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Bellow Seal Valve -FAQ

1# What Are The Design Features Of A Bellow Seal Valve?

A bellow seal valve has following the following parts:

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• Body
• Bonnet
• Seat ring
• Seat guide
• Bellow
• Stem
• Gasket
• Gland packing

These are the standard parts of a bellow seal valve. Their sizes and configurations vary as per the shared specifications of the clients. If you need to learn more about the requirements and configurations of a bellow seal valve, contact us immediately. We offer a customization facility to design all parts of a bellow seal valve according to your requirements to meet your industrial requirements.

2# How To Prevent A Bellow Seal Valve From Failing?

A bellow valve is a highly reliable device to avoid leakage in industrial piping systems. There are different causes of failure of a bellow valve, including improper selection, inappropriate installation, poor manufacturing quality, and lack of performance. However, you can prevent a bellow seal valve from failure. Follow the below-mentioned tips:

1. Keep on checking high inlet pressure variations and backpressure
2. Always choose the right size and type of a bellow seal valve
3. Make sure that it is working within stem stroke ranges, accurate temperature, and suitable pressure
4. Prevent cavitation, flashing, and inappropriate damage during operation

3# What Precautions Are Necessary While Using A Bellow Seal Valve?

You must follow some precautions while using a bellow seal valve. These precautions include:

1. Read all warnings are instructions to avoid equipment damage or personal injury
2. Follow regular maintenance steps and professional re-conditioning stages
3. In case of highly corrosive chemical environment, always use double seal bellows
4. If the valve cover is wet or there is a smell of media, there must be some kind of damage in the bellow.
5. Avoid prolonged negligence that can cause damage to the entire valve
6. Avoid excessive tightening that hinders the free movement of the plug system

4# What Are The Differences Between An Ordinary Valve Or A Bellow Seal Valve?

• In the case of heated oil transfer systems, other valve systems have high chances of hot oil spillage and loss of equipment. On the contrary, a bellow seal valve offers negligible leakage due to its construction.
• Other valves are less resistant to high temperature, high pressure, and corrosion. It causes leakage and destruction in the valve. On the other hand, a bellow seal valve works efficiently under high pressure, high temperature, and corrosive environments.
• As the internal parts of a bellow seal valve are made of stainless steel, they are highly durable than ordinary valves. They can withstand temperatures above 450C. At the same time, other valves made of standard materials cannot withstand high-temperature ranges.

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5# What Is Parts Inspection Test For A Bellow Seal Valve?

Parts inspection test ensures the working and efficiency of all parts of a bellow seal valve, and it requires special inspection conditions and ambience. These specific conditions include the temperature of 5-40C, humidity level of 20%-80%, and an atmospheric pressure of 86kPa to 106kPa. Usually, this test is performed in three cycles. After three rotations, a minimum value is taken to calculate the minimum cycle life. If a bellow seal valve passes all three test cycles, it is safe for use. It meets the quality standards. It is not considered qualified if it fails to qualify any test cycles.

6# What Is Sealing Test & Whole Machine Test Of A Bellow Seal Valve?

1# Sealing Test:

This test determines invisible leakage in a bellow seal valve. It is conducted in a water tank at specific conditions, including 0.16mpa under atmospheric pressure and 20C temperature for 3 minutes. Hence, it helps to maintain the quality standards of a bellow seal valve.

2# Whole Machine Test:

This test inspects all parts of a bellow seal valve in a fully assembled form to determine its efficiency. All parts and body cavities are cleaned before assembly. Moreover, you can remove the burr too. Once all parts are assembled, they are inspected and tested. It includes everything such as surface polishing, cleaning, painting, and polishing.

7# Which Points You Should Consider Before Installing A Bellow Seal Valve?

• Clean inside of the pipe for removing foreign substances, including pipe chips, scales, gravels, or welding spatters. It prevents leakage and damage to the valve.
• Follow a flow direction arrow on the valve casing to ensure that fluid flows in the same direction.
• Check if there is any hazardous scratch present on the surface of the flange.
• Tighten the flange equally and gradually tighten bolts diagonally to ensure the best alignment.
• Remove protection cap at the groove or the socket a moment before piping.
• Always keep the valve closed while welding the valve and piping system.
• Read the installation instructions provided by the manufacturer.

8# How To Store A Bellow Seal Valve?

If you have purchased bellow seal valves in bulk, you can store them for future use. However, follow these simple guidelines to keep a bellow seal valve for longer.

1. Please do not remove the packing or covering of the bellow seal valve unless you are ready to install it at a desirable location.
2. Always store bellow seal valves indoor places. Avoid placing them outdoor. Keep them away from moisture, dirt, or grease to enhance their lifestyle.
3. Remove polyethene cap or protection seal at the end of the valve just before installation.
4. Keep on monitoring them after a significant interval to ensure their packaging.

