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Check valves or Non-return valves (NRV) are normally installed in piping to avoid back flow. Rotating equipment such as pump, compressor, etc will always be equipped with NRV(s) on the discharge to avoid back flow when rotating equipment is shut. Back flow creates severe surging to the rotating equipment and potentially damage the equipment. In certain process system, NRV will be employed to avoid contamination, overheating, etc due to back flow.See the following animation how a dual disc check valve action to avoid back flow.
Courtesy of Goodwin
There are many types of check valve (NRV) available such as ball check valve, lift check valve, swing check valve, wafer check valve, disc check valve, dual disc check valve, tilted disc check valve, etc.
For details discussion on each type of check valves, please check out :
- Check valves or Non-return valves (NRV) - Wikipedia
- Check valve tutorial - Spirax Sarco
Out of many types of check valve, how do you make proper selection to suit your application ? An article by VAL-MATIC entitled "Design and Selection of Check Valve" is available for download. This article presented four (4) criteria which shall be considered for the selection of check valve type. There are :
- non-slam characteristic
- pressure loss
- cost
- application
Comparative rating for each type of check valve have been provided for these criteria (specifically first two technical criteria). These rating will be plotted on a Check Valve Comparative Selection Chart and together budget for final selection.
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