Threaded Brass Check Valves https://www.fadavalve.com/product/brass-check-valve/brass-threaded-check-valves.html Check valves also called reflux valve, non - return valve, foot valves. is a type valve shut-off by medium flows itself, it provide the flows just one way, when flows in arrow direction, check valve open and let it pass, but flow opposite direction check valves close to prevent passing.