Abstract: Pilot control circuits are useful, for example, for controlling the actuation of main control valves of load sensing hydraulic systems. Using the main supply pump as the source of pressurized pilot fluid sometimes results in inadequate pilot pressure for maintaining the main control valves in an actuated position under some operating conditions. The subject pilot control system includes an accumulator to store pressurized fluid received from the main supply pump for use by the pilot control circuit when the pressure level of the main hydraulic system momentarily drops below a level for proper pilot control operation. Thus, the main control valves are maintained in their actuated position irregardless of the pressure level of the fluid in the main supply system.

Abstract: Metering slots in valve spools are useful for modulatably controlling fluid flow through a control valve. The current metering slot configurations used in a meter out condition have high flow forces acting on the spool or metering areas that open or increase in size rather slowly relative to the valve spool movement. The subject metering slot is formed by plunging a ball-end end mill cutter into a control face of a valve spool at an acute angle and then moving the cutter laterally to provide the desired width of the metering slot. The resulting metering slot provides a metering area that increases in size rather quickly with a rather small increment of movement of the spool with the flow forces generated by the fluid passing through the metering slot being relatively low.

Abstract: The invention is concerned with an improvement in a hydraulic reservoir which comprises a tank having internally thereof filter means attached longitudinally between a first and a second generally parallel side thereof, said filter means including generally tubular filter element means extending generally longitudinally between said first and second side of said tank and means for introducing a hydraulic fluid from an exterior of said tank to an interior of said element means from adjacent said first side of said tank. The improvement comprises a tube within said tank surrounding said element means and extending longitudinally generally the length thereof, said tube including exit means therethrough through which said hydraulic fluid passes after passage thereof from the interior to an exterior of said element means, a first end of said tube sealing adjacent said second side of said tank and a second end of said tube sealing adjacent said first side of said tank.

Abstract: A fluid reservoir and filter combination includes a reservoir made of upper and lower sections with a filter support assembly comprising a base mounted in the lower section and a hold-down assembly mounted in the upper section. The filter assembly includes misalignment accommodating means comprising a particular configuration of the hold-down assembly including an elongated sleeve for extending into a filter element and a collar slidably mounted on the sleeve and biased toward the filter element for sealingly engaging the end of the filter element. The dimensions of the collar and sleeve element are such as to accommodate lateral misalignment of a filter element supported on the base member with respect to the hold-down assembly. Longitudinal misalignment is accommodated by means of the length of the sleeve member.

Abstract: A hydraulic circuit comprises a first tank elevated above a second tank and openly communicating therewith by a conduit adapted to continuously maintain the second tank at full capacity with a hydraulic fluid. The hydraulic fluid is pumped out of the second tank and to a work system wherefrom it is recircuited back through a filtering system, retained in the first tank. Upon malfunctioning of the filtering system to prevent the egress of hydraulic fluid therethrough, the increased pressure level of the recircuited hydraulic fluid will function to open a directional control check valve in the second tank to by-pass the conduit normally communicating hydraulic fluid from the first tank to the second tank.

Abstract: A hydraulic control system having a load-lifting hydraulic motor, a source of pressurized fluid and a pilot-operated directional control valve for directing fluid for operation of the motor is provided with a combined restrictor and shuttle valve assembly that is operative to direct fluid from a pump for pilot-operation of the main control valve when the pump is in operation, but is operative upon failure of the pump system to provide pressure from the load-lifting side of the lifting motors to a pilot control valve for pilot operation of the directional control valve. This assembly provides an emergency source of hydraulic pilot fluid for pilot operation of the main control valve for lowering the implements or load supported by the hydraulic motors should the engine of the vehicle fail.

Abstract: A hydraulic circuit comprises a first tank elevated above a second tank and openly communicating therewith by a conduit adapted to continuously maintain the second tank at full capacity with a hydraulic fluid. The hydraulic fluid is pumped out of the second tank and to a work system wherefrom it is recircuited back through a filtering system, retained in the first tank. Upon malfunctioning of the filtering system to prevent the egress of hydraulic fluid therethrough, the increased pressure level of the recircuited hydraulic fluid will function to open a directional control check valve in the second tank to by-pass the conduit normally communicating hydraulic fluid from the first tank to the second tank.