: Below 538°C (1000°F) vs below 425°C (797°F)

Read our article on butterfly valve design differences article for more details on the features of each design type.

Materials

The valve’s body and seat materials should be chosen carefully based on the needs of the application. Common body materials are iron, stainless steel, carbon steel, nickel alloy, titanium alloy, and nickel aluminum bronze. These materials vary in weight and resistance to corrosion and extreme temperatures.

Common seat materials are EPDM, EPDM white, FKM, XNBR, and NBR. Depending on the seat material, a butterfly valve can be used in temperatures ranging from -10°C to 180°C. Resilient and metal seated butterfly valves are also available, using the same materials listed here, and are designed to operate under more extreme temperatures and pressures.

Gate valves vs butterfly valves

There are many factors to consider when deciding whether a gate or butterfly valve is correct for a given application. Below are some of the most important:

  • Cost: A butterfly valve is typically less expensive than a gate valve, especially at larger port diameters.
  • Installation space: A butterfly valve takes up less installation space than a gate valve.
  • Weight: A butterfly valve weighs less than a gate valve; the latter may need support structures at larger port diameters.
  • Maintenance: While a butterfly valve is relatively easy to maintain, repair, or install due to its small size and low weight, its center disc makes it not suitable for systems that use pigging and swabbing for cleaning purposes. On the other hand, a gate valve is ideal for such maintenance.
  • Operation: A butterfly valve can close faster than a similar port diameter gate valve. However, this fact means that butterfly valves are more susceptible to water hammer.
  • Flow regulation: A butterfly valve can modulate or throttle flow, whereas a gate valve can only be on/off.
  • Flow resistance: A gate valve offers less flow resistance and, therefore, less pressure drop than a butterfly valve.
  • Pressure: Gate valves can handle higher pressures than butterfly valves.

Applications

  • Gate valves have a higher sealing tightness, and therefore are more suitable for applications that require zero leakage.
  • Butterfly valves are more suitable for applications that require flow modulation or throttling.
  • If a slurry flow does not need to be modulated, gate valves are preferable to butterfly valves.
  • Gate valves are more suitable for systems that require bi-directional, uninterrupted flow.

FAQs

Which is better, a gate valve or a butterfly valve?

A gate valve has a stronger seal and is more suitable for high-pressure applications. A butterfly valve is less expensive and available in very large sizes.

Can a butterfly valve be used instead of a gate valve?

A butterfly valve can be used instead of a gate valve in low-pressure systems for which some leakage is not a major concern.

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Idea to know Pneumatic Valve Materials

Pneumatic valves control the rate, pressure, and flow direction of compressed air and gasses in industries. These valves control the air or gas at the source and regulate its movement into hoses, tubes, or devices as needed in an automated pneumatic system. Pneumatic valves are commonly available in various housing materials like stainless steel, brass, aluminum, and industrial-grade plastics like PVC and have seal materials like NBR, FKM, and EPDM. Selecting the suitable material for a valve is crucial for its working. This article discusses the various types of materials used in pneumatic valve

What is a pneumatic valve?

Pneumatics is the technology that makes use of gas or pressurized air. A pneumatic system utilizes a compressor to reduce the air volume to increase its pressure. The air (or gas) is filtered and passed through pneumatic hoses, pipes, or tubes. During this transit, the air is controlled by valves, after which it reaches an actuator like a cylinder or a device that performs a function, for example, moving, lifting, or gripping.

A pneumatic valve controls the pressure, flow rate, and direction of air and gasses. According to these applications, a pneumatic valve is classified into the following categories:

  • Pneumatic pressure relief valves: Pressure relief valves keep the system pressure below a preset maximum value.
  • Pneumatic flow control valves: Flow control valves are used in pneumatic systems to govern the rate at which a media (liquid or gas) is allowed to flow. Flow control valves can typically be unidirectional or bidirectional.
  • Pneumatic directional control valves: Directional control valves like solenoid valves are used to start, stop, or direct airflow in a pneumatic system. By directing the flow of air, these valves control the action of other pneumatic devices like motors, cylinders, pumps, or other valves.

