Abstract: A check valve (14) with a valve opening actuator function and a bypass opening/closing valve (17) are disposed in parallel in a pressure oil supply/discharge passage (3) connected in communication with a hydraulic actuation chamber (2). The opening/closing valve (17) is adapted to be held at a valve opened position (Y) against a residual pressure holding spring (19) when the pressure on the check valve inlet (14a) side is normal and to be changed over to a valve closed condition (X) by means of the spring (19) when the pressure has lowered to a predetermined value. The pressure oil supply/discharge passage (3) and a pressure discharge passage (7) are connected in communication with each other through a pressure compensation valve (12). The opening/closing valve (17) is composed of a piston valve member (38) resiliently biased against a bypass valve seat (40) by means of the spring (19).

Abstract: A check valve (14) with a valve opening actuator and a bypass passage (16) are disposed in parallel in a pressurized oil supply/discharge passage (3) connected in communication with a hydraulic actuation chamber (2). A residual pressure holding valve (17) and a flow restrictor (21) are disposed in series in the bypass passage (16). The supply/discharge passage (3) and a discharge passage (7) are connected in communication by a pressure compensation valve (12). While the valve (17) is adapted to be moved to a valve closing position by means of pressure supplied at a check valve inlet (14a) and a residual pressure holding spring (19), it is adapted to be moved to its valve opening position by means of pressure supplied at a check valve outlet (14b). The valve (17) includes a valve member (38) resiliently urged to a valve seat (40) by means of a spring (19).

Abstract: In a three way valve assembly with a pressure compensating valve, a three way valve (2) is adapted to selectively communicate a work port (A) to a pressure supply port (S) and to a pressure discharge port (T). A pressure compensating valve (3) is adapted to release a pressure abnormally raised at a very slow speed within the work port (A) to the pressure discharge port (T). A first housing (10) of the three way valve (2) is fixedly secured between left and right end plates (4) (5) by means of assembly bolts (6) (7). A second housing (57) of the pressure compensating valve (3) is fixedly secured to one end surface (10c) of upper, lower, front and back end surfaces of the first housing (10) by means of a fixing means (67).

Abstract: An improved safety valve includes piston-actuated provisions for gradually pressurizing a fluid-actuated motor during start-up of the system, preferably by way of a changeable flow restriction. In addition such improved safety valve preferably includes a floating exhaust valve actuating apparatus movable in an exhaust closure chamber and that operates in response to the presence or absence of line pressure in the exhaust closure chamber for respectively blocking off or opening fluid communication between the safety valve's outlet port and exhaust port. A pilot operator is also included for selectively permitting or cutting off line pressure flow to actuate the piston actuator and the exhaust valve actuating apparatus. The preferred safety valve also includes a check valve for preventing back-flow from the safety valve's outlet port back to the piston actuator and back to the exhaust valve actuating apparatus.

Abstract: A control device for a cylinder including a spool type valve which includes a spool and is formed therein with a cylinder port. In the spool type valve is arranged an operation check valve for permitting only flowing of fluid to the cylinder. An orifice is formed so as to communicate a pilot chamber of the operation check valve and the cylinder port with each other. The spool is formed with a first control port and a second control port for selectively carrying out communication between the pilot chamber and the return passage. Thus, when the spool is moved to communicate the first control port with the pilot port, the pilot chamber is communicated with the return passage. This causes fluid to flow through the orifice to lead to a difference in pressure between both sides of the orifice, resulting in a poppet of the operation check valve being opened.

Abstract: In the neutral position of a directional control valve in which the connection of the constant pump to the consumer is interrupted the entire delivery of the constant pump is led via a bypass valve to the tank. According to the invention the regulating range of the bypass valve is increased by an additional connection which is controlled by a further piston which in the neutral position of the directional control valve is displaced by a weak spring into the open position and thus ensures a pressureless circulation of the pump working medium to the tank.

