A stop check valve works by automatically preventing backflow while also allowing manual shut-off for maintenance or isolation. In essence, it combines the functionalities of a check valve and a stop valve.
Here's a breakdown of how it functions:
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Automatic Non-Return (Check Valve Function): The core function is preventing backflow. A hinged disc (or clapper) inside the valve is designed to open when flow is moving in the desired direction and to close automatically when the flow stops or attempts to reverse. The pressure of the fluid pushes the disc open, allowing flow. If the pressure drops and backflow begins, gravity and the back pressure push the disc closed, sealing the valve.
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Manual Shut-Off (Stop Valve Function): A stop check valve also incorporates a stem and handwheel (or other actuator) that allows manual closure, overriding the automatic check function. This feature allows the valve to be positively closed, regardless of pressure conditions, facilitating maintenance, repairs, or isolation of specific sections of a system. The stem forces the disc onto the valve seat, creating a tight seal.
Here's a more detailed look at the key components and their roles:
| Component | Function |
|---|---|
| Valve Body | Provides the housing and flow path. |
| Disc (or Clapper) | The moving part that opens and closes to allow or prevent flow. |
| Valve Seat | The surface against which the disc seals. |
| Hinge Pin | Allows the disc to pivot freely. |
| Stem & Handwheel | Allows manual override to force the disc closed, stopping all flow. |
In summary:
The stop check valve is an automatic non-return valve (check valve) that also allows manual shut-off functionality via a stem and handwheel. In typical operation, it behaves like a check valve, preventing backflow. However, when necessary, the operator can manually close the valve completely, independent of the pressure conditions. A common application is in boiler systems, where it prevents backflow of steam from the main header to a non-firing boiler.
