Mounted on the side of the hydraulic oil reservoir on any standard Hydra-Tech Pumps Hydraulic Power Unit is the H.C. (or Hydraulic Control) Valve. The only exception to this is sound attenuated units. Since access to the hydraulic oil reservoir is limited, sound attenuated units do NOT have a H.C. valve. Think of this valve as an “on / off” switch for the hydraulic circuit on your HPU. Once an HPU has been started and warmed up and you are ready to send hydraulic fluid to a pump (or hydraulic tool) properly connected with hydraulic hoses, or deadhead the unit (troubleshooting), this valve should be turned all the way clockwise until the handle stops to engage the hydraulic flow. When you are ready to shut the system down, the H.C. valve should be turned all the way counterclockwise until the handle stops to shut off the hydraulic flow. This valve should not be used to attempt to control flow as doing so will generate heat and cause other problems. If you need to control flow or pressure, Hydra-Tech Pumps offers flow and pressure controls for their pumps and an adjustable inline flow control device as well.