Swing check valves allow flow in one direction, but not both. Swing check valves are also referred to as clack, non-return, stop, check and one-way valves. Other common check valve designs include the tilting disc (a variation of the swing check design), piston, butterfly and stop valve designs.
Swing check valves allow almost un-obstructed flow through the valve with a correspondingly low pressure drop. Gate valves also have this flow characteristic and are often used in series with check valves.
There are two designs of swing check valve, the Y-type and straight flow type. The valve construction and component design is relatively simple and easy to maintain. A large valve bonnet allows easy access to the valve internals (trim) which makes repairing the valve seat rings and disc possible, without needing to remove/replace the entire valve.
Swing check valves are not well suited for applications where pressure fluctuations often occur. Rapid or constantly varying pressure fluctuations will lead to the valve opening and closing frequently (chattering) and this will lead to wear of the disc and seat.
Swing check valves are ideal for low-medium velocity flow applications.
Flow is allowed through the valve in only one direction, inlet to outlet. If there is flow in the opposite direction, the valve disc will be pressed against the seat and all flow will stop (the valve is now closed).
The pressure differential across the valve determines if the valve moves to the open or closed position. A higher pressure on the outlet side will move the valve to the closed position, but the valve will open again once the pressure on the inlet side is greater than the outlet side.
The point at which flow starts to occur through the valve is known as the cracking pressure. The point at which all flow stops through the valve is known as the seating or sealing pressure.
3D Model Components
This 3D model shows all major components associated with a swing check valve, these include:
- Hinge Pin
How Swing Check Valve Work
The below video is an extract from our Introduction to Valves Online Video Course.