I.Introduction of Gate Valve
A gate valve is also known as a gate valve. Its opening and closing element is the gate plate. It is driven by the valve stem to do the lifting movement of the gate valve is called gate valve.
The direction of the gate plate’s movement is perpendicular to the fluid’s direction. Therefore, the gate valve can only be fully open and closed, not for regulation and throttling. Gate valves are sealed by contact between the valve seat and the gate plate. Usually, the sealing surface is overwhelmed with metal materials to increase wear resistance, such as overwhelmed 1Cr13, STL6, stainless steel, etc.
II.Working Principle of Gate Valve
Gate valve refers to the closure (gate) along the central line of the pathway of the vertical direction of movement of the valve. Gate valve in the pipeline can only be fully open and fully closed, blocking with, can not be used for regulation and throttling. Gate valve is the use of a wide range of valves. Usually DN ≥ 50 mm diameter with blocking device we will choose the gate valve. Sometimes a minimal diameter with a blocking device, we will also select the gate valve when the gate valve is used as a cut-off medium. It is fully open when the entire smooth flow of longitudinal when the pressure loss of the media operation is minimal. The gate valve is usually used in conditions that do not require frequent opening and closing and keep the gate fully open or fully closed. It is not suitable for use as a regulator or throttle.
The gate has two sealing surfaces. Thus the most common gate valves are wedge gate valves and parallel gate valves.
The wedge angle varies with the valve parameters and is usually 5°, 2°52′ when the medium temperature is not high. It can make the gate of a wedge gate valve into a single unit, called a rigid gate. You can also make it into a gate that can produce a slight deformation to improve its workmanship. It can compensate for the deviation of the sealing surface angle during processing, and this gate is called a resilient gate.
When the gate valve is closed, the sealing surface can only rely on the pressure of the medium to seal. That is, it can depend on the medium pressure will be the sealing surface of the gate plate to the other side of the seat to ensure the sealing surface of the seal, which is self-sealing. However, the majority of gate valves are forced to seal. That is, when the valve is closed, it depends on external force to force the gate plate to the seat to ensure the sealing surface of the seal.
A gate valve with a gate plate that moves in a straight line with the stem is called a lift stem gate valve (also called an open stem gate valve). Usually, a trapezoidal thread on the lift rod changes the rotary motion into a linear motion using a nut at the top of the valve and a guide slot in the valve body. It means that the manipulating torque is changed to a manipulating thrust.
When the valve is opened, the height of the gate promotion is 1:1 times the diameter of the valve. The fluid passage is entirely unobstructed, but this position cannot be supervised during operation. In actual use, it is marked by the apex of the valve stem. That is the position that does not open, as it’s a fully open position. Given the possibility of lock-up due to temperature changes, gate valves are usually opened to the apex position and then reversed by 1/2-1 turn as the fully open valve position. Therefore, the valve’s fully open position is determined by the position of the gate (i.e., stroke).
III.Characteristics of Gate Valve
Features
1. Lightweight
The body of the gate valve is made of high-grade ductile iron. It is 20%~30% lighter than traditional gate valves and easy to install and maintain.
2. Flat bottom gate seat
Conventional gate valves can fail to close tightly due to stones, wood, cement, iron filings, debris, etc., silting up in the recesses at the bottom of the valve, resulting in a leak. The bottom of the resilient seat seal gate valve is designed with the exact flat bottom as the water pipe machine, which is less likely to cause debris to accumulate. It also allows for unobstructed fluid flow.
3. Overall rubber covering
The gate plate comprises high-quality rubber for overall internal and external encapsulation. The European rubber vulcanization technology guarantees the precise geometry of the vulcanized gate. The rubber is firmly bonded to the tensile cast gate plate. It does not fall off easily and has an excellent elastic memory.
4. Precision cast valve body
The precise geometry of the valve body allows the valve to be sealed without any finishing work.
Advantages
1.Small flow resistance.
The media channel inside the valve body of the gate valve is straight through. Therefore, the medium is into a straight line flow, and the flow resistance is negligible.
2.Opening and closing of the more labor-saving.
It is compared with the globe valve. The reason is that whether open or closed, the direction of movement of the gate is perpendicular to the flow direction of the medium.
3.If the height is large, the gate valve opening and closing time are long. It is because the opening and closing stroke of the gate plate is larger. The lifting and lowering of the gate valve are carried out using a screw.
4.It is not easy to generate water hammer phenomenon. The reason is that the closing time is long.
5.The medium can flow on both sides and is easy to install. The two sides of the gate valve channel are proportional.
6.The length of the structure (referring to the distance between the two connecting ends of the shell) is small.
7.The gate valve is simple in shape and short in structural length. As a result, it has an exemplary manufacturing process and a wide range of applications.
8.The gate valve has a compact structure and good rigidity. It has smooth passage and a small flow resistance number. The sealing surface of the gate valve is made of stainless steel and hard alloy, with long service life. The gate valve adopts PTFE packing, which is reliable, light, and flexible.
Disadvantages
1.General gate valve has two sealing surfaces. Therefore, it is more complex processing and manufacturing than the globe valve.
2.Gate valve sealing surface between the relative friction is more wear and tear. In addition, if the sealing surface of the gate valve becomes worn, it is inconvenient to repair.
3.The valve cavity size is large, resulting in a long structure length and large external dimensions. Therefore, it requires a large installation space, and the large diameter gate valve is particularly bulky.
4.Valve opening and closing times are long.
5.It can form a closed valve cavity, so we should set up the pressure relief structure to prevent abnormal pressure rise in the cavity when needed.
