Abstract: A throttle point for a vibration damper, comprising a damper valve carrier with a circumferential annular groove, in which an annular valve body with a variable diameter is arranged. The annular valve body forms, with a guiding face for flowing damping medium, a throttle point, a throttle cross section of which decreases in the case of an increasing flow velocity of the damping medium within the throttle point. The circumferential annular groove forming a pressure chamber which is filled with damping medium. A radially outwardly directed actuating force acts on the valve body, wherein the pressure chamber is a constituent part of a hydraulic system which has a connector to at least one working space of the vibration damper and the hydraulic connection of which to the pressure chamber can be set.

Abstract: An air guide for a ceiling-type air conditioner is applied to the ceiling-type air conditioner comprising: an indoor unit having a heat exchanger and a blower embedded therein, and having a plurality of blowing passages for discharging, to the outside, air which has passed through the heat exchanger; a plurality of inlets for receiving the air discharged through the plurality of blowing passages; and a discharge panel having an inner space, of which at least a portion communicates with the plurality of inlets, and a ring or arc-shaped opening for discharging, into a room, air which has flowed into the inner space. The air guide includes: at least two partition parts formed in parallel to the radial direction of the opening, and dividing the inner space in the circumferential direction; and a curved part connecting the at least two partition parts, and formed in an arc shape, and is detachably inserted into the inside of the opening from the outside of the opening.

Abstract: A computer system trains a predictive model. A plurality of subsets of features are selected from a dataset comprising a plurality of cases and controls and a plurality of features. Cases and controls are matched to select a plurality of case-control subsets for each subset of features, each case-control subset having similar values for the corresponding subset of features. For each case-control subset, a statistical significance of each feature of the plurality of features absent from the subset of features used to match the case-control subset is identified. A final subset of features is selected based on satisfying a statistical significance of each feature for the plurality of case-control subsets. A predictive model is trained using the final subset of features. Embodiments of the present invention further include a method and program product for training a predictive model in substantially the same manner described above.

Abstract: Piston rings are disclosed that relate to seal performance in piston containing machines such as piston driven engines. The piston rings may include a piston ring contact side for contact with a cylinder wall in which the piston ring contact side has multiple cavities configured on alternating edges of the piston ring contact side. Certain examples of these piston rings have cavities with an average depth that is less than 1/300th of the piston ring width and which collectively occupy a cavity area percentage of the piston ring contact side that is between 20% and 30% of the total area of the piston ring contact side.

Abstract: A sealing rubber composition includes acrylic rubber, artificial graphite, and coupling agent.

Abstract: A piston-integrated seal has a seal lip integrally provided in a clutch piston of a hydraulic clutch and directed to a hydraulic chamber side. In the seal lip, a main seal edge portion in a hydraulic chamber side and a sub seal edge portion in an anti-hydraulic chamber side are formed in a sliding portion in relation to the other sliding surface. In the main seal edge portion and the sub seal edge portion, an angle of an inclined surface in the hydraulic chamber side is smaller than an angle of an inclined surface in the anti-hydraulic chamber side in a un-installed state, and the angle of the inclined surface in the hydraulic chamber side in relation to the other sliding surface is approximately equal to the angle of the inclined surface in the anti-hydraulic chamber side in an installed state, thereby reducing friction difference in a sliding direction.

Abstract: The invention relates to a hydraulic damper (1), in particular for the suspension system of a motor vehicle comprising a tube (2) filled with working liquid, inside of which a slidable piston assembly (3) is placed.

Abstract: A shock absorber including a cylinder having a first chamber and a second chamber where at least one of the first chamber and the second chamber includes a fluid. A piston is configured for reciprocal movement within the cylinder and defines at least one through-hole for enabling the fluid to move between the first and second chambers. A floating disc and a floating retainer are each movably connected to the piston, the floating disc and the floating retainer defining a space between the floating disc and the floating retainer, the space having a cross-sectional area. A seal element is seated in the space and has a cross-sectional area equal to the cross-sectional area of the space where an entire surface of the seal element engages and forms a seal with an inner wall of the cylinder during the reciprocal movement of the piston.