Abstract: A hydraulic control system capable of permitting an accessory component such as a port relief valve or the like to be mounted on a valve body. A cap member is interposedly arranged between a valve body and a solenoid, so that the valve body or the like and a casing of the solenoid or the like may prevented from interfering with each other when the accessory is mounted in the accessory port.

Abstract: A distributor for hydraulic cylinders (2), especially applicable to crane drive cylinders, which comprises an axial sliding runner (4) for selection of the oil circuit. Said runner (4) is hollow, forming two separate chambers (19,20) adjacent to the cylinder chamber supply and return ducts with which it is connected through holes in the wall of the said runner. One of the chambers (19) includes means for varying the degree to which the holes are opened, according to the return oil pressure from the cylinder withdrawal chamber. The other chamber (20) incorporates means for opening or closing the connection through it, according to the pressure being delivered by the pump, to the cylinder withdrawal chamber oil supply duct. Thus it is possible to regulate the flow as an inverse function of the load and to reduce the effect of induced pressure.

Abstract: A braking system for a dumping vehicle having a hydraulic drive system and a hydraulic dump container is disclosed. A two-section control valve is connected by conduit to a hydraulic fluid reservoir and a hydraulic motor. The control valve includes a first valve assembly for controlling the dump container and a second valve assembly for controlling operation and direction of the hydraulic motor. An anti-cavitation valve and relief valve are provided to prevent locking of the vehicle wheels during braking. Walk-behind, riding-step and riding-seat variations of the invention vehicle are disclosed.

Abstract: There is disclosed a pressure-drop sensor valve system for controlling the movement of a fluid operated, ram-type device, such as that used to drive a panel punch. The valve-like device includes a main passage having an inlet for pressurized fluid and an outlet connectable to the ram-type device. Disposed intermediate said inlet and outlet is a fluid chamber. A poppet valve is positioned between said fluid chamber and an accumulator chamber in the body of the device. A fluid by-pass is connected to the fluid passage and a reservoir, and is blocked when the poppet valve is closed and opened when said valve is opened. A piston member is provided with its stem in the accumulator chamber opposite the poppet valve, both said member and valve being slightably movable by separate compression springs. A check valve is positioned in an axial passage of the poppet valve.

Abstract: A load responsive system having at least one direction and flow control valve, the flow control of which is accomplished in response to a control signal above a certain predetermined pressure level and a fixed displacement pump, provided with a bypass type output flow control, operable to maintain a constant pressure differential between pump discharge pressure and load pressure of the load controlled by the direction and flow control valve. The output flow control is provided with an unloading control, which maintains the discharge pressure of the pump at any preselected minimum pressure level once the control signal transmitted to the direction and flow control valve drops below a certain minimum predetermined pressure level signifying that the system is in standby condition.

Abstract: A hydraulic proportional action valve apparatus includes a throttle valve, and a pressure balance which permits adjustment of the pressure difference between a supply pressure and a consumer pressure. The pressure balance, which may be provided with a spring, is hydraulically supported. A supporting assembly, which is provided for this purpose, is biased by a constantly controllable pressure-regulating valve. The control of the pressure-regulating valve may occur as a function of hydraulic parameter, such as, for example, the load pressure or the pilot pressure of the throttle valve.

Abstract: A valve for cooling a reversible hydraulic machine includes a valve piston in a connecting channel extending between supply and discharge passages. Pressure in these passages displaces the spring-centered piston from neutral position to an end position. A central reduced-diameter portion of the piston carries a spring-centered closing member which closes a discharge conduit leading to a leakage space when the piston is in its central position. When the piston is displaced out of the neutral position toward one of the end positions, pressure from one of the connecting passages which has the lower pressure prevailing therein is permitted to propagate through one of the spring-receiving spaces delimited by the closing member and through an annular throttling gap present between the closing member and the central portion of the piston into the other spring receiving space and from there into the discharge conduit and into the leakage space.

