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The Working Principle and Pressure Test Method of Ball Valves and Gate Valves

Ⅰ. Ball valves


1. The working principles of ball valves


The definition of a ball valve is a valve in which the opening and closing part (ball) is driven by the valve stem and rotates around the axis of the ball valve. Ball valves can also be used for fluid adjustment and control. Among them, the hard-sealed V-shaped ball valve has a strong shear force between its V-shaped ball core and the metal seat of the hard alloy. It is especially suitable for fibers and small solid particles. Materials and other media. The multi-way ball valve can not only flexibly control the confluence, divergence, and switching of the flow direction of the medium on the pipeline, but also close any channel and connect the other two channels. This type of valve should generally be installed horizontally in the pipeline.


According to the driving mode, the ball valve is divided into: pneumatic ball valve, electric ball valve, manual ball valve.


2. Pressure test methods of ball valves


(1) Floating ball valve tightness test: The valve is in a half-open state, one end is introduced into the test medium, and the other end is closed. Rotate the sphere several times, and open the closed end to check when the valve is in the closed state. At the same time, check the sealing performance of the packing and gasket, and there must be no leakage. Then introduce the test medium from the other end and repeat the above test.


(2) Tightness tests of fixed ball valves: rotate the ball several times without load before the test, the fixed ball valve is in the closed state, and the test medium is introduced from one end to the specified value. Check the sealing performance of the lead-in end with a pressure gauge, the accuracy of the pressure gauge is 0.5 to 1, and the range is 1.5 times the test pressure. Within the specified time, if there is no depressurization phenomenon, it is qualified, and then the test medium is introduced from the other end. Repeat the above test, and then put the valve in a half-open state, the two ends are closed, and the inner cavity is filled with medium. Check the packing and gasket under the test pressure, and there should be no leakage.


(3) The three-way ball valve should be tested for tightness at each position.


Ⅱ. Gate valves


1. The working principles of gate valves


The gate valve is a gate for opening and closing. The movement direction of the gate is perpendicular to the direction of the fluid. A gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate valve is sealed by the contact between the valve seat and the gate plate. Usually, the sealing surface is welded with metal materials to increase the wear resistance, such as 1Cr13, STL6, stainless steel, etc. The gate has a rigid gate and an elastic gate. According to the difference of the gate, the gate valve is divided into a rigid gate valve and an elastic gate valve.


2. Pressure test methods of gate valves


(1) The gate is opened to increase the pressure in the valve to the specified value. Then close the gate, take out the gate valve immediately, check whether there is leakage at the seals on both sides of the gate, or directly inject the test medium into the plug on the valve cover to the specified value, and check the seals on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for the sealing test of gate valves with a nominal diameter below DN32mm.


(2) Another method is to open the gate to increase the test pressure of the valve to the specified value; then close the gate and open the blind plate at one end to check whether the sealing surface is leaking. Reverse the head and repeat the test above until it is qualified.

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