Check Valve Symbols

This download collects check valve symbols from three kinds of drawing in one file: the P&ID check valve, the hydraulic check valve and pilot-operated check valve, the pneumatic check valve, and the valves that carry a check element inside them, the one-way flow control valve in both media and the pneumatic quick exhaust valve. That is 7 named blocks in DWG and DXF and a PDF sheet. Each block keeps its library name, such as IND_PID_SYMBOLS_CHECK_VALVE or IND_HYDRAULIC_SYMBOLS_PILOT_OPERATED_CHECK_VALVE.

Check valve symbol on a P&ID

On a piping and instrumentation diagram the check valve uses the common valve body, two triangles point to point, with a solid dot on the upper corner of the inlet side. Flow is allowed from left to right. The body is 10 mm long and 5 mm high like every in-line valve in the P&ID set, with the base point on the left connection, so it replaces a gate or globe valve on the same line. If the flow runs the other way, mirror the block rather than drawing a new one.

Some company legends draw a swing disc or add a flow arrow. This block keeps the plain form, so if a project legend asks for something else, that legend wins.

Non-return valve symbol in hydraulics and pneumatics

In fluid power circuits the same device is usually called a non-return valve. It is drawn as a ball resting in a V-shaped seat: flow that pushes the ball off the seat passes, from left to right here, and reverse flow presses it shut. The hydraulic and pneumatic blocks have the same geometry, 15 mm long, and live in both libraries so that each one is complete on its own. Insert them by the left connection.

Pilot operated check valve symbol

The pilot-operated check valve adds a dashed pilot line that reaches the seat from below. Pressure in that line lifts the ball and lets the fluid return. The usual place is between a directional valve and a cylinder that has to hold a load without creeping: the cylinder only moves back when the pilot line is pressurised. Here it is drawn without a spring and without an enclosing frame, both of which some charts show.

Check valves inside flow control and quick exhaust valves

The one-way flow control valve is an adjustable throttle with a check valve in parallel. Flow is restricted in one direction and passes freely through the check element in the other, which sets cylinder speed on one stroke only. In pneumatics it is normally fitted to throttle the exhaust air. The quick exhaust valve takes air in on the left, feeds the outlet on top, and when the inlet drops it vents the outlet straight to atmosphere on the right, so mount it close to the cylinder port.

The other in-line valves of a process drawing are on the valve symbols page, the valves that switch the cylinder are among the directional control valve symbols, and the complete process set is the P&ID symbols library.

The P&ID block follows ISO 10628-2 and the fluid power blocks follow ISO 1219-1. Both standards are sold by ISO; we only redraw their conventions and do not reproduce them.