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A valve returning pump flow to tank at low pressure.
Also known as: Pump unloading valve, Vent valve symbol
In ISO 1219 fluid power diagrams an unloading valve is drawn as a pressure valve piloted from a remote point, opening a path to tank so the pump circulates at little pressure when flow is not needed.
Denotes a valve that opens a low-pressure path to tank so a pump can idle without building pressure.
Contexts: Technical drawing
Is piloted remotely rather than from its own inlet, which is what distinguishes it in a drawing from a relief valve of the same outline.
Contexts: Technical drawing
A square with a spring and a dashed pilot line taken from a remote point in the circuit rather than from its own inlet.