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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.

RESILIENT SEATS

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.

TRUNNION DESIGN

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.

METAL-SEATED DESIGNS

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.

BALL VALVE STANDARDS

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!
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What-is-a-Gate-Valve-and-How-does-they-work

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.

Bonnets

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.

Gates

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

FAQ

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.

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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:

PTFE Seal

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®.

EPDM Seal

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.

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