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 3 /4 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.
Humphrey Products Co., Box 2008, Kalamazoo, MI 49003, (269) 381-4113, humphrey-products.com