Know your process media

Pneumatic valves have two distinct contexts of use in general:

  1. A pneumatic valve is a device used to control the flow of air or other gasses in a pneumatic system. The valve can be actuated manually, electrically through a solenoid, motorized, or pneumatically. In this case, the media being controlled is air or gas, and hence the materials chosen for the valve body and seal should be compliant with these media. Possible options include aluminum, stainless steel, brass, and industrial-grade plastics
  2. Air can be used as a control mechanism for the valve, but in this case, the media flowing through the valve may be something other than air like oil, water, or other fluids. Here it is necessary to check how compliant the valve housing material is with respect to the various media. Read our article on the chemical resistance of materials to check the compatibility of various housing and seal materials with the media and environment used.

Driving pneumatic media or gas

The pneumatic media or gas (like an inert gas or CDA air) used in an automation control process is high conditioned, dried, and filtered. Therefore the valve design need not consider the aggressive media nature or account for the high purity level of the media. Industrial grade plastics (like PVC) can be used for these highly conditioned media.

Process fluids

Pneumatic valves for process fluids deal with highly acidic, corrosive, alkaline, or high purity media. Therefore, it is mandatory to select the construction materials suitable for protecting the media and the valve. Stainless steel is a great option for the valve housing material for aggressive and corrosive media. For neutral and non-corrosive media, brass is commonly used as the housing material.

Pneumatic valve housing materials

Always select the housing material suitable for the medium and the working environment. The housings of pneumatic valves for automation control are typically manufactured with a mix of different materials discussed below:

Industrial grade plastics (like PVC and nylon)

Plastic valves are lightweight, durable, and cost-effective. The material is suitable for pneumatic applications involving air and corrosive chemicals. But plastic valves have a low pressure and temperature rating compared to brass and stainless steel valves.

Brass

Brass is an alloy of copper and zinc, and it is an excellent forgeable and robust material. Brass is used in pneumatic applications involving non-corrosive gases. The material can withstand more heat compared to PVC but comes at a higher price. Brass can be easily welded, and it is more versatile when compared to stainless steel. Brass is commonly used to construct pneumatic valve bodies and end pieces.

Stainless steel (304/316)

Stainless steel is a very durable and resilient material, but it is more expensive than brass. Valves made out of stainless steel effectively resist leaks, and these valves can be operated at very high temperatures when compared to brass. Stainless steel is corrosion-resistant and lasts much longer compared to brass, and it is an ideal choice for high temperature and high-pressure pneumatic applications. Stainless steel is commonly used in the pneumatic valve bodies and trim materials like seats, discs, and wedges.

Aluminum

Aluminum is a lightweight metal that has approximately one-third the weight of steel. Aluminum is corrosion-resistant to atmospheric gases and hence suitable for pneumatic valve applications. The material is mainly used to construct the exterior components of the pneumatic valve, like the identification tags or handwheels.

Pneumatic valve housing material comparison table

Table 1: Comparison of different materials for pneumatic valve housings

PVC Brass Stainless steel Aluminum
Cost Low High Very high High
Durability Average High Very high High
Corrosion resistance High Average Very high Low-average
Operating temperature and pressure Low High Very high High
Weight Light Heavy Heavy Light

Pneumatic valve seal materials

Seals in pneumatic valves help prevent the escape of volatile and hazardous gasses into the atmosphere. The various types of seal materials used in pneumatic valves are the following:

NBR (Nitrile-butadiene rubber)

NBR has good resistance to compression and general wear and tear but is highly sensitive to weather changes. NBR is suitable for air and inert gasses but has poor resistance to ozone, ammonia, and steam. NBR seals can provide continuous sealing for gaseous media only at low temperatures compared to the sealing properties of FKM.

FKM (Viton)

FKM is typically used to manufacture O rings, gaskets, and seals for pneumatic valves. FKM seals have excellent resistance to the media, aging, and ozone. FKM is suitable for medium-high temperature pneumatic applications and has higher thermal resistance than PTFE. Also, FKM has superior strength, sealing capabilities, and flexibility when compared to PTFE. The material has excellent overall chemical resistance making it suitable for gaseous fuels, and the material shows more chemical resistance universally compared to NBR.

PTFE (Teflon)

PTFE is suitable for high temperature and pressure pneumatic applications. The material is non-elastic and has good resistance to wear and tear abrasion and most chemicals. PTFE offers superior resistance to gaseous chemicals as compared to FKM.

