butterfly valves


This article takes a detailed look at butterfly valves.

Read further and learn more about:

  • What is a butterfly valves.?
  • How does it work?
  • Components of a butterfly valves.
  • Types of butterfly valves.
  • Materials for the construction of butterfly valves.
  • Advantages and disadvantages of butterfly valves.
  • And much more…








Chapter 1: What is a Butterfly Valve?

A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media. The disc is rotated and controlled by an external actuating mechanism through the stem attached to it. When the disc is coplanar to the flow cross-sectional area, the flow is fully obstructed. Otherwise, the fluid is fully or partially allowed to pass through the butterfly valve. It takes a 900 turn to fully open a butterfly valve from a closed position, which means the disc should lie perpendicular to the flow cross-sectional area.

Butterfly valves are quarter-turn valves like ball valves and plug valves. They have a fairly simple construction and operation mechanism, and they have a compact size designed to fit two pipe flanges.

They can be operated manually or by an automatic actuating mechanism that is integrated into the process control system of the pipeline. They are ideal for on-and-off applications, but their applications to flow throttling are limited.

There are several types and designs of butterfly valves available, rated in varying temperatures, pressures, and flow rates to suit the needs of pipeline systems handling liquids and gases.

Chapter 2: Components of a Butterfly Valve

The main components of a butterfly valve are the following:

Valve Body

Made from a tough and rigid material, the valve body houses and protects the disc and other internal components of the butterfly valve. It links the valve to the piping system and to the external operating mechanism that controls the disc.


The disc is the main feature of butterfly valves that permits, regulates, and stops the flow of the fluid in the pipeline. Flow is controlled by the rotary motion of the disc. The discharge flow rate depends on the degree of disc opening. When the disc is perpendicular to the flow‘s cross-sectional area, the fluid is fully obstructed from flowing out of the valve. Otherwise, the fluid is permitted to flow through the space between the seat and the disc. It takes a 900-rotation from a closed position of the disc to allow full opening of the valve and vice versa. Flow is throttled when the disc is rotated less than 900.

The butterfly valve disc is analogous to the ball for ball valves and the plug for plug valves.


The stem is a shaft that connects the disc to the external operating mechanism. It is sealed by O-rings and bushings to prevent fluid leakage. The stem can be made from a one-piece shaft or two-piece (split-stem) shaft. The placement of the stem axis and its connection to the disc depends on the type of butterfly valve.


The valve seat is a ring that provides sealing between the disc edge and the valve body when it is in a closed position. The sealing action is necessary to avoid leakage of any fluid to the discharge of the butterfly valve. Since the disc slides on the surface of the seat during valve opening, it must be made from a material with a low coefficient of friction.

The butterfly valve seat can be made a soft seat or a metal seat. The material of the seat limits the temperature and pressure rating of the butterfly valve. Soft seats, which are made from plastic and elastomeric materials, are limited to lower temperatures because they deform at elevated temperatures.

Operating Mechanism

The external operating mechanism of a butterfly valve controls the fluid flow across the valve. It may be operated by manual rotation of the stem or by automatic actuation.

Manual operation of butterfly valves involves the application of torque to the lever or handwheel attached to the stem. Levers can set the valve into a closed, fully-opened, or partially-opened position. Larger butterfly valves are equipped with handwheels and gearboxes to increase torque and to aid in the opening and closing of the valve.

Automatic actuation may be used to control the butterfly valve situated in harsh environments and remote locations. It makes the opening and closing of butterfly valves faster, especially for larger valves requiring larger amounts of torque. The types of actuations used in butterfly valves to turn the valve stem are electromechanical actuation, (which uses an electric-powered motor), pneumatic actuation (which moves a piston or a diaphragm with compressed air), and hydraulic actuation, (which moves a piston or a diaphragm with hydraulic pressure).

Chapter 3: Types of Butterfly Valves

There are three main types of butterfly valves:

Zero Offset Butterfly Valves (Resilient Seat Butterfly Valves)

In zero offset butterfly valves, the stem passes through the centerline of the disc that is centered in the seat; all of this is centered inside the valve body. The valve body, seat, and disc lie concentrically when it is in a closed position. The disc rotates on the central axis; this allows a 3600 rotation. In a fully-opened position, the flow is divided into two halves on each side of the disc, which is now parallel to the flow. The advantage of this type is that the flowing media does not come in contact with the valve body because the seat is covering it.

Zero offset butterfly valves have resilient soft seats because they depend on the flexibility and deformation of the soft seat during sealing. This causes the disc edges to slide onto the seat, which results in full friction between them during the operation. This reduces the service life of the valve. Since the design requires the seat to be made from a polymeric or elastomeric material, it is limited to lower pressure and temperature ratings.

Zero offset butterfly valves are used in liquid and gas pipelines, which have pressure and temperature ratings of 250 psi and 4000F, respectively.

Double Offset Butterfly Valve (High-Performance Butterfly Valves)

In double offset butterfly valves, the stem axis is offset behind the centerline of the seat and the body (first offset), then the stem axis is further offset from the vertical centerline of the valve (second offset). When the disc is opened, the seat is lifted from the seal; this reduces the friction during the first and last 10 degrees of the valve opening and closing, respectively. This results in a smoother valve operation, better sealing capability, and longer service life than the zero offset butterfly valve.

Like zero offset butterfly valves, double offset butterfly valves use a soft seat. They are available in moderate pressure and temperatures ratings, which are capable of withstanding higher pressures and temperatures than the zero offset butterfly valves in liquid and gas pipelines.

Double offset butterfly valves are typically used in water purification, wastewater treatment, HVAC, and fire protection systems (e.g., fire sprinklers). For increased temperature resistance, the amount of soft seat material is reduced by backing it with a layer of metal.


Ball Valve Basics

Welcome to the first in a series of Valve Basics articles, each focused on a major product type and written especially for newcomers to the industries that use and make valves and related products.