Abstract: A control block is made up of a plurality of directional valves which serve to actuate a plurality of hydraulic drives to which in some cases a different pressure is to be supplied. For this purpose two pressure-limiting valves adjustable to different pressures are provided, the valve adjustable to the lower pressure being connected to the last valve unit. This gives a simple construction and substantial freedom in the association of the drives.

Abstract: A signal valve (38) is connected to a supply conduit (16) connecting a pump (11) with a control valve (14) for transmitting an artificial load signal to a load signal chamber (34) of a pressure compensated unloader valve (27) when the control valve is at an operating position and the pressure in the supply conduit (16) is below a preselected value. This moves a valve member (31) of the unloader valve (27) to a blocking position causing essentially full pump flow to be directed to the hydraulic jack for decreasing the response time in situations wherein the hydraulic jack has cavitated and no positive load pressure signal is present.

Abstract: Apparatus for controlling the compaction of refuse in a refuse collection truck, and for controlling the operation of an ejection panel of the refuse collection truck, so as to provide for uniform compression of refuse in the truck. A hydraulic cylinder supports the ejection panel, and a combination sequence-relief valve is provided to vent hydraulic fluid from the cylinder when the fluid pressure output of the hydraulic pump exceeds a predetermined pressure and when the fluid pressure in the packing cylinder exceeds a selected pressure.

Abstract: A fluid pressure control system including a modulating pressure relief valve is normally needed in a power transmission having clutches that require smooth engagement. It is also desirable in many systems to maintain a difference in fluid pressure levels between the fluid in different selected clutches, such as speed range and directional clutches, during initial engagement. This arrangement ensures that the selected directional clutch engages only after the selected speed range clutch engages so that only the selected directional clutch absorbs the inertial load. In order to conserve horsepower, reduce fluid leakage, and thereby improve system efficiency and component reliability, it is also desirable to reduce the fluid pressure levels in the system once the selected clutches are fully engaged.

Abstract: A fluid pressure control system including a modulating pressure relief valve is normally needed in a power transmission having clutches that require smooth engagement. It is also desirable in many systems to maintain a difference in fluid pressure levels between the fluid in different selected clutches, such as speed range and directional clutches, during initial engagement. This arrangement ensures that the selected directional clutch engages only after the selected speed range clutch engages so that only the selected directional clutch absorbs the inertial load. In order to conserve horsepower, reduce fluid leakage, and thereby improve system efficiency and component reliability, it is also desirable to reduce the fluid pressure levels in the system once the selected clutches are fully engaged.

Abstract: A log debarker of the hollow-head type having a rotor journaled in a stator for rotation about a longitudinal axis of the rotor. A plurality of debarking tools are attached to the rotor for debarking a log being moved axially through the rotating rotor. Three independently and hydraulically-powered infeed spiked rollers are positioned on the infeed end of the stator for feeding logs into the rotor and three independently and hydraulically-powered outfeed spiked rollers are positioned on the outfeed end. The rollers are powered at differing rotational speeds to accommodate logs of uneven surfaces. An air-operated tensioning system including a quick release valve adjusts the position of the infeed and the outfeed rollers urging them towards the longitudinal axis and automatically jogs the rollers open when they are unable to mount a log. A lubricating system having lubricant filtering and flow control capabilities lubricate and flushes the bearings for the rotating rotor.

Abstract: A power steering system which includes an engine-driven pump, a fluid motor for supplementing manual steering torque, a fluid control valve for distributing fluid to the fluid motor, and a reaction device for applying hydraulic reaction or feeling to a steering wheel. A first flow control valve is utilized to deliver first fluid flow to a fluid control valve from the pump and to lead excess flow to a bypass passage. A second flow control valve is connected between the bypass passage and the reaction device to deliver second fluid flow to the reaction device and to lead excess flow to a reservoir. A magnetic pressure control valve is connected to the reaction device to control fluid pressure applied thereto in accordance with a predetermined vehicle operating condition, such as vehicle speed.