Materials for specific pneumatic valves

Directional control valves

Directional control valves are used in pneumatic systems to stop or direct the flow of compressed air or oil to their connected appliances. However, it is not recommended to use these valves for media other than air for most applications. Many pneumatic solenoid valves are piloted internally, and these valves vent a minimal amount of air required to actuate the valve. A small loss of air into the surroundings is acceptable in most applications but not in the case of oil, water, or other types of media. A few examples of materials for these valves that are compatible with the media and environment are:

  • Valve body: Aluminium, Plastic, Brass, Stainless steel
  • Seal: NBR, FKM, EPDM

Flow control valves

Pneumatic flow control valves are used to control the flow of media like a liquid or gas. These valves consist of a pneumatic actuator part and the valve part like a ball valve or butterfly valve. The actuator is mounted to the valve using a standard flange, allowing both the actuator and the valve portions to be swapped out with another one using the same flange size. Always choose the valve housing and seal materials to be compatible with the media used. A few options are:

  • Valve body: Cast iron, Stainless steel
  • Seal: EPDM

Pressure control valves

Pressure control valves reduce the pressure of incoming air to a set value at the output port. Brass is a viable choice for the valve’s body material, with a surface coating of nickel for added protection.

The material chosen for the connection cables and plugs used for transmitting the media to and from the valves should be compatible with the media chosen. Example:

  • Valve body: Polyurethane (for media like air, carbon dioxide, nitrogen, fuels, and oils)
  • Seal: EPDM

Pneumatic valve specifications

Knowing the valve materials is only one part of selecting a pneumatic valve. Some other factors to consider are discussed below.”

  1. Operating medium: The media types that the pneumatic valve can effectively control (compressed air in most cases)
  2. Flow capacity (Cv): Cv gives a measure of the valve capacity to move air through it
  3. Operating pressure: The range of pressure (in Pa, bars, or psi) that the valve is rated to handle
  4. Port size: The physical dimensional parameters that define the port sizes on the valve and the thread style
  5. Rated voltage of coil: For electrically actuated valves, the required voltage rating may be given in AC or DC volts.
  6. Response time: The amount of time required for the valve to switch states or positions once actuated.

Note: The discussed parameters are for general guidance only, and the individual valve suppliers and manufacturers may specify their valves differently.

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The different Stainless Steel 304 and 316

When selecting a valve’s housing material, it is important to know the differences between stainless steel 304 (EN steel number 1.4301) and stainless steel 316 (EN steel number 1.4401, 1.4436). Selecting between the two typically depends on an application’s corrosion resistance requirements. This article discusses the nature of each type of steel, how to choose between them, and how to determine which to use for a stainless steel valve.

What is stainless steel?

Steel, in general, consists of iron and carbon. Stainless steel, on the other hand, encompasses various steel blends containing at least 10.5% chromium by weight. These blends are primarily made to withstand corrosion or oxidation, which occurs when metals react with oxygen (in air or water) and form rust. Stainless steels are 100% recyclable.

When chromium (Cr), a durable metal, comes into contact with water or air, it undergoes a chemical reaction with oxygen. In stainless steel, chromium oxide forms a thin, stable film on the surface (Figure 2 labeled A), protecting the metal from corrosion by limiting oxygen exposure. This corrosion resistance process is known as passivation. The protective film can self-repair (Figure 2 labeled C) if scratched or disturbed (Figure 2 labeled B).

Stainless steel with a chromium oxide surface film. Chromium oxide intact (A), chromium oxide damaged (B), and chromium oxide self-reformed (C). The blue spheres are oxygen.Figure 2: Stainless steel with a chromium oxide surface film. Chromium oxide intact (A), chromium oxide damaged (B), and chromium oxide self-reformed (C). The blue spheres are oxygen.

Types of stainless steel

Varying the ratios of different elements has led to many kinds of stainless steel. Beyond chromium, other alloying elements are added to stainless steel, for example, molybdenum, nickel, and titanium. These elements enhance stainless steel’s formability, strength, and chemical resistance.

Austenitic stainless steel is the most widely produced family of stainless steel. It is created by alloying nickel, which gives it excellent formability and weldability. Stainless steels 304 and 316 are members of this family.

Stainless steel 304 vs 316

When selecting a specific grade of stainless steel for a given application, the first and foremost criterion is corrosion resistance. Other mechanical or physical properties may also need to be considered to meet service performance.

