Abstract: A door control apparatus and methods for controlling a door motion device for a hinged door and, optionally, illuminating a designated area on the floor. During the time the designated area is illuminated, a person can expect that the door will not close. The door control apparatus may include control circuitry, and a sensor, and optionally a light emitter and/or a sound emitter. The sensor detects a person proximate to the door and signals the control circuitry upon a detection event. The light emitter is also connected to the control circuitry. Upon a detection event, the control circuitry signals the light emitter to produce light and signals the door motion device to hold the door open. The light emitter directs light to form an image on the floor in the designated area. The light emitter may be, for example, a laser generator or a light emitting diode lamp.

Abstract: A spring power setting indicator for a closing apparatus for a wing such as a door or window, including a closer housing in which a compression spring is disposed. The spring power setting indicator includes a collar defining a threaded opening adapted to engage an adjustment screw for adjusting the bias of the compression spring. The collar may be substantially disc-shaped, and has a peripheral side that defines an annular channel in which a magnetic ball is disposed. An indicator housing with indicia of closer size may be mounted to the closer housing. Another magnetic ball may be disposed in the indicator housing. The magnetic balls are attracted to each other, and the ball in the indicator housing follows the ball in the channel as the collar moves in response to turning of the adjustment screw, permitting external reading of closer size with the indicia based on ball position.

Abstract: A door closer comprises a spindle journaled in a housing and connected to turn with a door. Upon rotation of the spindle, a cam carried by the spindle effects linear movement of a slide assembly relative to the housing. A piston is connected with the slide assembly. Passages are provided in the housing to permit flow of fluid in the housing in response to movement of the piston. A spring assembly disposed outside of the housing is connected to the piston. Rotation of the spindle and cam during door opening moves the slide assembly, thereby compressing the spring assembly for storing energy for urging the piston and the slide assembly in the opposite door closing direction.

Abstract: In automatically opening and closing an opening/closing member with regard to an opened/closed member via a hinge, a drive for this purpose mechanically independent from the opened/closed member is mounted on a side of the opening/closing member and so designed that it rotates together with the opening/closing member when it opens and closes; where the opened/closed member is in particular a main body of office equipment and the opening/closing member an original cover, and the hinge comprises at least a mounting member mounted on a side of the main body and a supporting member of original cover rotatably mounted on the mounting member. The drive mechanically independent from the main body is mounted on a side of the original cover and so designed that it rotates together with the original cover when it opens and closes.

Abstract: A track and arm type door controller assembly. A channel member and a gripping member each having a toothed surface are provided, with the gripping member slidably disposed in the channel member. When the pin is retracted, the gripping member teeth are spaced from the channel member teeth, and the gripping member may freely slide along the track. When the pin is advanced, the teeth engage and the gripping member is in a fixed, non-sliding position. An elongated spring and a spring clip or a latch may be provided that releasably engage to hold the door open. A set screw may adjust the tightness of the engagement of the elongated spring and spring clip of latch. A friction assembly may be provided to slow the motion of the door.

Abstract: A hydraulic door closer including an elongated housing, a connection rod extending into the housing, a piston secured at an inner end of the connection rod within the housing and a spring positioned within the housing about the connection rod. A throttle valve and a check valve are formed in the piston and define a throttle-valve fluid passage and a check-valve fluid passage, respectively. Both fluid passages are configured to be open for passing a fluid through the valves and closed to stop the fluid flow. The check-valve fluid passage is larger than the throttle-valve fluid passage and is closed during door closing for restricted fluid flow slowing the door motion. A stopping/holding mechanism includes a piston groove, a rod groove and a positioning pin disposed between the piston and the connection rod. The piston groove is defined by the piston for retaining the entire positioning pin during door opening/closing motion.

Abstract: An automatic door shutter includes a stationary plate and a pressing plate pivotally combined together and with a resilient body located therebetween. Additionally, a pivot of the stationary plate has a sliding notch accepting an S-shaped resilient sheet abutting the pressing plate. By attaching the stationary plate and the sliding base to a door frame and a door respectively, the resilient body pushes the pressing plate to shut the door automatically. When the door is pushing to fully open, the pressing plate pivots to the stationary plate, and the S-shaped resilient sheet slides in the sliding recess and is compressed to deform to become U-shape. Until the door is fully open, the resilient sheet which is U-shaped causes an outward pushing force to the pressing plate to keep the door open constantly.

