Abstract: An actuated valve assembly includes a valve, an actuator, and a nut retention sleeve. The nut retention sleeve has a first bore portion sized to closely receive and rotate with a portion of a coupling member extending from the actuator and a second bore portion sized to closely receive and rotate with at least a portion of a stem nut assembled with a valve stem of the valve. The nut retention sleeve is slideable between a nut retaining position in which the second bore portion engages the stem nut to rotationally fix the stem nut with the coupling member, and a nut adjusting position in which the second bore portion is disengaged from the stem nut to permit rotation of the stem nut on the valve stem.

Abstract: A hydraulic piston-cylinder group includes a cylinder containing a piston which defines internally of the cylinder at least a first and a second chamber, respectively communicating with a first and a second inlet/outlet hole of a pressurized fluid for actuating the piston between a first and a second position. The piston has a gully defined by a bottom wall, a first lateral wall that is proximal to the first free end, and a second lateral wall distal relative to the first free end, the first and second lateral walls serving as first and second abutments for the piston ring, the gully communicating through at least a passage with the first chamber. A depression is provided on the contact surface between the second lateral wall of the gully and the piston ring, the depression enables a controlled bleeding of the pressurized fluid between the piston ring and the second lateral wall.

Abstract: The subject matter of this specification can be embodied in, among other things, a positioning device that includes an actuator assembly configured to actuate an output shaft based on an input signal, and a position sensor assembly. The position sensor assembly includes a position sensor configured to detect a position of an input shaft not directly coupled to the output shaft, a first input receiver configured to receive the input signal, a first output transmitter configured to provide an output signal based on the position of the input shaft, and a second output transmitter configured to provide another output signal indicative of a failure of at least one of the input shaft and the output shaft. A moveable member is coupled to both the output shaft and the input shaft and is configured to alter the positional configuration of the input shaft and to be actuated by the output shaft.

Abstract: A fluid-actuated rotary drive device is provided, with a housing (2) in which is formed a working chamber (3), in which is a swivel piston (18) able to swivel around a central axis (5). Also fitted or able to be fitted in the working chamber (3) is a space divider and stop unit (38), comprised of a space divider element (24) and at least one stop element (42) fixed to the former. The components of the space divider and stop unit (38) are fitted to one another by snap-in connection, so that the space divider and stop unit (38) is easy to handle during its installation in the working chamber (3).

Abstract: A self-adjusting end position damping arrangement includes a stroke space 9 which is delimited by a movable stroke element 7, 24 and a part of the pneumatic cylinder 1, with the stroke space 9 being connected via a connecting duct 14 to the working pressure P1 which acts on the cylinder piston 22 or to the ventilation pressure (P3) in the outlet duct 3 and the stroke element 7, 24 being acted on via a damping duct 16 by the damping pressure P2 in the damping volume 19, a non-return valve 12 is arranged in the connecting duct 14 upstream of the stroke space 9, which non-return valve 12 blocks in the direction of the working pressure P1 or the ventilation pressure (P3), respectively, and a ventilation duct 5 is provided, which ventilation duct 5 can be opened by means of the movable stroke element 7, 24 and which is connected to an outlet duct 3.

Abstract: A double-acting cylinder and piston mechanism comprising a cylinder (1) substantially closed at both ends by front (5) and rear (7) end walls, a piston (8) axially displaceable within the cylinder (1), a first region (6) defined between the piston (8) and the rear end wall (7) of the cylinder (1) and a second region (4) defined between the piston (8) and the front end wall (5) of the cylinder (1), a piston rod (2) extending from the piston (8) through the front end wall (5) of the cylinder (1), an air inlet port (19) for communication with said first region (6) of the cylinder (1) and at least one exhaust vent (14) which is exposed during axial displacement of the piston (8) for release of air delivered to the cylinder (1) through the air inlet port (19).

Abstract: A power steering device for a vehicle which is disposed in the transmission path between a steering handle and a steerable vehicle wheel, comprises a servo cylinder having two pressure chambers, which are separated by a working piston and are each connected to a pressure supply unit. A valve plunger, which seals a bypass channel between the pressure chambers, is movably disposed on the working piston. Furthermore, an adjustment bushing comprising an adjustment section is disposed in the servo cylinder, the valve plunger being moved against this section upon approaching an axial limit position, thereby opening the bypass channel. The adjustment bushing is clamped into the servo cylinder, yet held displaceably, wherein, on the adjustment bushing, a sealing section is provided, which is to be moved into a sealing position with the working piston so as to interrupt the flow connection between the pressure chambers.

