Abstract: The invention relates to an apparatus for coupling a shaft or a hub by means of a radially resilient bush, which can be radially clamped to the shaft or hub by axially tightenable clamping elements by exposing the clamping elements to a radially operative spring assembly; the release of the coupling is effected by means of a hydraulically- or pneumatically-actuated cylinder and piston arrangement. The nucleus of the invention is that the spring assembly is accommodated in the cylinder chamber acted upon by the pressure fluid.

Abstract: A stem is fixed to a head tube of a bicycle by a fixing device. The stem has an aperture formed in a center. A hole is formed in an upper end of the vertical tube for receiving a spring and a bolt. Two holes are laterally and oppositely formed in a lower portion of the stem, and each receives a piston. The aperture and the holes are filled with oil. The pistons are pushed to engage with an inner surface of the head tube when the bolt is threaded into the upper hole so that the stem can be firmly fixed to the head tube.

Abstract: A quick change tool holder including two basic component assemblies, the first component assembly having a central boss portion and the second component assembly having a recess to receive the boss portion when the two component assemblies are attached together. A channel formed in the boss portion is engaged by a pivotally mounted lock bar member when the component assemblies are attached together. The lock bar is moved out of the channel which permits separation of one component assembly from the other by the action of air pressure against a piston.

Abstract: The mounting device for the squeegee or inking blade has an elastic clamping tube which can be expanded under a pressurized medium to clamp the squeegee or inking blade in place. The clamping tube is made of resilient material and ensures that the squeegee or inking blade is secured with a uniform linear pressure over the whole length. A spring may also be used to initially hold the squeegee or linking plate in place until the clamping tube is expanded.

Abstract: Connectors for connecting coilable tubing and other relatively thin walled tubing strings to downhole tools are provided which are releasable to permit withdrawal of the tubing without a member connected to the tubing that is substantially larger in diameter than the tubing itself. One embodiment of the connector includes a body member having plural collet fingers which are engagable with the tubing distal end through cooperating circumferential grooves and lands. The collet fingers are retained in gripping engagement with the tubing by a retainer sleeve having a piston head which catches a pump down ball to block a flow passage in the retainer and allow a fluid pressure force to shear plural shear screws which hold the retainer in the finger engaging position. Alternate embodiments includes recesses formed in the wall of the tubing for receiving ball keys which are held in registration with the recesses by the connector body and a cooperating slidable sleeve member.

Abstract: An apparatus is disclosed on the basis whereof the image cylinders seated in cantilevered fashion in drum scanners can be mounted in the scanner in a short time running centrally regardless of the dexterity of the operator.This thus enables the preparation of the image cylinders (application of the images, etc.) outside of the apparatus, this leading to short standstill times of the scanner.

Abstract: A release mechanism is triggered when the pressure differential on the siall of a sealed container reaches a predetermined threshold level at which the container either implodes or explodes to sufficiently decrease the spacing between the ends of the container and thereby achieve the release. False triggering due to percussion or shock waves may be precluded by disposing a shield about the sidewall.

Abstract: A device for detachable and repeatable accurate clamping in X-, Y- and Z-directions of a first object to a second object like a working table (2) to a machine table (1), the first object (1) having a house (3) with a truncated conical surface (15) intended to cooperate with a corresponding conical surface (25) of the second object (2) and clamping member (9), each intended when clamping the second object to the first object by pivoting the clamping member to engage a clamping surface (20) of the second object by a nose (12). According to the invention the house (3) is provided with a first stop face (17) extending across the axis (16) of the truncated conical surface (15) and cooperating with a second stop face (21) arranged in the second object, the mutual position in the Z-direction of the first and second objects being unambiguously determined.

Abstract: A plasticizing and injection group of mechanisms is detatchably secured on the injection side tool holder through a press-on and shift assembly. Releasable attachment occurs by automatically engageable and disengageable couplings each having a head, arranged at the end of an axially movable connecting element, e.g. of a piston rod of a press-on and shifting device. Slides engage the piston rod from behind a protuberance thereof slide back and forth crosswise to the connecting element. The slides are controlled by a central control unit of the machine. To perform maintenance work, the coupling is disengaged, and for better accessibility of the injection nozzle, the plasticizing and injecting group is moved away from the tool holder and can be pivoted out of the injection axis. Any manual work for releasing the attachment of the connecting element on the tool holder is eliminated.