Abstract: A refrigerator comprises a body defining a refrigerated enclosure, a door movable between a closed position and an open position, a hinge comprising a first member coupled to the body and a second member coupled to the door and pivotably coupled to the first member, and a closure mechanism configured to provide a varying force to the door depending on the position of the door relative to the body. The closure mechanism includes a guide slidably mounted in a slot on the first member, a biasing mechanism coupled to the first member, and a closer arm coupled to the door and to the biasing mechanism through the guide.

Abstract: A hinge mechanism 29 that rotatably provides a luggage board 27 and an auxiliary board 28 continuously with each other while interposing an integral hinge 13 therebetween, in which a space portion S is provided between mutually opposite end surfaces 20 and 21 of the luggage board 27 and the auxiliary board 28, wherein a restoring force generation portion 30a of a spring member 30 is housed in the space portion S, and in addition, both end portions 31 and 32 of the spring member 30 are fixed to the luggage board 27 and the auxiliary board 28, respectively.

Abstract: A door closer includes a housing; an output shaft supported by the housing and rotatable in opposite door opening and closing directions; a cam disc disposed in the housing and mounted on the output shaft; a damping piston disposed in the housing; an opening piston disposed in the housing; first and second force transmission rollers; and two fixing bolts extending in the axial direction of the housing and transversely to the axis of the output shaft. The fixing bolts being disposed on two opposite sides of the output shaft, respectively. Each of the can disc and the first and second force transmission rollers has a circumferential recess or comprises two pieces, the fixing bolts being disposed in the recesses or between the respective two pieces so that each of the damping piston and the opening piston is prevented from rotating with respect to the cam disc.

Abstract: A safety closing system for a shaft door panel of an elevator installation brings the shaft door panel into a closed setting in the absence of an opening force. The safety closing system includes a spring which is stressed in the open setting of the shaft door panel and a drive mass which is subject to gravitational force, the spring and mass being coupled by a flexible tension element with the shaft door panel.

Abstract: A mechanism and method for operating a track-mounted door is disclosed. The mechanism includes a pair of side drums that are connected by first cables to the bottom of the door. The side drums are coaxially mounted on a shaft for simultaneous rotation with a pair of cable drums. The cable drums are connected to high pressure gas struts by second cables. Each second cable is carried around a shiv wheel that slides along a guide track as the second cable moves. Each shiv wheel is operatively connected to one of the gas struts. As the shiv wheel moves along the guide track toward the cable drum, the gas strut is charged. As the shiv wheel moves away from the cable drum, the gas strut is discharged. A standard electric motor and screw driven lift-arm is used to initiate the opening and closing of the door. The charged gas strut stores sufficient energy to overcome friction and gravity to assist the electric motor and lift-arm to open the door.

Abstract: A security door closure system for cruise ships and other similar public entrance points to prevent terrorist attack or ship take-over is needed. Cruise ship passenger and ship provisioning entrance gangplanks pass through large hydraulically operated shell doors. The gangplank must be removed to close the shell door. The quick close security door system (Door-Gate) is a portable bullet resistant rapid close door system that is placed in conjunction with the gangplank or other entry system, which when closed prevents forced entry. A single lever either remotely or manually operated immediately closes the doors, which then cannot be forced opened from the entrance side.

Abstract: An object is to provide a storage in which a door can be attached using a similar hinge without any trouble even at a time when the door is rotated in reverse and attached, the storage includes a main body; a pair of upper and lower hinges attached to the main body; and a door having one side rotatably supported by both the hinges to openably close an opening, at least one of the hinges has two attachment portions which cross each other at right angles in a corner and which are attached to the main body, and two pivot support portions raised from both the attachment portions and provided with a rotary shaft rotatably supporting the door, and both the attachment portions and both the pivot support portions have a shape which is symmetric with respect to a line passing through the corner and forming an angle of 45° with respect to both the attachment portions.

Abstract: A door closer comprises a spindle journaled in a housing and connected to turn with a door. Upon rotation of the spindle, a cam carried by the spindle effects linear movement of a slide assembly relative to the housing. A piston is connected with the slide assembly. Passages are provided in the housing to permit flow of fluid in the housing in response to movement of the piston. A spring assembly disposed outside of the housing is connected to the piston. Rotation of the spindle and cam during door opening moves the slide assembly, thereby compressing the spring assembly for storing energy for urging the piston and the slide assembly in the opposite door closing direction.