9# What Are The Best Materials For Manufacturing A Bellow Seal Valve?

A bellow seal valve consists of three popular materials including:

• Stainless steel AISI 316Ti is the most popular material for manufacturing a bellow seal valve. It contains Titanium that can withstand high-temperature ranges.
• Inconel 600 or Inconel 625 offers excellent resistance, temperature resistance, and fatigue strength.
• Hastalloy C-276 is one of the most significant materials that offer excellent temperature resistance, corrosion resistance, and fatigue strength than Inconel.

These materials are highly durable for critical working environments. Please contact us now to find more information about the manufacturing materials of bellow seal valves.  

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10# What Is The Difference Between Single-Ply & Multi-Ply Bellow Seal Valve Designs?

1# Single-Ply Bellow Seal Valve:

It has a single layer thickness of the metal sheet. Single-ply bellow seal valve is suitable for low-pressure applications, less stroke length, less stroke pressure, and temperature, and it subjects to metal fatigue under critical working environments.

2# Multi-Ply Bellow Seal Valve:

It has a multi-layer thickness of the metal sheet. Multi-ply bellow seal valve is suitable for high-pressure handling fluids. It increases pressure by 80% to 100% than a single-ply bellow seal valve of the same thickness. Its material of construction, fabrication technique, stroke frequency, and stroke length make it reliable for complex industrial applications.

11# What Are Potential Failures In A Bellow Seal Valve & How To Troubleshoot Them?

12# What If A Bellow Seal Valve Is Operating Too Close To Set Pressure?

Operating too close to set pressure takes the valve in the simmer position. In this state, a valve is neither open nor close. It may cause galling or fatigue failure in a bellow seal valve. It is the leading causes of failures in bellow seal valves. You can reduce this type of failure by following the below-mentioned tips:

1. Lower the operating pressure
2. Use a pilot-operated relief valve. It offers a high tolerance between system pressure and the valve’s set pressure.

Feel free to contact our experienced, professional, and certified engineers for dealing with this problem.

13# What Are The Disadvantages Of A Bellow Seal Valve?

A bellow seal valve is an ultra-efficient device for managing leakage in various piping systems. Although it has a large number of benefits, there are some shortcomings. Its disadvantages include:

1. In the case of considerable fluid resistance, it requires a large amount of force to open and close valves.
2. It is not compatible with materials that have high viscosity, easy coking, and large particle size.
3. It shows a poor adjustment performance under certain conditions.

However, its disadvantages are very nominal than its benefits. Even these shortcomings can be overcome under strict supervision and regular maintenance.

14# Why BCST Is The Best Choice For Purchasing A Bellow Seal Valve?

BCST is one of the leading manufacturing companies in China. Being an experienced company for many decades, we have been the first choice of customers across the globe. If you require custom design, we can also offer this facility. All prices are very affordable. Our bellow seal valves are highly durable, ultra-efficient, withstand challenging working conditions, and suitable for numerous industrial applications. You can truly count on us because we hold ISO : license that describes our credibility. If you want to know about the price, customizations, and manufacturing material of the bellow sea valve, please contact us immediately.

15# How To Order Customized Bellow Seal Valve?

It is straightforward to order a customized below seal valve suitable for different applications. Being a valve expert manufacturing company, thousands of customers from other parts of the world choose to get personalized products at very affordable rates. Our customized high pressure, high temperature, and forged steel valves can meet challenging industrial environments. Please share your specifications, including working conditions, industrial application, bellow cartridges, bonnet, stem, sleeve nuts, and manufacturing material. Our experienced engineers analyze your requirements to design the best product within your budget. Feel free to contact with BCST team if you want to know more about the customization of the bellow seal valves!

16# What Is The Average Price Of A Bellow Seal Valve?

The average price of a bellow seal valve ranges from $50 to $450. The variation in price ranges is due to manufacturing quality, industrial application, size, and design features, and the price of bellow seal valves is compatible with their applications. We ensure superior quality, durability, and excellent performance at the lowest possible cost. We always test all products before shipment to ensure their credibility. Our premium-quality products can withstand all critical working environments and prevent potential damage from leakage at industrial units. If you want to know more about pricing-related information, please contact us immediately. Keep visiting our website for more queries.

17# What If You Are Using An Oversized Bellow Seal Valve?

Keep in mind that the size of the valve must be compatible with its uses. An oversized bellow seal valve leads to fluid instability, premature fatigue failure, and permanent valve damage. It is recommended to use a valve with an actual orifice area 3 to 5 times larger than the required area. However, if you have faced failures caused by using an oversized bellow seal valve, follow the below-mentioned tips:

1. Use a modulating pilot-operated relief valve
2. Change the set pressure to reduce fluid instability
3. Replace it with the right sized valve

Shut-off Valve vs Gate Valve: Which One To Choose?

