Abstract: A vehicle drive and work performing system including a rotary output, variable displacement, hydraulic drive motor (22) adapted to drive a vehicle, at least one hydraulic implement motor (14,16 and 18) adapted to power a work performing implement, a hydraulic pump (10) providing hydraulic fluid under pressure to the motors, a flow control valve (12) for controlling the fluid flow from the pump to at least the drive motor, and a pressure control valve (30) for controlling the displacement of the drive motor to achieve a desired fluid pressure level at the drive motor, and including the improvement wherein a load sensor (60,62) is connected to the implement motor for providing a signal representing the load thereon and a piston (54) is responsive to the signal for causing the pressure control valve to change the displacement of the drive motor to thereby change the fluid pressure level thereat to a value different from the desired fluid pressure level.

Abstract: A variable displacement pump supplies fluid to the single acting draft control cylinder of an agricultural tractor through a valve for controlling flow to and from the draft control cylinder. The valve houses a control rod activated valve spool that when displaced allows fluid to unseat a check valve between the spool valve and the draft control cylinder.Fluid is exhausted from the draft control cylinder when the control rod causes unseating of a main poppet by unseating a pilot valve in the main poppet. Fluid being exhausted from the draft control cylinder then passes through the valve to tank.

Abstract: A motor grader is provided with an electrical control circuit for automatically effecting engagement, speed, and direction control of an auxiliary hydrostatic front wheel drive system to augment the primary engine-driven rear wheel drive system.

Abstract: Two hydraulic brakes or clutches being primary users, are alternately, delayedly, hydraulically energized from a constant volumetric flow rate pump feeding also a secondary user via a pressure controller with a differential piston operated by feedback ducts from the primary users via a throttle valve. The latter valve is bypassed through a check valve for undelayed de-energization. A selector valve is disposed between the branch point for the secondary user and upstream as to energizing fluid from the feedback connection to the primary user. The pressure controller is described further as to several structural details.

Abstract: A vehicle engine accessory drive system is disclosed including a hydraulic fan motor and a power steering gear mechanism in series flow relationship. The vehicle power steering pump is the sole source of fluid for the system and has its flow control setting at a flow rate X, which is substantially greater than the flow rate Z required by the power steering gear. A temperature responsive bypass valve is connected in parallel across the fan motor and the bypass flow and motor outlet f1ow recombine, then flow to a steering gear flow control which communicates a flow rate Z to the steering gear mechanism and all fluid in excess of Z bypasses the steering gear, recombining with the output flow from the steering gear and returning to the pump inlet. This system provides a flow to the fan motor resulting in a fan speed-versus-engine speed similar to a "viscous curve".

Abstract: A vacuum union having a tubular body adapted for transmitting a vacuum signal from an intake pipe of an internal combustion engine of a vehicle to a vacuum-operated brake booster of a vehicle brake device, and a branch pipe adapted for transmitting a vacuum signal from the tubular body to other vacuum-operated engine controlling devices. An orifice for restricting the level of the vacuum signal, to be transmitted to the brake booster, is located downstream of a branch pipe with respect to the intake pipe. Therefore, a drop in the vacuum level is effectively decreased for maintaining the proper operation of the brake device, even if the controlling devices are damaged, thereby causing the branch pipe to be opened to the atmosphere.

Abstract: A motor grader is provided with an electrical control circuit for automatically effecting engagement, speed, and direction control of an auxiliary hydrostatic front wheel drive system to augment the primary engine-driven rear wheel drive system.

Abstract: A load responsive direction and flow control valve for use in fluid power load responsive system. The valve maintains a selected constant flow level for control of both positive and negative loads, irrespective of the change in the load magnitude or change in the fluid pressure, supplied to the valve. System is powered by a single fixed or variable volume pump. The direction flow control valve is equipped with a load responsive control which automatically regulates pump discharge pressure to maintain either a constant low pressure level or low pressure differential at the motor exhaust. The pump discharge pressure is either regulated by bypassing of excess flow to reservoir, or by a special load responsive control, which varies the pump displacement. Direction control valve may also be equipped with a control responsive to load pressure for controlling negative loads and an inlet pressure throttling control for simultaneous control of multiplicity of loads.

