Patent ID: 7165397

Claim:
In a hydraulic control system that has hydraulic pilot pressure operated valves for controlling hydraulic work devices and a prime mover that drives a hydraulic pump that supplies hydraulic fluid under pressure to the devices through the pilot pressure operated valves, the improvement comprising an orifice in a hydraulic line in which the fluid flow is dependent on prime mover speed and a spring return pilot pressure operated anti-stall valve in a pilot pressure fluid supply line, the anti-stall valve having opposed pilot pressure ports, one of said ports being connected to one side of said orifice and the other said port being connected to the other side of said orifice, such that a sufficient reduction in the speed of the prime mover causes the pressure drop across the orifice to diminish to a point that the anti-stall valve reduces the pilot pressure fluid flow through the anti-stall valve to the pilot pressure operated valves of the hydraulic control system and relieves the pilot pressure from the pilot pressure operated valves.