Abstract: In order to automatically initiate without any intermediate instrumentation chain the drop of absorbing members into the core of a nuclear reactor, in the of a drop in the cooling liquid level to below a given threshold and, optionally, a rise in the pressure to beyond a maximum permitted value, between each absorbing member and the bar supporting said member is provided an apparatus, which comprises tongs formed by at least two fingers, said tongs normally being locked in a gripping position by locking members, such as balls. A float mounted in the bar controls the unlocking of the tongs in either of the two conditions requiring the dropping of the absorbing members.

Abstract: A gripper with leaf springs having fingers near their ends to engage and disengage work. The springs are respectively connected in an annular array to the end of a cylindrical support. The springs are diverged or expanded to cause the fingers to engage the work and are converged or collapsed to cause the fingers to disengage the work. During the diverging and the converging each spring is pivoted about its junction with the support. The diverging and the converging of the springs is effected by an actuator or mandrel including a rod having a nose at its outer end. The actuator is reciprocable within the springs between advanced and retracted positions. Near its outer end the rod has a conical cam surface which engages cooperative internal cam-follower surfaces on the springs to diverge the springs when the actuator is in advanced position. The nose has a skirt which engages the outer ends of the springs, i.e. the fingers, to converge the springs near the ends when the actuator is in retracted position.

Abstract: A hydraulic tensioning device for tracked vehicles comprising a hydraulically chargeable piston-cylinder unit, coupled on one end with the body of the vehicle, and with the other end to a guide wheel for the track chain which is supported on a rocker arm. In order to obtain the proper track chain tension in any operating condition without providing a separate hydraulic pump, the piston unit is equipped with a tappet supported against the piston unit by means of a spring unit. The tappet closes off a secondary cylinder chamber in the piston unit which is connected with the principal cylinder chamber by two check valves which seal in opposite directions. The tappet effects a pumping action as the result of the vibration generated by the chain links running in and out the guide wheel, thereby pumping the hydraulic oil from a hydraulic oil reservoir into the secondary cylinder chamber and from there into the principal cylinder chamber.

Abstract: The clutch release mechanism includes a fluid actuator having an actuator member movable by fluid pressure in a clutch release direction to release the clutch, a release bearing assembly for connection to part of the clutch, and a coupling for connecting the release bearing assembly to the actuator member. The coupling is fluid operable whereby in one condition it prevents axial separation of the actuator member and release bearing assembly by engagement of pins and a groove and, in another condition, it allows axial separation and coupling of the release bearing assembly and the actuator member by disengagement of the pins and groove.

Abstract: An arrangement for fastening a roll ring (5) to an overhung roll shaft (1) by means of a taper sleeve (8) which transmits essentially the entire torque and which is loaded axially by a spring (43) supported on an abutment (47) adjustable on the free end of the roll shaft. The roll ring can be exchanged easily because of a cylinder part (21) arranged radially within the spring. This cylinder part forms a first annular cylinder space (40) for prestressing the spring, with which it interacts via a flange, and a second cylinder space (22) for drawing off the taper sleeve, to which it is connected via engagement means (28). The spring and the hydraulic devices can remain in place when a roll ring is assembled and removed, because their outside diameter is less than the bore of the roll ring.

Abstract: A releasable coupling for connecting a first and a second component to one another, includes a first sleeve-like hollow member affixed to an end of the first component and a second sleeve-like hollow member affixed to an end of the second component, an expander mandrel supported in the first hollow member and arranged for an axial motion with respect to the first hollow member to assume an advanced position in which it projects into the second hollow member to be surrounded simultaneously by the first and second hollow members. The expander mandrel includes an expander element and pressing elements operatively connected to the expander element for displacement generally radially outwardly by the expander element into an expanded position for a simultaneous engagement with the first and second hollow elements thereby clamping the first and second components to one another.

Abstract: A joint assembly to make firm but easily releasable contact between two components, for instance a vibration generator of magnetostrictive or piezo-electric type, an an internal plug or mandrel for use in the drawing or draw-bending of metal tube. The assembly comprising first and second ring-shaped members to engage the respective components, and an intermediate member which is fixed to one of the members and in sliding contact with the other so as to define with that other a sealed chamber of variable volume. The chamber is connected in use to a source of pressurized fluid, and when filled with such fluid the chamber is expanded and the two components are urged into firm contact.