In industrial pipelines, shut-off and gate valves control the flow of the medium, typically liquid and gases, passing through them. Although both the devices are ideal for similar settings, a few critical differences set the two apart. So, in this article, let’s discuss everything about shut off valve vs gate valve to decide which one to pick and when.

What is a Gate Valve?

Also known as sluice valves, a gate valve bought from reliable China valves manufacturers is typically employed in ancient houses to allow the residents to control the medium’s flow rate. It includes slow trickles instead of full flow but does not offer an immediate stop. Their mechanism involves a round knob that lowers and raises the internal gate or wedge when rotated to control the water flow rate.

A gate valve is the most prevalent in water supply systems. This liner-motion isolation device is not ideal for regulating the flow. Instead, it completely opens or closes the flow because a partial opening causes harm. It isolates parts of a water supply network for maintenance, repair, new installation, and rerouting the flow.

These devices are available in various sizes, materials, temperatures, pressure ratings, and designs. One can also find electric and pneumatic actuator gate valves for varied applications. It is among the most commonly used valves today because of its simple design and ability to use in various low-pressure-drop applications.

Gate valves typically have a full-port design to allow fluid to flow without obstruction and causing a pressure drop in the pipeline. Thus, it enables the use of a cleaning pig to clean the channels.

What is a Shut-Off Valve?

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Also known as ball valves, a shut-off valve is typically employed in modern houses to control the flow of the medium. As its name suggests, a shut-off valve uses a rotatory ball with a bore to prevent the flow of medium from one opening to the next.

It employs a handle to monitor the placement of a hollow, perforated sphere in the mechanism. When the handle rotates, the hole opens or closes the flow of water along with it. It is easy to determine whether the valve is open or closed through its handle placement. When available, the handle lies flat, aligning with the flow. When it completes, the handle is perpendicular to the flow.

A shut-off valve is the best choice for gaseous applications because of its strong seal, reliable and secure closing even after prolonged rest periods, and durability. The devices of an industrial valves company work well even after several cycles. They have a higher resistance to contaminated media than most other valve types, ensuring a good seal even when the medium is dirty.

All these characteristics make the ball valve suitable for shut-off and control uses in a pipeline.

Shut Off Valve vs Gate Valve

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Since valves are one of the most crucial parts of a functioning plumbing system, they should operate adequately to avoid leaks and unwanted flow. While several types of valves are available today, shut-off and gate valves are the most prevalent. It is vital to learn about shut off valve vs gate valve to decide which one to use for a particular application. So, let’s go!

BASIS OF DIFFERENCESHUT OFF VALVEGATE VALVESHUT OFF MECHANISMIt offers quick shut-off with only a quarter turn (90 degrees) to close the device.It offers slow shut-off as it requires more than a 360 degrees rotation to shut off.WATER HAMMERFast opening and closing of the valve may cause a water hammer.Slow start and finish of the valve reduces the risk of water hammer.VISUAL DETECTIONAn open or closed state is easily detectable by the handle position.A loose or closed form is not easily noticeable by the handle position.COSTMore expensive than a gate valve of similar specifications.Cheaper than a shut-off valve of similar specifications.INSTALLATION SPACERequires more space to accommodate a quarter-turn handle.Requires less installation space compared to a shut-off valve.SIZESuitable for bore sizes below two inches.Ideal for bore sizes above two inches.LEAKAGEIt offers tight sealing even after prolonged usage.More prone to leaks compared to a shut-off valve.DURABILITYDurable and less prone to damage.Less stable as the valve stem is prone to corrosion.APPLICATIONSFire protection systems and marine applications.Power plants, mining, and Water Treatment.ENVIRONMENTLow-temperature and low-pressure environments.High-temperature and high-pressure environments.MAINTENANCEDifficult to clean as the slurry particles may damage the rotatory ball, thus causing contamination.Perfect for applications with slurries and viscous media as they are easier to clean and maintain.SUITABILITYSuitable for new plumbing systems with frequent shut-off requirements.Ideal for applications where a frequent shut-off is not required.OTHER NAMESIndustrial ball valveMulti-turn or Sluice valve

How to Choose Between a Gate Valve and a Shut-Off Valve?

Here is a list of criteria to consider when deciding to purchase a gate and a ball valve:

Number of Ports: A gate valve includes two ports, while a shut-off valve has more than two ports.

The Flow capacity: A gate valve offers a larger flow capacity than a shut-off valve because of its larger diameters.

Pressure: For high-pressure applications, a gate valve is more suitable because a ball valve’s fast opening and closing may cause a water hammer. However, both are perfect for low-pressure applications.

Cost: A ball valve is generally more expensive than a gate valve purchased from gate valve manufacturers having similar specifications.

Maintenance: If the application requires less maintenance, a ball valve is more suitable than a gate valve. So, it is more pocket-friendly in the long run.

