Abstract: A spring brake actuator for a commercial vehicle includes a service brake portion (4) and a spring brake portion (6) that has a housing (8, 108) with a first end (10, 110) proximal to the service brake portion (4), a wall section (12, 112) extending from the first end (10, 110), a second end (14, 114) distal to the service brake portion (4), and a locking mechanism (16, 116) for locking the first and second ends (10, 110, 14, 114) to the wall section (12, 112). The locking mechanism (16, 116) is arranged between the wall section (12, 112) and the second end (14, 114) of the housing (8, 108).

Abstract: A brake actuator assembly including a pressure plate presenting an opening, a push rod that is coupled to the pressure plate, a diaphragm that is coupled to the pressure plate, and a retainer that engages the push rod. The push rod has an outer surface and at least one protrusion extending outward from the outer surface. The retainer engages the protrusion such that at least a portion of the diaphragm is positioned between the pressure plate and the retainer.

Abstract: A spring brake actuator is for braking a wheel of a vehicle. The spring brake actuator has an axially elongated housing having a parking brake chamber and a service brake chamber; a main compression spring in the parking brake chamber; a flexible diaphragm in the parking brake chamber; and a pressure plate in the parking brake chamber, the pressure plate located axially between the main compression spring and the flexible diaphragm. The flexible diaphragm has a contoured portion that inhibits radial shifting of the pressure plate with respect to the flexible diaphragm.

Abstract: A pneumatic brake actuator has a housing and a divider that divides the housing into a spring chamber containing a spring and a pressure chamber. The divider has an opening that receives an end of an actuator tube. A bearing that is positioned within the opening in the divider is joined to both the divider and the actuator tube. A caging bolt has a first end positioned within the actuator tube and extends from the first end through openings in the bearing and housing to a second end positioned outside of the housing. The connection between the bearing, divider and actuator tube contains the spring within the housing in the event that the housing and/or divider fails. The divider can be a piston or a diaphragm and pressure plate. The bearing can be joined to either of the divider and actuator tube with threads and/or by welding.

Abstract: This invention is related to a service brake chamber manufactured with a composite pressure housing and a non-pressure housing, used in the air brake system of heavy vehicles such as trucks, trailers lorries and buses and a connection method of pressure housing and non-pressure housing forms this chamber.

Abstract: A deflection assembly for a vehicle including a vehicle component to be fastened or connected to a vehicle body. A connecting member extends through the vehicle component in an axial direction and is used for fastening the vehicle component to the vehicle body. A fastener is arranged on the connecting member axially in front of the vehicle component. To optimize a deformation zone of the motor vehicle a deflection element is arranged on the connecting rod axially in front of the nut. The deflection element having, in one disclosed example, a cross-section that increases at least in sections in axial direction towards the vehicle component. In addition, the deflection element may include an outer surface extending obliquely to the axial direction of the connecting member.

Abstract: A pneumatic brake actuator has a housing and a divider that divides the housing into a spring chamber containing a spring and a pressure chamber. The divider has an opening that receives an end of an actuator tube. A bearing that is positioned within the opening in the divider is joined to both the divider and the actuator tube. A caging bolt has a first end positioned within the actuator tube and extends from the first end through openings in the hearing and housing to a second end positioned outside of the housing. The connection between the bearing, divider and actuator tube contains the spring within the housing in the event that the housing and/or divider fails. The divider can be a piston or a diaphragm and pressure plate. The bearing can be joined to either of the divider and actuator tube with threads and/or by welding.

Abstract: A combined service brake cylinder and spring brake cylinder for brake systems of vehicles is provided, wherein a bayonet coupling is configured between the spring brake cylinder and an intermediate wall. The bayonet coupling has locking segments protruding radially outward on an end-side edge of a wall of the spring brake cylinder and recess segments formed radially inward and recess segments corresponding thereto that are formed radially outward and formed on an annular chamber connected to the intermediate wall and locking segments protruding radially inward into the annular chamber. A bottom-side stop surface in the annular chamber forms an axial stop for the end-side wall edge of the spring brake cylinder. An annular seal is arranged between a circumferential surface of the edge of the wall of the spring brake cylinder pointing radially inward and the circumferential surface of the annular chamber pointing radially outward.