Abstract: An interlock for the throttle and parking brake of a vehicle for retaining the engine at a predetermined speed until the parking brake is released. Includes a fluid supply conduit connected to the parking brake actuating mechanism. The supply of fluid to the parking brake actuating mechanism is controlled. The parking brake is maintained in the brake engaged position in the absence of fluid supply to the brake actuating mechanism. A linkage is interposed between a first member connected to a vehicle operated control mechanism, and a second member connected to an engine speed control mechanism. The link has a first operating mode for effectively connecting the first and second operating members in a second operating mode for effectively disconnecting the first and second operating members. The first member is placed in its first operating mode when fluid is supplied to the parking brake and is placed in second operating mode when the supply of fluid is discontinued.

Abstract: In the field of fastening components together in such a way as to be able to transmit mechanical power, keyways and keys have been used; also, interlocking conical tapers have been used which are actuated either by a ring of screws or by oil-injection.The coupling according to the invention comprises an annular chamber housing an annular piston; the chamber and the piston have matching tapers. Oil is pumped into one end of the chamber to move the piston axially in one direction to cause radial expansion of the chamber to connect two components; oil is pumped into the other end of the chamber to move the piston in the opposite direction to disconnect said components.Uses of the coupling are, for example, to join the adjacent ends of coaxial shafts and to act as a locking bush to join concentrically arranged components.

Abstract: An accommodating linkage device which operates in three modes to provide, upon command, either: (1) a standard, resetable, rigid linkage between two objects; (2) a flexible linkage which responds to relative motion (forces) between two objects; (3) or an arbitrary, rigid linkage between two objects. The device includes two ball joints which connect to the two objects, a pair of locking pistons, and a pair of alignment pistons. Operation of the device is in response to either control signals or to forces generated by the relative motion of the two objects, depending upon operating mode.

Abstract: The hydraulic drive mechanism comprises an hydraulically actuated rod drive mechanism that cooperates with a pivotable latching mechanism. The pressurized reactor coolant is utilized to raise the drive rod into contact with and to pivot the latching mechanism so as to allow the drive rod to pass the latching mechanism. The pressure in the housing is then equalized which allows the drive rod to move downwardly into contact with the latching mechanism but remain in a raised position with respect to the reactor core. Once again, the reactor coolant pressure may be utilized to raise the drive rod and thus pivot the latching mechanism so that the drive rod passes above the latching mechanism. Again, the mechanism pressure can be equalized which allows the drive rod to fall and pass by the latching mechanism so that the drive rod approaches the reactor core.

Abstract: The invention relates to an actuating device for two clusters of control rods movable vertically in one and the same fuel array of the core of a nuclear reactor.The first cluster, used for running the reactor, is connected to a first actuating rod (2), the movements of which are effected by a mechanism (27, 28, 29, 30, 34). This rod (2) carries hooking fingers (41), the operation of which is effected by a device (45) mounted slidingly on the end of the rod (2). The device (45) causes the closing of the fingers by means of a spring (46), or on the contrary their opening by overstroke movement towards the top of the rod (2). The second cluster remaining fully inserted into the assembly during a part of the operating cycle of the reactor is connected to a second actuating rod (3).

Abstract: Flexible joint means in which a flexible bearing positioned between a hollow outer member and part of an inner member received within the outer member accommodates tension loads applied to either member and a substantially incompressible fluid contained within a fluid tight cavity in the outer member accommodates compression loads applied to either member.

Abstract: A shaft coupling and method of operating the same serves to establish a positive and reliable frictional connection or interference fit for the operative torque-transmitting interconnection of two shafts. The shaft coupling has an inner sleeve and an outer sleeve coacting with one another by means of conical surfaces or tapers. The shaft coupling, and particularly the sleeves, especially the outer sleeve has two outer support portions or sections and an intermediate portion or section located therebetween. The support portions are provided with infeed bores for the infeed of a pressurized fluid medium, typically pressurized oil, between the conical surfaces or tapers of the sleeves during the mounting of the shaft coupling. At the intermediate portion of either the outer sleeve or inner sleeve there is located an outflow bore for the withdrawal or discharge of the pressurized oil.

Abstract: The disclosed invention is an apparatus for connecting two current conducting tubes, which also conduct fluids such as for example, a coolant. The connection apparatus conducts current from one tube to the other through a sleeve, the said tubes having a machined external surface against which the sleeve is pressed. A hose receiving hydraulic pressure is disposed between the sleeve and an external casing for providing a removable pressure against the sleeve for clamping the pipes in the sleeve. The present invention may be used in conjunction with a holder assembly for electrodes in an electrothermal smelting furnace.