Abstract: A vehicle drive system including a wheel adapted to at least partially propel a vehicle over underlying terrain and a hydraulic motor coupled to the wheel to drive the same. A flow and pressure compensated pump has an output for providing hydraulic fluid under pressure to the motor and includes a control system having an input for receiving a hydraulic signal and for controlling pressure and flow output characteristics of the pump. A manually settable, pressure reducing valve interconnects the pump output and the control system input to provide a substantially constant, but adjustable, pressure signal to the control system so that output pressure from the pump to the motor may be controlled independently of loading on the motor to set the maximum torque delivery of the motor at a desired value.

Abstract: A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a filter to a supply pump for direction controlled fluid devices includes an unloading valve assembly on the return passage from the devices for limiting back pressure therefrom as long as the charge pump supplies sufficient pressurized fluid for the supply pump. The unloading valve assembly includes an unloading valve movable in response to the pressurized fluid at the connection between the supply pump and the filter to unload the return passage by connecting it to the reservoir and further to control the pressurized fluid going to the filter by connecting the charge pump to the reservoir at a predetermined maximum pressure of pressurized fluid. As the decvices require more fluid from the supply pump causing the pressure to the supply pump to drop, the unloading valve first blocks the charge pump from the reservoir and then the return passage.

Abstract: A fluid pressure actuator having a first member, a second member adapted to rotate relative to the first member, and a third member adapted to move on the second member. One of the first member and the second member is formed thereon with two flanges disposed in spaced-apart relationship for closing opposite ends of a first pressure chamber defined between the first and second members. The flanges are each formed in the outer periphery thereof with a groove communicating with passages formed in the first and second members for supplying therethrough power for moving the third member. The actuator is small in volume, dispenses with piping located outside the actuator, and is easy to provide a fluid seal thereto.

Abstract: A skid steer loader having an improved hydrostatic drive means. A skid steer loader comprises a main frame having a center compartment partially defined by a pair of longitudinally extending, laterally spaced side beams. The engine for the vehicle is mounted at the rear of the center compartment. An elongated transmission case is provided at a forward end of the center compartment and encloses the chain and sprocket drives for the vehicle. Side walls of the transmission case are displaced from the side walls of the main frame, with the drive means for the vehicle mounted on the outside of the case at a mid-portion thereof. The present improvement in the skid steer loader redesigns a drive system used with vehicles of substantially greater load capacity to provide a pair of independent hydrostatic drive means, each incorporating a hydrostatic transmission and having a gear reduction unit mounted on the outside of an elongated transmission case.

Abstract: A fluid control unit comprising a drive piston having first and second faces and a drive rod. The drive piston has first and second fluid responsive faces exposable to fluid under pressure. The fluid under pressure acting on the first face urges the drive piston in a first direction and the fluid under pressure acting on the second face urges the drive piston in a second direction. First and second overridable detents drivingly couple the drive piston and the drive rod for movement in first and second directions, respectively. The coupling force provided by the first detent varies with the pressure of the fluid to which the first face of the drive piston is exposed, and the coupling force provided by the second detent varies with the pressure of the fluid to which the second face of the drive piston is exposed.

Abstract: A valve assembly is provided in which a first poppet member and at least one subsequent poppet member each having a valve face engageable with a valve seat between first and second passages. A first and a subsequent pilot valve is operative for selectively establishing communication between a fluid reservoir and a space at one side of a piston portion of each poppet member and a pair of restricted flow passages are provided in each poppet member between such space and the first and second passages, such restricted flow passages being preferably formed in the poppet members with ball check valves provided therein. Such restricted flow passages operate upon closure of the pilot valve to develop a static pressure in the space corresponding to the pressure in the one of the first and second passage which has the higher pressure therein so as to move the poppet member to and hold it in its closed position in response to pressures applied from either of the first and second passages.

Abstract: A fluid control system includes a directional control valve assembly adapted for use in either an open center or a closed center configuration. The assembly is capable of incorporating one or more control sections, each with a manual control valve having its own variable pressure compensated flow controlling mechanism. Motor port lock-out valves are associated with each manual control valve, and a pressure responsive logic circuit automatically actuates the lock-out valves to hold them open when their associated manual control valve is in the power or float positions. When any manual control valve is in the float position, any other manual control valve may be operated in the power positions.

Abstract: A load responsive fluid power control system using servo type flow control valves and fluid motors supplied by a variable displacement pump. The pump displacement is regulated by an electro-hydraulic control valve in response to an electrical signal proportional to motor load or motor load pressure to vary the pump displacement to maintain a controlled constant or variable pressure differential between the pump outlet pressure and motor load pressure or to vary the pressure differential between pump outlet pressure and motor load pressure in response to a signal from a computing device. The pump control also limits maximum and minimum system pressures.

