Abstract: In this portless type master cylinder device, a cylinder bore is formed in a body thereof, and a piston member is fitted in the cylinder bore and is slidably movable from an initial axial position therein and defines a pressure chamber in cooperation with the cylinder bore. An intake valve communicates between the cylinder chamber and the fluid reservoir via a fluid flow path, and is opened when the piston member is in its initial axial position while it is closed when the piston member moves through more than a determinate relatively small axial distance from its initial axial position.

Abstract: A master cylinder for an hydraulic pressure system has a pressure cylinder (1) on which is mounted a reservoir (11), the cylinder having an open end closed by a cap (3). The cap is positively coupled to the cylinder (1) by a coupling device (26) arranged so that resulting from pressure applied to the interior of the cap (3) is transmitted via said device to the cylinder.

Abstract: A master-slave hydraulic control system preferably for actuating a vehicle clutch utilizes single-acting hydraulic cylinders which are both connected to a fluid reservoir. The higher mounted cylinder has a bleed valve in the line connecting that cylinder with the fluid reservoir. The lower mounted cylinder is connected to the fluid reservoir via a check valve. The check valve allows fluid communication between the reservoir and the lower cylinder when the pressure within that cylinder is below a predetermined value. The hydraulic system may be bled regardless of the position of extension of either cylinder.

Abstract: A fabricated master cylinder includes a pressure cylinder and a separately made reservoir mounted thereon by way of a mounting device on the cylinder and a mounting formation on the reservoir. The mounting device and reservoir provide restraint surfaces for engagement by a locking device which, when engaged, maintains the cylinder and reservoir in co-operative relationship. In an alternative arrangement, the restraint surfaces are on respective parts of the mounting device and formation which, themselves act as locking means.

Abstract: In order to accommodate all of the tolerances along the bore centerline plane of the reservoir mount for a master cylinder, the reservoir bayonets or projections extending into the boss bores of the master cylinder body are at a reduced diameter established by worst case tolerancing. This results in greater side-to-side clearance perpendicular to the bore center-line than is desired in many instances, giving a relatively loose reservoir fit. To reduce this side-to-side clearance, locally raised ribs or the like are added to the reservoir mount bayonets to better match the diameter in the machined body reservoir bosses provided by the boss reservoir mounting surfaces. The clearance is reduced by locally increasing the diameter of the reservoir bayonet mounts based on worst case tolerancing considering only one reservoir mounting member and its associated mounting boss independently of the other mounting member and its associated mounting boss.

Abstract: A master cylinder reservoir for use in a tractor hydraulic braking system has a pair of separate compartments, each adapted for connection to a respective one of a plurality of pressure cylinders. The compartments are interconnected by a flexible connector such as a convoluted tube, and the reservoir is advantageously made in a single piece by blow molding enabling the relative positions of the cylinders to vary so that the reservoir can be readily mounted by spigots engaging bores in the cylinders. The reservoir also has a flanged rigid tubular connection component molded into it during the reservoir molding operation, the material of the reservoir closely surrounding opposed surfaces of a flange of the component to resist longitudinal withdrawal of the component.

Abstract: An improved quick fill type master cylinder having a structure in which a piston consisting of a smaller diameter piston portion and a larger diameter piston portion is slidably fitted into a stepped cylinder bore to define a hydraulic pressure chamber as well as a hydraulic oil supply chamber therein, a relief port opening to the hydraulic pressure chamber and a supply port opening to the hydraulic oil supply chamber are placed in communication with an oil reservoir via a hydraulic oil flow passage formed longitudinally in a cylinder casing, and a valve device is incorporated in the hydraulic oil flow passage. The hydraulic oil flow passage is formed by drilling and the like from the rear end face of the cylinder casing and a valve chamber of the valve device is provided in the oil flow passage near outside opening thereof.

Abstract: Various buoyant valve arrangements are utilized to prevent quick take-up pressure from entering the master cylinder reservoir chamber until the quick take-up pressure reaches the desired value. A resiliently biased check valve is provided which opens at a predetermined quick take-up pressure to limit the amount of quick take-up pressure generated and then vents excess brake fluid from the quick take-up chamber into the reservoir chamber. The check valve may be resiliently biased by a spring or by elastic tension in an O-ring valve member.

