The metal ring valves, the first ones produced, are still valid mainly for lubricated use.
Metal ring valves with selflubricating guides are most suited for dry compressors, resist high pressures, and are adaptable to any kind of gas. They are mainly used on gas processing compressors and on diaphragm compressors, and adapt to be made in extremely small sizes.
Amongst the valves with lowest clearance there is a particular configuration with metal rings and sinusoidal springs.
Thermoplastic ring valves are the evolution of the metal ring valves for dry conditions, as well as lubricated, for aggressive gases and presence of impurity. They are used for gas processing and refining at high pressures.