Ball valves may not bounce very well but they work great at regulating flow. The popular valve is named for its round ball that sits in the interior of the valve body and pushes into a seat to control or provide on/off functions in fluid pipelines.

API 6D trunnion ball valves.

API 6D trunnion ball valves.

The heritage of ball valves is much shorter compared to gate, globe and check valve designs. Although the first ball valve patent was issued in 1871, it would take another 85 years for ball valves to become a commercial success. The discovery of polytetrafluoroethylene (PTFE, or “Teflon”) during the process design for manufacturing the atomic bomb in World War II, would be the catalyst that started the ball valve industry rolling. Ball valves come in all materials from brass to carbon steel and stainless steel to zirconium.

There are two basic types: floating ball and trunnion ball. These two designs allow for the construction of effective ball valves from ¼” through 60” and larger. Generally, the floating design is used for smaller and lower-pressure valves, while the trunnion type is used for larger and higher-pressure valve applications.

Floating ball valve.

Floating ball valve.

The reason for the two types of ball valves has to do with the way they seal and how the fluid force is distributed from the line flow to the ball and then to the seat. In the floating ball design, the ball is riding snugly between two seats, one upstream and one downstream. The force of the fluid acts on the ball to push it into the seat located in the downstream valve body. Since the ball covers the entire flow bore, all the force in the stream is pushing against the ball to force it into the seat. If the ball gets to be too large and the pressure too high, the force will be so great on the seat that the valve cannot be operated because the operating torque would be too high.

Floating ball valves come in a variety of body styles, although the two-piece, end entry type is the most popular. Other body styles include three-piece and top entry. Floating ball valves are manufactured in sizes up to 24” and class 300, but the practical realm of the floating ball valve is generally much lower—up to about 12”.

Although ball valves are designed primarily to be on/off or “block” valves, the addition of partial ball and V-port ball designs can make them good choices for control-type applications.


The smaller floating ball valves are found in many different applications from household plumbing to those containing the harshest chemicals. The most popular seating material in these valves is some form of thermoplastic, such as PTFE. PTFE seats work very well because they are soft enough to seal well on to the polished metallic ball, yet firm enough not to blow out of the valve. The two primary concerns with these soft-seated valves are that they are susceptible to scratching (and potential leakage) and are limited to temperatures below the melting point of the thermoplastic seats—somewhere around 450oF (232oC) depending on the exact seat material.

A ball valve

A ball valve “ball.”

A feature of many resilient-seated floating ball valves is the ability to moderately seal in the event of a fire that causes the primary seats to melt. This is called a fire-safe design; it features a seat pocket that not only holds the resilient seat in place, but also provides a metallic seating surface that can provide a partial seal as it contacts the ball. The fire-safe design is confirmed by testing the valve in accordance with the American Petroleum Institute (API) 607 or 6FA fire-testing standards.


When larger sizes and higher-pressure ball valves are needed, the design shifts to the trunnion style. The trunnion differs from the floating style in that the trunnion ball is held in the body via a trunnion (short, attached stem) in the bottom and by the stem at the top. Since the ball cannot “float” into the seat to attain positive closure, the seat must float to the ball instead. The trunnion seat is designed so that the seat is energized by the upstream pressure and is forced into the ball to seal. Because the ball is held securely in place, except for its 90o rotation, the extraordinary fluid force and pressure does not jam the ball into the seat. Instead, the force acts only on a small area on the periphery of the floating seat.

The trunnion ball valve is the brawny big brother to the floating ball valve and as such it gets to handle the big jobs—high pressures and large pipe diameters. By far the most popular use of trunnion ball valves is for pipeline service. These valves are especially popular in natural gas pipelines in diameters up to 60” and pressures up to class 600. Trunnion ball valves can also be used in higher pressures if required. By using trunnion designs the torque required to open and close the valve is lower, so smaller actuators can be used.

End-entry design.

End-entry design.

The trunnion design also lends itself well to double block and bleed service since both the upstream and downstream seats float independently and most designs also feature a body or drain connection. Trunnion designs often employ seat lubrication ports where a lubricant can be injected around the seat to assist in closure efficacy.


The biggest advancement in ball valve technology over the past 30 years or so is the metal-seated ball valve. While the idea of metal seats and a metal ball are not new—in fact, the first ball patent in 1871 featured a brass ball and brass seats—the design needed advancements in coating technology to really be perfected.

The metal-seated ball valve design has enabled ball valves to take a big chunk out of the market share dominated for decades by the venerable gate valve. The metal-seated, specialty-coated ball closes tightly against a set of precision coated and lapped seats, providing zero-leakage, if the hardened seating surfaces are not scratched by debris in the line.


The are several standards that apply to ball valves. The following table lists the most common ball valve design documents:

Ball valves have made huge inroads in replacing other valve types over the past 40 years. The cost to manufacture the smaller sizes has dropped greatly as well, making them even more competitive. The advances in coatings and metal-seated ball valve technology have created very robust designs that have resulted in an attractive total cost of ownership.

Table 1. Common ball valve standards.

Table 1. Common ball valve standards.

While the overall industrial valve segment is still dominated by gate and globe, linear-valve designs, the relatively young ball valve is steadily making up ground, and the metal-seated types have become the preferred valve design for severe-service applications around the world.

In need of assistance in selecting a ball valve ? The experts at STV VAlVE have the knowledge and experience to help. Shop stvvalve.com today!


Gate Valve – How They Work

Figure 1: Gate valve

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed). A gate valves distinct feature is the straight-through unobstructed passageway, which induces minimal pressure loss over the valve. The unobstructed bore of a gate valve also allows for a pigs passage in cleaning pipe procedures, unlike butterfly valves. Gate valves are available in many options, including various sizes, materials, temperature and pressure ratings, and gate and bonnet designs.

Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are slower in actuation than quarter-turn valves and are for applications where valve operation is infrequent, such as isolating valves. Gate valves should be used either fully open or fully closed, not to regulate flow. Automated gate valves exist with either an electric or pneumatic actuator, but a manual gate valve is cost-effective since they have infrequent usage.

Table of Contents

Functioning principle

Gate Valve ComponentsFigure 2: Gate valve components

A gate valves main components as seen in figure 2 are the handwheel (A), spindle (B), gasket (C), bonnet (D), valve body (E), flange (F), and gate (G). The primary operation mechanism is straightforward. Turning the handwheel rotates the stem, which moves the gate up or down via the threads. They require more than one 360° turn to fully open/close the valve. Lifting the gate from the path of the flow, the valve opens. Lowering the gate to its closed position seals the bore resulting in a full closure of the valve.

For a gate valve, the relationship between the gates vertical travel and the flow rate is nonlinear, with the highest changes occurring near shutoff. When used to regulate flow, the relatively high velocity of the flow at partial opening results in gate and seat wear, which along with possible vibrations of the gate, shortens the valves service life.

Gate valve design & types

Gate valves come in a wide variety of designs, each of which uses different technologies to meet various application requirements.


Bolted bonnet gate valveFigure 3: Bolted bonnet gate valve

A bonnet protects the internal parts of a gate valve (Figure 2). It is screwed in or bolted to the valve body, creating a leak-proof seal. Therefore, it is removable for repair or maintenance purposes. Depending on applications, gate valves can have screw-in, union, bolted, or pressure seal bonnets.

Screw-in Bonnets

Screw-in bonnets are the simplest in construction. They are common in small size valves and provide a durable leak-proof seal.

Union Bonnets

Union bonnets are held in place by a union nut. The union nut sits on the lower edge of the bonnet and screws into the valve bodys threads. This type of design ensures that the leak-proof seal created by the nut does not deteriorate by frequent removal of the bonnet. Therefore, union bonnets are common for applications that require regular inspection or maintenance.

Bolted Bonnets

Bolted bonnets provide sealing in larger valves and higher pressure applications. In this type, the bonnet and valve body are flanged and bolted together. Figure 3 shows a gate valve with a bolted bonnet.

Pressure Seal Bonnets

Pressure seal gate valves are ideal for high-pressure applications (more than 15 MPa). This type of construction uses internal pressure to create a better seal. Pressure seal bonnets have a downward-facing cup inserted into the valve body. When internal fluid pressure increases, the cups forced outward, improving the seal.


The gate comes in a variety of designs and technologies to produce effective sealing for differing applications.

Wedge Gates

In most gate valves, the gate has a wedge form and sits on two inclined seats (Figure 4). In addition to the primary force created by fluid pressure, a high wedging force on the seats created by the stems tightening assists with the sealing. The wedge-shaped gate does not stick to the seat in case of high fluid differential pressure and has an increased service life due to less “rubbing” on the seats.

Wedge gate valve vs parallel gate valveFigure 4: Wedge gate valve vs parallel gate valve

Parallel Slide Gates

Gate valves can also come in a parallel form where the gate is flat, and the seats are parallel. Parallel gate valves use line pressure and positioning to make a tight seal. Flat gates consist of two pieces and have a spring in the middle. The spring pushes the pieces towards the seats for enhanced sealing. Due to their inherent design, parallel gate valves have a safety advantage in higher temperature applications. In wedge-shaped gate valves, an additional compression load on the seats may result in thermal binding and restricted opening of the valve due to expansion. Furthermore, since there is no wedging action in parallel gates, closing torques are comparatively smaller, resulting in smaller, less expensive actuators or less manual effort. Due to their sliding into position, parallel gates keep dirt away from the seating surfaces.

Slab Gates

Slab Gate ValveFigure 5: Slab gate valve

Slab gates, also called through-conduit gate valves, are one-unit gates that include a bore size hole (Figure 5). In the open state, the bore is in line with the two seat rings. This alignment creates a smooth flow with minimal turbulence. This unique design allows for minimal pressure loss on the system and is perfect for the transportation of crude oil and natural gas liquids (NGLs). The valve seats remain clean. However, the disc cavity can capture foreign material. Therefore, the cavity typically has a built-in plug for maintenance purposes of draining the accumulated foreign material.

Parallel Expanding Gates

Expanding gate valves have two slab gates matched together that provide sealing through the mechanical expansion of the gate (Figure 6). When lifted, both of the slab gates cavity allows the media to flow. The upward force on one slab and the stoppage of the second slab, by a step in the valve body, allows for outward mechanical expansion for a proper seal. When closed, the slab gates block the media flow, and the downward force (stem) on one slab and upward force (step in valve body) allows for outward mechanical expansion for a proper seal.

These valves provide an effective seal simultaneously for both upstream and downstream seats. This seal makes them ideal for applications like isolation valves in power plants, block valves in process systems, and high-temperature valves in refineries.

Expanding gate functioningFigure 6: Expanding gate functioning

Knife Gates

Knife gate valves are for thick fluids and dry bulk solids. The gate is only one piece of metal, which is typically pointed. These valves are self-cleaning as they pass the seat rings every time they open and close.

Stem design

The gate is raised and lowered by the spinning of a threaded stem. A manual wheel or actuator spins the stem. Depending on the design, the stem is either considered rising or non-rising. So, as you spin the stem it either raises or stays in place with the spin as seen in Figure 7.

Outside Screw and Yoke (OS&Y), also referred to as rising stems, are fixed to the gate. Therefore, the threads are on the actuation side. So, as the gates raised or lowered, the stem moves with it up and down. Consequently, they have built-in visual indicators of the state of the valve and are easily lubricated. Since they have moving components, they cannot be used with bevel gears or actuators. Therefore, rising gate valves are suitable for manual actuation.

