Updated: Jun 29, 2019
A gate valve, also known as a sluice valve, is a valve which opens by lifting gate out of the path of the fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened. The gate faces can be parallel, but are most commonly wedge-shaped (in order to be able to apply pressure on the sealing surface). Compared with other valves, gate valve has a wider range of applications for pressure, temperature and caliber.
Advantages Of Gate Valves
1. The fluid resistance of the valve is small. Because the valve body of gate valve is straight-through type and the flow of the medium doesn’t change direction, the fluid resistance of it is small compared with other kinds of valves. 2. The sealing performance is better than that of the shut-off valve. The opening and closing of it is more convenient than those of the shut-off valve. 3. The range of applications is wide. In addition to steam, oil and other media, it can be used in medium containing granular solid and with a large viscosity. It can also be used as venting valve and low vacuum system valve. 4. Gate valve is a valve that has dual flow directions. It’s not subject to the flow directions of the medium. Therefore, it is suitable for use in pipeline where the medium may change the flow direction. It is also easy to install.
Disadvantages of Gate Valves
1. The opening and closing time is long. During the opening process, the valve plate needs to be lifted to the upper part of the valve chamber. During the closing process, the valve plate needs to fall into the valve seat. Thus, the opening and closing distance of the valve plate is large, leading to long opening and closing time. 2. Because there is friction during the opening and closing processes between the valve plate of the gate valve and the two sealing surfaces of the valve seat, the sealing surface is prone to scratch, which has an impact on the sealing performance and the service life. And it’s not easy for repair.
Gate valves are classified as either rising-stem or non-rising-stem valves. The non-rising-stem valve is shown in the photo. The stem is threaded into the gate. As the hand wheel on the stem is rotated, the gate travels up or down the stem on the threads while the stem remains vertically stationary. This type of valve will almost always have a pointer indicator threaded onto the upper end of the stem to indicate the position of the gate.
Valves with rising stem valves , are used when it is important to know by immediate inspection whether the valve is open or closed or when the threads exposed to the fluid could become damaged by fluid contamination. In this valve, the stem rises out of the valve bonnet when the valve is opened.
Usually, rising steam valves are used in fire resistant system, it helps the fire man to see if the steam is opened or closed with just a one look to the valve steam.
Gate Valve Components
The main part of gate valve is the valve’s body, which is considered the initial pressure boundary and can connect inlet and outlet pipes in a piping system. Wato Valves uses Ductile Iron (EN-JS 1050).
the other components of a gate valve are: 1- Body (Ductile Iron)
2- Seat Ring (Brass)
3- Wedge (Ductile Iron)
4- Wedge Ring (Brass)
5- Wedge Nut (Brass)
6- Stem (Stainless Steel)
7- Bonnet Gasket (Rubber)
8- Bonnet (Ductile Iron)
9- Stem Collar (Carbon Steal)
10- Thrust Washer (PTFE)
11- Gland Flange Gasket (Rubber)
12- Stem Sealing (Rubber)
13- Gland Flange (Ductile Iron) 14- Hand Wheel (GI)
How the gate valve works
A gate valve is used ONLY to start and stop the flow of liquid in water network.
Gate valves are most commonly used when restriction is needed. It is designed to be fully open or closed, and are not recommended to regulate the flow of liquid. Using it for "throttling" causes strain on the gate and eventually will damage it.
How to install Gate valve
Gate valves are delivered with their closed position wedge and ready for use. After the removal of the protection covers it is necessary to thoroughly clean inside the gate valve with compressed air without first opening the valve.
Closure of a valve is performed by turning the hand wheel in a clockwise direction. On the hand wheel is an arrow and the letter “C” indicating the closing direction, and another arrow and the letter “O” indicating the opening direction.
When installing gate valves with flange ends it is necessary to take into consideration the selection of adequate bolt material and the appropriate type of gasket depending on the type of working fluid, pressure, temperature, and the type of flange facing. It is necessary to install gaskets strictly in accordance with instructions given from the manufacturer of the gaskets.
Gate valves with welding ends should be welded onto the pipeline by an expert and with appropriate WPS. After welding, if necessary, local normalization should be performed and the inside of the pipeline should be cleaned to remove possible welding remains.
At the moment of installation the influence of the load of the pipeline on the gate valve should be reduced. The same also applies for temperature oscillation, hydraulic impact and similar. The gate valve should not be used as a support for a pipeline.
Each product after assembling is hydraulically tested leading to wetting the sealing of the package. As a result, before installation, may be difficult manipulation with hand wheel. This phenomenon does not affect the functionality of the product.
It is possible after the installation, start-up and operating parameters are set to detect a leakage on the stem packing. In this case it is necessary to tighten the gland nuts equally. The tightness should not exceed more than necessary to allow comfortable manipulation of the valve (opening / closing). If it is necessary, new stem packing rings of the same quality should be added to the packing.
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