Check Valve Cracking Pressure, Explained
Cracking pressure is the minimum forward pressure differential needed to push a check valve off its seat and start flow. It is one of the most misunderstood specs on a check valve, and getting it wrong is why a valve either starves your flow or fails to seal.
What cracking pressure is (and is not)
It is the pressure at which the valve first opens, not the pressure at which it is fully open. A valve with a 1 psi cracking pressure begins to pass flow at 1 psi differential, but needs somewhat more to open fully. It is also not the reseal or back-pressure rating, which is how much reverse pressure the valve holds when closed.
Why it matters
Too high a cracking pressure and the valve robs head your system may not have, throttling flow or preventing the valve from opening fully. Too low, and the valve may not reseal crisply against light back-pressure, allowing weep-back. The right cracking pressure is comfortably below your available forward pressure and high enough to close positively when flow stops.
Typical values by type
| Type | Typical cracking pressure | Notes |
|---|---|---|
| Swing | Near zero (gravity) | Opens on almost any forward flow; relies on orientation |
| Spring / inline | ~1 to 5+ psi, spec'd | Set by spring; choose to match the system |
| Ball | Low to moderate | Depends on spring or gravity design |
| Wafer (spring) | Low | Spring-assisted, non-slam |
Exact values vary by manufacturer and spring option; always confirm against the product spec for the valve you are buying.
How to choose it
Work out your available forward pressure differential at the valve during normal flow. Pick a cracking pressure well under that, so the valve opens fully. Then check the other direction: you want enough spring to reseat the valve promptly when flow stops, especially on vertical runs and pump discharge where a higher cracking pressure helps prevent water hammer. On gravity or low-head systems, a low cracking pressure (or a swing check) avoids starving flow.
Related
See how spring behavior differs from a swing in Swing vs Spring, the pressure and temperature limits in the ratings chart, and the full picture in the selection guide.
Free to reference - a link back is appreciated.
Technical data disclaimer: Specifications, dimensions, pressure/temperature ratings, and compatibility information on this page are compiled from manufacturer publications and are provided for reference only. Always verify suitability for your application against the manufacturer’s current documentation before purchase or installation. Apex Flow Solutions assumes no liability for errors, omissions, or misapplication of this information.