On the other hand, a non-rising stem is fixed to the actuator and threaded into the gate. An indicator is often threaded onto the stem to show the open or closed state of the valve. Non-rising gate valves are common in underground installations and applications with limited vertical space.

Mechanism of rising stem gate valves vs non-rising stem gate valvesFigure 7: Mechanism of rising stem gate valves vs non-rising stem gate valves


What is a gate valve?

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed).

How does a gate valve work?

By rotating the manual handle, the threaded stem moves the gate up and down. As the gate goes up it opens and down it closes the media flow.

What is a gate valve used for?

A gate valve is for on and off flow control.


What is a Y Strainer and How to Work

A Y strainer, sometimes referred to as a y strainer, is designed to mechanically remove solids and other particles from fluids. They are an essential component in numerous fluid control applications to ensure no down-stream component is affected by particles within the fluid. In this article we will review their design, use cases, how to size the mesh filter, materials, and how to clean them.

Table of Contents

Y Strainer Design

As its name implies, a Y strainer is shaped like a “Y” and is used to filter, or strain, out particulates from steam, gas or liquid. This mechanical straining process is made possible via a filter element comprised of mesh, perforated metal, or a wedge wire straining element. The most common kind of straining element is a wire mesh. Some also include “blow-off valves” that make the cleaning process easier in applications with more substantial dirt blowing. The strainer itself has a compact, Y shaped design. The Y shape has better flow characteristics then for example a T shaped strainer, because the fluid flows through the filter with less change of direction.

Why Use a Y Strainer?

In general, Y strainers are critical anywhere clean fluids are required. While clean fluids can help maximize the reliability and lifespan of any mechanical system, theyre especially important with solenoid valves. This is because solenoid valves are very sensitive to dirt and will only function properly with clean liquids or air. If any solids enter the stream, it can disrupt and even damage the entire system. Therefore, a Y strainer is a great complimentary component. In addition to protecting the performance of solenoid valves, they also help safeguard other types of mechanical equipment, including:

  • Pumps
  • Turbines
  • Spray nozzles
  • Heat exchangers
  • Condensers
  • Steam traps
  • Meters

A simple Y strainer can keep these components, which are some of the most valuable and expensive parts of the pipeline, protected from the presences of pipe scale, rust, sediment or any other kind of extraneous debris. Y strainers are available in a myriad of designs (and connection types) that can accommodate any industry or application.

Sizing Your Mesh Filter for a Y strainer

Of course, the Y strainer wouldnt be able to do its job without the mesh filter that is properly sized. To find the strainer thats perfect for your project or job, it’s important to understand the basics of mesh and screen sizing. There are two terms used to describe the size of the openings in the strainer through which debris passes. One is micron and the other is mesh size. Though these are two different measurements, they describe the same thing.

What is a Micron?

Standing for micrometer, a micron is a unit of length thats used to measure tiny particles. For scale, a micrometer is one thousandth of a millimeter or about one 25-thousandths of an inch.

What is Mesh Size?

A strainers mesh size indicates how many openings there are in the mesh across one linear inch. Screens are labeled by this size, so a 14-mesh screen means youll find 14 openings across one inch. So, a 140-mesh screen means that there are 140 openings per inch. The more openings per inch, the smaller the particles that can pass through. The ratings can range from a size 3 mesh screen with 6,730 microns to a size 400 mesh screen with 37 microns.

Micron-to-Mesh Conversion Chart

The chart below is a handy resource to help you convert from mesh to micron (or vice-versa).



Mesh Screen Mesh Size Microns
2000 10 0.0787
1680 12 0.0661
1410 14 0.0555
1190 16 0.0469
1000 18 0.0394
841 20 0.0331
707 25 0.028
595 30 0.0232
500 35 0.0197
420 40 0.0165
354 45 0.0138
297 50 0.0117
250 60 0.0098
210 70 0.0083
177 80 0.007
149 100 0.0059
125 120 0.0049
105 140 0.0041
88 170 0.0035
74 200 0.0029
63 230 0.0024
53 270 0.0021
44 325 0.0017
37 400 0.0015

In addition, it can be helpful to see an example of mesh sizes based on certain particles, as shown below:



Mesh Size Microns Example of particle size
14 0.05551400
28 0.028700 Beach Sand
60 0.0098250 Fine Sand
100 0.0059150
200 0.002974 Portland Cement
325 0.001744 Silt
400 0.001537 Plant Pollen

Determining Your Proper Filter Size

To select the right filter size for your application, youll need to consider the size, scope, and environment of the project. Some of the most important factors to gauge include:

  • The type of pipe system youre using.
  • The kind of material that makes up the system.
  • The size of the debris or particles you want to capture.
  • The systems pressure and temperature levels.

Its important to take the time to size your mesh filter correctly. Sizing it too small or too large can negatively affect your system as a whole. If your filter is too small (with a lot of openings), there will be a greater pressure drop from inlet to outlet. Additionally, removing too much debris can result in additional maintenance due to a collection of debris which can also cause an increased pressure drop. If it is too large (allowing large particles through), this can affect the performance and life span of your downstream equipment.

Housing Material Options

Now that weve covered why Y strainers are important and what theyre used for, lets discuss a few of the different kinds of Y strainers available. These strainers are available in a wide variety of material types and fall into different classes defined by the American National Standards Institute (ANSI). First, lets take a look at the different material housing options available, which include:

  • Brass
  • Stainless steel
  • (Carbon) Steel
  • Bronze
  • Cast iron
  • Ductile iron
  • Plastics

Note that these different kinds of housing materials are designed to fit certain environments and media.

Seal Material Options

The seal on a Y strainer helps ensure its functionality and extend its service life. Some of the common options are:


This is one of the most common types of seal materials. In addition to holding fast in even the most aggressive environments, these are also ideal for low and high temperatures.