Abstract: A ranch gate arm assembly which incorporates a gate arm that is mounted to allow swivelling about a longitudinal pivot when an external man or machine force is applied to either side of the gate arm thereby inducing the gate arm to swing out, and two torsion springs, one assembled on each side of the ranch gate arm which push against correlating sides of the gate and push the gate back to a center position after the external force has passed completely through the opening. This gate arm assembly is equipped with a smoothing release assembly, which eliminates the jolt force caused by the quick returning of the gate assembly to the center position that the gate was originally in before the external force was applied.

Abstract: A sliding door includes a track having a longitudinal channel to slidably receive a carrier, a door panel secured to the carrier, a bracket attached to one end portion of the track and having a pathway and a pulley, and a recovering device having a cable. The cable has one end secured to the track, and a middle portion slidably engaged through the pathway of the bracket, and the other end secured to the carrier. The door panel and the carrier are movable along the track, and the cable is engageable around the pulley of the bracket, to bias and to force the door panel and the carrier backward toward the one end portion of the track when the door panel is released. One or more spring members may be engaged in the cable.

Abstract: A door closer comprises a spindle journaled in a housing and connected to turn with a door. Upon rotation of the spindle, a cam carried by the spindle effects linear movement of a slide assembly relative to the housing. A piston is connected with the slide assembly. Passages are provided in the housing to permit flow of fluid in the housing in response to movement of the piston. A spring assembly disposed outside of the housing is connected to the piston. Rotation of the spindle and cam during door opening moves the slide assembly, thereby compressing the spring assembly for storing energy for urging the piston and the slide assembly in the opposite door closing direction.

Abstract: The present invention relates to an auto-door device and particularly to an auto-door device used for a hinged door panel, and the auto-door device includes an axle pivotally coupled to a door panel and an axle resilient hinge; characterized in that the axle is coupled to the one-way transmission mechanism at the same time, and the output end of the one-way transmission mechanism is linked to the magnetic damper mechanism. By changing a regular resilient damper mechanism to the magnetic damper mechanism, the auto-door device in accordance with the present invention can control the door shutting speed for an even, constant and stable movement and adjust the speed of opening a door arbitrarily without being affected by the external factors such as different seasons and temperature. The present invention has the advantages of being leakage free, pollution free, safe, and reliable as well as a long life of use.

Abstract: A door holder and a door closer and, in particular, and improvements in door holders and closers for use in screen doors, storm doors or any type of door which has the need for a device for maintaining the door in a particular orientation and/or for self-closing of the door.

Abstract: A door closer includes an anchor assembly for mounting on a door frame, an actuator assembly for mounting within the thickness of a door which is hinged for movement between open and closed positions, an operating member coupled by a linkage to the anchor assembly and mounted for a range of movements between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member, a damper mechanism operatively connected to the operating member so as to damp movement of the operating member at least in a direction towards the retracted position, and a resilient thrust device arranged to exert an increased driving force on the operating member over a defined part of its range of movement as the operating member approaches the retracted position.

Abstract: A device for closing a door, including a spring element, an attachment element for fixing the device to a door, and an actuation element. The actuation element and the attachment element are linked at opposite ends of the spring element in such a way that, when the door is opened, differential rotation of the actuation element and the attachment element cause the spring element to be stretched and the energy stored in the spring element causes the door to close automatically. The actuation element is embodied as a support element that can be placed against the door frame or the adjacent wall regions in a supporting manner, and the attachment element can be removably mounted on an edge of the door without the use of fasteners or adhesive.

Abstract: A mechanical door closer (10) that includes a spring (20) mounted in a track (13) to urge the door (11) to a closed position. A brake assembly (24) controls that rate at which the door (11) closes. The brake assembly (24) includes a brake hub (25) that has ramp slots (32) that receive balls (33) that engage a braking shell (34) to cause the braking assembly (24) to frictionally engage the track (13) to thereby control movement of the door (11).

Abstract: A spring connecting apparatus is disclosed for use in an exercise apparatus that has one or more springs fastened between a movable member and a stationary member. The connector apparatus is adapted to fasten one end of a spring to one of the members. This apparatus includes an elongated connecting member having a head end and a foot end, a polymer stopper body adapted to fit within one end of a coil spring, the body having an axial bore through which the foot end of the connecting member extends, and a washer disc on the connecting member between the polymer stopper body and a deformed section of the connecting member near the foot end.