Sealing: A shut-off valve offers tight sealing and complete closing than a gate valve. So, it is better suited for applications like natural gas.

Shut-off Speed: A shut-off valve is suitable for applications requiring faster opening and closing speed, especially during an emergency. But an industrial gate valve needs more than 360 degrees turn, making it slower to operate than a ball valve.

Parting Thoughts

A ball valve includes a rotatory ball with a bore and a stem. When the handle attached to a stem turns, the ball also rotates to open or close the flow. It is also known as a quarter-turn valve because its grip takes a quarter (90 degrees) turn to permit or block media flow.

A gate valve includes a gate to control the flow of media passing through the pipe. It has a solid disk structure connected to the stem. The gate lifts to open the valve and returns down to its original position to close it. It includes a bonnet to control the gate when it rotates.

Depending upon the application, one can decide whether to use a gate or a shut-off valve. Please contact us to purchase these devices in durable quality at typically cheaper rates than the market.

Introduction to Gate Valves and Gate Valve Types (With PDF) – What Is Piping

A Gate valve is a linear-motion manual valve that has a vertical rectangular or circular disc that slides across an opening to stop the flow that acts as a “gate”. Generally used for isolation purposes fully open or closed, Gate valves are not suitable for throttling service because the high-velocity flow will cause a partially open disk to vibrate and chatter and will hasten the erosion of the disc and seating surfaces.

Functions of Gate Valve

The open/close flow is achieved by moving the gate of the gate valve into or out of the fluid-flow stream. The flow of the fluid through the valve can be in either direction. Gate Valve is commonly used in refineries and petrochemical plants where pressure is low, and less used in upstream facilities due to high operating pressure, long on/off times (requiring many turns of the handwheel to open it or to close it), and severe environmental conditions.

A full port gate valve provides a full line size (equal to pipe dimensions) thus resulting in a minimum-flow pressure drop, On the other hand, A Reduced port gate valve smaller than the line size (Flow area less than the pipe) causes a slightly high-pressure drop than a full port.

Gate Valve Parts

Refer to the below-attached figure (Fig. 1) which shows the main components of a gate valve.

Fig. 1: Full-Port Gate Valve

The items in Fig. 1 as per the corresponding numbers are given below:

Body

Bonnet

Wedge

Stem

Gland

Seat ring

Yoke

Packing

Gland Flange

Valve port

Yoke Bush

Lantern

Back Seat Bushing

Gland eyebolts & nuts

Bonnet bolts & nuts

Hand Wheel

Hand Wheel nut

Bonnet Gasket

There are three main parts in a Gate valve: body, bonnet, and trim.

The valve body is connected to piping or equipment by means of flanged, welded, or screwed connections.

The bonnet contains the moving parts which are connected to the body with bolts.

The valve internal parts (removable and replaceable) that come in direct contact with the fluid are termed Valve trim which consists of the stem, the gate, the disc or wedge, and the seat rings.

Types of Gate Valves/ Gate Valve Types

Gate valves are divided into a number of classes, depending on their disc and type of stems. Gate Valves are classified by:

I. Gate Valve types as per Type of Closing Element:

1. Parallel disk Gate Valve:

Parallel disk gate valves consist of two discs that are forced apart against parallel seats by a spring at the point of the closure. The most famous type is the knife gate valve which has a flat gate between two parallel seats (an upstream and a downstream seat) to achieve the required shut-off. The application of a parallel gate valve is limited to low pressures and low-pressure drops.

Fig. 2: Parallel Disk Gate Valve

2. Solid-Wedge Gate Valve:

The solid, or single wedge gate valve is the most widely used and the lowest cost used in the process industry for oil, gas, and air services. The purpose of the wedge shape is to introduce a high supplementary seating load. Solid-Wedge Gate Valve can be installed in any position, suitable for almost all fluids and practical for turbulent flow services.

In some situations, the valve cannot be reopened until the system temperature reheats the valve; this phenomenon is known as “Thermal blinding”. Wedge gate valves can be further described as inside screw or outside screw patterns. Solid wedge gate valves in the waterworks industry are popular as Sluice valves.

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Fig. 3: Solid Wedge Gate Valve

3. Flexible Wedge Gate Valve

A flexible wedge gate valve employs a flexible wedge that is a one-piece disk with a cut around the perimeter (the cut varies in size, shape, and depth). Thermal expansion and contraction entail no problems in such kinds of gate valves as the disk is able to compensate for this and remains easy to open. Flexible wedge gate valves are widely used in steam systems to prevent thermal blinding.

Fig. 4: Flexible Wedge Gate Valve

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Types of Pipes | Classification of Pipes (PDF)

4. Split Wedge Gate Valve

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Split wedges of this type of gate valve are made in two separate halves. This allows the wedge angle between their outer faces to fit the seat (self-adjusting and self-aligning to both seating surfaces).