Abstract: The invention concerns a means for saving energy in a hydraulic circuit where pressurized oil supplied by a hydraulic pump is used to activate various functions by the aid of one or several valves (2,3,4) controlling the function. Such a hydraulic circuit is especially suitable for use in agricultural tractors, where the pressurized oil comes from a hydraulic pump driven by the engine. In conventional hydraulic circuits, a drawback is that the pressurized oil is directed through a pressure regulating valve, thereby causing unnecessary waste of energy and a need to cool the oil.

Abstract: The invention relates to a hydraulic control valve assembly for controlling a consumer unit such as a servomotor of a vehicle steering system. The valve assembly has a conventional port arrangement which includes two selectively pressurizeable and drainable motor ports connectable to a servomotor and supply and exhaust ports connectable respectively to a pump and a drain tank. A slide valve has a central wall section between two motor ports which completely block a central supply port when the slide valve is in a neutral position. Two metering control load sensing ports are on opposite sides of the supply port and when the slide valve is in a neutral position the load sensing ports are in throttling relation to the slide valve motor ports.

Abstract: Clutch-clutch-brake steering unit having hydraulically actuated cylinders for controlling same to control rotation of a track-drive sprocket in a crawler tractor. Specifically, one of the clutch cylinders and a brake cylinder provided in the unit have an inlet-outlet port in common, and are so arranged on a spring-applied-brake, hydraulically-applied-clutch basis that a single pressure signal in the inlet-outlet port alternately operates the cylinders to apply the brake and release the one clutch, to apply the one clutch and release the brake or, by proper modulation, to partially engage either, i.e., slip the clutch or drag the brake to intermediate degrees as desired.

Abstract: A log debarker of the hollow-head type having a rotor journaled in a stator for rotation about a longitudinal axis of the rotor. A plurality of debarking tools are attached to the rotor for debarking a log being moved axially through the rotating rotor. Three independently and hydraulically-powered infeed spiked rollers are positioned on the infeed end of the stator for feeding logs into the rotor and three independently and hydraulically-powered outfeed spiked rollers are positioned on the outfeed end. The rollers are powered at differing rotational speeds to accommodate logs of uneven surfaces. An air-operated tensioning system including a quick release valve adjusts the position of the infeed and the outfeed rollers urging them towards the longitudinal axis and automatically jogs the rollers open when they are unable to mount a log. A lubricating system having lubricant filtering and flow control capabilities lubricate and flushes the bearings for the rotating rotor.

Abstract: A valve combining in a single unit a multiplicity of functions including isolation, thermal and pressure relief, return check and bypass. The valve includes a pair of spool valves, one slidably positioned within the other, disposed with a bore in a housing and interconnected with system pressure and return and an appropriate control valve.

Abstract: A gripping device includes a plurality of articulate gripping fingers coupled to a support structure turnable with respect to a neck structure. The articulate fingers respectively have first and second segments pivotally movable by oil hydraulic cylinders. Oil hydraulic pressure is applied to the oil hydraulic cylinders from an oil hydraulic pump. A pilot relief valve which can provide a variable relief pressure according to a pilot pressure, is provided on the discharge line leading from the oil hydraulic pump, and can be connected to a directional control valve to an oil hydraulic cylinder, which can provide a variable pilot pressure according to the extent of depression of a clamping force setting pedal provided in an operator's room.

Abstract: A compensated fluid flow control of a positive load, which automatically maintains a relatively constant pressure differential across a control orifice of a direction and flow control valve and which permits the variation in the level of this pressure differential in response to an external control signal, while this pressure differential is maintained constant at each specific level.

Abstract: A control valve for controlling the flow of fluid to and from a single-acting cylinder and having a metered flow-controlling valve section and a rotatable valve member movable to four different positions to provide four different operations of the single-acting cylinder, namely: rapid advance, slow metered advance, hold and return.