Abstract: Various buoyant valve arrangements are utilized to prevent quick take-up pressure from entering the master cylinder reservoir chamber until the quick take-up pressure reaches the desired value. A resiliently biased check valve is provided which opens at a predetermined quick take-up pressure to limit the amount of quick take-up pressure generated and then vents excess brake fluid from the quick take-up chamber into the reservoir chamber. The check valve may be resiliently biased by a spring or by elastic tension in an O-ring valve member.

Abstract: A master cylinder includes a housing movably supporting a pair of pistons and carrying a fluid reservoir assembly. The fluid reservoir assembly carries a differential area piston and a float which cooperate to activate a single reed switch, thereby generating a warning signal for a vehicle operator.

Abstract: A reservoir tank includes a cap, a strainer, and a cap seal which is attached to the cap so as to prevent hydraulic fluid in the reservoir tank from leaking out. The cap seal is integrally formed with a cylindrical projection which is adapted to be pressed in resilient engagement with the outer periphery of the strainer, so that an inner space within the strainer defined by the inner side of the cap, the cap seal, the wall of the strainer, and the surface of the hydraulic fluid is separated by the projection from an outer space defined by the wall of the reservoir tank, the wall of the strainer and the surface of the hydraulic fluid. A tip of the projection of the cap seal is lower than the lower end of a thread portion of the cap when the cap engages with the reservoir tank. Therefore, hydraulic fluid adhering to an inner part of the cap and the cap seal does not drip and adhere to the thread portion of the cap.

Abstract: A modular structure for a hydraulic cylinder permitting the cylinder to be used in combination with a reservoir of hydraulic fluid either installed on the cylinder itself or at a remote location with a conduit connection to the cylinder. The cylinder is provided with a peripherally threaded portion over which a tubular member formed integral with the reservoir, or in the alternative, provided with a connector for connection of the cylinder to a remotely located reservoir is fitted. The tubular member-fluid reservoir assembly and the tubular member-connector assembly are interchangeable.

Abstract: An inlet assembly for a brake master cylinder including an inlet member made of synthetic resin installed in the cylinder body of the master cylinder for connecting with a hose communicated with a reservoir installed in a vehicle body. The inlet member includes a first member integrally forming a first tubular portion on a cylinder body side of the inlet member which is fitted into an inlet portion of cylinder body, a second tubular portion for operative engagement with the hose, and a second member having a mounting portion for mounting on the cylinder body, the first member being integrally connected with said second member by heat welding or a similar form of connection.

Abstract: An arrangement for supplying pressurized fluid into a user circuit, particularly a master cylinder of a clutch, includes a cylinder housing defining a bore. A cylinder sleeve is slidably accommodated in the bore and bounds an external feeding compartment with the housing, as well as an internal pressure chamber. A piston is received in the pressure chamber for displacement in the axial direction of the arrangement in response to the application of an external force, especially that of a clutch pedal, thereto, to exert pressure on the fluid present in the pressure chamber. The sleeve has a connecting port at its end remote from the point of application of the external force, and the housing has an auxiliary port communicating with an auxiliary reservoir and a supply port which communicates with the user circuit.

Abstract: The die-casting mold and the die-cast brake master cylinder housing comprise an axial master cylinder piston bore and a compensating bore, whose latter axis extends parallel to the axis of the master cylinder piston bore. The compensating bore has one end terminating in a compensating reservoir port oriented transversely relative to the housing's longitudinal axis and its other end terminating in a sealing chamber that is formed by an extension of the master cylinder piston bore. To render the casting process for manufacturing a die-cast brake master cylinder housing simpler, the mold comprises a core for the compensating bore whose longitudinal cross-sections containing the longitudinal axis are of conical construction, with the narrowest point being adjacent to the compensating reservoir port and whose cross-sections extending vertically to the longitudinal axis are of substantially reniform construction, while the concave sides of the cross-sections are close to the master cylinder piston bore.

Abstract: A housing for a master brake cylinder having a forwardly projecting piston, including a bottom wall for underlying the piston and at least the forward portion of the cylinder, a pair of upstanding side walls on laterally opposite sides of the bottom wall, and a front wall joined to the bottom wall and spanning the side walls, a top wall joined to the front wall and spanning the side walls, the top wall overlying the piston and being inclined upwardly rearwardly, the top and bottom walls being forwardly convergent.

