Abstract A pilot operated load compensated variable displacement pump is controlled by a servomotor and a pilot valve to maintain a constant pressure drop across an adjustable orifice in the pump delivery line. The available pressure differential for operating the pilot valve is increased without increasing the pressure drop in the main flow through the adjustable orifice by providing a small restrictor in the operating line to the pilot valve and establishing a continuous bleed flow through that restrictor to establish a large pressure differential supplementing that at the adjustable orifice in the main pump delivery line. The bleed is established through a pressure compensated flow control valve. Maximum pressure limiting is obtained by a pilot relief valve establishing a parallel bleed. Alternatively, a special pilot relief valve establishes both the bleed flow and the maximum pressure limiting.
A pilot operated load compensated variable displacement pump for maintaining a predetermined pressure drop across an adjustable orifice comprising a servomotor for adjusting the pump displacement, a pilot valve for controlling the servomotor, a connection from the pump output ahead of the adjustable orifice for urging the pilot valve toward a position of lesser pump displacement, a second connection from the pump output beyond the adjustable orifice for urging the pilot valve toward a position of greater displacement, a restrictor in the second connection and a bleed restriction comprising a pressure responsive flow regulator from the restrictor to maintain a small and fixed continuous flow therethrough independent of system pressure and sufficient to create a pressure drop through the restrictor several times as great as the pressure drop through the adjustable orifice under steady state conditions, whereby a large pressure differential for operating the pilot valve is available without imposing a large pressure drop in the main flow through the adjustable orifice.
Claim 2
Dependent Claim
162 words
A pilot operated load compensated variable displacement pump for maintaining a predetermined pressure drop across an adjustable orifice comprising a servomotor for adjusting the pump displacement, a pilot valve for controlling the servomotor, a connection from the pump output ahead of the adjustable orifice for urging the pilot valve toward a position of lesser pump displacement, a second connection from the pump output beyond the adjustable orifice for urging the pilot valve toward a position of greater displacement, a restrictor in the second connection and a bleed restriction comprising a pressure responsive flow regulator from the restrictor to maintain a small and fixed continuous flow therethrough independent of system pressure and sufficient to create a pressure drop through the restrictor several times as great as the pressure drop through the adjustable orifice under steady state conditions, whereby a large pressure differential for operating the pilot valve is available without imposing a large pressure drop in the main flow through the adjustable orifice.
Claim 3
Dependent Claim
28 words
A pump as defined in claim 1 wherein the flow regulator comprises an additional restrictor and a compensator for maintaining a constant pressure drop across the additional restrictor.
Claim 4
Dependent Claim
24 words
A pump as defined in claim 1 which includes a pilot relief valve connected to the restrictor to limit the maximum pump output pressure.
Claim 5
Dependent Claim
24 words
A pump as defined in claim 2 having a pilot relief valve connected to the first restrictor to limit the maximum pump output pressure.