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US 4,360,322 AGranted
Positive displacement pump systems
AssigneeHobourn-Eaton Limited
InventorsIan T. Bristow, Nigel J. Petts
Life of this patent
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AssigneeHobourn-Eaton Limited
InventorsIan T. Bristow, Nigel J. Petts
Estimating the term…
A positive displacement pump system has two delivery passages communicating under the control of a valve with a main discharge passage and/or an overspill duct. The valve is constituted by a valve member slidably mounted in a valve bore and the valve member has lands and intermediate recesses controlling communication between the delivery passages and the overspill duct. The pressures upstream and downstream of a discharge orifice in the discharge passage are applied to the valve member in opposition to each other, increase of the pressure drop tending to move the valve member to increase the amount of fluid passed to the overspill duct. To overcome the known tendency for a valve member to be subjected by the hydraulic forces to a large closing force when the valve is open to only a small extent, the valve is designed to provide for a relatively large opening force at least when the valve is commencing to open. In one construction this is achieved by passing the flow from the second to the main discharge duct through the valve member in a manner producing a jet reaction on the valve member to assist the normal regulating force on the member. In alternative arrangements the additional force is derived from an additional pressure drop induced in the flow from the delivery passage, the higher pressure being applied to valve member in a sense to increase the amount of fluid passed to overspill.
A positive displacement pump system having first and second delivery passages for pumped fluid, a main discharge passage which incorporates a discharge orifice and which is in permanently open communication with the first delivery passage, a valve controlling the supply of fluid from the second to the first delivery passage and the quantity of fluid supplied from the first delivery passage to the main discharge passage and comprising a valve bore and a valve member slidably mounted in the valve bore, overspill porting opening to the valve bore, said valve member having applied to it a force derived from the pressure drop across the discharge orifice and operating in response to an increase of said pressure drop above a predetermined value to move the valve member to cause fluid from the first and second delivery passages to be by-passed through the overspill porting, and means for superimposing on the valve member an additional force which is derived from the delivery pressure in one of said delivery passages and which operates in the same sense as the first said force.
A positive displacement pump system incorporating a valve comprising a valve bore and a valve member slidably mounted in the valve bore, first and second delivery passages respectively opening to an extension of the valve bore and to the valve bore, a main discharge passage opening to the extension of the valve bore at a location axially spaced from the first delivery passage in a direction towards the main part of the valve bore, a restrictor disposed in the main discharge passage, the valve member having a reduced diameter end portion disposed in but having a radial clearance with respect to the extension of the valve bore to form therewith an annular restriction and providing an axially facing shoulder at the location of the reduction in diameter, a chamber being formed at the end of the valve bore remote from the extension, a spring disposed in said chamber and pressing axially against the valve member, overspill porting opening to the valve bore between the second delivery passage and the main discharge passage, first, second and third lands on the valve member disposed respectively axially between the chamber and the second delivery passage, between the second delivery passage and the overspill porting, and between the overspill porting and the main discharge passage, an enlargement of the valve bore being formed where the second discharge passage opens to the valve bore, an axial bore formed in the valve member and opening permanently at one end to said enlargement of the valve bore and at the other end to the downstream end of said annular restriction, a spring-loaded ball valve mounted in the valve member and adapted to close off the axial bore in the valve member if the fluid pressure in the second delivery passage falls substantially to the same value as at the upstream end of the annular restriction, the second and third lands operating respectively to place the enlargement of the valve bore and the downstream end of the annular restriction in communication with the overspill porting when the resultant of the forces on the valve member exceeds a predetermined value.
Dependencies are inferred from the claim text.