Abstract: A hydraulic valve device for a hydraulic circuit controlling clutches, brakes and similar mechanisms comprises a non-return valve provided between a tank and a chamber. The non-return valve incorporates a ball accommodated in a cylindrical cavity and interacting with a leak-proof seat located on the same side as the tank, and a permeable seat located on the same side as the chamber. This arrangement eliminates the risk of the hydraulic liquid in the tank overloading the circuit during abrupt depressurization of the circuit.

Abstract: In a reservoir tank which includes an oil seal mounted to the cap of the reservoir tank and adapted to be in resilient engagement against the inner peripheral surface of the reservorir tank, the oil seal is integrally formed with an annular projection the tip portion of which is positioned at the braking fluid side of the cylindrical portion of the cap.

Abstract: A master cylinder comprises a plastic reservoir (24) and a metal housing (26). The housing defines a support portion (40) with slots (64, 66) and the reservoir includes integral tabs (76, 78) which extend into the slots to attach the reservoir to the housing. The tabs also locate a boss (72) relative to a stepped bore (50) during assembly of the reservoir and housing.

Abstract: A hand held manually operable hydraulic auxiliary device for lifting or pressing of loads or for operating of tools includes a hydraulic cylinder having pressure and activating pistons disposed between which is a valve housing including inlet and discharge channels and being furnished with non-return valves.The hydraulic cylinder including both the actuating piston operable by a manually operated lever, and the pressure piston, as well as the valve housing are disposed within an outer casing receiving the hydraulic fluid. The outer casing at least on the pressure piston side thereof is provided with a tool adapter. The valve members include a forced reset guide. Disposed in the area of the pressure side of the hydraulic cylinder is a randomly operable detent.

Abstract: A liquid reservoir for a hydraulic master cylinder, having a body with a detachable cap for refilling the reservoir, and a diaphragm secured in position by the cap and dividing the reservoir into an air chamber, vented to atmosphere via a hole in the cap and a liquid chamber connected to the master cylinder. An inlet port is provided in the wall of the reservoir for initial charging of the liquid into the liquid chamber without removal of the cap, the port being closed by a plug after the liquid reservoir has been filled. The method of filling a hydraulic control system which has such a reservoir is by the application of vacuum to the system via the inlet port, introducing liquid into the system through the port and subsequently sealing the port with the plug.

Abstract: A master cylinder of resin material includes a cylinder having a receiving portion within which a piston is sealingly slidable, a cylindrical portion having a diameter which is larger than that of an outer periphery of the cylinder and coaxially rearwardly extending from the fore part of the receiving portion, and mounting flanges radially extending from a rearward end of the cylindrical portion. Each of the cylinder, the cylindrical portion and the mounting flanges are integrally formed.

Abstract: A plastic compensating reservoir for hydraulic brake systems, such as for brake systems of automotive vehicles, is provided with two interconnected brake fluid chambers which are in communication each other over one port for connection to each one pressure chamber of a tandem master cylinder. To enable manufacture of a like compensating reservoir by one single injection molding process, there is provided a tube which extends transversely to the reservoir's vertical axis and which projects from one of the brake fluid chambers, the said projecting end being adapted to be closed.

Abstract: A liquid reservoir for a hydraulic master cylinder, having a body with a detachable cap for refilling the reservoir, and a diaphragm secured in position by the cap and dividing the reservoir into an air chamber, vented to atmosphere via a hole in the cap and a liquid chamber connected to the master cylinder. An inlet port is provided in the wall of the reservoir for initial charging of the liquid into the liquid chamber without removal of the cap, the port being closed by a plug after the liquid reservoir has been filled. The method of filling a hydraulic control system which has such a reservoir is by the application of vacuum to the system via the inlet port, introducing liquid into the system through the port and subsequently sealing the port with the plug.

Abstract: A fluid reservoir for supplying fluid to a master cylinder arranged in hydraulic system of an automotive vehicle comprises a reservoir tank having at least one fluid chamber therein and is provided at lower portion thereof with at least one outlet which is offset from a center of the fluid chamber and supplies fluid within the fluid chamber to the master cylinder. The fluid chamber is divided by partition wall into larger and smaller chambers the latter of which is in free fluid communication with the outlet and is in free fluid communication at top thereof with the larger chamber. The smaller chamber is much smaller than larger chamber in both longitudinal and transverse directions of the vehicle. The partition wall is provided with a passage for establishing a restricted normal fluid communication between the larger and smaller chambers.