Abstract: A system providing auxiliary power to the non-driving steerable wheels of a four-wheel vehicle utilizing hydraulic power in a parallel circuit from the existing hydrostatic drive system. The steerable wheels are driven by hydraulic motors connected in parallel through a flow divider valve and supplied by the variable displacement pump of the existing drive system through a selector valve which has a free-wheeling position allowing the steering wheels to free-wheel with the return oil from each motor flowing in a closed loop back through the flow divider valve while providing charging pressure to that closed loop circuit.

Abstract: A load responsive fluid power control system using servo type flow control valves and fluid motors supplied by a variable displacement pump. The pump displacement is regulated by a control valve in response to the motor load pressure to vary the pump displacement to maintain a constant preselectable ratio between the pump outlet pressure and motor load pressure and to vary the pressure differential between pump outlet pressure and motor load pressure with variation in magnitude of the load. The pump control also limits maximum and minimum system pressures.

Abstract: A hydraulically operated driving and controlling unit includes a power plant--(prime mover)--with a fluid flow producing means for the supply of at least one pair of hydraulic flows of equal rate of flow. One separated fluid line is exclusively communicated to one outlet of the flow producing means and to one hydraulic motor. A further separated fluid line is exclusively communicated to another outlet of the flow producing means and to another hydraulic motor. The motors carry fluid stream creation means like propellers. The said flows flow through said fluid lines to drive the said motors and fluid stream creation means at all times with, relative to each other, equal rotary velocities for the creation of equal thrusts by said fluid stream creation means. The flow supply device may be variable for proportionate variation of the said rotary velocities and thrusts. In addition a further control means is provided for governing variation of rotary velocities and thrusts relative to each other.

Abstract: A load responsive fluid power control system using servo type flow control valves and fluid motors supplied by a variable displacement pump. The pump displacement is regulated by a control valve in response to the motor load pressure to vary the pump displacement to maintain a constant preselectable ratio between the pump outlet pressure and motor load pressure and to vary the pressure differential between pump outlet pressure and motor load pressure with variation in magnitude of the load. The pump control also limits maximum and minimum system pressures.

Abstract: A work vehicle with a fluid pressure circuit system comprising an actuator pump, a work equipment mounted on the vehicle and adapted to swivel on a vertical axis, a fluid pressure circuit connected to the actuator pump to actuate the work equipment, and a drive for swivelling the whole of the work equipment. A fluid pressure circuit portion of the fluid pressure circuit is connected to the actuator pump and to the drive to actuate the drive and a control valve is provided on the fluid pressure circuit for actuating the drive. A by-pass route is connected to a supply route and a discharge route of the circuit, at a portion of the fluid pressure circuit between the control valve and the drive. The arrangement is adapted to permit part of the fluid supplied by the actuator pump to short-circuit by way of the by-pass route and smooth the operation of the work equipment.

Abstract: A hydraulic system for feeding a plurality of independent hydraulic servo-operated devices, such as servo-assisted brakes, clutch and/or servo-operated steering, in which a single pump draws fluid from a common reservoir and fluid pressure is automatically distributed by one or more modulating valves to the or each of the devices requiring power at any one time. The or each modulating valve comprises at least one piston in a cylinder, the piston being displaced by an increase in pressure due to displacement of one or more operating member such as brake or clutch pedal, or steering wheel, this controlling the flow of fluid through an axial passage in the piston by controlling its proximity to a valve shutter element and thereby controlling the fluid pressure in a chamber of the modulating valve, which pressure is fed to a control chamber of at least one distributor associated with a servo actuator of one of the servo operated devices of the system whereby to control the operating pressure applied to this.

Abstract: The disclosure is directed to a closed center, pressure compensated hydraulic system which uses a multiple section hydraulic control valve in conjuction with a variable output hydraulic pump. The hydraulic control valve has a plurality of independently operable power spools each of which is used to control the flow of hydraulic fluid to a separate hydraulic actuator and load. Each valve section includes an automatic spool positioner which enables the operator to move the valve handle to a preselected position, the power spool thereafter being retained in such position until the actuator completes its stroke. After completion of the stroke, the automatic spool positioner causes the power spool to return to the neutral position. The multiple section hydraulic control valve also includes means for selecting the highest demand or work port pressure, and for controlling the variable output pump as a function of this selected pressure.

