1. What is gate valve?

Gate valve is a type of valve commonly used for the purpose of opening/closing the fluid flow, not often used to regulate flow. Gate valve works with the valve disc moving up and down through connection with the control arm like a gate. It is also for this reason that it is called a gate valve.

Gate valve is also known as an industrial valve that does not affect the flow through the pipeline, because when the valve is fully opened, the valve will no longer be on the pipeline.

2. Structure & working principle of gate valve

a. Structure of gate valve

 

Gate valves, like other valves (ball valves, globe valves, butterfly valves, etc.), are made up of many different parts and details. Here is one of the main parts of gate valve:

- Valve body:  The valve body is usually made of many different materials such as copper, cast iron, steel, stainless steel, etc. has the function of containing & linking other parts of the valve, forming a system. most, subject to the external effects of the environment, impact and protect the internal components and allow the refrigerant to move inside, without leaking to the outside.

- Valve shaft (Stem):   Also known as valve stem, is the transmission part of the valve, directly deciding the opening / closing mechanism of the valve. One end of the valve shaft is linked to the valve arm, the other is mechanically linked to the valve disc. To open/close the valve, the user transmits torque to turn the valve handle, controls the shaft associated with the valve disc, moves up/down to close or open the valve. The valve shaft is usually made of hard metal, with good corrosion and friction resistance, because it bears a lot of force.

- Disc:  The part located in the middle of the valve body, has the shape of a gate and is in direct contact with the medium, so it is usually made of materials with high hardness & good corrosion resistance. The valve disc is usually fixed directly to the valve shaft through welding or casting, linked to the handwheel, from which to control up / down to allow or prevent the refrigerant from passing through the valve.

- Sealing gasket (Seal & gasket):  Like other valves, the sealing gasket is designed for the purpose of sealing the body with the valve shaft, the valve body with the valve cap, the pieces of the valve body, etc. to minimize the risk. valve leakage risk. These parts are usually made from synthetic rubber, Teflon, etc. have good elasticity, heat resistance and corrosion resistance.

- Valve cap (Bonnet):  The part located between the control arm and the valve body, outside of the valve shaft, has the effect of protecting the valve shaft and sealing.

- Valve arm:  A part that receives force directly from the user to operate the valve opening/closing. Gate valves are usually used with a rotating handwheel, also known as a handwheel operating, by the opening/closing mechanism of the globe valve through which the valve arm rotates/counterclockwise to control the valve disc up/ down.

b. The principle of operation of gate valve

 

The opening / closing mechanism of this type of valve is through the valve shaft to control the valve disc to move up / down like a gate. When the valve disc is in the lowest position (closer to the valve seat), it means that the valve is closed - the flow does not circulate. And vice versa, when the valve is open, the position of the valve port is at the highest position.

- Purpose of gate valve:

With the above operating mechanism, the gate valve is susceptible to corrosion and should only be used in the fully open or closed positions (because in the case of a partially open/closed valve, the valve disc will be shaken by the impact of the current. melt and easily lead to damage).

c. Gate valve classification:

Like ball valve, globe valve or butterfly valve, gate valve also has many criteria to classify. In the following article, we would like to allow you to classify gate valves based on some of the most common criteria, if there are shortcomings, we would like to receive your comments.

Based on connection type:

- Threaded gate valve:  The threaded gate valve, whose English name is Thread Gate Valve, is a type of valve with a threaded connection, used to connect to threaded pipes, commonly used for valves with a threaded connection. Small size (under 2 inches). The connection thread standards of gate valves have many types such as G thread, NPT thread, BSP thread, etc.

- Flange connection gate valve:  Flange connection gate valve has English name Flange Gate Valve, is a valve with flange connection part (there are many standards such as ANSI, JIS, BS, DIN, ...), used to connect Connected to the pipeline through a flange, sealed with a gasket. Flange connection gate valves are usually used for large sizes, but there are also a few user applications that require flange connections for small sized valves, for some specific reason.

 

- Welded Gate Valve: Welded Gate Valves have many types, collectively known as Welded Gate Valve. Depending on the type of weld, it is divided into Socket Weld Gate Valve (cage welding, Butt Weld Gate Valve) These are valves designed to be welded directly to the pipeline, in locations where it is rarely needed. dismantling & minimizing the risk of leakage Normally, welded gate valves are only used for small sizes.

Based on the structure of the valve shaft (also known as the valve stem):

- Submersible gate valve: Is a valve with a valve inside the valve body, when operating the valve from closed to open or from open to closed, the size of the whole valve does not change, only the valve disc moves up. down. This type of valve does not change the valve size when used, so it is suitable for places with narrow space, or underground pipelines. There are two types of gate valves, one with a cap and one with a steering wheel. This type is usually used mainly in plumbing, fire pipelines.

- Floating gate valve: In contrast to the submerged gate valve, the gate valve can clearly see the shaft during operation. When the valve is open, the valve stem will rise and the valve stem will decrease when the valve is closed. This also makes it easy for the user to monitor the valve's status from a distance.

Based on operating method:

- Operation manual gate valves:  The most commonly used manual control valve today, the operator can easily control it based on the force it exerts on the handwheel. Through the valve shaft, the valve disc is raised / lowered at will, thereby closing / opening or regulating the flow. This type of valve is usually designed for small-sized valves, in the case of larger pipes, a transmission gearbox or electric/pneumatic controller must be used.

- Electric actuated gate valves:  Also known as electric gate valves, is a combination of globe valve and electric actuator. The electric control unit will perform the rotation of the valve shaft, from which the valve disc will move as if it were manual operation. This type of valve is used for situations where it is difficult for the operator to operate, the access to the valve is limited, or the environment where the valve is installed is not good for human health.

- Pneumatic actuated gate valve: Commonly referred to as pneumatic gate valve, it is a combination of a globe valve with a pneumatic actuator (pneumatic actuator), instead of a manual handwheel. This type of valve is commonly used for installation sites that are inaccessible to operators or hazardous operating environments.

 

 

d. Advantages & disadvantages of using gate valves:

* Advantages:

- Gate valve / gate valve has high durability, low maintenance and maintenance.

- Gate valve has low flow & flow rate when passing through the valve, helping the system to operate stably.

- Operating the gate valve is relatively easy.

- Narrow body width, easy to install in any position.

* Defect:

- Because of the specificity in the operating mechanism, gate valves are rarely used for the purpose of regulating flow.

- The opening and closing stroke is slow, so it is not suitable for fast opening and closing positions.

- When the valve is not closed completely, noise will be generated.

- High maintenance and maintenance costs due to complex structure. Often users will skip the valve repair phase, but will replace the valve completely when damaged.