Abstract: A shock absorber is attached coaxially with a reciprocating rod driven by a reciprocating unit for absorbing an impact force without bending the reciprocating rod. The shock absorber has a hollow rod provided with a through hole. The hollow rod is mounted within an outer cylindrical body. An accommodating space is formed between the hollow rod and the outer cylindrical body. A spring force toward one end portion side of the hollow rod is applied to the outer cylindrical body by a compression coil spring. An annular piston provided in the hollow rod partitions the accommodating space into two liquid chambers. When the impact force is applied to the hollow rod, the liquid flows from one liquid chamber to another liquid chamber through a gap, whereby a resistance force is applied to the hollow rod.

Abstract: A friction damper is proposed, in particular for drum-type washing machines with a spinning cycle, with a movable piston rod which is arranged in a housing (1) parallel to the longitudinal axis of the housing and is guided out of the housing (1), wherein the housing (1) comprises at least one plastic element (3) and at least one metal element (2) which is both producible cost-effectively and at the same time also withstands relatively high stresses. This is achieved according to the invention in that at least the metal element (2) has at least one metal with a heat conductivity of at least 150 watts per meter and Kelvin (150 W/(m*K))).

Abstract: In a vehicle-height adjustment apparatus of a motorcycle having the hydraulic jack attached to the damper, damping force characteristics of a damper are stabilized, the influence of the charged gas pressure of an oil reservoir chamber is eliminated, and the sealing performance of a hydraulic jack is reduced. In the vehicle-height adjustment apparatus of a motorcycle, a back pressure chamber is provided on a side opposite to a jack chamber, with a plunger being interposed therebetween inside a hydraulic jack, and this back pressure chamber is communicated with a hydraulic chamber inside a damper tube.

Abstract: An air damper capable of stabilizing a damping force of the air damper is obtained. When a rod member (16) is pulled out of a cylinder member (20), a suction member (60) hits against the other side surface (56) of a piston member (30) so as to close an air passage (28), and an airflow path communicating between an air chamber (26) and an outside is only orifice portions (42). On the other hand, when the rod member (16) is pushed into the cylinder member (20), the suction member (60) moves away from the other side surface (56) of the piston member (30) so as to open the air passage (28). Consequently, compared to a conventional structure in which an O-ring rolls by a friction force with an inner peripheral surface of a cylinder so as to open or close the air passage, the air passage (28) can be opened and closed as intended so as to be capable of stabilizing the damping force.

Abstract: An air damper is provided which can exhibit an appropriate braking force in accordance with an input load. There is provided an air damper including: a tubular cylinder 1 in which both end portions are opened; a piston 2 which moves within the cylinder 1; and a cap 3 which closes a one-end opening of the cylinder 1, wherein the cylinder 1 has an annular seal surface 4 formed on a circumferential surface of the one-end opening, wherein the cap is mounted on the one-end opening side of the cylinder 1 so as to be moveable or deformable along an axial direction of the cylinder 1, wherein the cap is brought into contact with or separated from the seal surface 4 in accordance with a pressure change due to a movement of the piston 2 within the cylinder 1, and wherein a first orifice 14 is opened in a base plate 12 of the cap, characterized in that: a second orifice having an inlet area smaller than the first orifice is defined between the cap 3 and the cylinder 1 during an operation of the first orifice 14.

Abstract: A stop damper including a damper member with a cylinder. A piston is moveably guided inside a receiving space of the cylinder. The cylinder has a sliding surface against which the piston rests with a sealing element. A braking force that acts upon the piston can be applied using the air pressure generated in the receiving space because the piston is displaced, the receiving space being connected to the environment via an air-conducting connection to reduce the air pressure. In order to improve the braking effect of the sliding element, the sealing element of the piston and the sliding surface of the cylinder can contact each other in at least some areas via a defined rubbing surface geometry, the peak-to-valley height of the sliding surface being <1 ?m and the peak-to-valley height of the facing surface of the sealing element being =4.5 ?m in at least some areas.

Abstract: A hydraulic damper device for retarding movement of a movable member toward a stationary member, includes a cylinder, an axially shiftable plug disposed in the cylinder to partition a receiving chamber into liquid and air compartments, a piston axially movable in the liquid compartment to divide the same into plug-side and end-side sub-compartments and having a passage, a piston rod secured to the piston and extending along the axis through the axially shiftable plug to permit axial movement of the piston. When the piston proceeds with a final stage of retarding movement, the axially shiftable plug is urged to move by virtue of an increased pressure in the plug-side sub-compartment for generating an increased counteracting force in the air compartment against the increased pressure, thereby further slowing down the retarding movement of the piston.