Abstract: A hydrostatic vehicle transmission and control for automatically controlling vehicle operation in accordance with pre-selected operator settings. The hydrostatic transmission automatically adjusts to operational conditions of the vehicle to obtain the pre-selected function and automatically adjusts the vehicle transmission until the preselected operational conditions can be obtained.

Abstract: Each consumer is provided with a load-compensated direction-reversing valve. Each valve performs a throttling function and a pressure-compensation function in order to establish a selected volumetric flow rate, and also a direction-control function. Each valve comprises a first control valve stage and a second control valve stage. One stage performs the throttling function, the other the pressure-compensation function. One of the two control valve stages also performs the direction-control function. The pressure drop across the stage which performs the throttling function at least in part controls the setting of the stage which performs the pressure-compensation function. Each valve is provided with an electromechanical transducer generating electrical signals indicative of the settings of the stage which performs the pressure-compensation function.

Abstract: A steering system for articulated vehicles having two or more pivotally connected vehicle modules. The invention provides for such a vehicle a dual hydraulic power steering system cooperating with a plurality of telescoping hydraulic cylinders to initiate steering about the pivot point connecting the two or more vehicle modules. Auxiliary, emergency, and back-up steering capabilities are imparted through the use of independently operated double-acting cylinders on both sides of the vehicle pivot attachment, with one hydraulic power system supplementing or replacing the other in case of failure. A series of pumps, accumulators, reservoirs, and other associated hydraulic elements cooperate with the synchronized valve metering construction to accomplish steering of the vehicle.

Abstract: A first device for controlling the position of a displacement control member of a variable displacement pump has an actuator connected to the control member and a valve member which is movable between a first position at which a pump discharge pressure signal is in communication with the actuator and a second position at which said pump discharge pressure signal is blocked from communication with the actuator and the actuator is connected to a drain. The valve member has an end substantially continuously exposed to the pump discharge pressure signal and is responsive thereto for biasing the valve member toward one of the first and second positions. A spring apparatus biases the valve member toward the other of said positions in opposition to the biasing force of said pump discharge pressure signal and establishes a preselected minimum discharge pressure.

Abstract: A simple load sensitive hydraulic system having a variable displacement pump, a priority dependent work circuit, at least one secondary work circuit, priority means preferencing fluid flow to the priority dependent work circuit over the secondary work circuit, flow and pressure compensating means responsive to requirements of either work circuit for controlling displacement of the variable displacement pump and a relief valve which when overridden allows fluid flow to the secondary work circuit.

Abstract: A multi-range pressure compensated fluid delivery system gives output flow over at least two pressure ranges. The system comprises a prime mover driven variable displacement pump having an inlet from a source of hydraulic fluid and a delivery outlet. A delivery circuit from the output has at least two work circuits selectively connected thereto. A first of the circuits is operable up to a first pressure and a second of the circuits is operable only up to a second lower pressure. An actuator system controls pump displacement responsive to a pressure applied thereto. A system selectively applies a first signal determined by the first pressure to the actuator system to adjust the operating pressure of the pump. A device reduces the first pressure to the second pressure responsive to connection of the second circuit to the delivery circuit to thereby decrease the maximum compensated pressure setting of the pump.

Abstract: An electronic control for hydraulic operation of forks on a lift truck wherein in the motor and pump speed can be matched to the particular flow requirements of each hydraulic ram and wherein a smoothly variable speed of the motor and pump is obtained for operation of the lift ram by the degree of manipulation of the lift lever.

Abstract: The drive system comprises an annular member carrying first engagement means which couple to second engagement means carried by drive motor means. The drive motor means are effective to rotate the annular member about an axis of rotation. Specific features of the invention include the use of hydraulic drive motor means operated through the use of a hydraulic system. The drive system also includes a pair of annular members which cooperate with respect to each other in combination with drive motor means disposed adjacent to each of the annular members. A plurality of drive motors may be used in some of the particular combinations and a single drive motor having a central pinion means and a satellite group of gears may also be used in conjunction with the drive motor means.

Abstract: An improved pressure sensitive valving arrangement is provided for a power steering unit for a lift truck, and in particular for a battery powered lift truck. To the conventional implement valve is added an accumulator charging means which includes an additional valve, herein called a "blocking or control valve", which additional valve is downstream from the implement valve and which additional valve, when actuated, blocks the flow of fluid through the implement valve to thereby build up pressure for charging an accumulator. The blocking valve includes a blocking spool which operates against a pressure-actuated pilot plunger such that when the pressure in the accumulator reaches or exceeds a predetermined amount, the pilot plunger shifts the blocking spool to permit the fluid to again flow through the implement valve.

