Knowledge of Gate valves

What is a gate valve?

A gate valve has a flat closure element that slides into the flow stream to stop the fluid. They are one of the most commonly used valves, and are primarily used to permit or prevent the flow of liquids.

It is also known by other names like knife valve or slide valve or stop or block valve as its primary purpose is to stop the flow. This valve has become an important piece of fluid control equipment for more than 150 years. In fact, this was the first valve patent issued in the United States. The gate valve has become a one-stop solution for fluid control call with relatively little basic design change.

Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher pressure applications.
Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 2250 psi (15 MPa). The unique feature of the pressure seal bonnet is that the bonnet ends in a downward-facing cup which fits inside the body of the valve. As the internal pressure in the valve increases, the sides of the cup are forced outward. improving the body-bonnet seal. Other constructions where the seal is provided by external clamping pressure tend to create leaks in the body-bonnet joint.
Gate valves may have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Gate valves are typically constructed from cast iron, ductile iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels.
All-metal gate valves are typically used in ultra-high vacuum chambers to isolate regions of the chamber.

Types of gate valves:
There are two types of gate valves depending on the disc design. They are:

  • Parallel gate valve: This uses a flat disc gate between two parallel seat—up upstream and downstream. Parallel gate valve is widely used the pipeline industry. Unlike the wedge gate valve, the parallel gate valve needs some assistance to seal properly which is usually done in the form of a spring loaded or mechanically activated spreading action between the two disc halves. These types of valve design can fit into angularly or asymmetric misaligned valve seats.

A diagrammatic representation of different types of pipe valves.

  • Wedge-shaped gate valve:
    This type of valve is of three types:
    1. Solid wedge: The solid wedge is the oldest form of gate valve and a drawback to this design is that it does not have any flexibility. There is the chance of solid disc getting jammed in the seats if there is any valve body/seat distortion due to extreme temperature fluctuations.
    2. Flexible wedge: With the addition of a groove or slot around its periphery, the flexible wedge gate valve can adapt to temperature changes and adverse piping stresses without binding. This design is little easier to manufacture and is the most common type seen on commodity gate valves used in industrial applications.
    3. Split wedge: This is of a two-piece design having mating surfaces on the back side of each disc half. This allow the downward stem thrust to be uniformly transferred to the disc faces and onto the seats. This provides protection against jamming due to thermal expansion.

Designs of gate valves:
There are five popular body/bonnet joint designs in gate valves. They are:

  • Screwed: This is the most simple design available and it is used for inexpensive valves.
  • Union: This design allows for easier disassembly for repair and maintenance.
  • Bolted-bonnet: The most popular design and used in large number of gate valves. This requires a gasket to seal the joint between the body and bonnet.
  • Welded-bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
  • Pressure-seal: The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve. They are used extensively for high-pressure high-temperature applications.

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.

Parallel vs wedge-shaped gate valves

Gate valves can be divided into two main types: Parallel and wedge-shaped. The parallel gate valves use a flat gate between two parallel seats, and a popular type is the knife gate valve designed with a sharp edge on the bottom of the gate. The wedge-shaped gate valves use two inclined seats and a slightly mismatched inclined gate. 

Metal seated vs resilient seated gate valves

Before the resilient seated gate valve was introduced to the market, gate valves with a metal seated wedge were widely used. The conical wedge design and angular sealing devices of a metal seated wedge require a depression in the valve bottom to ensure a tight closure. Herewith, sand and pebbles are embedded in the bore. The pipe system will never be completely free from impurities regardless of how thoroughly the pipe is flushed upon installation or repair. Thus any metal wedge will eventually lose its ability to be drop-tight. 
A resilient seated gate valve has a plain valve bottom allowing free passage for sand and pebbles in the valve. If impurities pass as the valve closes, the rubber surface will close around the impurities while the valve is closed. A high-quality rubber compound is soft enough to absorb impurities, yet strong enough to wash the impurities through when the valve is opened again. This means that the rubber surface will regain its original shape securing a drop-tight sealing. 

Parts of a gate valve

why prohibit the use of gate valves on oxygen pipes - Knowledge of Gate valves

gate valve is comprised of certain parts that allow it to function properly. The most principal part of this particular valve is the valve’s body or shell, which is considered the initial pressure boundary and can connect inlet and outlet pipes in a piping system. The shape of the body is often cylindrical and houses the gates, also known as the valve’s disks, and the valve’s seats.