Abstract: Provided is a chamber case of a brake chamber of a vehicle, which may reduce the weight of a vehicle by applying a plastic resin-based material to the chamber case and also enhance rigidity and durability of the chamber case by forming a reinforcement rib at the chamber case and adjusting a thickness of the chamber case to reinforce weak portions of the chamber case. The chamber case of a brake chamber of a vehicle is configured to surround a power spring and a piston, and a top portion of the chamber case is formed to have a relatively greater thickness than a side portion thereof to reinforce the strength of the chamber case.

Abstract: A braking system is provided that enables application and release of a parking brake with fluid control and that also maintains application of the brake during a loss of fluid pressure—all without using springs and using only a single fluid control conduit. The brake actuator for the system includes a housing defining service and parking chambers. A pushrod in the parking chamber is configured for movement with a diaphragm in the chamber. The parking brake is applied by introducing fluid on one side of the diaphragm. A clutch surrounds the pushrod and includes a tooth configured to engage corresponding teeth on the pushrod to hold the position of the pushrod even during a loss of fluid pressure. The clutch is rotated under fluid control to move the clutch tooth into and out of alignment with the teeth on the pushrod to hold and release the parking brake.

Abstract: A fluid pressure operable actuator includes a housing, with an end wall, and a pushrod projecting through an opening in the end wall for reciprocation upon service pressure application or release. A shield, configured as an annulus, is disposed on the pushrod to restrict contamination of an interior chamber of the actuator housing through a gap existing between an edge of the opening and a pushrod outer surface. To facilitate connecting the shield and the pushrod together, the annulus has a slit with an enlarged void at a radially outer end of the slit. This enlarged void engages an outer pushrod surface as the shield and the pushrod are joined.

Abstract: Provided is a diaphragm mounting of a brake chamber for a vehicle, and in particular, to a diaphragm mounting of a brake chamber for a vehicle, which may exclude a return spring for restoring a diaphragm to an original position. The diaphragm mounting of a brake chamber for a vehicle includes a spring diaphragm assembled between a head and a flange case, a push rod having a top surface closely adhered to a bottom surface of the spring diaphragm, a piston located between the head and the spring diaphragm, and a power spring disposed between a top surface of the piston and a bottom surface of the head to pressurize the piston with an elastic force, wherein a center hole is formed at the center of the spring diaphragm, and the push rod located below the spring diaphragm and the piston located above the spring diaphragm are integrally connected by a coupling unit through the center hole.

Abstract: The “no tools” pump removal system comprises a bearing housing attached to the drive housing. The bearing housing has a hinged door that when opened allows removal of the pump pin and then the pump. The bearing housing is provided with a latch assembly and a handle. A safety latch retains the handle in place during operation and until it is desired to remove the pump.

Abstract: A brake cylinder for pneumatic vehicle brakes, especially for commercial vehicles, includes in addition to a pneumatic locking mechanism, a manual release mechanism for manually releasing the spring brake section, and a device designed to visually recognize the manual release condition of the spring brake section outside of the housing.

Abstract: A spring-type brake actuator for a pneumatically-operated vehicle brake is provided, in which the parking brake release piston is formed from at least one stamped actuator piston plate, preferably a stamped aluminum plate. Preferably the biasing force of the power spring of the spring brake actuator bears on a stamped spring seat cap element which is interposed between the power spring and the stamped actuator piston plate. In addition, the parking brake release piston flexible diaphragm may be captured between the stamped actuator piston plate and a stamped backing plate by affixing the backing plate to a joining member, where the joining member includes a threaded insert to receive a manually-actuated parking brake release actuation tool.

Abstract: An assembly includes an actuator assembly having a housing, a piston positioned at least partially within the housing and movable relative to the housing for an overall actuation stroke, a first spring operatively engaged between the piston and the housing to provide actuation biasing force therebetween, a second spring operatively engaged with the piston, and a spring guide. The spring guide is operatively engaged with the first spring and operatively engaged with the piston via a sliding connection. The spring guide is further configured to limit a stroke of the first spring such that the first spring contributes actuation biasing force between the piston and the housing for only a fractional portion of the overall actuation stroke of the piston.