Abstract: A hydraulic multi-speed, multi-torque transmission system for vehicles for storing and converting energy resulting from braking of the vehicle, such transmission utilizing multiple fixed displacement hydraulic pump-motors coupled to the vehicle wheels and a fixed displacement pump driven by the engine.

Abstract: A control system for providing precise speed control for a rotary air modulator, and particularly for providing synchronized speed control as between two or more rotary air modulators. A common reference frequency is used for controlling rotational speed of one or more rotary air modulators wherein each modulator deploys an individual feedback system responsive to the reference frequency input to provide precise rotational speed and angular position coordination and, therefore, synchronism of frequency and phase output as between two or more individual modulators. The individual feedback systems include feedback and summation circuitry which derives angular velocity correction, angular position correction and hydraulic pressure drive variation for thereafter correcting and maintaining precise speed control of the rotary drive system.

Abstract: A fluid system has first and second hydraulic jacks each having a load supporting end connected to a source of fluid through a control valve. First and second pilot operated valve assemblies are positioned between the control valve and the load supporting ends with each valve assembly having a first check valve positioned in a chamber and being movable between a first position at which communication between the associated load supporting end and the control valve is blocked and a second position at which the associated load supporting end is in fluid communication with the control valve. A second check valve is associated with the first check valve and is movable between a first position at which communication between the chamber and the control valve is blocked and a second position at which the chamber is in fluid communication with the control valve.

Abstract: A hydraulic system includes a fluid responsive means that controls the effective output of the pump in response to pressurization of signal fluid that is supplied by the pump. The signal fluid is pressurized by flowing through a synthetic signal generator and on into a fluid motor in opposition to the working pressure therein. This signal fluid is directed to the fluid motor by the directional control valve when the directional control valve is in an operating position; and it is directed to a sump by the directional control valve when the directional control valve is in a standby position. The present invention provides pressure actuated means to divert or occlude this signal fluid from the directional control valve except when the directional control valve provides a load sensing flow path which communicates this signal fluid to the fluid motor.

Abstract: The invention is concerned with an improvement in a hydraulic fluid system of a vehicle which comprises a variable displacement pump; a first work element; and a device for receiving a first load signal from the first work element and controlling the pump discharge responsive thereto. The improvement includes a plurality of second work elements which receive fluid flow from the pump via a common supply line connected to the first work element, said fluid flow not passing via any independent load responsive delivery system, and a load responsive controller having flow restricting means in a signal line which communicates with the common supply line for sensing a load pressure in the common supply line, said load pressure being a maximum load pressure of any of the second work elements and delivering a second load signal representative of the load pressure to combine with the first load signal to control the discharge of the pump to be responsive to the larger of the first and second load signals.

Abstract: In a fluid system having a main control valve and bypass control valve both responsive to pilot pressure for actuation thereof for supplying fluid to a pair of hydraulic actuators and a pair of bypass valves, the pump's flow is supplied to the first actuator and the exhaust therefrom to the second via a third control valve, the exhaust from the second actuator returns via the third control valve and the main control valve to sump, the pump's flow being subjected through the bypass control valve to the first of the bypass valves whereby once a first predetermined pressure has been reached, the pump's flow passes via the bypass valve through the second end of the first actuator and is combined with the exhaust of the first actuator for driving the second actuator.

Abstract: A hydraulically driving and controlling - unit comprises a power plant which drives a fluid flow producing device for the separate production and supply of pairs of flows of hydraulic fluid under pressure. The unit supplies at least one pair of flows to at least two fluid motors. Rates of flow in flows are proportionate to each other whereby motors of same pair of flow are actuated and maintained to act with to each other proportionate speed of motion. Unit may be transportable and adaptable to machines or vehicles. The drive unit may include a plurality of power plants and fluid flow producing devices. In such multiple unit one way valves are set into fluid lines which may combine partially after those one way valves for directing each one flow from a different power plant to the same motor. Thereby the unit can continue to operate, when one of the plurality of power plants fails.

Abstract: A direction flow control valve for control of positive and negative loads equipped with a load responsive control which automatically blocks the pump flow to the motor while controlling negative load, providing the motor inlet with fluid from the motor exhaust.

Abstract: A combined brake and steering system for a vehicle having hydraulic braking and hydraulic steering. A single pump is utilized to supply both the brakes and steering. Two priority valves are arranged to assure that the brakes take precedence and receive an approximately constant flow of hydraulic fluid subject to a maximum pressure. The steering mechanism also normally receives a constant flow, subject to a maximum pressure which usually is different from the other maximum pressure.