A stainless steel 304 pipe end stamped to indicate its steel gradeFigure 3: A stainless steel 304 pipe end stamped to indicate its steel grade

Corrosion resistance

Stainless steel 304 (EN steel number 1.4301) and stainless steel 316 (EN steel number 1.4401, 1.4436) have very similar physical and mechanical properties, but their primary difference remains in their resistance to corrosion in different environments:

  • 304 Stainless Steel
    • Contains 18% chromium and 8% nickel
    • Cost-effective choice if high concentrations of chloride are not present.
  • 316 Stainless Steel
    • Contains 16% chromium, 10% nickel, and an additional 2% molybdenum
    • The added molybdenum provides greater corrosion resistance to acids and localized pitting attack by chloride solutions such as seawater and de-icing salts.

The corrosion resistance of stainless steel in acidic or basic solutions depends on the kind and concentration of acid or base and the solution temperature.

A stainless steel 316 tee pipe fitting stamped to indicate its steel gradeFigure 4: A stainless steel 316 tee pipe fitting stamped to indicate its steel grade

Corrosion resistance to acids

Stainless steel type Resistance to acids
Stainless steel 304
  • Good resistance to moderately aggressive organic acids, such as acetic acid and formic acid
  • Prone to corrosion (e.g., pitting and crevice corrosion) by strong acids such as sulfuric or hydrochloric acids
  • Resistant to most concentrations of phosphoric acid and nitric acid but may have stress corrosion cracking in hot concentrated solutions
Stainless steel 316
  • Better acid resistance than stainless steel 304, especially if chloride ions are in the system
  • Better resistance to sulfuric acid than stainless steel 304. Can experience corrosion at concentrations above 20% or temperatures above 50 °C (122 °F)
  • Prone to corrosion by hydrochloric acids
  • Better resistance to phosphoric, acetic, formic, and tartaric acid solutions at a wide range of concentrations and temperatures

Table 1: Stainless steel 304 vs 316 resistance to acids

Corrosion resistance to bases

Stainless steel type Resistance to bases
Stainless steel 304
  • Good resistance to alkalis
  • Can withstand exposure to weak bases, such as sodium hydroxide or potassium hydroxide
  • May experience localized corrosion in the presence of strong bases at high temperatures
Stainless steel 316
  • Higher resistance to bases than stainless steel 304
  • Can maintain corrosion resistance to strong bases, such as sodium and potassium hydroxide, even at elevated temperatures

Table 2: Stainless steel 304 vs 316 resistance to bases

Other factors

As mentioned in the above section about corrosion resistance, most of the other properties of stainless steel 304 and 316 are similar. Understanding the following properties can help select the right stainless steel, but does not need a lot of focus unless the application has very precise demands:

  • Mechanical properties: 304 and 316 have similar tensile strength, yield strength, and elongation. 316 has slightly higher strength and toughness due to molybdenum.
  • Cost: 304 is less expensive than 316 due to the absence of molybdenum. The lower cost can be significant for large materials or projects.
  • Heat resistance: 316 has a slightly higher heat resistance than 304.
  • Fabrication and formability: 304 is slightly easier to work with than 316 when fabricating, welding, and forming.
  • Weight: 316 is slightly denser than 304 due to molybdenum.

Stainless steel valves

Stainless steel valves are widely used primarily due to their corrosion resistance. With everything else equal, 304 and 316 valves have a negligible difference in temperature and pressure rating. Look for a stamped number on the valve’s body to determine if it’s 304 or 316, similar to the objects in Figures 3 and 4. The following table describes factors to consider when selecting between stainless steel 304 and stainless steel 316 valves.

Property Stainless steel 304 valve Stainless steel 316 valve
Corrosion resistance Good resistance but inferior to 316 Superior to 316 due to the addition of molybdenum
Applications Food processing, water treatment, general plumbing and other applications that require moderate corrosion resistance Marine environments, chemical processing, pharmaceutical industries, and other applications with high corrosion resistance demands
Cost Less expensive More expensive

Table 3: Selecting between stainless steel 304 and stainless steel 316 valves

FAQs

How do I tell the difference between stainless steel 304 and stainless steel 316?

Unless stamped, the only way to tell the difference between these two types of stainless steel is to test them chemically. There are no visual markers or mechanical properties that make them easy to differentiate.

How do I choose between stainless steel 304 and stainless steel 316?

Choosing between these two stainless steel types typically comes down to understanding how much corrosion resistance is necessary. Stainless steel 316 has superior corrosion resistance but is also more expensive.