Abstract: An automotive tandem type master cylinder comprising a cylinder body mounted in a frontwardly upwardly inclined manner for increasing the effective engine room space under the cylinder body, and an oil reservoir disposed at rearward, or lower position on the cylinder body for avoiding an increase in height of the hood. An oil passage is formed in the cylinder body in a rearwardly upwardly inclined manner for eliminating air bubbles in working fluid, and a mounting flange projects at the rear end of the cylinder body perpendicularly to the cylinder axis, whereby the cylinder body can be made easily and be shortened in its overall length.

Abstract: A stationary pressure bleed stem and a movable pressure bleed stem are mounted on a base plate to adjust for varied spacing between the master cylinder ports at the reservoir bottom. The fixture is clamped over the master cylinder reservoir. The stems may be interchangeable with other similar stems of various dimensions to accommodate for variations in dimensions of different master cylinders. The device simplifies and expedites pressure bleeding of master cylinders having different configurations.

Abstract: A tandem brake master cylinder which includes a single inlet union having two inlet union portions which are connected to each other as a single, unitary body via a connecting portion, the connecting portion having at approximately a central portion thereof a mounting portion which projects toward a cylinder body and which has an insertion hole formed therein. The distance between each inlet union and a common mounting screw may be double that as compared with the distance between the inlet union and its associated mounting screw in conventional master cylinders and therefore the play of the inlet union portions may be greatly reduced.

Abstract: A hydraulic fluid reservoir for automobile including a plurality of fluid chambers separated by a partition, the fluid chambers being communicated with hydraulic systems in the automobile respectively, and a baffle plate between the upper end of the partition and an inlet at the upper portion of a reservoir body to define openings of the respective fluid chambers at predetermined ratios which define the flow rates of fluid into respective fluid chambers.

Abstract: A master cylinder includes a housing (12) with a bore (14) receiving a pair of pistons (32, 34). A bearing (50) extends from the housing (12) to one of the pistons (32) to define a passage (65) communicating fluid to a pressure chamber (40). The bearing (50), the passage (65) and the pressure chamber (40) extend outwardly of the housing bore (14) to permit the length of the housing to be reduced.

Abstract: A reservoir assembly for a master cylinder includes a housing with a surface adapted to interface with the reservoir assembly. The reservoir assembly comprises a first part made from a lightweight plastic material and a second part made from a metallic material. The second part is adapted to fit on the surface while attachment of the reservoir assembly to the housing is provided for by the second part.

Abstract: A hydro-pneumatic actuator for providing a two-stage buildup of the hydraulic output pressure. A primary hydraulic piston, to which a pneumatic input piston actuator is connected, acts in a larger bore of a hydraulic cylinder to transfer fluid via a central passage in a spring-loaded, differential area, secondary hydraulic piston, that is coaxially disposed in the hydraulic cylinder in spaced-apart relationship with, and downstream of, the primary piston. A larger face of the secondary piston is in the larger bore and the smaller face is in a reduced diameter bore of the hydraulic cylinder, so that a pressure buildup in the hydraulic cylinder effects actuation of the secondary piston to close a check valve and thereby inter-fluid communication between the larger and smaller bores of the hydraulic cylinder via the central passage.

Abstract: A master cylinder includes a housing (22) with a bore (24) for receiving a pair of pistons (36, 38). The housing defines a reservoir (28) with an outer wall (26). The housing also defines at least one outlet passage (62, 66) communicating fluid from the bore (24) to a brake assembly (16). The outlet passage (62, 66) is partially defined by a boss (60) formed integrally with the housing (22) and the boss (60) cooperates substantially with the outer wall (26) to separate the reservoir (28) into a pair of cavities (84, 86).

Abstract: A differential master cylinder adapted for use as fluid pressure generating source in a brake system comprises a cylinder body having a stepped cylinder formed therein; a stepped piston arranged to be slidable within the stepped cylinder; a first chamber defined by the end of a portion of smaller diameter of the stepped piston and a portion of smaller diameter of the stepped cylinder; a second chamber defined by the stepped piston and a portion of larger diameter of the stepped cylinder; a first fluid passage provided at the stepped piston and arranged to have the first and second chambers intercommunicate; a check valve arranged in the first fluid passage to close when fluid pressure within the second chamber reaches a first setting value; and a relief valve arranged to open to return the fluid from the second chamber to a reservoir when the fluid pressure within the second chamber reaches a second setting value which is higher than the first value.