Abstract: A load responsive fluid power multiple load control system using load responsive direction and flow control valves in combination with pump control responding to highest system load. Each direction flow control valve is equipped with a load responsive positive load control which automatically regulates valve inlet pressure to maintain a relatively constant pressure differential between pump inlet pressure and load pressure at a first level and a load responsive negative load control which automatically regulates valve inlet pressure to maintain a relatively constant pressure differential between pump inlet pressure and load pressure at a second higher level. The load responsive control of each direction control valve blocks the pump flow to the motor while controlling negative load, providing the motor inlet with fluid from the motor exhaust.

Abstract: A load responsive fluid power control system using servo type flow control valves and fluid motors supplied by a variable displacement pump. The pump displacement is regulated by a control valve in response to the motor load pressure to vary the pump displacement to maintain a constant preselectable ratio between the pump outlet pressure and motor load pressure and to vary the pressure differential between pump outlet pressure and motor load pressure with variation in magnitude of the load. The pump control also limits maximum and minimum system pressures.

Abstract: A pressure system for driving the wheels of a vehicle in which the wheel driving motors are arranged in pairs on opposite sides of the vehicle comprising a duplex pump assembly composed of two pumps connected in parallel and coupled in open circuit with a respective pair of wheel driving motors. A flow divider is provided in each circuit for dividing the pressure fluid delivered by the respective pump to the wheel driving motors of the associated pair.

Abstract: A combined brake and steering system for a vehicle having hydraulic braking and hydraulic steering. A single pump is utilized to supply both the brakes and steering. Two priority valves are arranged to assure that the brakes take precedence and receive an approximately constant flow of hydraulic fluid subject to a predetermined maximum pressure. The steering mechanism also normally receives a constant flow, subject to a different maximum pressure. The fluid from the steering mechanism is recirculated through a reservoir back to the pump. The fluid from the brakes is recirculated to the pump without going through the reservoir.

Abstract: A blow molding machine wherein a shield is movable to and from an operative position in which it prevents access to the mold sections. The hydraulic motors which move the mold sections can receive pressurized fluid only when the shield is locked in the operative position by a roller. When the roller is retracted from its arresting position, a mechanical power train automatically closes valves which are installed in conduits connecting the motors with oil pumps. The valve elements of the valves are mechanically coupled to each other and to the roller, and are biased by a spring which tends to maintain the roller in the arresting position. A single-acting hydraulic cylinder is employed to move the roller from the arresting position. The shield can be moved by hand and/or by a double-acting hydraulic cylinder.

Abstract: A demand compensated hydraulic system includes a pump responsive to pressurized fluid in a demand feedback pilot line. The pilot line is connected to sense fluid demand between a hydraulic motor and its associated control valve which is closed by servo feedback from the motor. A flow sensitive device is interposed in an output line connecting the pump and the control valve to sense when the flow decreases until it is insufficient to operate the function. At a predetermined decreased flow rate, the flow sensitive device operates to momentarily connect the demand feedback pilot line to a reservoir to cause the pump to go into a stand-by condition.

Abstract: A hydraulic system having fluid flow feedback from a fluid motor to a demand control valve which operates to change pump output to compensate for motor demand includes a pressure amplifier between the feedback system and the valve. The pressure amplifier includes a chamber with a piston therein which is slidable to connect or block pump output fluid flow to the valve in response to feedback pressure variations from the motor.

Abstract: A demand compensated hydraulic system includes a pump responsive to a pressurized fluid in a demand feedback pilot line. The pilot line is connected to sense fluid demand between a hydraulic motor and an associated control valve which is closed by servo feedback from the motor. A dither is connected to the pilot line to continuously oscillate the pressurized fluid in the pilot line to prevent the occurrence of a situation wherein the flow across the control valve is sufficient to prevent the pump from going to a stand-by condition while being insufficient to operate the motor to close the valve to thereby cause the pump to go into the standby condition.

Abstract: an open center hydraulic system in which a pair of flow divider valves is connected in series with the system's hydraulic pump to create a parasitic pressure upstream of these flow valves and the feeder and separator clutches are controlled remotely by simple solenoid actuated two-position valves. The cylinders actuating the clutches are of sufficient size upon application of the minimum parasitic pressure to hold the clutches in a given position so that no center neutral position is necessary on the two-position valves.