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Gate Valve vs Butterfly Valve

At first glance, it is not simple to decide between a gate valve and a butterfly valve for an application. Therefore, it is important to understand the differences between these two valve types to avoid unnecessary setbacks in an operation. This article lays out the fundamental similarities and differences between a gate valve and a butterfly valve, which can be seen in Figure 1, and looks at their application suitability, advantages, and disadvantages.

Gate and butterfly valves are both used to turn on and off the flow, but butterfly valves can also regulate flow via partial disc closure. Butterfly valves are part of the quarter-turn family of valves and can be shut off much faster than gate valves, which are multi-turn valves. Gate valves are preferable for high-pressure systems whereas butterfly valves are preferable for larger port sizes.

Gate valves

How does a gate valve work?

A gate valve is named after its disc, which behaves like a gate by either stopping or allowing media flow. It has a simple operation compared to other control valves, which makes it one of the most commonly used valves. Because a gate valve is a full-port valve, which means that the valve’s ports are the same size as the inner diameter of the connecting pipes, there is very little resistance to liquid or gas media that flows directly through it. Therefore, the pressure drop through the valve is quite low. For a more extensive understanding, read our article on gate valves.

Operating a gate valve

Gate valves are multi-turn valves, meaning the handwheel must turn more than 360° to fully open or close the valve. Turning the handwheel in one direction or the other moves the gate up or down via the stem. When the gate is completely up, the passageway is unobstructed, and media can flow. When the gate is down, media is blocked and cannot flow. Gate valves cannot modulate or throttle flow because there is a nonlinear relationship between the gate’s travel and flow rate. If the gate is partially open, the flow will crash into it while traveling through the valve, causing the flow to move at a higher velocity and create turbulence, both of which lead to increased wear on the disc and seats.

The three common means for actuating a gate valve are manually, pneumatically, or electrically. The manual method requires an on-site user to spin the handwheel to open or close the valve. This method is the most cost-effective since gate valves are not typically opened or closed often. The pneumatic and electric solutions allow for remote operation of a gate valve. Pneumatic actuation requires a pneumatic system on-site and electrical actuation requires electrical power on-site.

Gate valve types

As mentioned above, there exist different styles of gate valves. Three factors typically determine a gate valve’s style: the gate type, the bonnet type, and the stem type.

Gate type refers to the disc that blocks the flow when the valve is closed, for example:

  • Wedge disc: The gate is shaped like a wedge and it sits on two inclined seats. This provides a high wedging force which assists with sealing.
  • Knife disc: The gate is a piece of metal with a beveled edge like a knife. It can be used to cut through thick fluids and dry solids.
  • Double disc: The gate is two discs which sit on two seats. The discs expand away from each other to provide a tight seal.

Bonnet type refers to how the bonnet is attached to the valve body. It can be:

  • Screwed: This is the simplest type of bonnet construction and is normally used in small size valves.
  • Bolted: These bonnets are used in larger valves and high-pressure applications.
  • Welded: The bonnet is threaded in and the body-bonnet joint is welded. This offers extra protection against leaking.
  • Pressure sealed: The body-bonnet joint seal enhances as pressure within the valve increases. Used typically for high-pressure applications above 100 bar.

Stem type refers to the position and action of the stem

  • Rising vs non-rising: Rising stem gate valves require more space above the valve than non-rising.
  • Remains within the valve vs rises out of the valve upon opening: Rising out of the valve makes the stem easier to lubricate.

Materials

The correct material depends on the application’s fluid service and temperature. Common materials used for a gate valve are:

  • Body and bonnet: cast steel, stainless stell, cast iron, gunmetal, bronze, brass, and PVC
  • Disc: stainless steel, polypropylene, Teflon, rubber lined (e.g., wedge disc)
  • Seal: EPDM, NBR, Teflon

  • Butterfly valves

    How does a butterfly valve work?

    The essential operation of a butterfly valve is achieved by turning its handle 90° or using a pneumatic or electric actuator. This turns the valve’s stem, which rotates the disc. In the fully closed position, the disc is perpendicular to the flow, and in the fully open position, the disc is parallel to the flow. Partial opening or closing of the disc can achieve proportional or throttled flow rates. In cases of a large butterfly valve or a valve used in a liquid application for which fast closure could produce water hammer, a butterfly valve can be gear operated via a gearbox (Figure 2, right). The gearbox’s handwheel must be turned more than 90°, though, which eliminates the butterfly valve’s relatively fast closing speed. For a more comprehensive understanding, read our article on butterfly valves.