Fig. 5: Split Wedge Gate Valve

5. Double-disc Valves

In these types of valves, the gate is in the form of two discs that are forced apart against parallel seats by a spring. this provides tight sealing without relying on fluid pressure, making this type of valve particularly suitable for steam duties as well as handling gases and light oils.

6. Bellows Seal Gate Valves

Bellows seal gate valves are designed to minimize exposure to harmful substances through valve-stem leakage. The bellow is a metallic device capable of sealing between the valve stem and the bonnet to prevent the escape of the system fluid to the atmosphere. The bellows take the form of convolutions that can move linearly. During operation, the bellows eliminate the leak path to the atmosphere.

II. Gate Valve types as per Type of Stem:

1. Rising Stem Gate Valve with Outside Screw

This type of gate valve is also known as OS & Y type (Outside steam and York). The stem rises while opening and lower while closing the valve offering an indication of the gate valve position. The stem threads never contact the flow medium (not subject to corrosion/erosion).

Fig. 6: Rising Stem gate valve

2. Non-Rising Stem Gate Valve

Also known as the Insider screw Valve, The stem of the non-rising stem gate valve is threaded into the gate. The hand wheel and stem move together and there is no rising or lowering of the stem. The stem is in contact with the flow medium.

Fig. 7: Non-Rising Stem gate valve

Working of Gate Valves

The working of a gate valve is quite simple. When the gate of the valve is lifted from the flow path, the valve opens and when the gate again returns to its position, the gate valve closes. This gate movement is achieved by manually turning the hand wheel. The hand wheel rotates the valve stem and the internal threaded mechanism provides a vertical movement of the gate. As the hand wheel is turned more than one full cycle to fully open or fully close the gate valve, they are also known as multi-turn valves. Electrically actuated gate valves are available but not cost-effective.

Actuation of Gate Valves

Manual actuation of gate valves is invariably by screw and handwheel. The screw mechanism may be exposed or protected and the screw rising or non-rising. A variety of materials for the working parts is offered by some manufacturers.

Power actuators are very often fitted when the gate valves are difficult to access and are operated frequently. automation and semi-automation control schemes make extensive use of actuators.

Advantages of Gate valve

Gate valves are adequate for high-pressure and temperature applications. The main advantages of gate valves are:

Provide very good shutoff characteristics.

Low Pressure-Drop; very low frictional loss.

the maintenance requirement is less.

can be used as a Bi-directional valve

low cost

available in various sizes.

Disadvantages of Gate valve

Cannot be used for throttling service.

Slow disc movement in operation, it takes time to fully open or fully close.

Lapping and grinding repairs are difficult to accomplish.

May create noise and vibration when partially open.

Prone to Seat and Disk wear.

Gate Valve Materials

Various types of materials are used for gate valve construction. Typical common materials used are cast carbon steel, cast iron, ductile iron, gunmetal, bronze, alloy steel, stainless steel, and forged steel. Brass and PVC gate valves are used for plumbing services. The material selection for gate valves primarily depends on fluid service and its design temperature. The following table provides a typical example of common materials used in Gate valve construction.

Fig. 8: Gate valve materials

Applicable codes and standards for gate valve design

The following codes and standards govern the design specification of gate valves:

Valve Design: API 600/ API 602/ BS/ API 603/ API6D/ IS780 /BS / BS

Valve Pressure Testing: API 598

Valve Pressure Temperature Rating: API B16.34

Face-to-Face Dimensions: ANSI B16.10

Flange Drilling: ANSI B16.5 / ASME B 16.47/ BS 10 Table / DIN /IS /JIS Standards

Butt/ Socket Welded End: ANSI B16.25 and B16.11

Screwed End: ANSI B 1.20.1 (BSP/NPT)

Gate Valve Symbols

The gate valve symbols used in the different organization varies a little bit. Normally any one of the following three types of gate valve symbols given in Fig. 9 is used as a gate valve symbol.

Fig. 9: Gate Valve Symbols

Gate valve vs Ball Valve

Both the gate valve and Ball valve are widely used for isolation services in the oil and gas industries. However, there are a few differences between the gate valve and the ball valve. Some of such differences are listed below in a tabular format for reference:

ParameterGate ValveBall valveWorking PrincipleGate valves control the valve using its gate. When lifted up, allows full flow, and when down, no flow.Ball valves feature a stem and a ball with an opening inside. When the opening is lined up with the pipe by turning the control lever fluid can pass, otherwise, the valve is off.CostGate valves are Relatively cheaperBall valves are comparatively Costlier.Turning of lever or hand-wheelGate valves feature a Multi-Turn mechanism.Ball valves are Quarter-turn valves.WeightThe weight of the Gate valve is normally less than the ball valve for the same size and rating.Ball Valve weights are comparatively more than gate valves.Shut off capabilities The shut-off capabilities of gate valves are not at par with ball valves.Comparatively better than gate valves; more reliable.Surge ProbabilityAs the operation of a gate valve is slow, less probability of water hammer.Ball valves are more prone to water hammer or surge creation.Vibration probabilityPartially open gate valves cause vibration or noiseThe possibility of noise production is less in ball valves.Operating Space requirementThe operating space requirement for gate valves is usually less.More space is required to operate a ball valve.Visual Clue for on/off positionNo clue from the outside, it’s simply guessing.Easy to understand if the ball valve is in the open or closed position.Gate Valve vs Ball Valve in a Tabular Format