Fluoro Rubber Seal

When youre shopping for a Y strainer, you might come across a few different kinds of seals that sound similar. These include:

  • FKM
  • FPM
  • Viton®

These individual designations all describe the same base material: Fluoro rubber. Why the different names? In short, the ASTM abbreviates the material as FKM while the DIN/ISO abbreviates the entire fluoroelastomer category as FPM. And, DuPont Performance Elastomers trademarked the material as Viton®.


Standing for ethylene-propylene-diene-monomer, EPDM is an elastomer similar to Fluoro rubber. However, it features a different chemical resistance and temperature range compared to FPM.

How to Clean Your Y Strainer

How often youll need to clean your component depends on the process youre running, mesh size, and the materials youre filtering. Remember to close off all valve connections on both sides of the Y strainer to relieve pressure as you start to clean. From there, you can loosen and remove the plug at the end of the filter leg to access the filter. Empty out all of the collected material and debris, clean the filter and replace.

Y Strainer Selection Criteria

There are different kinds of Y strainers on the market designed to meet various industry needs. As you research which one is best for you, keep the following criteria in mind:

  • Port size
  • The temperature in your environment
  • The pressure level in your environment
  • Preferred installation orientation
  • The kind of debris you need to strain
  • Ease of maintenance

There is no one-size-fits-all Y strainer that meets every need. Thats why its important to understand your application requirements before moving forward.

Typical Y Strainer Applications

A Y strainer is most valuable in an environment that requires constant protection from debris and contamination. Lets take a look at a few of the most common applications that require their use.

Steam Applications

These strainers are a go-to resource in most steam applications, as its shape is built to handle the high pressure that exists in these environments.

Liquid Applications

Liquid applications tend to become infiltrated by sand and gravel, and Y strainers can help keep those particles out to ensure the liquid stays clean. Especially when they work in tandem with other water-handling applications, these strainers can protect important (and expensive) equipment from damage, corrosion or clogs that could result from such contamination.

Natural Gas and Air Applications

Natural gas and air applications tend to have a low operating pressure, so proper sizing to reduce a pressure drop from inlet to outlet is important.

Frequently Asked Questions

Its easy to become overwhelmed when youre researching the best Y filter for your needs. To that end, lets take a look at a few common inquiries and how to solve them.

How Should I Install My Strainer?

Y strainers have an arrow from inlet to outlet. It is important to install them in this orientation for proper filtration.

What Kind of End Connections are Available?

Depending on your needs, Y filters can include a variety of end connections, including flanged, threaded and welded. You can also find special flanges, such as ring joints.

What Kind of Housing Material Should I Choose?

Depending on your environment and media, a different Y strainer housing material and seal material should be selected. Ensure you know the chemical resistance of them to select the proper one.

Are Y Strainers Affordable?

Yes! This type of strainer is also an affordable alternative to other types of strainers, made even more economical as you scale down in size. Considering they protect more expensive components, they are a good investment.

Should I Choose on My Own?

This article should help you select the proper Y strainer for your application. However, feel free to contact our technical support with any questions.


Ball Valves vs Globe Valves,Which Valve is Best for You?

There are many different types of valves available for different applications. With so much choice it can be difficult to decide which valve is most suitable for your application. In this article, STV Supplies explores the merits of ball valves versus globe valves.






The main difference between ball and globe valves is the way they close. Ball valves have a stem and ball, which turns horizontally, and are commonly referred to as “rotational” valves. Whereas, globe valves have a stem and plug, which strokes linearly, and gives them their other name of “stroke” valves. Ball valves are best suited to applications requiring on/off control without pressure drop. While globe valves excel at regulating flow.


Ball valves are designed with a ball inside the valve. A ball valve is a form of quarter-turn valve which uses a hollow, perforated and pivoting ball (called a “floating ball”) to control flow through it. It is open when the ball’s hole is in line with the flow and closed when it is pivoted 90-degrees by the valve handle. The handle lies flat in alignment with the flow when open, and is perpendicular to it when closed, making for easy visual confirmation of the valve’s status.


Globe valves were for many years the industry standard in control valves. They are named for their spherical body shape, with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug (or disc) can be screwed in to close the valve. Typically, automated globe valves use smooth stems rather than threaded and are opened and closed by an actuator assembly.


Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff applications, where they are often preferred to gates and globe valves. On the flip side, ball valves do lack the fine control in throttling applications offered by globe valves.




STV stock a wide range of ball valves, from quarter-inch to six-inch at our works in Bishopbriggs. From general purpose two-piece ball valves, v-ball control valves, hygienic valves, to heavy duty ball valves for steam; we have a variety of sizes, end connections and materials to suit many applications. We also stock globe valves up to six-inch in size, and can supply many size and material variants on a next-day basis.

What is a Gate Valve

The gate valve is a fairly common valve that can be seen in the piping systems of many homes and structures. It is the preferred valve for houses because it is rather easy for any homeowner to operate. It can also be used for more industrial purposes and are instantly recognizable.

Since this particular valve’s design is for it to either be opened all the way or closed all the way, the drop in pressure across the actual valve is extremely limited when opened, making it possible for fluid to flow through nearly seamlessly and the seal that exists between the valve’s disk and the valve’s seat is strong enough to resist any pressure that may be coming from the fluid.

Like with any other kind of valve, the gate valve has its advantages and disadvantages and recognizing what these are will provide any potential user the ability to make a better informed choice in what kind of valve they should use. Also, knowing the pros and cons can make the user know what to expect and what needs more looking after.

One of the advantages of gate valves is its high capacity as well as its ability to seal tightly, making the shutoff of any flow possible and any leakage nearly impossible. This particular kind of valve is also known to be very cost effective, which is probably why it is a popular choice for countless residences. Gate valves also have low friction loss because there is almost nothing obstructing the flow of the fluid when the valve is fully opened, creating little resistance to the flow.