Abstract: A pneumatic brake actuator has a spring brake actuator with spring and spring brake pressure chambers, and a service brake actuator with service brake pressure and pushrod chambers. A control valve has a seal that is moveable between an open position and a closed position for regulating fluid flow between the spring chamber and service brake pressure chamber. A first surface of the seal is in fluid communication with the service brake pressure chamber and a second surface of the seal is in fluid communication with a valve chamber that is not in fluid communication with the service brake pressure chamber or spring chamber. The seal moves between its open and closed positions based on a pressure in the service brake pressure chamber. Movement of the seal is not dependent on the rate of flow of fluid between the spring chamber and the service brake pressure chamber.

Abstract: A brake actuator is provided, in which a diaphragm, used in conjunction with a piston which compresses a parking brake-actuating spring, is arranged such that its outer peripheral region is captured between opposing housing flange portions such that a seal between the interior and exterior of the brake actuator housing is provided in a radially-oriented region of the diaphragm and the housing flange portions away from housing portion jointing components such as a clamp ring or individual fasteners. The diaphragm may also be provided with a wedge-shaped portion at its outer periphery which is axially oriented and configured to reside in a corresponding annular gap between the opposing housing flange portions.

Abstract: The present disclosure is directed to ensuring a brake to be smoothly locked and released by preventing an air pressure of a spring chamber or a pressure chamber of an air operated brake actuator from being excessively compressed, and also solving a buckling phenomenon of a compression spring.

Abstract: The invention relates to a pneumatic brake cylinder including a piston for transferring the pneumatic pressure to a brake, a pressure chamber defined by the piston and part of the inner wall of the brake cylinder, and a sealing ring sealing a gap between the piston and the inner wall of the brake cylinder. According to the invention, the sealing ring is vulcanised onto the piston.

Abstract: Actuators having override apparatus are described herein. An example actuator having an override apparatus includes a first actuator stem coupled to a control actuation member. The override apparatus is operatively coupled to the actuator. A spring is coupled to an override member to move the first actuator stem to a predetermined position in response to an override condition.

Abstract: A brake cylinder for a pneumatic vehicle brake, particularly for a commercial vehicle includes a spring-loaded brake section for performing parking brake operations by a spring-loaded spring, and a service brake section for performing compressed air-actuated service brake operations. The spring-loaded brake section and the service brake section are combined in a structural unit in a housing. The housing is divided by a piston into a pressure chamber to which compressed air can be applied and a further space. The pressure chamber serves the actuation of the service brake section in the pressure space and the spring-loaded spring of the spring-loaded section being disposed in the additional space on the opposite side of the piston. The spring-loaded spring acts on an additional spring-loaded piston in the space. The piston is lockable in relation to the piston by a pneumatically operable locking mechanism and releasable from the same by releasing the locking mechanism.

Abstract: A pneumatic actuator includes a housing defining a chamber. A diaphragm is positioned within the chamber. A rod member is attached to the diaphragm and is movable between a first position and a second position. A cam member is attached to the diaphragm and to the rod member. The cam member has a cam surface. A deflection rod has a first end portion and a second end portion, where the first end portion of the deflection rod is attached to the housing A follower is attached to the second end portion of the deflection rod. The follower engages the cam surface of the cam member so as to time the rod member towards the second position.

Abstract: A pneumatic brake actuator has a housing and a divider that divides the housing into a spring chamber containing a spring and a pressure chamber. The divider has an opening that receives an end of an actuator tube. A bearing that is positioned within the opening in the divider is joined to both the divider and the actuator tube. A caging bolt has a first end positioned within the actuator tube and extends from the first end through openings in the hearing and housing to a second end positioned outside of the housing. The connection between the bearing, divider and actuator tube contains the spring within the housing in the event that the housing and/or divider fails. The divider can be a piston or a diaphragm and pressure plate. The bearing can be joined to either of the divider and actuator tube with threads and/or by welding.

Abstract: A fluid pressure operable actuator includes a housing, with an end wall, and a pushrod projecting through an opening in the end wall for reciprocation upon service pressure application or release. A shield, configured as an annulus, is disposed on the pushrod to restrict contamination of an interior chamber of the actuator housing through a gap existing between an edge of the opening and a pushrod outer surface. To facilitate connecting the shield and the pushrod together, the annulus has a slit with an enlarged void at a radially outer end of the slit. This enlarged void engages an outer pushrod surface as the shield and the pushrod are joined.