Abstract: A multi-way valve for precisely controlling supplying pressure to a load device, comprising a housing and a control slide slidably mounted in the housing. The housing has annular, internal passages axially spaced along the length of the housing, with first and fifth passages located on opposite sides of second, third and fourth passages in fluid communication with a supply tank, the load device and a fluid pressure source, respectively. The control slide is slidably mounted in the passages and has parts axially spaced along the slide and axially separated by annular grooves, and an internal, longitudinal passages. First and second springs are coupled to opposite ends of the slide and bias the slide to a middle, rest position. First and second control chambers are located in the housing adjacent the slide opposite ends for applying varying pressures to the slide opposite ends.

Abstract: A hydraulic control device for a hydraulic working cylinders, comprising a lide control valve, in which the flow of working pressure medium is controllable by a piston slide displaceable within a housing bore auxiliary control passage connected to the housing of the slide control valve in which a bore leads to the housing bore, the bore discharging into a longitudinal section of the housing bore which is swept by ends of the piston slide. The discharge of the bore is connectable to a selected control position by the control edge and is connectable with the housing bore, which is connected in this section with a pressure medium reservoir or a return flow passage.

Abstract: A load supporting hydraulic system having main control valve provided with a load check valve and a vent valve; the load check valve, which has a hose connection to the main control valve, is operative to permit free flow of fluid from the control valve toward the load supporting chamber of the system and to block fluid flow from the load supporting chamber toward the control valve, whereas the vent valve is operative with the control valve to permit the load check valve to be opened by fluid pressure from the load supporting chamber to allow fluid flow therefrom thru the hose connection and control valve to drain. A cancelling valve is added to the system to override the vent valve upon failure of the hose connection and reblock fluid flow from the load supporting chamber toward the hose connection and control valve.

Abstract: A pneumatic drive for actuating switchable devices such as valves and the like includes a cylinder and a cylinder base, the cylinder having an annular slot which extends in a plane transverse to the axis of the cylinder between an interior cylinder space and the outside. A piston is movable within the cylinder space and is connected to one end of a piston rod, the other end of the rod being coupled to the device to be actuated. A supply line communicates pressurized gas to the cylinder space to move the piston away from the cylinder base, while a spring biases the piston in the direction toward the cylinder base. An annular groove is formed in at least one of two annular surfaces which bound the annular slot in the axial direction, and a sealing ring is seated in the groove for axial movement so that the ring projects into the annular slot in response to pressurized gas communicated through a branch line into the closed end region of the groove.

Abstract: In an agricultural vehicle in which a power takeoff modulating valve is shifted in response to a control lever so as to pass pressurized hydraulic fluid through a groove in the outer surface thereof between recesses in an adjacent bore wall for application to a power takeoff clutch to cause engagement of the clutch, application of the hydraulic fluid pressure to the clutch is modulated by an arrangement which selectively diverts the pressurized hydraulic fluid away from the clutch and to a sump in accordance with the rate of pressure increase of the hydraulic fluid to prevent excessively rapid engagement of the clutch. The hydraulic fluid is sumped by a trimmer valve having a first end which immediately responds to high fluid pressures by sliding into a position which sumps the conduit supplying hydraulic fluid to the clutch by an amount directly related to the pressure.

Abstract: A hydraulic positioning system for precisely and rapidly positioning objects of the type likely to impose impact loadings on the system. The system is particularly adaptable for use in sawmill setworks for precisely positioning logs preparatory to sawing thereof. High impact loads are compensated for by special rapid-acting shock-absorbing hydraulic relief circuitry responsive to differences between impact overpressure and system pressure.

Abstract: A multiple section control valve bank is provided having a control valve section and an inlet section operatively connected to provide smooth proportional metering control over a wide band of operating pressures while simultaneously metering the operation of two or more fluid actuated devices from a single fluid source. This is accomplished by providing metering and logic elements in the control valve section connected to a signal chamber in the inlet section to vary the flow of fluid through the inlet section to the control section in accordance with signals from the meter and logic elements.