Fig. 10: Typical gate valves

The Ever-Popular Gate Valve

This low-tech valve may not have changed much in the last 100 years, but the gate valve plays a major role in virtually every refinery, chemical plant and industrial facility in the world.

The most popular style of valve in the world of flow control is the gate valve. They are the on/off switches of the fluid control industry and they are found in every refinery, chemical plant, power plant and industrial facility. Gate valves exist for one primary purpose- to stop flow. Because of this, they are often referred to as “stop” or “block” valves. Gate valves are manufactured in a wide range of sizes- from ¼” through 144”.

It is not recommended to operate gate valves in the partially open position, or to use them in throttling service. When a gate valve is partially open, it closure element (disc or wedge) can vibrate against the seats and become scratched causing them to lose their seating integrity.

The chief advantage of a gate valve is that it offers virtually no resistance to flow in the open position. Only a full port ball valve can equal the gate valve’s flow characteristics. Due to their symmetrical design and equilateral seating, gate valves can be used to stop flow from either direction. They are available in every material from the shiny brass construction of the diminutive ½” water valves on the hardware store shelf, to the exotic high alloy models found in nuclear power installations.

Gate valves have been an important piece of fluid control equipment for over 150 years. In fact, the very first valve patent issued in the United States was for a “gate valve”. Since those humble beginnings in the 19th century, the gate valve has answered the fluid control call with relatively little basic design change.

From the outside, most gate valves look somewhat similar. However, inside there are a host of different design possibilities. Most gate valves consist of a body and bonnet that contains a closure element, called a disc or a gate. The closure element is attached to a stem that passes through the bonnet of the valve, ultimately interfacing with a handwheel or other device to operate the stem. Pressure around the stem is contained through the use of packing material which is compressed into a packing area or chamber.

Trim

The word “trim” is often overheard when valve professionals are talking about industrial gate valves. Trim has nothing to do with how slim and fit a valve is, rather it refers to the internal components of a valve that are exposed to great stress or subject to a harsh combination of erosion and corrosion. In a gate valve the trim components are the stem, disc seating area, body seats and backseat, if applicable. Common utility bronze or brass valves usually have trim parts of the same material as the body and bonnet. Cast and ductile iron valves have either all iron trim components or occasionally bronze trim. The term for an iron valve with bronze trim is “iron body, bronze mounted” or IBBM for short.
Because of their weldability, steel valves can be furnished with a number of different trims. Stellite, Hastelloy, 316ss, 347ss, Monel, and Alloy 20 are some of the materials regularly used for gate valve trim.

During most of the 19th century, valves were predominantly supplied with screwed end connections, even in sizes as large as 12” NPT. Since that time the flanged end connection has become the most popular. Other end connection types in use today include screwed, ring-type-joint (RTJ), Victaulic, Greyloc and water works “mechanical joint”.

Disc Design

Gate valves can have one of two different disc designs: parallel or tapered type. Both operate on the principle of a closure element (disc or gate) sliding into a slot in the pipeline and closing off the fluid path. The tapered disc of the “wedge gate” valve is machined to match a pair of body seats set at the same angle, usually about 10o. If machined correctly, as the tapered disc engages the seats, it locks firmly into place, stopping the flow.

Three types of wedge gates are available: solid disc, one piece flexible type, and two piece split design.

The solid wedge has been around the longest and at one time virtually all wedge gates were the solid type. The drawback to a solid design is that it does not have any flexibility and if there is any valve body/seat distortion due to extreme temperature fluctuations or pipe stresses, the solid disc can become jammed in the seats. The solid disc is still standard on bronze, cast iron, water service and compact carbon steel valves (API 602 type). Today, solid discs are usually only available as special order items on large diameter gate valves.

The flexible wedge type is just that- flexible. By the addition of a groove or slot around its periphery, the flexible disc can adapt to temperature changes and adverse piping stresses without binding. The flexible design also is a little easier to manufacture, in that minor imperfections in the seating surface angles can be compensated for by the disc’s flexibility. The “flex-wedge” design is by far the most common type seen on commodity gate valves used in industrial applications.

