Gas cylinders are open-ended. To allow a gas to be contained within a cylinder a valve is usually fitted into the open end of the cylinder, normally at the top, or shoulder of the cylinder. The valve may have several functions.
- It is a means of closing an opening in a cylinder.
- It provides an inlet port to allow a cylinder to be filled.
- It provides closure to contain the contents within the cylinder.
- It provides an outlet port to allow the gas to be released.
- it can accommodate safety devices, such as non-return valves, pressure relief valves and residual pressure valves.
- It can incorporate an integrated pressure regulator.
- It can incorporate an outlet flow regulating device
- It can incorporate a contents level (pressure) gauge
- It can provide a mounting for external components, such as regulators and pipelines.
Gas cylinders and their associated valves that are, or are intended to be, used to transport dangerous goods have to comply with the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations.
Valves are designed, constructed, inspected, tested and approved against authorised standards. Due to the many properties of the various gases, valves have to be manufactured from compatible materials. Valves should not be used if their test pressure is below that of the cylinder.