Abstract: In load sensing systems, pressure compensating valves are normally used to maintain a predetermined pressure differential across the orifices in the directional control valve at a predetermined level. The predetermined pressure level acting across the directional control valve can be adversely affected by flow forces acting on a valving element of the pressure compensating valve. In the subject invention, flow force compensation is provided by having a forced balancing device connected to a pressure compensated valve device so that a force that is directly proportional to the degree of flow forces acting on the pressure compensating valve device is transferred to a valving element thereof in opposition to the flow forces that are acting on the valving element. The subject arrangement is also applicable to providing flow force compensation for negative load pressure compensating valve devices.

Abstract: The flow changing response of fluid systems having variable displacements pumps are greatly effected by the inertia of the displacement changing mechanisms, such as, the swashplate and at least half of the fluid pumping piston assemblies. In the present invention, a fluid system is provided which has a first flow changing mechanism operable to maintain a relatively constant pressure differential across a variable orifice device in a valve mechanism to change the flow of the fluid being delivered from the fluid pump to the fluid system. Simultaneously therewith, a second flow changing mechanism having a fast acting bypass mechanism acts in parallel with the first flow changing mechanism to more quickly bypass fluid being delivered from the fluid pump to the fluid system thus eliminating pressure spikes in the fluid system. The second flow changing mechanism is operable to establish a second larger differential pressure across the variable orifice device.

Abstract: A hydraulic piston type motor having a rotating piston barrel abutting a fixed porting plate or head with a starting charge device including a differential area piston operating to supply a limited hydrostatic pressure between the porting plate and rotating barrel to reduce starting friction and improve starting torque.

Abstract: In the present fluid system, a variable pressure inlet system is provided and operational to control the operating pressure level of a charge pump in response to various operating parameters of the fluid system. The charge pump provides pressurized fluid to an inlet of a hydraulic pump to insure filling of the pumping chambers therein. By having the operating pressure level of a variable pressure relief valve that is connected to the charge pump controlled between a minimum pressure level and a maximum pressure level responsive to various operating perimeters of the system, the degree of horsepower needed to drive the charge pump is controlled.