Abstract: A mechanism and method for operating a track-mounted door is disclosed. The mechanism includes a pair of side drums that are connected by first cables to the bottom of the door. The side drums are coaxially mounted on a shaft for simultaneous rotation with a pair of cable drums. The cable drums are connected to high pressure gas struts by second cables. Each second cable is carried around a shiv wheel that slides along a guide track as the second cable moves. Each shiv wheel is operatively connected to one of the gas struts. As the shiv wheel moves along the guide track toward the cable drum, the gas strut is charged. As the shiv wheel moves away from the cable drum, the gas strut is discharged. A standard electric motor and screw driven lift-arm is used to initiate the opening and closing of the door. The charged gas strut stores sufficient energy to overcome friction and gravity to assist the electric motor and lift-arm to open the door.

Abstract: The present invention relates to a hold-open apparatus for controlling the position of a door, preferably a screen door or storm door. The apparatus is used in conjunction with a piston assembly and can maintain a door in a predetermined open position, such as about 45° to about 100° in relation to a closed position. In a preferred embodiment, the apparatus can automatically lock and/or unlock when the door reaches predetermined positions. The apparatus advantageously can be retrofitted to existing door assemblies.

Abstract: A door closing mechanism, involving a shaft rod that moves in relation to, and is installed inside a tube unit. On the shaft rod is an open/close unit.

Abstract: The invention provides a retracting apparatus of a sliding rail in which a self locking state is not cancelled without intention, a structure and an adjustment are simple, and a cost is inexpensive.

Abstract: An automatic door closer for a sliding door. The closer has a reel with a cable extending around a pulley on the end of the rod of a return mechanism. In preferred embodiments, the return mechanism is an oil dammed gas spring or a magnetic spring. A spool rotates on a common shaft with the reel and is wound with a flat tape which is attached to the door frame. The reel, spool, return mechanism and cable are attached to the door so that application of an opening force will cause the cylinder rod to retract. Upon release, the stored energy will cause the rod to extend, rotating the reel and spool to wind the tape onto the spool applying a controlled rate closing force. The spool has a core with a greater diameter than the core of the reel so a mechanical advantage exists between the spool and reel and friction is reduced.

Abstract: A door closer includes a housing having one or more bulges, a shaft rotatably received in the housing and having an axle, and one or more resilient rings engaged between the shaft and the housing. The bulges of the housing may be engaged with the resilient rings for preventing the shaft from moving axially relative to the housing. An adjustable spring biasing device may apply a spring biasing force between the housing and the shaft for recovering the shaft relative to the housing. One or more spring biased projections may limit the movement between the shaft and the housing.

Abstract: A self-closing safety gate hinge comprises a bracket, a bottom seat, a top seat and a hinge pin. The bracket is attached to a top of a gate post. The bottom seat is attached to one side of the bracket and an inclined top surface is cambered on the bottom seat. A through hole is defined vertically through the bottom seat. The top seat has an inclined bottom surface corresponding to the inclined top surface and is attached to one side of a gate at top. A stepped through hole is defined vertically through the top seat. The hinge pin is mounted through a spring and the through holes and is held in place by a C-clip.

Abstract: A sliding door closer assembly including an elongated anchor bracket that is attached to a wall section above the trailing edge of a sliding door. One end of a spring is attached to the anchor bracket at a selected point along the length thereof, and the opposite end of the spring is attached to the leading edge of the sliding door. Upon opening the sliding door, the spring is tensioned between the stationary anchor bracket and the advancing edge of the sliding door, and upon release of the sliding door, the tensioned spring pulls the sliding door back into the closed position as the spring returns to the non-tensioned configuration.

Abstract: An assembly (50) adapted to a reciprocative door closer device (10) and contingent door (62), the device (10) comprising a rod (16) and a body (12) having a biasing means (11) normally operating to comprise decreasing actuation and causing the rod (16) and door (62) towards a closed position (62-A); the assembly (50) including as extensible bracket (50-A) joined to a fixated bracket (50-B) and a spring means (54) capable of providing a counter biasing means (55) normally operating as substantially inactive, unless, said assembly (50) detects an excessive inward force (11-B) as exceeding said device (10), wherein said assembly (50) responsively opts to regulate the a increasing outward actuation (55-B) towards the closed position (62-A) and a decreasing inward actuation (55-A) towards the opened position (62-B).