Abstract: A cylinder assembly includes a piston rod connected to a piston which is movably received in a cylinder and the interior of the cylinder is defined into a first room and a second room by the piston. A first groove and a second groove are respectively defined in the inside and the outside of the piston, and the two grooves are longitudinally aligned with each other. Two seal rings are respectively engaged with the first and second grooves. The first groove includes a first inner surface and the second groove includes a second inner surface. A distance is defined between two respective extension lines of the first and second grooves. Each of the two respective extension lines is defined by extending a line from the first/second inner surface of the first/second groove. The outer diameter of the piston is reduced for being used with a smaller cylinder.

Abstract: The invention concerns a pneumatic retarding device with a cylinder dividing the cylinder into a displacement chamber and a compensation chamber and including a piston with a piston rod movably supported in the cylinder and having a piston seal element wherein, upon movement of the piston, a piston movement opposing force is generated while an air leakage flow is established past the piston for damping piston movement. The piston and the piston rod are formed integrally and the piston seal element has at least two deformation zones of which one responds faster to a pressure change in the displacement chamber then the other which is subjected to the pressure change via a restrictive passage. Also, a guide system is provided with such a retarding device.

Abstract: A shock absorber comprises a sleeve, a cylindrical piston with a seal attached to the cylindrical surface of piston with two side surfaces, a rod coupled with the piston, a piston cap enclosing the sleeve on the piston's side, and a rod cap enclosing the sleeve on the rod's side. The piston and rod move within the sleeve overcoming resistance of oil/gas cross-flows from one sleeve's chamber to the other, friction between the seal and the sleeve's walls, and friction between the rod and a seal mounted in the rod cap. The proposed absorber allows increasing the resistance offered to the movement of piston thereby improving the efficiency of damping, and suppressing/avoiding auto-oscillation and resonance regimes. This is achieved by providing a number of narrowing/widening necks arranged on the sleeve's walls within regions adjoined to the caps. Different embodiments combine features conditioned by various diameter differences for the necks, etc.

Abstract: A vibration damper, comprising a damping medium-filled cylinder, in which a piston rod is guided with freedom of axial movement, where, inside a working space in the cylinder, a stop spring in the form of a circular ring is located, which, after the piston rod has reached a defined stroke position, is compressed between a stop surface on the piston rod side and an end surface forming an axial boundary of the working space, and where the stop spring also forms a boundary of a radially inner space, which is connected to the working space outside the stop spring by means of at least one radial channel. The stop surface on the piston rod side and/or the axially limiting end surface is formed by a rigid body and is provided with at least one radial channel, which extends from the radially inner space to the radially outer working space, “inner” and “outer” being defined with respect to the stop spring.

Abstract: A damping device includes a cylinder (11) in which a piston (10) is housed for reciprocable movement. The piston has a skirt (12) which expands resiliently outwardly when the piston is moved in the direction of arrow A to provide a frictional damping force. The interior of the cylinder is undercut at its distal end (13a) to allow the skirt to relax.

Abstract: The invention relates to a piston for a piston-cylinder arrangement, particularly a shock absorber piston, which includes a piston body, that has a circumferential surface. A sealing collar has an outer circumferential surface, an inner circumferential surface, a first peripheral surface, and a first sealing lip, and extends around the circumferential surface of the piston body and covers at least part of the circumferential surface in the axial direction. The first peripheral surface connects the two circumferential surfaces to each other at a first end of the sealing collar. The first sealing lip is delimited by the first peripheral surface and the outer circumferential surface, and the first sealing lip is configured evenly in the circumferential direction.

Abstract: A damper including a cylinder, a piston inserted in the cylinder, a movable member disposed in the piston to be movable in the cylinder in a length direction of the cylinder, and a weight sensor mounted on an inner surface of the cylinder, facing an end of the piston, to perceive weight loaded on the piston through contact with the movable member. When applied to a washing machine, the damper is capable of perceiving accurate weight of the laundry supplied in the washing machine.

Abstract: Oil damper for a drum type washing machine including a hollow cylinder having an oil chamber for filling oil therein, a tub holder fixedly secured to one end of the cylinder for securing the damper to a tub side, a shaft passed through, and exposed from the other end of the cylinder, a base holder fixedly secured to the shaft at an end thereof exposed to an outside of the cylinder for securing the damper to a base side of the cabinet, and a piston having a plurality of oil holes, for sliding inside of the cylinder, wherein at least one of above components is formed by plastic injection molding, thereby providing a new oil damper which reduces a production cost significantly, and has a good productivity, and high operation reliability.