Abstract: A short master cylinder uses solenoids to control the master cylinder compensating and bypass functions. The pressurizing pistons each use only one seal. There is a unitary primary piston and booster output push rod. The booster power piston return spring returns the primary piston and, through a lost motion interconnection, the secondary piston, omitting the secondary piston spring. Brake pedal travel and pressure sensors control the solenoid valves, reducing lost brake pedal travel.

Abstract: A master cylinder assembly has a low pressure, high volume displacement quick take-up chamber and a high pressure, low volume displacement pressurizing chamber formed by a stepped bore and a stepped piston. A compensation control and blow-off valve unit has a peripheral lip seal type valve providing compensation flow on brake release but preventing flow from the quick take-up chamber during brake apply. A valve body is integrally molded as a part of the reservoir. A normally closed check valve can open to provide communication between the quick take-up pressurizing chamber and the fluid reservoir. When the pressurizing cup for the high pressure chamber closes its compensation port, the check valve is subjected to the pressure in the quick take-up pressurizing chamber. Initial fluid flow is obtained from the quick take-up chamber past the pressurizing cup into the high pressure chamber.

Abstract: An upper sealed reservoir and a lower vented reservoir are connected by a conduit and tube extending into the lower reservoir. A shroud forms a chamber around the end of the tube within the lower reservoir and is vented at its upper end. Openings are provided in the tube and the shroud and are indexed in diametrically opposite relation, with the opening in the tube pointing in the direction of the center of the lower reservoir. The arrangement maintains proper hydraulic fluid level balance between the two reservoirs under a wide range of vehicle attitudes and accelerations. When either the vehicle attitudes or acceleration, or both, momentarily reorients the actual fluid level in the lower reservoir and the shroud, trapped fluid within the shroud chamber prevents air from entering the upper reservoir through the tube and conduit so that excess fluid cannot flow into the lower reservoir from the upper reservoir.

Abstract: In a pneumatic-hydraulic system for driving a hydraulic actuator, a single pneumatic-hydraulic converter includes a cylinder casing with inlet and outlet ports and a plunger reciprocably disposed within the casing to form a hydraulic chamber in open communication with the inlet and outlet ports and a pneumatic chamber for connection to a pneumatic pressure source, the hydraulic chamber having a displacement capacity filled with a predetermined amount of hydraulic fluid necessary for producing at least one reciprocating motion of the actuator.

Abstract: An hydraulic pressure master cylinder has a cylinder usually of metal, and a separately made plastics reservoir. The reservoir is retained on the cylinder by means of a pair of resilient arms, the internal faces of which are recessed to conform the external surface of the cylinder. The reservoir is fitted to the cylinder by deforming the arms outwardly to enable them to shap-engage around the cylinder so that the latter seats within the recesses. If desired, the free end portions of the arms may be joined by a fixing device such as a rivet.

Abstract: A fluid reservoir for use with a tandem master cylinder is divided into two compartments by a partition wall with one of the two compartments being directly connected to a first outlet port connected to the master cylinder and the other of the two compartments being connected to a second outlet port connected to the master cylinder disposed in the one of the two compartments by a channel formed within the reservoir extending from the other of the two compartments through the partition wall to the second outlet port. This construction ensures the freest possible arrangement of the first and second ports at the bottom of the reservoir.

Abstract: Friction clutch release apparatus for a motor vehicle comprises a driver-operable master cylinder, a slave cylinder and a conduit which connects the master outlet to the slave cylinder inlet. A liquid reservoir communicates with the bore of the master cylinder between the piston and the outlet when the piston is retracted and has a vent port. The apparatus is assembled, filled with liquid and bled before being installed on the motor vehicle. The vent port may be closed temporarily for convenience of transport and storage after the apparatus is bled, for example by use of a suitable removable closure device which would be removed after installation of the apparatus on the motor vehicle, or may include a movable wall within the reservoir chamber by which liquid within the chamber is separated from that part of the chamber with which the vent port communicates.

Abstract: A master cylinder assembly has a reservoir mounted on the master cylinder body. The reservoir includes a reservoir body having a top opening and a cap attached to the reservoir body for covering the top opening. Between the reservoir body and the cap, there is disposed a flexible diaphragm which also covers the top opening of the reservoir body. A depressing plate is provided between the cap and the diaphragm for forcing the peripheral portion of the diaphragm against the reservoir body when the cap is attached to the reservoir body. Projection and aperture arrangements are provided between the diaphragm and the depressing plate so that they can be held together. The cap is formed with hook-shaped portions for engagement with the outward edge of the depressing plate. The cap, the depressing plate and the diaphragm can be assembled together before they are installed on the reservoir body.