As earlier mentioned, gate valves are meant to be fully opened or fully closed and partially opening the valve is bound to cause vibration which in turn leads to damage to the valve. Another thing that needs to be taken into consideration is that the valve disks and valve seats go through a great deal of wear and tear, making it necessary to replace them more often than compared to other kinds of valves. Because it is either fully opened or fully closed, gate valves are thought to have difficulty in controlling flow.

Overall, the gate valve remains a great choice as a control valve for any piping system that does not need to be constantly turned on or off. It is able to handle large flows of fluid, making it work for industrial purposes as well. Gate valves can also work with several materials such as oil, gas, air, steam, heavy and corrosive liquids, non-condensing gases, and slurries, making it a versatile selection.

The most important thing to remember when gate valves are used in a piping system is how it is maintained. According to an article entitled how to maintain a gate valve, the proper maintenance of gate valves can help ensure that they function properly and last for years so making sure that these valves are taken care of accordingly enables there to be more pros than cons.


To Understand About Parts Of A Ball Valve

While contemplating on the brand and type of ball valve to purchase for use in your shut off application or flow control system, be in the know of its various parts. Having an adept knowledge of its parts will give you an idea of how the valve entirely works when it is installed.

1. Body :

This part is regarded as the principal part of a valve, regardless of its shape and type. It is the part that gives framework to the whole valve because it holds all the other parts intact. It also serves as the pressure boundary of the valve because it is the first line of resistance against the volume and pressure of the liquid flowing through all the pipes connected to it.

2. Bonnet:

This part covers the opening in the valve’s body. It also serves as the second pressure boundary. Valve bonnets are usually bolted and screwed with the body. It is also usually made of the same material as the body to make the whole valve firmer and stronger.

3. Trim:

This part is a collection of differentinternal valve parts such as disk, seat, stem and sleeves. Because of these internal parts, the valve can perform basic motions to provide flow control. The disk together with the seat is important in determining the performance of the valve system. In most designs, the disk serves as the third layer of pressure boundary. It can permit and prohibit fluid flow due to its pressure-retaining capacity.

The seat, also called as seals ring provides an interface to where the disk is seated. The seal rings can either be forged within the body by welding or by machine. The stem is responsible for positioning the disk. It connects the actuator and the disk usually though welded joints.

4. Actuator:

This part works in conjunction with some internal parts located in the valve trim. This part is responsible for running the stem and disk. There are many types of actuator that are available in the market today. Some are handwheels, levers, motors, solenoids, pneumatic operators or hydraulic arms. Most valve manufacturers’ provide a design where the actuator is mounted with the bonnet through a yoke.

5. Packing:

This part commonly prevents leaks from the space between the valve stem and bonnet. The valve packing can be made from fibrous materials like flax or some other materials like Teflon. Regardless of the valve packing composition, it should be able to form a seal between the internal parts and the outer valve environment where the stem extends from the valve body. The packing must be properly placed to prevent leaks that can cause further damages to the entire valve system. The packing must neither be too loose nor too tight.

In summary, knowledge of the different parts of a ball valve will give you a generalized idea of how it will work during the entire span after it has been installed by your designated workforce. It will also help you to have a rough estimate of the cost of implementing a flow control system with the use of a ball valve.





how to select Gate Valve

Knowing the right kind of gate valve to select depends greatly on how you are planning to use it in your piping system. A professional’s advice and guidance can help whittle down the choices and recommend which one will work best in your precise setup.

There are two basic types of gate valves that can be purchased and installed as part of the plumbing system of a structure. These two types depend on the manner in which the disk is designed in the actual gate valve. As mentioned in the article parts of a gate valve, the gate valve disk is basically the gate that can seal shut when the valve is closed, meaning no water flow is possible, and can open when the valve is opened, allowing water pressure to pass through.

The two basic types of gate valves are:

1. Parallel Gate Valve


The parallel gate valve is used in valves that have parallel valve seats. The two halves of the parallel disk can either be thrust together or spread apart and there is often a spring-like mechanism that assists in the proper sealing of the disks to the seats. There is a variety of designs that use the parallel gate valve but the bottom line for each design is to make sure that there is optimum sealing that occurs between the disks and the seats.

2. Wedge Gate Valve


The wedge gate valve is separated into three categories:

  • Solid Wedge: The solid wedge gate valve is considered to be the most commonly used disk and is known for the simplicity in its design that belies its strength. The solid wedge gate valve functions well in any position it is placed in and can handle almost any kind of fluid.
  • Flexible Wedge: The flexible wedge gate valve is a singular disk whose perimeter has a cut around it in order to be able to fit better in the valve seats. The cut depends on the design of the valve seats and the flexible wedge gate valve works best with steam systems since heat can cause expansion and cold can cause contraction, making it necessary for more flexibility to occur within the disk.
  • Split Wedge: The split wedge gate valve has a ball and socket design that are able to self-adjust and self-align to the valve seats’ surfaces. This makes it possible for half the disk to adjust and align itself if the other half is unable to do so due to something being lodged that makes it impossible for it fit snugly into the valve seat. The split wedge gate valve is appropriate for systems that handle non-condensing gases and liquids.

Knowing the right kind of gate valve to select depends greatly on how you are planning to use it in your piping system.One particular type of design may work specifically for plumbing purposes in a home while another type of design may work better in an industrial setting. This is why it is important to have the correct information on each type of gate valve and whether they will meet your specific requirements and needs. A professional’s advice and guidance can help whittle down the choices and recommend which one will work best in your precise setup.


how to maintain a gate valve

Like other mechanical products, valves also need maintenance. This work well, can extend the service life of the gate valve, the following will introduce the maintenance of the Gate valve.