Abstract: A hydraulic system (40) for an excavator (10) which utilizes regeneration, minimizes cavitation, and provides hose break protection is disclosed. A valve assembly (50) is permanently connected to a hydraulic actuator (30) which is to be controlled. A hydraulic power supply (42) remote from the hydraulic actuator is connected to the valve assembly (50) through a pair of flexible hoses (56, 58). Pressurized hydraulic fluid can flow to the valve assembly through either of the flexible hydraulic hoses, but the valve assembly (50) includes a check valve (60) so hydraulic fluid return is only possible through one hose (56). A two position valve (62) is provided in the valve assembly (50) between a pair of operating ports (36, 38) on the hydraulic actuator (30). The two position valve (62) can be opened in response to a signal from the operator, connecting the two ports (36, 38) together to permit regeneration.

Abstract: A hydraulic flow control apparatus is provided which is adapted to provide a constant pressure differential between a pump and an external load. The apparatus includes a housing, and a balance piston slideably mounted therein. The pump pressure acts to bias the piston in a direction toward a pump bypass position, and the piston is urged in the other direction and toward its operating position by the consumer pressure and a spring. Means are also provided whereby the pressure of the pump necessary to move the piston toward its bypass position and against the force of the spring, may be minimized during operation in the idling mode, to thereby minimize power consumption.

Abstract: A control valve bank is provided having a working section and an inlet section wherein inlet fluid from a pump is proportionally metered at the inlet of each valve section so that the input volume to each work port is generally uniform regardless of pressure variations.

Abstract: A fluid control system for controlling a fluid motor (12) wherein a pressure regulating pilot valve (10) controls a directional control valve (11) by manipulation of handle (21) associated with the pilot valve (10). The directional control valve (11) includes a make-up valve (84). The pilot valve (10) includes a spool (26) having a recess (98) providing selective communication between the backside of the movable valve member (86) of the make-up valve and an exhaust recess (100) communicating with the reservoir tank (36). A direct mechanical connection is provided from the handle (21) to the spool (26) as the result of an abutment of an upper end portion (102) of the spool (26) with a surface (49) on the plunger (28) engaged by the control handle in effecting the positive movement of the spool (26) to effect the desired communication between the recess (98) and recess (100). The spool normally is resiliently movable to effect a desired pressure regulation fluid flow through the pilot valve (10).

Abstract: A relief valve mechanism for a hydraulic booster provides in an open position a by-pass passage leading to a power steering and relieves excess pressure on the upstream side of the hydraulic booster. The relief valve in the open position forms a second throttle besides a normal fixed orifice to decrease through flow rate to the drain to thereby supply sufficient quantity of oil to the power steering when steering is steeply operated.

Abstract: A hydraulic positioning system for precisely and rapidly positioning objects of the type likely to impose impact loadings on the system. The system is particularly adaptable for use in sawmill setworks for precisely positioning logs preparatory to sawing thereof. High impact loads are compensated for by special rapid-acting shock-absorbing hydraulic relief circuitry responsive to differences between impact overpressure and system pressure.

Abstract: Load responsive system controls to vary output flow control of a system pump to control the pressure differential, acting across a control orifice positioned between system pump and a fluid motor. The system controls permit variation in the level of pressure differential in response to an external control signal, while this pressure differential is maintained constant at each controlled level.

Abstract: A pilot operated flow control valve of a bypass type, which automatically regulates the quantity of flow delivered to the control orifice to maintain a relatively constant pressure differential between the supply pressure and the load pressure and which permits variation in the level of pressure differential in response to an external control signal while this pressure differential is maintained constant at each controlled level.

