Patent ID: 8689823

Claim:
A hydraulic system, comprising: a source of hydraulic fluid; a hydraulic pump in communication with the source of hydraulic fluid to draw fluid from the source of hydraulic fluid and deliver the fluid under a supply pressure to a supply of hydraulic fluid; a source of compressed air; an air motor in communication with the source of compressed air that is powered by the source of compressed air to drive the hydraulic pump; a pressure limiting valve in communication with the source of compressed air and in communication with the supply pressure of the hydraulic fluid, said valve comprising: a valve housing having an air inlet port in communication with the source of compressed air and an air outlet port and a hydraulic fluid sense port in communication with the supply pressure of the hydraulic fluid; a valve element in the housing having a hydraulic section and a pneumatic section, the hydraulic section being in fluid communication with the hydraulic fluid sense port and the pneumatic section being in fluid communication with the air inlet port and the air outlet port and openable to provide fluid communication between the air inlet port and the air outlet port in an open position and operable to close fluid communication between the air inlet port and the air outlet port in a closed position; wherein the hydraulic section has an unbalanced area in fluid communication with the hydraulic fluid sense port such that a pressure limit at the hydraulic fluid sense port acts on the unbalanced area to move the valve element to the closed position which moves the pneumatic section into a position between the air inlet port and the air outlet port to block the flow of air between the air inlet port and the air outlet port.