Abstract: A dampening mechanism is described having a pressure tube defining a working chamber between a rod guide proximate a first end and an end cap proximate a second end. A piston is disposed within the pressure tube and divides the working chamber into an upper working chamber and a lower working chamber. A piston rod is secured to the piston. A reservoir tube surrounds the pressure tube defining a reservoir chamber between the reservoir tube and the pressure tube. At least one passage is disposed through the pressure tube between the reservoir chamber and the working chamber and a bypass valve is disposed between the piston and the at least one passage.

Abstract: Disclosed herein is a damper for use in a drum type washing machine, which can support a tub of the washing machine and absorb vibration of the tub. The damper comprises a cylinder, a piston partially inserted inside the cylinder, and a fixed damping member and movement prevention means, which are installed around an inserted portion of the piston inside the cylinder so that they are spaced apart from each other, and adapted to allow the piston to be stably supported inside the cylinder even in case that a tub of the washing machine vibrates in a non-axial direction of the cylinder and piston, thereby restricting a relative angular rotation of the cylinder and piston and preventing rubbing and collision caused between a lower end of the cylinder and the piston.

Abstract: A piston is slidably displaced inside of a cylinder tube, and damper grooves are provided on both end surfaces of the piston, which extend substantially perpendicular to the axis thereof. The damper grooves penetrate along the end surfaces of the piston, and respective dampers formed from an elastic material are installed therein. On the dampers, base members thereof are inserted into first grooves that make up the damper grooves, and guide members, which are expanded in width with respect to the base members, are inserted into second grooves that lie adjacent to and are expanded in width with respect to the first grooves.

Abstract: A string type air damper includes a cylinder formed in a tubular shape, defining a guide hole at one end portion thereof, a piston, which moves in the cylinder, a helical spring for biasing the piston toward the other end portion of the cylinder, and a string member guided from inside of the cylinder to outside thereof through the guide hole. The piston and the string member are integrally formed. Since the string member is formed integrally with the piston, unlike a method according to a related art, it becomes unnecessary to form a loop at the base end portion of the string member with a complicated work and form a hook portion at the piston and hook the base end portion of the string member at the hook portion of the piston. Therefore, the string type air damper can be very easily assembled.

Abstract: A damper includes: a cylinder: a piston rod inserted to be movable linearly in the cylinder; a guide member provided with a coupling hole to which an insertion portion of the rod member is coupled at a center thereof, and provided with first and second grooves at an outer circumferential surface thereof; a fixed damping member fitted into the first groove and adhered to an inner surface of the cylinder; and a movable damping member up and down movably fitted into the second groove and selectively adhered to the inner surface of the cylinder.

Abstract: A piston rod and a piston are installed with freedom of axial movement in a cylinder filled with a working medium, the piston dividing the working space into a space on the piston-rod side of the piston and a space on the side of the piston facing away from the piston rod. A stop disk is mounted on the piston rod in addition to the piston rests against a retainer provided on the cylinder to limit the outward movement of the piston rod during a fire.

Abstract: A piston rod with a piston is installed with freedom of axial movement in a damping medium-filled cylinder, where, as a function of the stroke position of the piston, a bypass connects the two working spaces separated from each other by the piston. The piston has at least one through-channel for at least one flow direction, which channel is at least partially covered on the outlet side by at least one valve disk, so that a first pressure-actuated surface to which pressure can be applied in the opening direction is present on the valve disk. In addition to the first pressure-actuated surface, the valve disk has a second pressure-actuated surface, which is separated from the first when the valve disk is closed and which can be actuated via the bypass, in which case the effects of the two pressure-actuated surfaces are additive.

Abstract: A high-pressure, inert gas cushion assembly for the ram or bolster of a metal stamping press includes a manifold having fluid-flow passages defined therein, along with a plurality of cylinder mounting locations each in communication with at least one of the fluid-flow passages. A plurality of cushion cylinders are located respectively in the cylinder mounting locations. Each cylinder includes a body having an inner wall that defines a bore of diameter D. A piston is located in the bore and includes opposite inner and outer faces, wherein the outer face is oriented outwardly relative to the bore and manifold. A fluid seal is supported on the piston and is slidably engaged with the wall defining the bore. One or more bearings are supported on the piston and slidably engaged with the inner wall that defines the bore. The bearing(s) support the piston slidably in the bore for reciprocal sliding movement between extended and retracted positions.

