Selection criteria:
1. In order to prevent backflow of media, check valves should be installed on equipment, devices and pipelines;
2. The check valve is generally suitable for clean media, not suitable for media containing solid particles and high viscosity;
3. Generally, vertical lifting check valves should be selected on horizontal pipes with nominal diameter of 50mm;
4. The straight-through lifting check valve can be installed on both horizontal and vertical pipelines;
5. For the inlet pipeline of the pump, the bottom valve should be selected. The bottom valve is generally only installed on the vertical pipeline at the inlet of the pump, and the medium flows from bottom to top;
6. The lifting type has better sealing performance than the swing type, and the fluid resistance is large. The horizontal type should be installed on horizontal pipelines, and the vertical type should be installed on vertical pipelines;
7. The installation position of the swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines. If it is installed on vertical pipelines, the medium flow direction should be from bottom to top;
8. The swing check valve should not be made into a small-diameter valve, which can be made into a very high working pressure, PN can reach 42MPa, and DN can also be very large, the maximum can reach more than 2000mm. Depending on the material of the housing and the seal, any working medium and any working temperature range can be applied. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196--800℃;
9. The applicable occasion is low-pressure large-caliber, and the installation occasion is limited;
10. The installation position of the butterfly check valve is not limited. It can be installed on horizontal pipelines or vertical or inclined pipelines;
11. Diaphragm check valve is suitable for pipelines that are prone to water hammer. The diaphragm can well eliminate the water hammer generated when the medium is countercurrent. It is generally used in low pressure and normal temperature pipelines, especially suitable for tap water pipelines, and general media work The temperature is between -12--120℃, the working pressure is <1.6MPa, but the diaphragm type check valve can achieve a larger diameter, and the maximum DN can reach more than 2000mm;
12. The spherical check valve is suitable for medium and low pressure pipelines and can be made into large diameters;
13. The shell material of the spherical check valve can be made of stainless steel, and the hollow sphere of the seal can be wrapped with PTFE engineering plastic, so it can also be applied to the pipeline of general corrosive media, and the working temperature is -101--150 Between ℃, its nominal pressure ≤ 4.0MPa, the nominal warp range is between 200-1200;
14. For the selection of check valves for incompressible fluids, the required closing speed must be evaluated first. The second step is to select the type of check valve that may meet the required closing speed;
15. For the selection of check valves for compressible fluids, the selection can be based on the similar method of check valves for incompressible fluids. If the medium flow range is large, the check valves for compressible fluids can be used. A deceleration device, if the medium flow is stopped and started rapidly continuously, like the outlet of the compressor, a lifting check valve is used;
16. The check valve should determine the size of the response. The valve supplier must provide the data of the selected size, so that the valve size when the valve is fully opened at the given flow rate can be found;
17. For high-medium pressure check valves with a caliber of less than 50mm, vertical lift check valves and straight-through lift check valves should be used;
18. For low-pressure check valves with a diameter of DN50mm or less, butterfly check valves, vertical lift check valves and diaphragm check valves should be used;
19. For high and medium pressure check valves with a caliber greater than 50mm and less than 600mm, a swing check valve should be used;
20. For medium and low pressure check valves with diameters greater than 200mm and less than 1200mm, wear-free spherical check valves should be used;
21. For low-pressure check valves with a caliber greater than 50mm and less than 2000mm, Iraq uses butterfly check valves and diaphragm check valves;
22. For pipelines that require relatively little water hammer impact or no water hammer when closing, slow-closing swing check valves and slow-closing butterfly check valves should be used.
Check valve definition, function and classification
Check valve definition
Check valve refers to a valve that automatically opens and closes the valve flap depending on the flow of the medium itself to prevent backflow of the medium. It is also known as a check valve, check valve, reverse flow valve, and back pressure valve.
Check valve function
The check valve belongs to an automatic valve. Its main functions are to prevent backflow of the medium, to prevent the pump and drive motor from reversing, and to release the medium in the container. Check valves can also be used to replenish auxiliary piping where the pressure may rise above the system pressure.
Classification of check valves
Check valve can be divided according to its structure and installation method:
1. Swing check valve: The flap of the swing check valve is disc-shaped and rotates around the rotation axis of the valve seat channel. Because the channel in the valve is streamlined, the flow resistance is higher than that of the lift check valve. It is small and suitable for low-velocity and large-diameter occasions where the flow does not change frequently, but it is not suitable for pulsating flow, and its sealing performance is not as good as the lifting type. There are three types of swing check valves: single-petal, double-petal and multi-half. These three types are mainly divided by the valve caliber. The purpose is to prevent the medium from flowing or backflow, and weaken the hydraulic impact.
2. Lift check valve: a check valve with a flap that slides along the vertical centerline of the valve body. The lift check valve can only be installed on horizontal pipelines. On high-pressure small-diameter check valves, the flap can use round balls . The valve body shape of the lift check valve is the same as that of the globe valve (can be used with the globe valve), so its fluid resistance coefficient is large. The structure is similar to the globe valve, and the valve body and valve flap are the same as the globe valve. The upper part of the valve disc and the lower part of the valve cover are processed with guide sleeves. The valve flap guide can be freely raised and lowered in the valve seat guide. When the medium flows downstream, the valve flap opens by the medium thrust. It lands on the valve seat to prevent the medium from flowing backwards. Straight-through lift check valve media inlet and outlet channel direction is perpendicular to the valve seat channel direction; vertical lift check valve, its medium inlet and outlet channel direction is the same as the valve seat channel direction, its flow resistance is smaller than the straight-through type.
3. Disc check valve: a check valve with a flap that rotates around a pin in the valve seat. The disc-type check valve has a simple structure and is installed on a horizontal or vertical pipeline, with poor sealing performance.
4. Pipeline check valve: a valve that slides along the centerline of the valve body. Pipeline check valve is a new type of valve. It has small volume, light weight and good processing technology. It is one of the development directions of check valve. But the fluid resistance coefficient is slightly larger than the swing check valve.
Fifth, check valve: This valve is used as a boiler feed water and steam cut-off valve, it has a comprehensive function of lifting check valve and globe valve or angle valve.
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