Abstract: A camlock for engaging the inside of tubular members thus suspending apparatus from the tubular members comprises a movable spacer disposed on a slidable member between two metal rings. The relative motion of the spacer and slidable member causes the metal rings to be expanded against the inside of the tubular member thereby supporting the apparatus. The metal rings have a thin wall with internal ribs that fit closely to the slidable member. The internal ribs act as stops on the inside of the metal rings so as to prevent their overexpansion.

Abstract: A pressure coupling for securing a part to a shaft rotatable about and centered on the axis has an inner sleeve fitted snugly over the shaft and in good contact therewith and having a pair of axially outwardly flared frustoconical outer surfaces centered on the axis. An outer piston ring and a separate outer cylinder ring on the sleeve respectively have outwardly flared frustoconical inner surfaces flatly engaging the outer surfaces and axially limitedly slidable thereon. The rings are displaceable axially relative to each other between juxtaposed inner positions relatively close to each other and bearing at most lightly on the outer surfaces and spaced-apart outer positions bearing strongly on the outer surfaces and radially inwardly deforming the sleeve against the shaft. The cylinder ring overreaches the piston ring and forms therewith a substantially closed pressurizable chamber.

Abstract: In a mechanical press brake, a photoelectric sensor causes extension of an air cylinder in the linkage between the operating pedal and the clutch lever, thereby disabling the pedal whenever the operator's hand or arm is in dangerous proximity to the machine's ram. The piston of the air cylinder is connected to the pedal through a lost-motion, and the pedal is continuously urged toward its rest position by a spring. The lost-motion and spring prevent repeated extension and retraction of the cylinder from causing dangerous and annoying operation of the pedal during preparation for a forming operation.

Abstract: A tightly fitted assembly including an impeller mounted on a tapered shaft with an interference fit. The impeller includes a piston and cylinder arrangement adapted to supply an axially acting force to the impeller to disengage it from the shaft while fluid pressure is applied to the bore of the impeller to break the interference fit between the shaft and impeller.

Abstract: The invention relates to a device for providing a friction joint by pressing a number of first elements against a second element by means of a pressure medium acting on said first elements. In order to obtain an improved ability of transmitting a torque and an improved stability regarding radial load, said first elements are so arranged that they encircle or are encircled by said second element and are acted upon by a number of mutually independent portions of the pressure medium, each portion acting on its own element.

Abstract: A wheel of a turbomachine is secured to a shaft of the machine by initially securing the wheel between one end of the shaft and a piston-like member. A space is formed between opposed sides of the member and wheel by moving the member relative to the wheel. A spacing member is placed in the space for placing a compressive force on the wheel for positively securing the wheel to the shaft.

Abstract: A pressurized hydraulic fluid actuated coupling assembly for detachably coupling to an element. The assembly has first and second concentric walls secured together at the ends. The second wall is adapted for engaging the element. One of the walls has grooves defining corresponding recesses between the first and second walls. Ridges on such one wall are defined between adjacent recesses. Means is provided for introducing hydraulic fluid into the recesses. Means is provided for varying the pressure of the hydraulic fluid such that in the absence of fluid pressure, the ridges on the one wall are in contact with the other wall and upon pressurization of the fluid the second wall moves away from the first wall such that the second wall rigidly couples to the element and such that the ridges are spaced a predetermined distance from the other wall.

Abstract: A composite carrier bar for oil well pumping units that utilize sucker rod to operate bottom hole pumps, including a recessed cavity for receiving a hydraulic ram to operate as a polish rod jack and also including a secondary carrier bar for receiving a secondary polish rod clamp for use in respacing bottom hole pumps and serve as a safety clamp during operation.

Abstract: In the several representative embodiments of selectively-operable well bore apparatus disclosed herein for dependently coupling a well tool to a suspension cable, a collapsible assembly of two or more retaining members is arranged within an enclosed chamber and operatively positioned for normally retaining upper and lower tool-support members in a position where they are tandemly coupled or interconnected. In each of the several embodiments of the invention disclosed herein, electrically-responsive securing means normally maintaining the collapsible assembly in its initial position are cooperatively arranged to be selectively failed so as to allow collapse of the retaining assembly should it become necessary to separate the cable from the well tool while it is in a well bore. Provisions are also made for admitting well bore fluids into the enclosed chamber upon collapse of the retaining assembly so as to assure release of the cable even under extreme well bore pressures.