1. Gate Valve storage and maintenance

The purpose of storage and maintenance is not to damage the valve or reduce the quality. In fact, improper storage is one of the important reasons for valve damage.
The Gate valves should be kept in good order. The small valves should be placed on the shelf. The large valves can be arranged in order on the ground of the warehouse. They should not be stacked disorderly. The flange connection surface should not contact the ground. This is not only for the sake of beauty, but also to protect the valve from damage.
Due to improper storage and handling, broken handwheel, crooked valve stem, loose nut between handwheel and valve stem, etc., these unnecessary losses should be avoided.
Asbestos packing should be taken out for valves not to be used for a short time to avoid electrochemical corrosion and damage of valve stem.
Check the valve just entering the warehouse. If there is rain or dirt in the process of transportation, wipe it clean and then store it.
The inlet and outlet of the valve should be sealed with wax paper or plastic sheet to prevent dirt.
The valve surface that can rust in the atmosphere should be coated with antirust oil for protection.
The outdoor Gate valves must be covered with rain proof and dust-proof materials such as linoleum or tarpaulin. The warehouse where the Gate valves are stored should be kept clean and dry.

2. Gate valves operation and maintenance

The purpose of operation and maintenance is to extend the service life of the valve and ensure the reliability of opening and closing.
Stem thread, often with the stem nut friction, to apply a little yellow dry oil, molybdenum disulfide or graphite powder, lubrication.
Do not often open and close the valve, but also regularly turn the hand wheel, add lubricant to the stem thread to prevent seizure.
For outdoor valves, theGate valves stem shall be protected from rain, snow, dust and rust.
If the Gate valves is mechanical, add lubricating oil to the gearbox on time.
Always keep the valve clean.
Always check and maintain the integrity of other parts of the valve. If the fixing nut of the hand wheel falls off, it should be matched and can not be used properly, otherwise it will grind the square on the upper part of the valve stem, gradually lose the reliability of matching, and even can not start.
Do not rely on the Gate valves to support other heavy objects, do not stand on the Gate valves.
The valve stem, especially the thread part, should be wiped frequently, and the lubricant that has been contaminated by dust should be replaced with a new one, because the dust contains hard debris, which is easy to wear the thread and the surface of the valve stem, affecting the service life.

3. Maintenance of valve packing

The packing is directly related to the key seal of valve leakage when opening and closing. If the packing fails, causing leakage, the valve will be equivalent to failure, especially the valve of urea pipeline, because of its high temperature, corrosion and easy aging of packing. Strengthening maintenance can prolong the life of packing.
When the valve leaves the factory, in order to ensure the elasticity of the packing, it is generally subject to the static pressure test without leakage. After the valve is installed into the pipeline, due to the temperature and other factors, the leakage may occur. At this time, the nuts on both sides of the packing gland should be tightened in time. As long as there is no leakage, the leakage can occur again in the future. Do not tighten it once, so as to avoid the loss of elasticity and sealing performance of the packing.
Some valve packing is filled with molybdenum disulfide grease. When it is used for several months, the corresponding grease should be added in time. When it is found that the packing needs to be supplemented, the corresponding packing should be added in time to ensure its sealing performance.


4. Maintenance of valve transmission parts

In the process of valve opening and closing, the original lubricating oil will be continuously lost. Coupled with the effect of temperature, corrosion and other factors, the lubricating oil will continue to dry up. Therefore, the transmission parts of the valve should be checked frequently, and the lack of oil should be added in time, so as to prevent the increase of wear due to the lack of lubricant, resulting in inflexibility of transmission or failure of case


5. Maintenance of valve during grease injection

When the Gate valves is greased, the amount of grease is often ignored. After the grease gun is filled with oil, the operator selects the valve and grease connection mode to carry out the grease injection operation. There are two situations: on the one hand, the amount of grease injection is less, and the sealing surface is worn faster due to the lack of lubricant. On the other hand, excessive fat injection causes waste. The reason is that there is no accurate calculation for the sealing capacity of different valves according to the valve type. The sealing capacity can be calculated according to the valve size and type, and then a reasonable amount of grease can be injected.
When the valve is greased, the pressure problem is often ignored. During the operation of fat injection, the pressure of fat injection changed regularly from peak to valley. If the pressure is too low, the seal leaks or fails, if the pressure is too high, the grease injection port is blocked, the grease in the seal is hardened, or the seal ring is locked with the valve ball and valve plate. Usually, when the grease injection pressure is too low, the injected grease flows into the bottom of the valve chamber, which usually occurs in small gate valves. On the one hand, check the grease nozzle, if the grease hole is blocked, judge the situation and replace it; On the other hand, it is the hardening of grease. It is necessary to use cleaning fluid to soften the failed sealing grease repeatedly and inject new grease for replacement. In addition, seal type and seal material also affect the grease injection pressure. Different seal forms have different grease injection pressure. Generally, the grease injection pressure of hard seal is higher than that of soft seal.

When greasing the valve, pay attention to the problem that the valve is in the on / off position. Ball valve maintenance is generally in the open state, special circumstances choose to close maintenance. Other valves can not be treated as open. The gate valve must be closed during maintenance to ensure that the grease fills the sealing groove along the sealing ring. If it is open, the grease will directly fall into the flow channel or valve cavity, causing waste.