    A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the rightFigure 2: A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the right

    Butterfly valve types

    There are two key topics when discussing types of butterfly valves: body and stem offset. Body refers to how the valve’s body connects with piping, and stem offset refers to whether the stem passes through the center of the disc or is offset.

    The butterfly valve body types are:

    • Double-flanged: This design is typically used for larger butterfly valves.
    • Wafer: Most cost-effective design; sandwiched between two pipe flanges.
    • Single flange: This design uses bolts and nuts passed through the valve’s holes to connect to both sides of the piping.
    • Lug type: This design has threaded inserts, and bolts are used to connect pipe flanges to each side. Suitable for removing piping from one side without affecting the other.
    • Flangeless: Like the wafer style, this design is sandwiched between two pipe flanges.
    • Butt-welding ends: Prepared for welding directly to piping.
    • U-section: Also clamped between pipe flanges and suitable for end-of-line service.

    The stem can pass through the centerline of the disc (concentric) or be offset behind the centerline (eccentric). Offset, which can be single-, double-, or triple-offset, is used to reduce how much the disc rubs against the seating while closing. The higher the offset, the more the disc moves towards fully closed before contacting the seal. Any rubbing against the seal can reduce the service life of the valve. High-performance butterfly valves are specifically designed to withstand more demanding applications in terms of pressure and temperature.

    The following compares a high-performance butterfly valve with a standard butterfly valve:

    • Maximum shutoff pressure: Approximately 50 bar (725 psi) vs approximately 14 bar (203 psi)
    • Tight shutoff: Below 260°C (500°F ) vs below 120°C (248°F)
    • Shutoff with allowable seat leakage: Below 538°C (1000°F) vs below 425°C (797°F)

    Read our article on butterfly valve design differences article for more details on the features of each design type.

    Materials

    The valve’s body and seat materials should be chosen carefully based on the needs of the application. Common body materials are iron, stainless steel, carbon steel, nickel alloy, titanium alloy, and nickel aluminum bronze. These materials vary in weight and resistance to corrosion and extreme temperatures.

    Common seat materials are EPDM, EPDM white, FKM, XNBR, and NBR. Depending on the seat material, a butterfly valve can be used in temperatures ranging from -10°C to 180°C. Resilient and metal seated butterfly valves are also available, using the same materials listed here, and are designed to operate under more extreme temperatures and pressures.

    Gate valves vs butterfly valves

    There are many factors to consider when deciding whether a gate or butterfly valve is correct for a given application. Below are some of the most important:

    • Cost: A butterfly valve is typically less expensive than a gate valve, especially at larger port diameters.
    • Installation space: A butterfly valve takes up less installation space than a gate valve.
    • Weight: A butterfly valve weighs less than a gate valve; the latter may need support structures at larger port diameters.
    • Maintenance: While a butterfly valve is relatively easy to maintain, repair, or install due to its small size and low weight, its center disc makes it not suitable for systems that use pigging and swabbing for cleaning purposes. On the other hand, a gate valve is ideal for such maintenance.
    • Operation: A butterfly valve can close faster than a similar port diameter gate valve. However, this fact means that butterfly valves are more susceptible to water hammer.
    • Flow regulation: A butterfly valve can modulate or throttle flow, whereas a gate valve can only be on/off.
    • Flow resistance: A gate valve offers less flow resistance and, therefore, less pressure drop than a butterfly valve.
    • Pressure: Gate valves can handle higher pressures than butterfly valves.

    Applications

    • Gate valves have a higher sealing tightness, and therefore are more suitable for applications that require zero leakage.
    • Butterfly valves are more suitable for applications that require flow modulation or throttling.
    • If a slurry flow does not need to be modulated, gate valves are preferable to butterfly valves.
    • Gate valves are more suitable for systems that require bi-directional, uninterrupted flow.

    FAQs

    Which is better, a gate valve or a butterfly valve?

    A gate valve has a stronger seal and is more suitable for high-pressure applications. A butterfly valve is less expensive and available in very large sizes.

    Can a butterfly valve be used instead of a gate valve?

    A butterfly valve can be used instead of a gate valve in low-pressure systems for which some leakage is not a major concern.

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