I was looking in a few different hydraulic power textbooks for symbol information and I noticed that on of them referenced a check valve with this symbol:

Full logical symbol of a "Non-Return Valve"

Is this "full" block symbol ever actually used in industrial diagrams or is this simplified version usually used? Which should I use for documentation for a university report?

Simplified Non-Return Valve


1 Answer 1


The bottom one is a simple check valve.

The top one looks like back pressure from the top will push the spool into the closed position. Forward pressure from below will work with the spring to open the valve for forward feed.

It appears to me that if the top pressure falls that the spring should cause the valve to open in which case the system can drain. (I'm an EE so this isn't really my area but I have worked on a few hydraulic systems.) I can only think that it allows the system to drain or relax after pressure is lost.

  • $\begingroup$ The more complicated one describes the same function as the simplified one, two flow pressures on each side of the valve determine the ball or spool position. The spring just ensures the valve is in the shut position normally. I am just not sure which symbol should be used in a technical document, and what is common best practice. $\endgroup$
    – Austin Fox
    Sep 13, 2022 at 16:37
  • $\begingroup$ No, the ball check-valve can never reverse flow. The valve with the spool can, hence the bi-directional arrow. The version with the spool looks like the spring will open the valve if there is not enough counter-pressure on the top side. $\endgroup$
    – Transistor
    Sep 13, 2022 at 17:25
  • $\begingroup$ Oh got it, so only use the more complex one if you actually have a spool style non-return valve. Thank you. $\endgroup$
    – Austin Fox
    Sep 13, 2022 at 17:50

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