Oxygen Bottle Valve QF-2C7 for oxygen gas cylinders.
-Mat:brass;
-DN:4mm;W.P:15Mpa; 
-Inlet Thread: PZ 27.8;
Outlet thread: W21.8X1/14.

           
(referenced QF-8 with the same specs for oxygen gas cylinders).

A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically valves fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. 

The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a check valve, as it prevents or "checks" the flow in one direction. 
Valves have many uses, including controlling water for Irrigation, industrial uses for controlling processes, residential uses such as on / off & pressure control to dish and clothes washers & taps in the home. Even aerosols have a tiny valve built in. Valves are also used in the military & transport sectors. 

Gas cylinder valves are found in virtually every industrial process, including water & sewage processing, mining, power generation, processing of oil, gas & petroleum, food manufacturing, chemical & plastic manufacturing and many other fields. 

Should you have any intersts or some more info needed on our (chromed)gas cylinder valves, just pls feel free to enquire us!