This is a full range pressure compensating variable flow control. It is designed so that the orifice area varies as the lever is rotated. The outlet flow is smooth and constant regardless of the pressure on the control flow or excess flow ports. 3 port flow control valves without relief will send a specific amount of oil to the control flow port and any additional oil will be sent to the excess flow port. The specific amount sent to the control flow port is adjusted by roatating the control lever as needed.