There is a covering used for a valve body’s opening at the top and this is called the bonnet. A valve’s bonnet is often screwed in so as to enable any sort of maintenance or repair work to be done without having to remove the entire gate valve from the piping system, which would cause more headaches than necessary. The bonnet houses other internal parts of the valve such as the stem, gland packing, and gland follower.

The internal parts are known collectively as a valve’s trim and these are the parts that enable the valve to control the flow of water and other basic actions to be made. The first integral part of the trim is the disk, which has different kinds of designs as mentioned in the article entitled gate valve selection guide. The disk is what closes and opens, thus explaining why it is often referred to as the gate in this particular kind of valve. When the hand wheel or actuator is turned closed, the disk also seals up, preventing any water flow from occurring. When the hand wheel or actuator is turned open, the disk opens up, allowing water flow to happen.

The seat is thought of as the partner of the disk and can either be in a “V” shape or pointed valley for a wedge disk or in a parallel shape to that of a parallel disk. It is vital that both the disk and the seat are able to have a snug enough fit in order for it to be sealed, thus, making it impossible for any flow to occur when the valve has been closed.

The stem of the valve connects the hand wheel or actuator to the disk. The stem rotates as the hand wheel is turned, making it possible for the disk to rotate in the same motion as the stem and hand wheel. There are two kinds of stems: the rising stem and the non-rising stem. A rising stem rises above the hand wheel as the valve is opened while a non-rising stem does not.

The hand wheel is the circular part found at the very top of a gate valve. It is what controls the stem, which in turn controls the disk. It is turned clockwise to close the valve and counter-clockwise to open the valve.

The gland packing is composed of a material that creates a seal between the stem and the trim. The gland follower extends into the gland packing. It is necessary for the gland packing to be properly compressed to ensure no breach occurs.

How to maintain a gate valve

The proper maintenance of a gate valve, or any valvefor that matter, is important in ensuring that it will last for many years and work as efficiently as it should. Thinking that it can simply be installed and left alone afterwards is the beginning of the end since the time will definitely come that the valve will either have to be repaired or totally replaced due to lack of maintenance. So, if you want to spare yourself a few headaches and several dollars in repair or replacement costs, learn how to maintain your gate valves effectively.

The points at which an inlet pipe and an outlet pipe are connected to the valve can end up becoming weak points, especially if there happens to be some sort of blockage that impedes the flowof fluidor if the pipesfreeze up during the winter season. In order to make sure that the points of connection are maintained well, use some silicone plumbers tape or Teflon tape to wrap the threads on a regular basis or at least once a year. This will ensure that the connection between the pipesand the valve remain problem-free.

If the valve begins to prove to be too difficult to open or close, this probably means that there is not enough lubrication. So as to have smoother operations, lubricate the stemof the gate valve as well as its shaftwith some spray lubricant. During the winter months, remember to lubricate more often since the tendency of the valves ticking becomes more prevalent then. The proper lubrication of the valve makes it easier for you to operate it, allowing fluid to flow when it needs to and allowing the valve to stop any flow when the need for the fluid has been met.

Gate valves can be made from a variety of materials and the one that you have is made of steel or some other similar metallic substance, the possibility of rust forming is very much real. Piping systems that are located outside of a structure have a greater chance of become rusty so make sure to check regularly. Once you notice rust forming, you can try scraping off the rust with a wire brush or steel wool pad. Consider painting your valves and pipesin order to prevent rust from forming. If there is already rust, remember to remove it first before proceeding with the painting part. Getting rid of any current rust formation and preventing any further rust from forming will ensure your pipes last longer and will not need replacing any time soon. Remember that rust does spread so the sooner you fix the problem, the better.

Make sure the nuts and bolts are tightly screwed in to maintain the right amount of water pressureinside.

The gate valve selection guide

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.

Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@metallicsteel.com

Please notice that you might be interested in the other technical articles we’ve published:

  • How To Choose A Valve

  • Knowledge of a filter and a gate valve

  • What Are the Needle Valves

  • What are Thread Valves

  • What is a Butterfly Valve

  • What are Pipe Valves

  • Knowledge of globe valves

  • Knowledge of ball valves

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