Abstract: A method and an arrangement in an energy-accumulating piston-cylinder arrangement (A) has a piston/piston rod part (2), guide/end (3) and tubular casing (1). The casing (1) is provided with a fracture or sprain mark (7) in order to initiate a controlled deformation of the casing in the event of a load that produces a stress in excess of a sprain or fracture limit, or of repeated cyclical stressing that gives rise to material fatigue, so that an excess pressure in the arrangement (A) is discharged past the deformed casing.

Abstract: A piston for a piston-cylinder arrangement, in particular a shock absorber piston exhibiting a piston body (6) provided with one peripheral web (12) protruding from the peripheral surface, disposed on said peripheral surface in both areas, each of which defining one end of the piston. Supporting connector elements (10), which extend longitudinally in the direction of the other end of the piston, are arranged successively at a distance from each other in a parallel manner contiguous to the peripheral web, whereby each two adjacent supporting connector elements (10) define a groove-shaped recess (11) and are provided with a collar-shaped seal (9) made of a thermoformable sealing material, which is formed on the piston body (6) in such a way that the peripheral webs (12) as well as the supporting connector elements (10) are incorporated into the material of the collar-shaped seal (9) over only a portion of their height.

Abstract: The air damper includes a piston reciprocating within a cylindrical housing. The piston includes a lip seal which is coated with a minimum of 0.5%/seal part weight graphite powder/molybdenum disulfide. This provides for increased smoothness of operation of the air damper, particularly at low speeds.

Abstract: In a master/slave cylinder system for clutches or brakes, primary seals have bevels which interact with similar bevels of formations on housings of the respective cylinders. Along with the lowest possible friction in the region of the sealing lips, this permits carrying out uncomplicated pressure/negative-pressure filling in the case of the master cylinder. The primary seals slide by the wedge of effects in the direction of the pressure on the bevels of the annular formations and reduce the annular bearing face of the sealing lip in a frictionally optimized manner.

Abstract: A controlled equilibrium device comprising a housing; at least one spring, each at least one spring having a spring stiffness; and a load leveling device movable through the housing between a first maximum displacement position and a second maximum displacement position, the load leveling device comprising a deadband displacement zone defined between a first deadband displacement threshold and a second deadband displacement threshold, the displacement required to reach the first and second deadband displacement thresholds being less than the displacement distances required to reach the first and second maximum displacement positions, the at least one spring stiffness being substantially constant when the displacement of the load leveling device is within the deadband zone, the stiffness of the at least one spring being modified to a second stiffness when the load leveling device is equal to or beyond either the first deadband displacement threshold or the second deadband displacement threshold.

Abstract: The invention relates to a piston-cylinder arrangement, especially a shock absorber piston, comprising a piston body fitted with a peripheral web protruding from the peripheral surface in a section adjacent to the end of the piston to which support webs are attached, said web extending parallel and spaced in relation to each other in longitudinal direction towards the other end of the piston. Two adjacent support webs limit a groove-shaped recess, said webs being open on the ends opposite the peripheral web in longitudinal direction. The piston also comprises a collar-shaped sealing element made of thermoformable plastic material that is formed on the piston body in such a way that only part of the height of both the peripheral web and the support webs is formed in the material of the collar-shaped sealing element.

Abstract: A hydraulic damper includes a friction member arranged inwardly with respect to a seal member and mounted to one of a cylinder and a piston rod. The friction member slidably contacts another of the cylinder and the piston rod to produce friction greater than that produced at the seal member.

Abstract: A spring bushing, in particular for prestressing a piezoelectric actuator in a valve for controlling fluids, is disclosed, which is a one-piece deep-drawn part, which is hollow and at least approximately cylindrical. The one-piece body is provided with a number of openings distributed over the circumference and length of the body.

Abstract: The air damper includes a piston reciprocating within a cylindrical housing. The piston includes a lip seal which is made of rubber or thermoplastic elastomer impregnated with a minimum of 3% molybdenum/seal part weight, or a minimum of 2% polytetrafluoroethylene or silicone/seal part weight or a minimum of 1% wax/seal part weight. The lip seal is coated with a minimum of 0.5%/seal part weight graphite powder/molybdenum disulfide. The housing is made with a minimum of 2% silicone impregnated thermoplastic or a minimum of 2% moly sulfide impregnated thermoplastic. This provides for increased smoothness of operation of the air damper, particularly at low speeds.

