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Check valves must be installed in pipelines

2024-04-07

What is a check valve?

The function of this type of valve is to allow the medium to flow in one direction only and prevent the flow in the opposite direction. Usually this kind of valve works automatically. Under the pressure of fluid flowing in one direction, the valve disc opens; when the fluid flows in the opposite direction, the fluid pressure and the self-weight of the valve disc act on the valve seat, thus cutting off the flow.

Check valve is a valve whose opening and closing parts open or close by themselves by the force of medium flow to prevent the medium from flowing back. Check valves are automatic valves and are mainly used on pipelines with one-way flow of media. They only allow the medium to flow in one direction to prevent accidents.

Check valves are classified according to structure:
According to the structure, it can be divided into three types: lift check valve, swing check valve and butterfly check valve:

Lift check valves are divided into two types: vertical and horizontal.

Swing check valvesare divided into three types: single-disc type, double-disc type and multi-disc type.

Butterfly check valve is straight-through type.

The above check valves can be divided into four types of connection forms: threaded connection, flange connection, welded connection and clamping connection.

Check valves are classified according to material:

Cast iron check valve

Brass check valve

Stainless steel check valve

Carbon steel check valve

Forged steel check valve

Check valves are classified according to their functions:

Silent check valve

Rubber flap check valve

Swing check valve

Installation methods of different types of check valves:

Swing check valve:

The valve disc of the swing check valve is disc-shaped and rotates around the rotating axis of the valve seat channel. Because the inner channel of the valve is streamlined, the flow resistance is smaller than that of the lift check valve. It is suitable for low flow rates and infrequent changes in flow. It is suitable for large diameter occasions, but it is not suitable for pulsating flow, and its sealing performance is not as good as that of the lifting type. Swing check valves are divided into three types: single-disc type, double-disc type and multi-disc type. These three forms are mainly divided according to the valve diameter. The purpose is to prevent the medium from stopping the flow or backflow and weakening the hydraulic impact.

Lift check valve:

A check valve whose valve disc slides along the vertical centerline of the valve body. The lift check valve can only be installed on horizontal pipelines. The valve disc can be made of round balls on high-pressure small-diameter check valves. The valve body shape of the lift check valve is the same as that of the stop valve (can be used universally with the stop valve), so its fluid resistance coefficient is larger. Its structure is similar to that of a globe valve, and its valve body and disc are the same as those of a globe valve. The upper part of the valve disc and the lower part of the valve cover are processed with guide sleeves. The valve disc guide sleeve can be freely raised and lowered in the valve guide sleeve. When the medium flows forward, the valve disc opens by the thrust of the medium. When the medium stops flowing, the valve disc opens by itself. It falls vertically on the valve seat to prevent the backflow of the medium.

The direction of the medium inlet and outlet channels of the straight-through lift check valve is perpendicular to the direction of the valve seat channel;

The direction of the medium inlet and outlet channel of the vertical lift check valve is the same as that of the valve seat channel, and its flow resistance is smaller than that of the straight-through type.

Wafer type check valve:

A check valve in which the disc rotates around a pin in the valve seat. The disc check valve has a simple structure and can only be installed on horizontal pipelines, so its sealing performance is poor.

Bottom valve, spring type, Y-type and other check valves are not suitable for installation at the pump outlet.

Precautions for installation of check valve:

① Do not allow check valves to bear weight in the piping system. Large check valves should be independently supported so that they are not affected by the pressure generated by the piping system.

② When installing, please note that the direction of medium flow should be consistent with the direction of the arrow marked on the valve body.

③ Lift type vertical flap check valve should be installed on vertical pipelines.

④ Lift type horizontal flap check valve should be installed on horizontal pipelines.

Applicability of different check valves:

① Butterfly double-disc check valve is suitable for water supply pipe networks in high-rise buildings, pipe networks with certain chemically corrosive media, pipe networks with limited installation space, and sewage pipe networks.

② The lift-type silent check valve is suitable for pipe networks with high quality requirements for water supply and drainage projects; pipe networks with relatively high pressure requirements (PN2.5Mpa); it can be installed at the outlet of the pump and is an economical and practical waterproof hammer check valve.

③ The lift type silencer check valve is suitable for water supply and drainage systems and high-rise building pipe networks. It can be installed at the outlet of the pump. With a slight structural modification, it can be used as a water suction bottom valve, but it is not suitable for sewage pipe networks.