When the Gate valves is greased, the effect of greasing is often ignored. During the operation, the pressure, amount and switch position were normal. However, in order to ensure the effect of valve greasing, sometimes it is necessary to open or close the valve, check the lubrication effect, and confirm that the surface of valve ball or ram is evenly lubricated.
Attention should be paid to the blowdown of valve body and the pressure relief of screw plug during grease injection. After the pressure test of the valve, the gas and water in the valve chamber of the sealing chamber will be increased due to the rise of the ambient temperature, and the blowdown and pressure relief should be carried out before the grease injection, so as to facilitate the smooth progress of the grease injection. The air and water in the sealing cavity are fully replaced after grease injection. The pressure of the valve chamber is released in time, which ensures the safety of the valve. After grease injection, the drain and pressure relief plugs must be tightened to prevent accidents.
When injecting fat, pay attention to the problem of even fat. During normal fat injection, the nearest fat hole to the fat injection port first gets fat, then goes to the low point, finally to the high point, and then gets fat one by one. If not in accordance with the law or not out of fat, prove the existence of blockage, timely clearing treatment.
When greasing, the valve diameter and sealing ring seat should also be observed. For example, for ball valve, if there is open position interference, the open position limiter can be adjusted inward, and it can be locked after confirming that the diameter is straight. The adjustment of the limit should not only pursue the position of the opening or closing side, but should be considered as a whole. If the opening position is flush and the closing position is not in place, the valve will not be closed tightly. In the same way, the corresponding adjustment of the opening position should also be considered when adjusting the closing position. Ensure right angle travel of the valve.
After the grease injection, the grease injection port must be sealed. Avoid impurities entering or lipid oxidation at the grease injection port. The cover shall be coated with anti rust grease to avoid rusting. So that it can be applied in the next operation.

When greasing, we should also consider the specific problems in the future oil sequential transportation. In view of the different quality of diesel and gasoline, the scouring and decomposition capacity of gasoline should be considered. In the later valve operation, in case of gasoline section operation, timely add grease to prevent wear.
When greasing, do not ignore the greasing of the valve stem. There is sliding sleeve or packing on the valve shaft, which also needs to be lubricated to reduce the friction resistance during operation. If the lubrication can not be ensured, the torque will be increased during electric operation, and the worn parts will be worn, and the switch will be laborious during manual operation.
Some ball valves are marked with arrows on the valve body. If there is no English fiow handwriting attached, it is the direction of action of the sealing seat, not as a reference for the flow direction of the medium. The direction of self discharge of the valve is opposite. In general, double seat sealed ball valve has two-way flow direction.
During valve maintenance, attention should also be paid to the problem of water inflow in the electric actuator and its transmission mechanism. Especially in rainy season. One is to rust the transmission mechanism or shaft sleeve, the other is to freeze in winter. When the electric valve is operated, the torque is too large, and the transmission parts will be damaged, which will make the motor no-load or over torque protection jump off, and the electric operation cannot be realized. The transmission parts are damaged, and manual operation cannot be carried out. After the over torque protection action, manual operation is also unable to switch, if forced operation, the internal alloy parts will be damaged.
Valve maintenance should be treated with a scientific attitude in order to achieve the desired effect and application purpose. In order to make the production run normally, reduce the shutdown and increase the economic benefits, we must do these three things well in the aspect of valves

Correct selection of valves is the foundation.
Correct use of the valve is the key.
Correct maintenance is the guarantee.


Gate valve Overview

Overview of gate valve standard: the opening and closing part of gate valve is gate.

The movement direction of the ram is perpendicular to the direction of the fluid.

The gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate has two sealing surfaces. The two sealing surfaces of commonly used gate valves are wedge-shaped, and the wedge angle varies with the valve parameters. Wedge gate valve gate can be made into a whole, known as the rigid gate; It can also be made into a ram that can produce a small amount of deformation, so as to improve its processability and make up for the deviation of sealing surface angle in the processing process. This kind of ram is called elastic ram.
Working principle of gate valve: when the gate valve is closed, the sealing surface of flange gate valve can only be sealed by medium pressure, that is, the sealing surface of gate valve is pressed to the valve seat on the other side by medium pressure to ensure the sealing of secret cover, which is self sealing. Most gate valves use forced sealing, that is, when the valve is closed, the gate must be pressed to the seat by external force to ensure the sealing surface. Gate valve gate and stem linear movement, lifting stem gate valve (also known as rising stem gate valve). Generally, there is a trapezoidal thread on the lifting rod, which passes through the nut on the top of the valve and the guide groove on the valve body. The rotary motion becomes linear motion, that is, the operating torque becomes the operating thrust.

When the gate valve is opened:
When the lifting height of the flange gate valve is equal to 1:1 of the valve diameter, the fluid passage will be completely unobstructed, but this position cannot be monitored during operation. In practical use, the apex of the stem is used as a mark, that is, the position where it cannot be opened, as its fully open position. In order to consider the locking phenomenon caused by temperature change, it is usually opened to the top position, and then returned to 1 / 2-1 circle as the position of full open gate valve. Therefore, the full open position of the valve is determined by the position (i.e. stroke) of the ram. In some gate valves, the stem nut is installed on the gate valve, and the handwheel rotation drives the stem to rotate, so as to lift the gate. This kind of valve is called rotary stem gate valve or Non rising stem gate valve.

Gate valve type: according to the configuration of sealing surface, flange gate valve can be divided into wedge gate valve and parallel gate valve. Wedge gate valve can be further divided into: single gate type, double gate plate type and elastic gate type; Parallel gate valve can be divided into single gate plate and double gate plate. According to the thread position of the stem, it can be divided into two types: rising stem gate valve and Non rising stem gate valve.

Gate valve structure features:

1. Gate valve fluid resistance is small, sealing surface is less media scrubbing and corrosion.

2. The workload of opening and closing is saved.

3. The flow direction of the medium is not limited, it will not interfere with the flow, and it will not reduce the pressure.

4. Simple shape, short structure length, good manufacturing process and wide application range.

Application scope of gate valve: gate valve is widely used in domestic steel plant, petroleum, chemical, natural gas, boiler, paper making, textile, medicine, food, transportation, water supply and drainage, energy, polysilicon, electric power and other industrial pipelines for medium cutting and circulation. Flange gate valve is suitable for pipes with nominal pressure of pn1.6 ~ 6.4Mpa and working temperature of – 29 ~ 600 ℃. It can cut off or connect pipeline medium without adjustment and throttling. The applicable medium of gate valve is water, oil, steam, acid medium, etc.