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A single box with an arrow and a spring, limiting pressure.
Also known as: Pressure relief valve, Safety valve symbol
A relief valve opens above a set pressure to protect the circuit, drawn as one box with an offset arrow, a spring and a pilot line sensing the pressure. The pilot line is the working part of the symbol: it says what the valve is measuring.
Limits system pressure by opening a path to tank above a set value, drawn as a single box with a spring and a pilot line.
Contexts: Technical drawing
Shows what the valve senses through its pilot line, which distinguishes a direct-acting relief from a pressure-reducing or sequence valve of similar outline.
Contexts: Technical drawing
A square containing an offset arrow, with a zigzag spring drawn on one side and a dashed line leading to the pressure port.