Hose check valves

From GAWDAwiki

A non-return valve is an example of a hose check valve. Non-return valves are fitted to the end of the gas hoses to prevent the backfeeding of one gas into another. For example, if the oxygen working pressure is much higher than that for the fuel gas and a hose check valve is not fitted, oxygen could backfeed into the fuel gas hose, creating an explosive mixture. ^[1]

References

1. http://www.bocindustrial.co.uk/bocindustrial/technical/glossary/a.asp