Check valve
A triangle pointing in the direction of intended flow. Check valves prevent reverse flow and are mechanical-only. No PLC channel, no actuator.
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How it’s drawn.
A simple body with a pointer in the direction flow is allowed to pass. The check valve has no actuator and no signal. It works mechanically on flow direction alone. The pointing direction is the content of the symbol, so it is always drawn to match the intended flow.
Typical usage.
Pump discharge protection, condensate return lines, anywhere a backflow event would damage equipment or contaminate upstream service. The symbol's arrow direction is mandatory. Reversing it is a documentation error.
Telling it apart.
- The arrow direction is mandatory and carries the meaning. Drawn the wrong way it reverses what the valve is meant to do.
- A check valve has no actuator or signal. If something is drawn on top driving it, it is not a plain check valve.
- It prevents reverse flow on its own. It is not a remotely operated block valve.