P&ID Valve Symbols
Common valve and actuator symbols on P&IDs: gate, globe, ball, butterfly and check valves, control valve actuators, solenoid and motor operated valves, relief valves and fail positions.
Gate valve
Isolation (block) valve, full bore: two triangles meeting at the tips.
Globe valve
Throttling valve: valve body with a filled circle at the centre.
Ball valve
Quarter turn valve: valve body with a circle at the centre.
Butterfly valve
Quarter turn disc valve: commonly drawn as two end lines with a disc across the pipe.
Check valve
Non return valve allowing flow in one direction only; the arrow or filled side shows the allowed flow.
Three way valve
Diverting or mixing valve with three ports.
Angle valve
Body with inlet and outlet at 90°, often used for control and relief service.
Control valve, diaphragm actuator
Modulating valve with a spring and diaphragm actuator (dome on the stem).
Control valve, piston actuator
Valve with a pneumatic cylinder (piston) actuator: rectangle on the stem.
Solenoid operated valve
Valve operated by a solenoid: box with S on the stem.
Motor operated valve
Valve with an electric motor actuator: circle with M on the stem.
Hand operated valve
Manually operated valve with handwheel: T shape on the stem.
Pressure relief or safety valve
Spring loaded relief valve (PSV): angle body with a spring on top.
Fail closed (FC)
Valve closes on loss of air or power: arrow pointing to the closed position, or FC written below.
Fail open (FO)
Valve opens on loss of air or power: FO written below the valve.
Valve with positioner
Control valve with a positioner, shown as a box beside the actuator, receiving the electric signal.
How to Read These Symbols
Common valve and actuator symbols on P&IDs: gate, globe, ball, butterfly and check valves, control valve actuators, solenoid and motor operated valves, relief valves and fail positions. Instrument symbols and identification letters follow ISA 5.1. Valve, equipment and some line symbols vary between companies and with ISO 10628, so every project issues a legend sheet: when it differs from this page, the legend sheet wins.
Frequently Asked Questions
What is the symbol for a control valve?
A valve body (two triangles) with an actuator on the stem; a dome for a diaphragm actuator, a rectangle for a piston actuator.
How is fail closed shown?
With FC written below the valve or an arrow showing the fail direction.
Are valve symbols standardised?
Partly. ISA 5.1 covers instrument symbols; valve body symbols follow common practice and ISO 10628, so always check the project legend sheet.
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