The PF Series ParTrol Flow Control Valves meter flow of air or oil in one direction and allow free flow in the reverse direction. ParTrol valves are standard with a two step needle. Fine metering is accomplished over the first adjustment turns and nominal metering is provided over the last turns. Once the desired flow is selected, a setscrew can be tightened to hold the setting. Brass valves are recommended for pneumatic services and the steel valves are recommended for hydraulic services.