Abstract: A reinforcement plate for use in attaching a doorjamb bracket to a doorjamb, the plate member having an aperture through which the arm of a conventional doorjamb bracket may be inserted. A plurality of holes in the plate member are available for receiving fasteners to secure the reinforcement plate to the doorjamb. The base of the conventional doorjamb bracket is received within an chambered area in the plate member so that the reinforcement plate lies substantially flush with the surface of the doorjamb. At least one opening in the reinforcement plate is positioned and shaped to allow a fastener to extend simultaneously through both the reinforcement plate and a hole associated with the doorjamb bracket so as to simultaneously attach both the reinforcement plate and the doorjamb bracket to the doorjamb.

Abstract: A door closer comprises an actuator assembly (20) adapted for fitting within the thickness of a door and an anchor member (10) adapted for fitting in a door frame in opposed relation to said edge face of the door. An operating member (30) is driven by spring means (45) and coupled to said anchor member (10) to draw the door towards the door frame. An adjustable fluid-filled damper (50) is coupled to said operating member (30) and arranged to provide variable regulation the rate of movement of the operating member under the force of said spring means (45). Resilient thrust means (85) are arranged to exert an increased driving force of said operating member (30) and adjustable control means (100) are provided whereby said thrust means (85) is operative to augment the driving force to said operating member (30) over a defined but variable part of said range of movement corresponding to movement of the door over the final part of its movement into its closed position.

Abstract: This is a door closing mechanism, involving a shaft rod that moves in relation to, and installed inside a tube unit. On the shaft rod is an open/close unit. Inside the tube unit and matching the shaft rod is a catch unit. With interacting forces of the catch unit and open/close unit, the shaft rod can be extended out of the tube unit and positioned, or automatically retract inside the tube unit, so the door joined to the shaft rod can swing to position or be automatically closed.

Abstract: A gate closer apparatus is provided in the form of a coil spring arranged to be installed onto a selected one of the corresponding, hinge-mounting, vertically extending gate post or gate frame members of a fence gate arrangement, the coil spring member fixedly mounted at one of its ends thereto and extends and encircles a portion of the selected vertical member.

Abstract: A check mechanism for a motor vehicle door includes a housing secured to either the vehicle frame or the door and a check arm secured to the other one of the vehicle frame and the door. The door check extends into the housing through an opening in the housing. A pair of opposed guides are located within the housing and engage opposite sides of the check arm. Each guide has a generally V-shaped portion, in cross-section, engaging the check arm to generally form a line contact between the guide and the check arm. Spring members such as elastomeric springs bias the guides toward each other and the check arm. The guides and the check arm are adapted to resist movement of the closure relative to the vehicle frame when the guide engages predetermined locations of the check arm. When the door is moved relative to the frame, the guides slide along the exterior surface of the check arm.

Abstract: A door closer with an oblong, one-piece body such to achieve a compact and aesthetic unit which can be produced with a minimum material consumption. The door closer has lateral faces which each have a curvature and/or bevel that shapes towards each other, which curvature or bevel starts at the lower surface and ends at the upper surface of the door closer. The door closer also has bearing blocks that are built between their fronts and the lateral faces ascending from the body's lower surface.

Abstract: An assembly (50) adapted to a reciprocative door closer device (10) and contingent door (62), the device (10) comprising a rod (16) and a body (12) having a biasing means (11) normally operating to comprise decreasing actuation and causing the rod (16) and door (62) towards a closed position (62-A); the assembly (50) including a hinge bracket (50-A) joined to a fixated bracket (50-A) and a spring means (54) capable of a ligamentous movement (55) normally operating as substantially inactive, unless, said assembly (50) detects an excessive inward force (11-B) exceeding said device (10), wherein said assembly (50) responsively opts to regulate increasing actuation towards the closed position (62-A) without cause to said rod (16), to dampen, protect, and compensate said excessive force (11-B) and return said device (10) and door (62) towards normal operation.

Abstract: A control mechanism for use with a door closer having a pinion shaft. The control mechanism comprises a coiled torsion spring around the shaft with a free end of the spring lying along part of a strap. The strap is connected to the shaft and normally held in tension, in use, by its connection to a movable hydraulic piston of the door closer which is biased in one direction. On normal closing of the door, in use, the strap remains tensioned and the spring is thus prevented from tightening on the shaft. However, if an external closing force is applied to the door, the strap becomes untensioned, thereby allowing the spring to tighten about the shaft to retard its angular door closing movement.

