First， What is Check Valves, the definition of a check valve.

Check valve refers to rely on the medium itself flow and automatically open and close valve disc, used to prevent media backflow of the valve,

also known as one way  flow valve,  non return valve,  and back pressure valve.  Check valve is a kind of automatic valve, its main function is to prevent the backflow of the medium, prevent the pump and the drive motor from reversing, and the discharge of the container medium. Check valves can also be used to feed lines in which the pressure may rise to exceed the system pressure.

 

Second, the key points of check valve construction and installation:

1, the installation position, height, import and export direction must meet the design requirements, pay attention to the direction of the medium flow should be consistent with the direction of the arrow marked by the valve body, the connection should be firm and close.

2, the valve must be inspected before installation, valve nameplate should meet the current national standards. For the valve whose working pressure is greater than 1.0MPa and plays a cutting role on the main pipe, the strength and tight performance test should be carried out before installation, and the qualified valve can be used. Strength test, the test pressure is 1.5 times the nominal pressure, the duration is not less than 5min, the valve shell, packing should be qualified without leakage. For tightness test, the test pressure is 1.1 times of the nominal pressure.

3. Do not make the check valve bear weight in the pipeline. Large check valves should be supported independently so that they are not affected by the pressure produced by the pipe system.

 Third, Fault and solution

Ⅰ, Internal leakage

1. The sealing surface is attached with dirt.

2. The sealing surface is damaged by hydraulic impact.

3. Remove dirt from disc and seat sealing surfaces and clean them with kerosene.

4. Rework disc and seat or replace seal.

 Ⅱ, External leakage

Leakage at valve body and bonnet connection

1. Connection bolts are not evenly tightened or the pre-tightening force is insufficient.

2. Flange sealing surface is damaged.

3. The gasket is improperly installed and damaged or fails after too long use.

4. Evenly tighten the bolts and nuts connecting the valve body to the valve cover.

5. Rework and repair flange sealing surface.

6. Replace the gasket and install it correctly.

 Ⅲ, Disc is broken

The medium pressure before and after the check valve fluctuates, the disc frequently collides with the seat, and the disc of some brittle materials is easy to be broken.

1. Choose a ductile material disc.

2. Adjust the process to reduce or avoid frequent pressure fluctuations before and after the check valve.