Abstract: A hydraulic piston assembly includes a cylinder assembly having an inner bore that defines an internal space. A piston is disposed in the space and divides the space into first and second fluid chambers. The piston comprises a side annular surface, a first surface adjacent the first fluid chamber and a second surface adjacent the second fluid chamber. The side annular surface comprising a first portion, a second portion and an annular groove between the first and second portions. The first portion has a maximum diameter that is less than the maximum diameter of the second portion. A sealing member is positioned within the annular groove. In some embodiments, the cylinder assembly forms part of a dampening system that interrelates at least two suspension assemblies. Methods for assembling the hydraulic piston assembly are also disclosed.

Abstract: The invention relates to a piston-cylinder arrangement, especially a shock absorber piston, comprising a piston body fitted with at least two peripheral webs on its peripheral surface, said webs limiting a groove and also including a collar-shaped sealing element made of thermoformable plastic material that overlaps the webs. Said piston also comprises axial passage channels in the piston body that are closed by throttle valves opening on one side and at least one radial hole connecting at least one passage channel to the groove formed between two webs.

Abstract: An air damper for a movably supported structural part in automobiles comprises a hollow cylinder closed at one end thereof, a closure cap mounted on the other end of the cylinder, a piston slidably guided within the cylinder, an annular recess at the circumference of the piston, and an annular sealing ring in the recess. The block-like sealing ring is made of a thermoplastic elastomer coated with a layer which has the same static and sliding frictions with the inner wall of the cylinder and the bottom of the recess. A coil spring is placed between the closure cap and the piston. A piston rod of the piston has an elongated rib contacting the spring when the spring is in a relieved state.

Abstract: A dashpot piston in halves, the face of each resting against that of the other. The piston can be fastened to the end of a piston rod either directly or by way of a connector. Each half (1 & 2) is provided with a depression (7) along the circumference remote from the face of the other, creating a continuous groove (8) with a shorter diameter and accommodating a piston-assembly ring (9). Manufacture is facilitated by the inclusion of at least one resilient supporting ring (11) between the piston-assembly ring and the base of the groove.

Abstract: The invention relates to a piston-cylinder arrangement, especially a shock absorber piston, comprising a piston body fitted with at least two peripheral webs on its peripheral surface, said webs limiting a groove and also including a collar-shaped sealing element made of thermoformable plastic material that overlaps the webs. Said piston also comprises axial passage channels in the piston body that are closed by throttle valves opening on one side and at least one radial hole connecting at least one passage channel to the groove formed between two webs.

Abstract: An axially movable switching sealing ring within a groove having an axial width greater than the axial width of the ring, in particular in the piston of a piston-cylinder unit, where the switching sealing ring has sealing surfaces on its upper side surface, lower side surface and radial outer wall surface in each instance. The upper and lower side surfaces each have an axially relieved section adjacent the radially outer diameter of the ring, so that the upper and lower sealing surfaces are formed optimally by only part of the upper and lower side surfaces.

Abstract: The damper includes a housing assembly and a piston assembly with reciprocates within the cylindrical walls of the housing assembly. The piston assembly is formed from two disks which are spaced apart by a spacer with includes radially and longitudinally oriented planar projections which extend to a position radially inward of a periphery of the disks. The distal ends of the projections form longitudinally oriented surfaces upon which a toroidal seal slidably rides. At least one of the longitudinally oriented surfaces includes an air communication groove in communication with a groove on the trailing disk which extends to the periphery of the trailing disk. When the piston assembly is retracted from the housing assembly, the seal engages the leading disk thereby inhibiting air from flowing through the air communication groove thereby effectuating damping.

Abstract: A number of embodiments of piston sealing arrangements for shock absorbers having a hydraulic cylinder in which a piston is slidably supported to define a pair of fluid chambers. The piston is provided with a peripheral groove in which a sealing piston ring is provided. A number of different communicating passage arrangements are formed in the piston ring that communicate the exterior surface of the piston ring which engages the cylinder bore with the interior surface of the piston ring which faces the ring groove so as to balance the pressure therebetween. In each embodiment a seal is provided between the piston ring groove and the piston ring so as to preclude fluid flow from one fluid chamber to the other through the piston ring groove and the communicating passage arrangement.