Abstract: A brake actuator having a plurality of actuator housing portions includes a diaphragm seal partially delimiting a parking brake de-actuation chamber and retained between adjacent portions of the housing. To produce brake actuation upon depressurization of the parking brake de-actuation chamber, a push rod extends into and out of a service brake actuation chamber upon release of fluid pressure from and supply of fluid pressure to the chamber. A clip or similar element receivable over the end section of the push rod is securable on the end section to compress the diaphragm seal axially relative to the push rod against a seat carried by the push rod while permitting a radial inner edge of the diaphragm seal to remain spaced from an outer surface of the end section.

Abstract: A brake stud housing assembly and method of construction of such assembly for vehicles that exhibits increased shock resistance and vibration reduction capability, allowing for increased durability of a brake housing assembly. The housing assembly includes a vibration dampening layer having an adhesive material that provides a permanent connection between the housing shell and reinforcing plate, which transfers both tensile and compressive loading forces between the housing shell and reinforcing plate in order to reduce vibration and stress.

Abstract: A brake cylinder for pneumatic vehicle brakes, especially for commercial vehicles, includes in addition to a pneumatic locking mechanism, a manual release mechanism for manually releasing the spring brake section, and a device designed to visually recognize the manual release condition of the spring brake section outside of the housing.

Abstract: A brake cylinder is provided for vehicle brakes, in particular for commercial vehicles brakes, that is equipped with a brake cylinder housing, in which a spring-loaded piston, a service brake piston, a spring-loaded spring and a piston return spring are arranged. The brake cylinder is simple to construct and extremely compact. The spring-loaded piston is in a primary chamber of the brake cylinder and is arranged between the service brake piston and a front side of the brake cylinder housing having the compressed air connections.

Abstract: An improved diaphragm-type pneumatic brake actuator includes a flange case, a cover cooperable with the flange case, a flexible diaphragm extending between the flange case and the cover forming a lower pneumatic chamber and an upper pneumatic chamber on opposed sides of the diaphragm. A piston assembly is disposed in the cover for moving a spring between compressed and decompressed positions. A spring guide is disposed between the cover and the piston assembly in the upper chamber. The spring guide prevents direct contact of the spring with the cover to prevent formation of a corrosion cell.

Abstract: A combined service brake and the stored-energy brake cylinder is provided, in which a ventilation valve which forms or shuts off a flow connection between the spring chamber and the service brake chamber of the brake cylinder ensures that disruptive noise is avoided while also preventing loss of air volume for building up the service brake force.

Abstract: A brake actuator system of a vehicle comprising a diaphragm design with a hole and sealing element in the center. The design allows for the sealing element to seal and slide on the outer diameter of the center pushrod for the exposed length. This eliminates the need for a fixed joint to permanently attach the diaphragm to the center pushrod, and allows for the pushrod to be attached to the spring piston or a separate fixed plate and reduces stress of the diaphragm at its interface.

Abstract: A brake actuator having a plurality of actuator housing portions includes a diaphragm seal partially delimiting a parking brake de-actuation chamber and retained between adjacent portions of the housing. To produce brake actuation upon depressurization of the parking brake de-actuation chamber, a push rod extends into and out of a service brake actuation chamber upon release of fluid pressure from and supply of fluid pressure to the chamber. A clip or similar element receivable over the end section of the push rod is securable on the end section to compress the diaphragm seal axially relative to the push rod against a seat carried by the push rod while permitting a radial inner edge of the diaphragm seal to remain spaced from an outer surface of the end section.

Abstract: A brake cylinder for pneumatically actuated vehicle brakes includes a parking brake spring-loaded brake section and a service brake section combined to form a structural unit in a housing. The housing is divided into two chambers by a piston. A cylinder spring of the spring-loaded brake section acts on another spring-loaded piston in the chamber, which can be blocked in relation to the first piston by a pneumatically actuated locking mechanism, and can be released from the first piston by the releasing action of the blocking mechanism. Following the release, the cylinder spring acts between the two pistons and moves the two pistons in relation to each other during a parking brake process. The pneumatically actuatable blocking mechanism acts only in an expansion direction of the spring.

Abstract: A spring-loaded brake cylinder for commercial vehicles includes at least one spring-loaded brake piston that can be actuated by a pre-loaded spring and is supported in a housing. A mechanical emergency release device is provided for the emergency release of the spring-loaded brake cylinder. The emergency release device includes an indicator that has an indicator rod indicating the position of the spring-loaded brake piston. The rod extends through a threaded spindle of the emergency release device and is movable in the axial direction. A stop body is disposed in the region of one end of the indicator rod. The stop body is positively connected to the indicator rod by a detent connection produced by an axial relative movement between the indicator rod and the stop body.