Abstract: The control device for a hydraulically operated load includes a multiway piston valve defining a plurality of working chambers, a plurality of control chambers, a piston having axial and radial bores acting as first choke channels and a control collar cooperating with the control chambers to act as additional choke channels, a piston manometer valve biased by a spring and connected between a pump channel and a return flow channel. A control conduit including at least one choke is connectable via additional choke channels between the pump channel and the return flow channel and has a branch conduit leading to the spring-biased end of the manometer piston. The valve piston is displaceable from its neutral position into an intermediate control position in which in the range of the fine adjustment of the flow the pressure from the load is applied through the control conduit to the manometer piston to provide a load compensated control.

Abstract: In a load responsive fluid power and control system employing plurality of control valves with positive and negative load compensation, a pressurized exhaust system supplied with make-up fluid from pump discharge circuit by a pressure reducing valve and deactivating valve of the pressure reducing valve operable when the pessurized exhaust system is completely unloaded during control of positive load.

Abstract: The invention relates to a drive-assisting device comprising at least a fluid relief engine, a source of pressurized fluid, an engine supply pipe connecting the delivery connector of the fluid source to the inlet connector of the engine, and a calibrated discharge valve, shunt-connected to the supply pipe and provided with means for adjusting its calibration, the control of which is deliberate.

Abstract: A hydraulic system (9) includes a hydraulic motor (10), a main control valve (17) for controlling said motor (10), a make-up valve (78,79) operatively associated with said main control valve (17) and a vent line (93,94,95,99) for selectively venting said make-up valve (78,79). In such hydraulic systems, and in particular, in prior art hydraulic systems used to raise and lower a load, there is always the possibility that should hydraulic pressure not be maintained in the vent line the make-up valve could come open and the load could unexpectedly move. Such a situation could occur with, for example, air trapped in said vent line and the simultaneous failure of a pump of the system. The present invention solves this problem by providing pressure maintaining arrangement (200) in fluid communication with said vent line (93,94,95,99).

Abstract: A hydraulic pressure actuated power brake system having a hydraulic power booster with operating pressure on both sides of the power piston power wall. The booster is therefore hydraulic pressure suspended so that the hydraulic pump of the system need not be operating to maintain this pressure while the booster is inactive. An accumulator is also charged by this pressure to provide power brake booster operation for several booster actuations without recharging by the pump. When the pump is operating, a pilot valve which is sensitive to a drop in booster operating pressure will control charging or recharging the accumulator and booster from pressure generated by the pump to maintain a desired charge pressure. A pressure relief valve will also prevent overcharging of the accumulator and booster. A check valve prevents loss of booster operating pressure toward the pump outlet if the pump pressure falls below the charged pressure.

Abstract: A hydraulic pressure actuated power brake system having a hydraulic power booster with operating pressure on both sides of the power piston power wall. The booster is therefore hydraulic pressure suspended so that the hydraulic pump of the system need not be operating to maintain this pressure while the booster is inactive. An accumulator is also charged by this pressure to provide power brake booster operation for several booster actuations without recharging by the pump. When the pump is operating, a pilot valve which is sensitive to a drop in booster operating pressure will control charging or recharging the accumulator and booster from the pressure generated by the pump to maintain a desired charge pressure. A pressure relief valve will also prevent overcharging of the accumulator and booster. A check valve prevents loss of booster operating pressure toward the pump outlet if the pump pressure falls below the charged pressure.

Abstract: A hydraulic drive circuit for a load-handling machine such as hydraulic crawler crane, shovel or the like in which the maximum output pressure of the circuit is determined by a main relief valve provided on the delivery side of a hydraulic pump. The drive circuit is capable of producing a surge of power or output by automatically increasing the relief pressure of the main relief valve above a rated pressure of the circuit for a short time period of about a few seconds, when required for extracting an implanted pile, for pulling a bucket which is caught on a large stone, or for getting a machine out of a muddy spot. At the end of the predetermined time period, the circuit pressure is automatically returned to the level of the rated pressure. The surge output is from 130% to 150% of the rated output but allows use of hydraulic components or an engine of a capacity designed for the rated output without troubles or engine stops.