They stop lubricant back-flow through the control valve on the exhaust cycle that lets progressive oil flow to the cylinder, and have a full-formed seating-surface. The valves are available in a range of port sized from #10-32 to ¾-in., can operate at speeds up to 600 CPM, have a pressure range to 150 psig, and a working temperature range from −25 to +180° F.