Abstract: A tamper resistant spring brake actuator with a stroke position indicator has a cover attached to a flange case by a removable clamp, with a head permanently attached to the flange case by a one-piece continuous clamp member, which is permanently deformed in place during assembly. The cover, flange case and head have annular rims, which are relatively flat and smooth. The one-piece continuous clamp ring is in contact with and clamps the outer flanges of the flange case, the parking chamber diaphragm and the head. The stroke position indicator can be treated with a surface protector to minimize the accumulation of oil and road debris.

Abstract: A combined service brake and spring brake cylinder has a diaphragm arranged in a housing of the service brake cylinder. At one side, the diaphragm delimits a service brake chamber acted on with a service brake pressure, and at the other side delimits a chamber accommodating a return spring. A spring brake piston is arranged in a housing of the spring brake cylinder, which at one side delimits a spring brake chamber and at the other side delimits a spring chamber. A piston rod supports a ventilation valve which produces or blocks a flow connection between the spring chamber and the service brake chamber. The ventilation valve includes a piston interacting with a valve seat. At least one further piston interacts with a further valve seat and opens at least one further flow cross-section when in its position raised from the further valve seat.

Abstract: An improved diaphragm-type pneumatic brake actuator includes a flange case, a cover cooperable with the flange case, a flexible diaphragm extending between the flange case and the cover forming a lower pneumatic chamber and an upper pneumatic chamber on opposed sides of the diaphragm. A piston assembly is disposed in the cover for moving a spring between compressed and decompressed positions. A spring guide is disposed between the cover and the piston assembly in the upper chamber. The spring guide prevents direct contact of the spring with the cover to prevent formation of a corrosion cell.

Abstract: A brake actuator system of a vehicle comprising a diaphragm design with a hole and sealing element in the center. The design allows for the sealing element to seal and slide on the outer diameter of the center pushrod for the exposed length. This eliminates the need for a fixed joint to permanently attach the diaphragm to the center pushrod, and allows for the pushrod to be attached to the spring piston or a separate fixed plate and reduces stress of the diaphragm at its interface.

Abstract: A clamp band for spring brakes which comprises an annular clamp band pre-formed with a side wall and a rim extended perpendicularly from a first end thereof, wherein during assembling of a spring brake when an edge of a first chamber, a diaphragm and an edge of a second chamber are positioned in sequential order on the rim a second end of the side wall is deformed to bend inwards to encompass the edge of the second chamber to secure the edges of the two chambers and the diaphragm in place. The annular clamp band comprises a first clamp band and a second clamp band having identical semi-annular shape.

Abstract: A brake cylinder for brakes of a motor vehicle, in particular for utility vehicles, comprising a spring loaded brake section and a service brake section is configurable in such a way that a total length is substantially shortened. In the inventive cylinder, the spring loaded brake section and the service brake section are constructed in such a way that they form a single unit. The brake cylinder comprises a pressurized piston for service braking and a spring-loaded piston for parking braking. The two pistons are connected to each other through a shift cylinder and are disconnected by the pressure relief in a second pressure chamber through the shift cylinder in such a way that the piston is displaceable by a spring-loaded spring. In order to release the brake, the piston for service braking is pressurized and reconnected to the piston. The unit is displaced to a release position by the action of a return spring through the pressure relief of the piston.

Abstract: A combined service brake and spring-loaded brake cylinder includes an air-bleed valve having a piston supporting a valve body, which is guided inside a cylinder in an axially displaceable manner, and at least one first pressure spring supported on the piston being loaded against a first valve seat on the piston. The piston is loaded by at least one second pressure spring which is supported on the piston rod, in such a manner that the valve body is pushed toward a second valve seat on the piston rod and away from the first valve seat.

