The Installation and Maintenance of Gate Valve

The following should be paid attention to when installing and maintaining gate valves: hand wheel, handle and transmission are not allowed to make lifting, and collision is strictly prohibited. Double-gate-plate valve should be vertically installed (valve stem is in the vertical position and the hand wheel is at the top). Before opening gate valve with bypass valve, the bypass valve should be first opened (to balance the pressure difference at the inlet and outlet and reduce the opening force). For gate valve with drive mechanism, install it according to the instruction manual of product. If the valve is frequently used, lubricate it at least once a month. Gate valve is used to shut off the medium. When it’s fully opened, the fluid flows through, at which time the pressure loss of the medium is the smallest. Gate valve is usually used for working conditions where there’s no need to frequently open or close the valve and the gate plate is kept fully open or fully closed. It’s not suitable for use in regulating or throttling. For fast-running medium, gate plate can cause the vibration of the gate under partially open conditions, and vibration can in turn damage the sealing surface of the gate plate and valve seat. Throttling will cause the gate plate to be eroded by the medium. From the structural form, the main difference is the difference of the form of the sealing component used. According to different types of sealing component, gate valve can usually be divided into several different types, such as wedge gate valve, parallel gate valve, parallel double gate plate valve, wedge double gate plate valve, etc. The most commonly used types are wedge gate valve and parallel gate valve.

The role of this type of valve is to only allow the medium to flow in one direction. Usually this type of valve works automatically. Under the pressure of fluid flowing in one direction, the valve flap opens. When the fluid flows in the opposite direction, the fluid pressure and the weight of valve flap have effect on the valve seat, shutting off the flow. Check valve falls into this category. It consists of swivel sanitary check valve and lift check valve. Swivel check valve has a hinge and a valve flap that is like a door leaning freely on the surface of the valve seat. To ensure that every time the valve flap can reach the proper position of the surface of the valve seat, the valve flap is designed to be at the hinge, so as to leave enough swivel room for it and make it truly and fully accessible to the valve seat. The valve flap can be fully made of metals, or the metal can be fitted with leather, rubber, or synthetic cover, depending on performance requirements. Swivel check valve, in fully open condition, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The valve flap of lift check valve is on the sealing surface of the valve seat. For this kind of valve, except the valve flap can be freely lifted, the rest is like those on the shut-off valve. Fluid pressure lifts the valve flap from the sealing surface of the valve seat, and backflow of the medium causes the valve flap to drop back to the valve seat, shutting off the flow.

Depending on the conditions of use, valve flap can be of all-metal structure. Or it can be fitted with rubber pad or rubber ring. Like the shut-off valve, the passage of the lift check valve through which fluid flows is also narrow, so the pressure drop of lift check valve is somehow bigger than that of the swivel check valve. Also, there’s little limit on the amount of flow of swivel check valve.

In the process of production, in order for parameters like medium pressure and the amount of flow to be in line with the requirements of the process, adjustment mechanism needs to be installed to regulate those parameters. The main mechanism of adjustment mechanism is to change the circulation area between valve flap and valve seat to achieve the purpose of regulating those parameters. All valves falling into this category is called regulating valve. Those relying on the medium to drive are called self-driven regulating valve, such as pressure relief valve and pressure maintaining valve. Those relying on external power (electricity, compressed air and liquid power) to drive are called outside-driven regulating valve, such as electric regulating valve, pneumatic regulating valve and hydraulic regulating valve.