The split wedge type consists of a two-piece design with mating surfaces on the back side of each disc half. These mating surfaces allow the downward stem thrust to be uniformly transferred to the disc faces and onto the seats. This flexible design also provides protection against jamming due to thermal expansion. A disadvantage to the split design is that in “dirty” services, residue or debris can cake in between the disc halves, causing the valve to improperly seat or even jam. Split wedge designs are commonly found on stainless steel and high alloy valves, as well as many small bronze valves.

Wedge gates are guided by grooves or ribs cast or welded into the body of the valve. These wedge guides keep the disc in alignment as it opens or closes and also keeps the disc from sliding against the downstream seat during opening and closing.

The second disc design is the parallel type. Unlike the wedge type gate valve, which relies on the stem thrust to “wedge” the disc into the seats to seal, the parallel seat valve needs some assistance to seal properly. The sealing assistance is usually in the form of a spring loaded or mechanically activated spreading action between the two disc halves as the valve closes fully. On most parallel seat designs the friction and sealing force is relieved as the gate disengages from the seats.

The most common use for parallel disc valves today is in the pipeline industry, where elastomer seat seals and ambient operating temperatures make valve virtually leak proof. Parallel gates are also used in some high pressure, high temperature steam applications, to help reduce the possibility of locking the disc in the closed position due to a radical change in temperature.

Regardless of disc design or type, the gate valve closure element must come in perfect contact with seats in the valve body. The body seats may be welded, screwed, pressed or swaged in, or be integral with the valve body. Most industrial steel gate valves utilize seat rings that are welded into the valve body. For most of the 20th century the norm was screwed in seat rings in steel valves. However, advances in welding and valve repair techniques made the screwed-in rings obsolete. Seat rings and valve discs are also often overlaid with corrosion or abrasion resistant alloys to increase their service life.

Body-Bonnet Design

Gate valves are normally available in five different body/bonnet joint designs. They are: screwed, union, bolted-bonnet, welded-bonnet & pressure-seal.

The screwed joint is the simplest design. However it is only used for inexpensive bronze valves that rarely if ever require disassembled.

The union joint is also primarily used on bronze valves, but the union design allows for easier disassembly for repair and maintenance.

The bolted-bonnet joint is the most popular joint and it is used on the vast majority of gate valves in industrial use today. Unlike threaded and union bonnet valves, the bolted-bonnet connection requires a gasket to seal the joint between the body and bonnet. On lower pressure valves, sheet gasket materials are used. ANSI Class 150 steel valves usually employ a corrugated soft iron or graphite/corrugated soft iron gasket. Valves of class 300 and higher employ either a spiral-wound or ring joint type gasket.

The pressure-seal joint is energized by the fluid pressure in the valve body acting upon a wedge shaped, soft iron or graphite gasket wedged between the body and bonnet. On a pressure-seal valve, the higher the body cavity pressure, the greater the force on the gasket. Pressure-seal bonnets are used extensively for high-pressure high-temperature applications, such as the power industry. Pressure-seal valves are much lighter than their corresponding bolted bonnet designs. Due to the pressure energization of the seal ring, they are normally not used in pressure classes below ANSI class 600.

Welded bonnets are a very popular body-bonnet joint for compact steel valves in sizes ½” through 2” and pressure classes 800 through , where disassembly is not required. The higher pressure welded-bonnet type valves rely on threads to handle the force generated by the body cavity pressure, while a small peripheral weld bevel actually contains the pressure. Like pressure-seal valves, welded-bonnet valves are much lighter than their bolted-bonnet counterparts.

Stem Design

Three different bonnet/stem designs are predominant in gate valve construction. They are: inside screw, rising stem (ISRS), non-rising stem (NRS), and outside screw and yoke (OS&Y).

The ISRS bonnet/stem design is the most popular design in use today on bronze valves. Due to the fact that it exposes the stem threads to the process fluid and potential corrosion damage which could cause a stem to disc failure, the ISRS design is not used for critical service industrial applications.

The NRS type is another special purpose type that is used in applications where there is limited vertical clearance above the handwheel, because on an NRS valve, the stem does not rise up as the valve is opened. Most NRS valves today are manufactured of either iron or bronze. Some applications such as marine use, where clearances are tight, often use NRS steel gate valves.

The most common stem/bonnet design in use on industrial valves is the OS&Y. The OS&Y design is preferred for corrosive environments because the threads are outside the fluid containment area. It also differs from other designs in that the handwheel is attached to a bushing at the top of the valve yoke, and not to the stem itself, thus the handwheel does not rise as the valve is opened.

Also in the gate valve family are knife and sluice gates. The bonnetless knife gate is especially suited for use in slurries such as in pulp and paper mills. Knife gates are very thin, only slightly wider than there closure element (disc). Because of their unique geometry and thin cross-section, knife gates are limited to low pressure applications.