Abstract: A reservoir for use with a tandem master cylinder consisting of an elongated housing generally extending along the longitudinal axis of the master cylinder and including top and bottom walls and side walls, a partitioning wall provided between the top and bottom walls and extending laterally from either of the side walls toward the other side wall thereby partitioning the interior of the housing into two chambers. The partitioning wall further extends longitudinally along the other side wall and is spaced therefrom to define therebetween a corridor-like passage communicating the two chambers. The corridor-like passage has an opening which is spaced from the bottom wall by a predetermined height. A liquid level warning device receiving chamber is formed in one of the two chambers and is defined by the laterally and longitudinally extending portions of the partitioning wall and by an additional wall having a slit which extends between the top and side walls.

Abstract: A reservoir tank having a flexible diaphragm disposed above the liquid received in the reservoir tank for intercepting the liquid from being exposed to atmospheric air. The diaphragm has a corrugated form consisting of at least one annular upwardly projecting portion and at least on annular upwardly projecting portion surrounded by the annular downwardly projecting portion, and at least one cut-out portion is formed in the annular downwardly projecting portion to define a horizontally extending escape passage across the annular downwardly projecting portion.

Abstract: The invention relates to a two-compartment reservoir for liquid, comprised of two superposed parts and provided with a transfer channel which opens into both compartments and which runs parallel to the plane of the liquid contained in the reservoir.The junction plane of the two parts of the reservoir is inclined, with respect to the bottom of each of them, at an angle ".alpha./2", which permits to manufacture with the same parts two types of reservoirs: the first one for horizontal installation and the other one for inclined installation, at an angle ".alpha.".Suitable grooves, provided in the walls, of the two parts cooperate in both cases to form the transfer channel parallel to the plane of liquid.The invention is particularly useful in hydraulic braking systems for automotive vehicles.

Abstract: A master cylinder and reservoir assembly comprises a reservoir (2) having a depending foot portion (13). For ease of assembly of the reservoir on the master cylinder (1), the foot portion (13) has opposed laterally extending projections which slide in complementary longitudinal recesses (12) at the top of the master cylinder. The reservoir may be held in place by friction, or some arrangement for positively retaining the reservoir may be provided.

Abstract: The invention relates to a hydraulic brake booster for a vehicle brake apparatus which is provided with a pressurizing apparatus which has a pump and a reservoir (accumulator). When the reservoir pressure fails, a switchover piston which is subject to the reservoir pressure can disengage a stop for the push rod of the control valve.The push rod is supported on the stop when the pressure supply to the reservoir is intact and after the control valve switches over in the direction of brake activation.In this manner, a stop for the brake pedal, which activates the push rod is formed which is subject solely to the resiliency of a travel-limiting spring. The stop operates when reservoir pressure is available to effect a longer pedal stroke. When the reservoir pressure fails, it is automatically disengaged.

Abstract: A rotary master cylinder means including a housing having a cylindrical bore, a rotary piston rotatably mounted in the cylindrical bore and having a peripheral recess, a dam means slidably supported by the housing and radially inserted into the recess so as to define a pressure chamber in the recess, wherein the rate of delivery of brake fluid from the pressure chamber relative to rotation of the rotary piston effected by stepping on the brake pedal can be non-linearly varied by varying radial depth of the recess in accordance with its angular position.

Abstract: In a reservoir comprising a container for liquid at least one portion of the top wall of the container is depressed to form a window, the depressed portion and at least a part of the surrounding area being transparent or translucent so that the reservoir can be filled with a liquid until the liquid is in visible contact on the under surface of the window with the surrounding part untouched.

Abstract: Hydraulic operated blind riveting apparatus includes a pneumatic/hydraulic intensifier 23 and a reservoir 45 of hydraulic fluid for making up loss of hydraulic fluid. The reservoir is connected to the hydraulic system by a quick acting priming valve 47, actuated by the pneumatic feed to the intensifier. This priming valve is arranged to open and close before there is any effective change in pressure in the hydraulic system due to the action of the intensifier.