Abstract: First and second cushion rings are arranged respectively on both end surfaces of a piston constituting part of a fluid pressure cylinder, through fitting grooves. The first and second cushion rings are formed with substantially hollow cylindrical shapes by press working a metal material, wherein the cushion rings effectuate a cushioning action, which decelerates the displacement speed of the piston, as a result of being displaced in the axial direction together with the piston and being received and accommodated within a recess of the head cover and a rod hole of the rod cover.

Abstract: A cushioned hydraulic cylinder assembly including a hydraulic cylinder having a reciprocating piston movable between an extended position and a retracted position and a hydraulic fluid port proximate an end thereof for ingress and egress of hydraulic fluid. A cushion member is carried by the piston, wherein the cushion member obstructs hydraulic fluid flow out of the port in the retracted position and is spaced from the port in the extended position. A continuous spiral groove is formed in an outer surface of the cushion member and has a beginning at a first end of the cushion member away from the piston and terminates proximate a second end adjacent the piston. The beginning of the spiral groove has a cross-sectional volume, the cross-sectional volume decreasing toward the second end of the cushion member. The spiral groove gradually reduces hydraulic fluid flow out of the port as the piston moves toward the retracted position.

Abstract: A hydraulic piston pump in which a cylinder port (4b) can be communicated with a discharge port (9) after a system pressure (Po) and a chamber pressure (Pi) in a cylinder bore are in an equilibrium state. A through-hole (16) opened in that surface of a valve plate (7) on which a cylinder block (3) slides is communicated with one end surface (21a) side of a balance valve (20), and the system pressure (Po) on the discharge port (9) side is supplied to the other end surface (21b) of the balance valve. A balance piston (21) is built-in in the balance valve, and the balance piston (21) slides by a pressure difference between the chamber pressure (Pi) in the cylinder bore (4) and the system pressure (Po). Before a cylinder port (4b) is communicated with an oil guiding groove (15), the chamber pressure (Pi) and the system pressure (Po) can be brought into an equilibrium state by actuation of the balance piston (21).

Abstract: A hydraulic cylinder comprising a cylinder, a piston which is adjustable in the cylinder, and at least one pressure connection which is disposed in the vicinity of an end position of the piston and through which a pressure fluid can be introduced into the cylinder, is characterized in that the piston is provided with a valve element which can cooperate with the pressure connection, in order to cover the pressure connection when the piston approaches its end position, and in order to uncover the pressure connection when pressure fluid is introduced into the cylinder.

Abstract: A hydraulic drive (1) has a position selection device (2) in communication with a control valve (3) which, as a function of the actuation of the position selection device (2), controls the connection of an actuating cylinder (8) with a hydraulic fluid source (5) and a reservoir (6). A correction device provides a synchronization between the position of the position selection device (2) and the position of the actuating cylinder (8). The correction device has a sliding valve means (15) which detects a reference range of the actuating cylinder (8) and an on-off valve means (16) effectively connected mechanically with the position selection device (2). The on-off valve means (16) is open when the position selection device (2) is in the reference range and is closed when the position selection device (2) is not in the reference range.

Abstract: A reciprocating compressor includes a linear motor having a piston reciprocating inside a cylinder. A cylinder head is provided with suction and discharge orifices. A valve means is mounted inside the cylinder and has an operative position, seated against the discharge orifice. The operative position is defined when the top of the piston is within a certain distance from the cylinder head. The distance is defined, so that, at the end of the compression stroke of the piston, a determined pressure is reached inside the cylinder, and the pressure results in a force on the piston. The force is opposite to a force which is impelling the piston and which is sufficient to interrupt its compression stroke before impacting the cylinder head.

Abstract: A rotary actuator has a cushion mechanism for stopping a vane at a rotational terminal end position in a cushioning manner. The cushion mechanism has first and second openings. The first opening discharges an exhaust air pressed out from a cylinder hole by a rotating vane to an external portion without limiting a flow amount. The second opening discharges the exhaust air to the external portion in a state of limiting a flow amount. A flow amount adjusting mechanism connects to the second opening. The first opening is provided at a position sealed by the vane before the vane of a hole surface in the cylinder hole reaches a rotational terminal end position. The second opening is provided at a position which is not sealed by the vane after the vane reaches the rotational terminal end position.