In appearance, the sluice gate doesn’t look like it even belongs in the gate valve family, however based upon its sliding disc design; it is characterized as a gate valve. Sluice gates are limited to very low pressures, in most cases, simple head pressure. They are used primarily in waste water and irrigation systems.
Valve Standards

Gate valves standards are produced by several standards making organizations, for a multitude of industries. Here are some of the better known gate valve specifications:

American Petroleum Institute
*API 600 “Steel Gate Valves, Flanged & Buttwelding Ends”, it is a companion document to ISO .
*API 602 “Compact Steel Gate Valves”
*API 603 “Corrosion Resistant Bolted Bonnet Gate Valves”
*API 6D “Specification for Pipeline Valves”, it is a companion document to ISO .

Manufacturers Standardization Society
*SP-70 “Cast Iron Gate Valves”
*SP-80 “Bronze Gate, Globe, Angle and Check Valves”
*SP-81 “Stainless Steel Bonnetless, Flanged, Knife Gate Valves”

American Waterworks Association
*AWWA C500 “Metal-Seated Gate Valves for Water Supply Service”
*AWWA C509 “Resilient-Seated Gate Valves for Water Supply Service”
*AWWA C515 “Resilient-Seated Gate Valves for Water Supply Service”

American Society of Mechanical Engineers
*B16.34 “Valves- Flanged, Threaded and Welding End”

Materials of Construction

Gate valves are manufactured in virtually every metal from Aluminum to Zirconium. They are also manufactured in a variety of engineering plastics. The most common materials however, are steel, iron and bronze.

Bronze offers the greatest machinability and the lowest manufacturing cost. The features that make bronze easy to machine, its lower strength and softness, also make the valve only suitable for lower pressure applications. The predominant service for bronze valves is on water and utility lines where pressures are lower than about 300 psi.

Iron valves are in between bronze and steel as far as strength goes. The iron is slightly harder to machine, but the iron castings are relatively easy to pour. Iron for valves is commonly two types; grey or cast iron and malleable iron. In refinery and petrochemical service iron valves are usually restricted to low pressure water lines. The high carbon content and better rust resistance of iron valves makes them more suitable for buried service than steel valves.

For industrial valves, steel is the material of choice. A broad spectrum of steels are utilized for valve construction, from the lowest grade WCB, to the chrome/moly’s. Unlike the brasses, bronzes and irons, most steels and low alloys are readily weldable, which makes them easier to modify, repair and in some cases even easier to manufacture. Gate valves are also manufactured in a number of exotic alloys from Titanium to Zirconium.

There have been several attempts to make the gate valve obsolete and take away its market share, but they have only met with limited success. The first challenger to the gate valve throne was the ball valve, which came into prominence during the middle part of the 20th century. Ball valves have been substituted for gate valves in many lower pressure and lower temperature applications, but in some cases they are more expensive to manufacture and repair. The elastomer seats of the ball valve also limit them to temperatures below about 500 degrees F.

Butterfly valves have supplanted gate valves in some of the larger (48” and above) low pressure applications, such as water works usage. The metal-seated butterfly valve has also been successful in certain critical service applications that once were solely the realm of the gate valve, but their high initial cost and very high repair costs make them unlikely to ever completely replace the venerable gate valve.

Gate Valve Actuation

The most common method of opening and closing (actuating) a valve is through a handwheel attached to the yoke or bonnet. This works fine on moderate size valves operating at reasonable pressures, but some severe operating situations call for more muscle. For example, an 18”, class , main steam isolating valve in a power plant operating at psi and degrees F. requires a huge amount of torque to open under pressure. The only solution is remote actuation- usually in the form of an electric motor or hydraulic actuator.

Additional gate valve actuation can be provided by pneumatic cylinders. In some cases these sit directly on top of the yoke and are attached directly to the stem, to provide a quick-opening form of actuation. For additional leverage a standard gate valve might have a manual gear operator attached to it to decrease the amount of force required to open and close it under pressure. These devices are called bevel gears.

Repair of Gate Valves

Industrial gate valves are often used in harsh environments and sometimes these valves need to be repaired. The decision to repair or replace a valve usually is a result of comparing the replacement cost to the repair cost. When the repair cost exceeds 50-65% of the cost of a new valve, the decision is usually to replace the valve, unless the delivery is unacceptable.

Generally speaking, all bronze valves, except for expensive cryogenic designs, are replaced rather than repaired. Iron valves, except for the largest sizes, are also replaced rather than repaired. Steel and alloy gate valves are the most repaired types. Steel valves smaller than 12”, class 150 are usually not repaired, unless replacements are not readily available. On the other hand, high alloy gate valves as small as ½” size may be repaired because of their high cost and long lead time.

Some gate valves, such as large diameter, buttweld end and pressure-seal types are often repaired in the field. These field repairs are often difficult and pose logistical challenges, but compared to the cost of removing them from the line and shipping them to a repair facility, field repair is more economical option.

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