Abstract: A coupling includes at least one thin-walled sleeve which forms an axially extending defining wall of a substantially annular chamber. The chamber is arranged to be supplied with a pressure medium to elastically deform said sleeve in a radial direction into clamping engagement with a surface on an element which is to be connected to the coupling, the shape and dimension of said surface substantially corresponding to the shape and dimension of a surface on the sleeve remote from said chamber. The chamber has extending therefrom a channel arrangement which is arranged to cooperate with coupling-release means which can be activated by relative movement between said surfaces, or by a given torsional deformation thereof, to a state in which pressure medium can flow through said channel arrangement from said chamber to relieve the chamber of pressure acting therein.

Abstract: A coupling is mounted between a valve stem of a valve and a rod of a valve actuator. The rod includes an extension having a piston member at the end thereof which is received within a cylinder member mounted on the end of the valve stem. The extension and piston member thereof define with the cylinder member a chamber within the cylinder member. Force can be transmitted from the rod to the stem by full insertion of the piston member within the cylinder member. A pressurized gas is contained within the chamber to limit the force transmitted from the rod to the stem when the relative position of the rod with respect to the stem causes the piston member to be located intermediate of the cylinder member.

Abstract: A device for logging trailers which have telescoping reaches providing for adjustment of the length of the trailer reach. The device is an expandable compressed air chamber positioned within the inner reach near the end contained by the outer reach. Four shoes are retained in contact with the expandable chamber. The shoes are provided with friction material adapted to contact the inner walls of the outer reach through openings in the walls of the inner reach. Compressed air is supplied to the expandable chamber through a hose from the truck cab. The truck operator is able to lock the inner reach relative to the outer reach at a desired length by control from the cab.

Abstract: A coupler for removably coupling a tool attachment at an end of a supporting arm of a powered digging or material-moving machine. The coupler includes a latch which permits quick interchanging of tool attachments on the arm. One embodiment provides a means for remotely disengaging the latch so that a machine operator may interchange tool attachments without having to dismount the machine to manually assist interchanging of attachments.

Abstract: A swivel joint comprises a journal fitted in a hole. The journal is conical and axially formlocked in the hole. A working chamber is arranged behind one of the mantle surfaces of the hole and the journal. The chamber has an integral flexible wall defining one of said surfaces. When hydraulic pressure is applied to the chamber, the flexible wall expands the journal is centered in the hole and locked against rotation, and the journal end engages the hole bottom.

Abstract: Disclosed is a mechanical locking device for locking a rod in a conventional hydraulic actuator, such as a hydraulic cylinder or a rotary actuator. The device comprises a radially contractible locking ring having a cylindrical inner surface for gripping the rod when the locking ring is contracted and an outer surface which is axially inclined, means for positively securing the locking ring around the rod in a position axially fixed in at least one direction with respect to the actuator housing, a ring-contracting member around the locking ring and having an inner surface which is axially inclined at the same angle as the outer surface of the locking ring for engaging that surface, and means for applying an axial force to the ring-contracting member in the direction of the inner surface axial inclination to cause the ring-contracting member to slide axially on the locking ring thereby causing the locking ring to contract and grip the rod.

Abstract: A column in which an inner elongated member of circular cross section is partly received in the polygonal bore of an outer, tubular member and secured against angular displacement about the common axis by guide elements secured against longitudinal movement in respective recesses of the inner member open toward the outer member and engaging the outer member in respective corners of its polygonal cross section. A manually controlled arresting mechanism permits the two column members to be arrested against relative longitudinal movement in a multiplicity of relative positions.

Abstract: A coupling device for releasably coupling machine parts or other like structures. The coupling device comprises a pressure sleeve of a deformable material provided in one or more bores in one of the machine parts or an intermediate spacer body with the pressure sleeve having an associated screw clamp means. The coupling device provides coupling of the machine parts or other structures by use of a coupling device which is non-concentric with the machine parts or other structures.