Abstract: A mid-power spring brake actuator includes first, second, and third actuator housing portions, with the first actuator housing portion interposed between the second and third housing portions. A parking brake release actuator is received within the third housing portion, and a connecting shaft is attached at a first end to the parking brake release actuator and extends through a dividing wall defined by the first housing portion. A service brake apply actuator is received within at least one of the first and second housing portions. Between the dividing wall defined by the first housing portion and a second end of the connecting shaft, a brake actuator spring is provided, and a service brake actuation chamber is interposed between the brake actuator spring and the service brake apply actuator. A parking or emergency brake de-actuation chamber is defined between the parking brake release actuator and the first housing portion.

Abstract: A spring-actuated air-brake cylinder as the diaphragm cylinder for vehicle brake systems includes a diaphragm, an actuator-spring chamber in which there is received a spring-actuated piston, which is acted on by a compression spring as the actuator spring and is actively connected to the diaphragm, which is disposed between the actuator-spring chamber and a pressure chamber, in which there is guided moveably a sealed push rod, which can include a pressure member on its diaphragm side. The spring-actuated diaphragm is connected to the push rod or to the pressure member or to the spring-actuated piston by means of vulcanization.

Abstract: A combined service brake and spring brake cylinder for the braking system of a motor vehicle, in particular for utility vehicles, includes service and spring brake pistons guided inside a casing which is common for the two brake cylinders. The spring brake piston is loaded by at least one storage spring and has an external diameter greater than that of the service brake piston. The spring brake piston is in the form of an annular piston, and at least a part of the rod thereof is constructed in the form of a piston tube, which surrounds the service brake piston and forms an external radial running and sealing surface therefor.

Abstract: An axially driven piston-cylinder unit comprising a cylinder, a piston that can be moved back and forth in the axial direction of the cylinder, between first and second piston positions, and a drive element that can be moved back and forth in the axial direction of the cylinder and is mechanically connected to the piston by means of a piston rod. The piston rod is connected to the piston or the drive element against the pretension of an elastic device, in such a way that it can be moved axially in relation to the piston or the drive element, such that when the piston head comes into contact with the front wall of the cylinder borehole, on the side of the cylinder head, the other movement of the drive element is performed against the force of the elastic device, thus braking the drive element.

Abstract: A mid-power spring brake actuator includes first, second, and third actuator housing portions, with the first actuator housing portion interposed between the second and third housing portions. A parking brake release actuator is received within the third housing portion, and a connecting shaft is attached at a first end to the parking brake release actuator and extends through a dividing wall defined by the first housing portion. A service brake apply actuator is received within at least one of the first and second housing portions. Between the dividing wall defined by the first housing portion and a second end of the connecting shaft, a brake actuator spring is provided, and a service brake actuation chamber is interposed between the brake actuator spring and the service brake apply actuator. A parking or emergency brake de-actuation chamber is defined between the parking brake release actuator and the first housing portion.

Abstract: In an actuator for a brake system or a method for making a brake actuator, an attachment mechanism for attaching a diaphragm to a piston includes a plurality of protrusions on one of the piston and diaphragm and a plurality of cavities on the other of the piston and diaphragm, each protrusion being insertable into a corresponding cavity to attach the diaphragm to the piston. Alternatively, a retaining ring is provided that need not be precisely made and yet can attach the diaphragm to the piston securely and sealingly.

Abstract: An air-operated brake actuator system of a vehicle comprises a spring brake actuator and a service brake actuator, the spring brake actuator including a sealed housing with a spring chamber and a pressure chamber, and a hollow actuator rod disposed in the spring brake actuator and axially moveable for applying a parking brake, the service brake actuator including a service pressure chamber for applying a service brake, in which a control valve of the brake actuator system includes a valve body placeable within the hollow actuator rod, the valve body including an opening formed therein for allowing fluid communication between the spring chamber of the spring brake actuator and the service pressure chamber of the service brake actuator through the hollow actuator rod, the control valve including a membrane formed of an elastic material and having a breathing hole formed there-through, the membrane positioned within the opening of the valve body and configured to seal the opening except the breathing hole when t

Abstract: A driveline vehicle parking brake actuator including a reciprocable piston, a spring guide having a tubular distal portion telescopically received on the piston and a radial proximal portion which is telescopically supported within the housing by an annular wear guide, and nested cylindrical coil springs including an outer cylindrical coil spring biased between the housing and the radial portion of the spring guide and a nested inner coil spring having a greater spring rate biased between the spring guide and the piston functioning in series. The distal end of the piston is attached to a cable and the springs are compressed by hydraulic or pneumatic pressure acting against the piston.