Check valves, abbreviated as CV, are valves that are designed to allow the process fluid to flow in only one direction to prevent backflow. Check valves are also known as non-return valves, clack valves or one-way valves. There are many different types of check valves. These are:
- Ball Check Valve
- Diaphragm Check Valve
- Dual Plate Check Valve
- Lift Check Valve
- Piston Check Valve
- Stop Check Valve
- Swing Check Valve
- Tilting Disk Check Valve
They are self-acting, meaning they operate automatically and do not require any outside inputs for it to operate. This means that they will keep working if the processing plant loses electricity or instrument air. When operating properly, the valve is kept open by the force developed by the velocity in the line. When the flow stops or reverses, the valve closes.
These valves are opened, and kept in the open position, by the forces developed by the velocity. When the flow rate slows or stops, the valve closes. The seating load and tightness is dependent upon the amount of back pressure.
Typical check valves include swing check, tilting disc check, lift check, and stop check. Other check valve types are available, however.
Types of check valves
Back Pressure Check Valve
Ball Check Valve
Diaphragm Check Valve
Dual Plate Wafer Check Valve
A dual plate check valve is lighter and more compact than a conventional swing check valves. This valve takes less space in a pipe run where space could be a problem and can be installed in a horizontal or vertical up positions. With a spring loaded, dual plate design and the discs open 85°, it ensures a low pressure drop with very low cracking pressure. The valve has positive sealing under most conditions and closes before the flow reverses at zero velocity. With the spring to assisted in closing, water hammer is pretty much eliminated. The way the valve is designed it is fundamental non-slamming because the plates closing before the product flow reverses. There are 3 types of this valve: wafer, lug and flange.
Dual Plate Lug Check Valve
Dual Plate Flange Check Valve
Nozzle Check Valve
Piston Check Valve
Check Valve Design Considerations
The following design considerations are offered in the specification of check valves for typical process plant applications:
- While it may be tempting to add a check valve directly to a valve to eliminate a weld during fabrication. While a weld is eliminated, it makes assembly more difficult. When two valves are connected flange-to-flange, the valve bodies make it difficult to insert the bolt into the bolt hole.
- Do not use check valves in vertical lines the flow is downward. In this configuration, the valve won’t close and it loses the ability to do its job properly.
- Dual and single-plate wafer check valves should not be used for reciprocating compressor or reciprocating pump applications. The pulsation can lead to pulsation induced fatigue which will cause the spring to fail prematurely.
- Ball or piston check valves should not rely only on flow reversal to close the valve. These types of check valves should either use gravity to assist closure (vertical orientation, flow up) or use a sprint to assist closure.
- Lift check valves should not be used in services subject to fouling, coking deposits, or erosion.
- A check valve should never be used as an isolation valve. Ever.
- Consideration should be made for isolation and gauges to periodically check whether or not the check valve is functioning as intended.
Check Valve Datasheets and Dimensional Information
The following are links to our datasheets that contain dimensional information on various types of check valves. Abbreviations that are used in the descriptions are:
- CI - Cast Iron
- DI - Ductile Iron
- CS - Carbon Steel (Note that materials may be substituted for carbon steel such as Stainless Steel. Check with your valve vendor for materials)
Dimensions shown are in inches unless otherwise noted.
Check valve Datasheets
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Tags: Equations for Valves