Abstract: A door closer includes a cylinder and a piston sliding along the cylinder with a piston rod extending from the cylinder, with the closer mounting at one end to the door and at a second end to the door frame. The door closer has a speed adjustment know extending from a first end for varying the closure rate. Adjustable mounting brackets provide for flexibility in mounting configurations and closing force. A door lock maintains the piston in an extended position and keeps the door open. The lock includes a washer sliding on the piston rod in a first position and locking the rod at a second position. The washer has a tab that engages an angled surface in the first position to prevent locking engagement with the piston rod. A rotatable end cap rotates the washer between the locked position and the unlocked position.

Abstract: A gear driven dial indicator is used to indicate the door closer size for a door closer having an adjustable closing force. A drive gear is attached to the door closer adjustment screw. In the preferred embodiment, this drive gear engages a ring gear which is formed as part of the dial indicator. As the door closer adjustment screw is turned to change the door closer size, the drive gear turns with the adjustment screw. The drive gear then turns the planetary gear which turns the dial indicator, thereby changing the indicated size of the door closer.

Abstract: In order to provide a closing device for an original cover in which a spring case is not cracked or broken during use even if zircon by which the spring case can be cheaply manufactured and which has excellent mechanical characteristics is especially used, the closing device has the spring case made of a synthetic resin provided for either an attaching member attached to a machine body or a supporting member for holding the original cover rotatably connected to the attaching member via a hinge pin and the rotation moment of the original cover attached to the supporting member is controlled by using a compression force of a compression coil spring housed in the spring case, wherein a reinforcing frame member made of a metal for reinforcing the spring case is attached to the spring case.

Abstract: A door closer actuated by an eccentric cam plate includes a one-piece piston that is displaced axially by the rotation of the eccentric cam plate. The one-piece piston includes a damping piston portion located axially on one side of the eccentric cam plate and a spring support element located on the opposite side of the eccentric cam plate. The one-piece piston incorporates in a unitary piece both functions of a separate damping piston and spring support element to increase the relative efficiency of the door closer.

Abstract: The invention relates to a design for covering and protecting an overhead door spring assembly from the coercive and deteriorating effects caused by the environment that overhead spring assembley's operate in. This includes preventing rust accumulation and deterioration of the spring assembly. The invention includes a tubular telescopic cover and bearing for a spring assembly that is water resistant and prevents rust from accumulating and dripping on vehicles below the door.

Abstract: An automatic closure assembly for a sliding panel, particularly of the screen door type, is disclosed. One or more power springs, operable in their linear ranges are mounted within a compact housing configured for ready attachment to a surface adjacent the sliding panel. The springs apply tension to a cord wound on a take-up reel within the housing. One end of the cord is screwed to the sliding panel such that as the panel is moved in an opening direction, the power spring(s) are wound in tension to apply closure forces to the panel. Different selections are provided for enabling an operator to select a plurality of different discrete tension forces to be applied by the closure assembly to the sliding panel.

Abstract: An assembly is arranged to include a tensioning means mounted within a housing structure. The assembly attaches to the head of an installed door hinge pin in order to store energy into such attachment to cause the door to close after having been opened then released, by reason of extended ends of the tensioning means interacting against the opposing door and wall.

Abstract: A device for closing a sliding door comprises a pair of slidable telescoped tubes. The device is secured at its outer ends to the sliding door and to a supporting door frame. A compression spring is located within the tubes urging the sliding door to return by itself from its open to its closed position. A string extends between the end portions of the tubes to prevent the tubes from being separated and a clamping means is adapted for locking the sliding door in any desired open position.

Abstract: A pneumatic door closer has an elongated cylinder with a bore extending axially thereof and end walls, and a piston is slidably reciprocable within the bore. The piston is integrally fabricated of a synthetic resin with a generally circular cross section, and it has a circumferential groove adjacent one end thereof providing a neck portion dividing the axial length thereof into a head portion and a body portion. The groove has a generally radially extending wall surface on the head portion, an outwardly diverging wall surface on the body portion, and an axially extending bottom wall surface. The head portion has at least one passage extending through the head portion into the groove to allow air to flow therethrough. A sealing ring of resiliently deformable material is disposed in the groove and is of greater diameter than the piston so as to project outwardly thereof.