Standard for selection of check valves
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Standard for selection of check valves
The selection standard of check valve is as follows:
Check valves should be installed on equipment, devices, and piping to prevent media backflow;
Check valve is generally suitable for cleaning medium, not suitable for containing solid particles and viscosity of larger media;
Generally in the nominal through 50mm horizontal pipeline should be used on the vertical lift check valve;
Straight-through lift check valves can be installed in both horizontal and vertical pipelines.
For the pump inlet pipeline, it is advisable to choose the bottom valve, the bottom valve is generally only installed in the vertical pipe at the pump inlet, and the medium flows from bottom to top;
Lifting type rotary seal is good, the fluid resistance is big, horizontal type should be installed in the horizontal pipeline, vertical installed in the vertical pipeline;
Swing check valve installation position is not limited, it can be installed in the horizontal, vertical or inclined pipeline, such as installed in the vertical pipeline, the flow of media from the bottom up;
Swing check valve is not suitable for small diameter valve, can be made of high working pressure, PN can reach 42MPa, and DN can be very large, can reach more than 2000mm.It can be applied to any working medium and any working temperature range according to the material of the shell and sealing parts.The medium is water, steam, gas, corrosive medium, oil, medicine, etc.Medium operating temperature range between -196 ℃ and 800℃;
Applicable occasions are low pressure large diameter, and installation occasions are limited;
Butterfly check valves can be installed in an unrestricted position, either on a horizontal line or on a vertical or sloping line.
Diaphragm check valve is suitable for water shock easily generated on the pipeline, diaphragm can be very good to eliminate the medium countercurrent water shock, it is generally used in low-pressure room temperature pipeline, especially for the water pipeline, the general medium operating temperature between -12--120℃, the working pressure <1.6mpa, but diaphragm check valve can achieve a larger diameter, DN can reach more than 2000mm;
Spherical check valve is suitable for medium and low pressure pipeline and can be made into large diameter.
Spherical check valve shell material can be made of stainless steel, sealing parts of the hollow sphere can be wrapped in ptfe engineering plastics, so in general corrosive medium pipeline can also be applied, operating temperature between -101--150℃, its nominal pressure ≤4.0MPa, nominal through range between 200 -- 1200;
When selecting check valves for incompressible fluids, the required closing speed should be evaluated first. The second step is to select the type of check valves that may meet the required closing speed.
For compressible fluid with check valve when the choice according to non-compressible fluid using similar methods to choose the check valve, if the medium flow field is very big, the check valve can be used for compressible fluid, a speed reducer, if the medium flow continuous period of not to stop and start quickly, as the export of compressor, use the lift check valve;
The check valve shall determine the size of the response, and the valve supplier shall provide the data of the selected size so that the valve size when the valve is fully open at a given flow rate can be found.
For high and middle pressure check valve below DN50mm, it is advisable to choose vertical lifting check valve and straight through lifting check valve;
For low pressure check valve below DN50mm, it is advisable to choose butterfly check valve, vertical lifting check valve and diaphragm check valve;
For high and middle pressure check valves with DN greater than 50mm and less than 600mm, swing type check valve should be selected.
For middle and low pressure check valves with DN greater than 200mm and less than 1200mm, it is recommended to use non-wear spherical check valve;
For low pressure check valves with DN greater than 50mm and less than 2000mm, butterfly type check valve and diaphragm type check valve are used.
For pipe lines requiring small or no water impact when closed, slow closing swing check valve and slow closing butterfly check valve should be selected.