④ Horizontal check valve is suitable for submersible, drainage and sewage pumps, especially for sewage and sludge systems.

⑤ Swing rubber check valve is suitable for domestic water pipe networks; but it is not suitable for sewage with a lot of sediment.

⑥ Swing single-disc check valve is suitable for water supply systems, petroleum, chemical industry, metallurgy and other industrial sectors, and is most suitable for places with limited installation space.

Check valve selection:

1. In order to prevent the backflow of the medium, check valves should be installed on equipment, devices and pipelines;

2. Check valves are generally suitable for clean media and are not suitable for media containing solid particles and high viscosity;

3. Generally, horizontal lift check valves should be used on horizontal pipelines with a nominal diameter of 50mm;

4. The straight-through lift check valve can only be installed on horizontal pipelines;

5. For the water pump inlet pipeline, a bottom valve should be used. The bottom valve is generally only installed on the vertical pipe at the pump inlet, and the medium flows from bottom to top;

6. The lifting type has better sealing and greater fluid resistance than the swing type. The horizontal type should be installed on horizontal pipes, and the vertical type should be installed on vertical pipes;

7. The installation position of the swing check valve is not restricted. It can be installed on horizontal, vertical or inclined pipelines. If installed on a vertical pipeline, the medium flow direction must be from bottom to top;

8. The swing check valve should not be made into a small-diameter valve. It can be made into a very high working pressure. The nominal pressure can reach 42MPa, and the nominal diameter can also be very large, up to 2000mm or more. Depending on the materials of the shell and seals, it can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196--800℃;

9. The swing check valve is suitable for low pressure and large diameter, and the installation location is limited;

10. The installation position of butterfly check valve is not restricted and can be installed on horizontal pipelines, vertical or inclined pipelines;

11. The diaphragm check valve is suitable for pipelines prone to water hammer. The diaphragm can well eliminate the water hammer produced when the medium flows back. It is generally used on low-pressure and normal temperature pipelines, especially suitable for tap water pipelines and general medium work. The temperature is between -12--120℃, and the working pressure is <1.6MPa, but the diaphragm check valve can have a larger diameter, and the maximum DN can reach more than 2000mm;

12. Ball check valve is suitable for medium and low pressure pipelines and can be made into large diameter;

13. The shell material of the ball check valve can be made of stainless steel, and the hollow sphere of the seal can be wrapped with polytetrafluoroethylene engineering plastic, so it can also be used in pipelines with general corrosive media. The working temperature is -101--150 ℃, the nominal pressure is ≤4.0MPa, and the nominal throughput range is between DN200-DN1200;

14. When selecting a check valve for incompressible fluids, you must first evaluate the required closing speed. The second step is to select the type of check valve that may meet the required closing speed;

15. When selecting check valves for compressible fluids, you can select them in a similar way to check valves for incompressible fluids. If the medium flow range is large, check valves for compressible fluids can be used. A reduction device. If the medium flow stops and starts quickly in succession, such as at the outlet of a compressor, a lift check valve is used;

16. The check valve should be sized accordingly, and the valve supplier must provide data on the selected size so that the valve size when the valve is fully open at a given flow rate can be found;

17. For high and medium pressure check valves below DN50mm, vertical lift check valves and straight-through lift check valves should be used;

18. For low-pressure check valves below DN50mm, butterfly check valves, vertical lift check valves and diaphragm check valves should be used;

19. For high and medium pressure check valves with DN greater than 50mm and less than 600mm, swing check valves should be used;

20. For medium and low pressure check valves with a DN greater than 200mm and less than 1200mm, it is advisable to choose a wear-free spherical check valve;

21. For low-pressure check valves with DN greater than 50mm and less than 2000mm, butterfly check valves and diaphragm check valves should be used;

22. For pipelines that require relatively small or no water hammer when closing, slow-closing swing check valves and slow-closing butterfly check valves should be used.

Check valve troubleshooting:

The valve disc is broken:

The reason why the valve disc is broken is that the pressure of the medium before and after the check valve is close to balance and "see-sawing" with each other. The valve disc often slaps against the valve seat. Valve made of certain brittle materials (such as cast iron, brass, etc.) The flap was shattered.

The preventive method is to use a check valve with a flexible material.

Media reverse flow:

The reasons for medium backflow include:

① Damage to the sealing surface;

② Inclusion of impurities.

Repairing the sealing surface and cleaning impurities can prevent backflow.

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