Abstract: A coupling is mounted between a valve steam of a valve and a rod of a valve actuator. The rod includes an extension having a piston member at the end thereof which is received within a cylinder member mounted on the end of the valve stem. The extension and piston member thereof define with the cylinder member a chamber within the cylinder member. Force can be transmitted from the rod to the stem by full insertion of the piston member within the cylinder member. Hydraulic fluid under pressure from an accumulator secured to the cylinder member is in communication with the chamber to limit the force transmitted from the rod to the stem when the relative position of the rod with respect to the stem causes the piston member to be located intermediate of the cylinder member.

Abstract: Fluid links are interposed between manual levers which control the motions of a machine such as a construction crane and associated spool valves which regulate the machine motions. In normal operation within predetermined safe limits of machine motions, pressurized fluid delivery valve means connected with the fluid links is conditioned by a normal signal from a safe machine motion sensing means and delivers pressurized fluid to the fluid links rendering the links "hard" so that the manual levers are enabled to effect safe machine motions. When an unsafe machine motion is sensed by the sensing means, the valve means responds to the interruption of the normal signal from the sensing means and is conditioned to interrupt delivery of pressurized fluid to the fluid links thus rendering the links "soft" and thus disabling the manual levers from causing machine motions beyond safe limits.

Abstract: Apparatus for restraining an aircraft against the combined forces of a cault launching shuttle and aircraft takeoff power during a catapult assisted takeoff until a predetermined combined force level has been reached. Release of the aircraft is triggered by the relative movement of a central piston within a housing which causes disengagement of gripping lugs from a tensile bar attached to the aircraft. The relative movement is enabled by the compressibility of hydraulic oil confined within the apparatus and loaded by the combined forces.

Abstract: A holdback bar for temporarily restraining an aircraft against the combined orces of engine thrust and catapult force prior to a catapult assisted launch of the aircraft which utilizes strain of a mechanical component to measure the level of combined forces. Housing stretch beyond a pre-determined amount actuates a floating trigger rod to lift a valve from its seat and permit escape of hydraulic fluid from a pressure chamber. The holdback bar includes a compensator for absorbing fluid volume changes caused by thermal expansion or contraction of the hydraulic fluid, and a rupture disk for limiting the pressure obtainable within the hydraulic fluid pressure chamber.

Abstract: A holdback bar for restraining an aircraft temporarily prior to catapult isted launch which utilizes a ball and piston unloader valve to insure rapid, positive release of a pressurized hydraulic fluid. Compensator chambers each having a resilient piston cushion against release shock caused by rapid release of stored strain energy in the hydraulic fluid and provide hydraulic fluid make-up to allow for expansion and contraction and slight leakage losses.

Abstract: A gripping device comprising two pivotally mounted gripping claws is operated by a double acting hydraulic cylinder. The entire gripping device is pivotally mounted from a crane or the like by means of a universal joint. A member is provided which is operated on by a pressure fluid in the double acting hydraulic cylinder and which serves to temporarily lock the universal joint against pivotal movement to provide a secure and firm connection between the gripping claws and the crane or the like on which the claws are supported. In one embodiment of the invention a rod engages with a ball shaped head to prevent pivotal movement of the universal joint, and in a second embodiment bellows are inflated by hydraulic fluid to prevent movement of a pivotal joint.

Abstract: A quick-hitch type coupler for front end loaders, and the like, for attaching various attachments to the front end loader without having to leave the vehicle. The lift mechanism of a front end loader has a coupler connecting and locking portion attached thereto, and each attachment for the loader has pairs of coupling brackets attached thereto, so that the front end loader lifting mechanism can be coupled or uncoupled from the attachment, and locked to it by the actuating of a single cylinder.

Abstract: Means for mounting a work roll on a shaft. A cylindrical collet having at least one tapered surface, either exterior or interior, is pushed into an annular space between the roll shaft and work roll, one or both of these latter components having a reversely tapered surface which cooperates with the tapered surface or surfaces on the collet to provide a self-locking frictional connection. The collet is inserted and withdrawn from the annular space by mechanical or pneumatically operated mechanisms which coact with the collet and the shaft end or work roll.

Abstract: The clutch release mechanism includes a fluid actuator having an actuator member movable by fluid pressure in a clutch release direction to release the clutch, a release bearing assembly for connection to part of the clutch, and a coupling for connecting the release bearing assembly to the actuator member. The coupling is fluid operable whereby in one condition it prevents axial separation of the actuator member and release bearing assembly by engagement of pins and a groove and, in another condition, it allows axial separation and coupling of the release bearing assembly and the actuator member by disengagement of the pins and groove.