Abstract: The invention provides a rotary actuator having a rack driven in an oscillating manner by an air pressure, a pinion engaged with the rack, and a cushion mechanism for stopping the rack to at least one normal or inverse stroke end in a cushioning manner. The cushion mechanism has an exhaust port open to a pressure chamber at a position close to a chamber end rather than a port hole, a flow amount adjusting mechanism for restricting a flow amount of the exhaust air discharged from the exhaust port, and a cushion packing mounted to an outer peripheral surface of the piston and operating so as to shut the port hole from the pressure chamber immediately before the piston reaches the stroke end, thereby discharging the air within the pressure chamber through the flow amount adjusting mechanism.

Abstract: A piston and cylinder assembly is described having a piston which partially defines a fluid chamber in the cylinder from which fluid is expelled through an outlet port of the cylinder by movement of the piston along the cylinder, the assembly including a flow restrictor providing a first restricted flow path between the chamber and port, and also providing an auxiliary restricted flow path of which a first portion communicates with the chamber and of which a second portion extends between the first portion and the port.

Abstract: In a linear actuator in which a slide table on a pedestal is caused to reciprocate linearly by two air cylinder mechanisms mounted in the pedestal, exhaust holes are provided to positions adjacent at ports and, flow rate restricting mechanisms for restricting a flow rate of exhaust are provided between the exhaust holes and the ports, and pieces of cushion packing for being positioned over one of through holes of the ports on an exhaust side immediately before the piston reaches a stroke end are provided at an outer peripheral face of the piston to cause compressed air in pressure chambers of the actuator to be discharged from the exhaust hole through the flow rate restricting mechanism.

Abstract: The invention provides a rotary actuator having a rack driven in an oscillating manner by an air pressure, a pinion engaged with the rack, and a cushion mechanism for stopping the rack to at least one normal or inverse stroke end in a cushioning manner. The cushion mechanism has an exhaust port open to a pressure chamber at a position close to a chamber end rather than a port hole, a flow amount adjusting mechanism for restricting a flow amount of the exhaust air discharged from the exhaust port, and a cushion packing mounted to an outer peripheral surface of the piston and operating so as to shut the port hole from the pressure chamber immediately before the piston reaches the stroke end, thereby discharging the air within the pressure chamber through the flow amount adjusting mechanism.

Abstract: A small-sized and inexpensive air cylinder with a cushion mechanism having a simple structure is provided. Therefore, discharge outlets for discharging cushioning air are disposed in positions closer to ends of the stroke than the openings of the ports in the cylinder tube, respectively, and check valves and throttling mechanisms are arranged in parallel between discharge outlets and ports, respectively. On the outer peripheral surface of the piston, one of the piston packing rings is disposed in one position which does not pass through the opening of the port while another of the piston packing rings is disposed in another position which passes through the opening but does not pass through discharge outlet, when the piston reaches the terminal ends of the stroke.

Abstract: A dynamic pressure regulator cushion for use with a fluid power actuator to smoothly and linearly decelerate the piston at end of stroke. The dynamic pressure regulator cushion comprises a pressure sensor attached to a valve. A side of the pressure sensor tending to close the valve is exposed to driving pressure. A side of the pressure sensor tending to open the valve is exposed to fluid pressure in the cylinder ahead of the piston. An adjustable valve pre-loading is provided to maintain the fluid pressure in the cylinder ahead of the piston at a constant, pre-determined level above the driving pressure during the cushion stroke. This pre-set pressure differential across the piston serves to smoothly and linearly decelerate the piston to near zero at end of stroke. Two pressure sensor embodiments taught are a pressure sensor piston reciprocating within a plenum, and a diaphragm whose outer edge is attached to, and sealed to, an inside wall of a plenum.

Abstract: In a device for stroke end cushioning and speed regulating the movement of a piston (3) in a fluid pressure cylinder (1,2) a common adjusting means (9) is arranged for simultaneous setting of the throttle means (7,8) for regulating the stroke end cushioning as well as the piston speed, for the purpose of avoiding very time consuming adjustment. In connection with the setting of the adjusting means (9) the ratio between the flow areas of the respective throttle means is held within the range of 10-60%. In the most uncomplicated embodiment the common adjusting means (9) may be comprised by a screw being fixed to the valve bodies of the respective throttle means.

Abstract: Piston sealing and dampening device in a pressurized-fluid cylinder, where a piston (3) has a central recess (3a) facing towards a cylinder end cap (1a) and disposed such that when the piston is in the vicinity of its end position, said recess accommodates a sleeve portion (5) provided with an internal pressurized-fluid connection (6) and projecting from the cylinder end cap. An integrated sealing ring (10) seals against the outside of the sleeve portion (5) with an inner sealing ring lip (10e) and against the inside of the cylinder tube (2) with an outer sealing ring lip (10c).

Abstract: An improved cylinder structure for a pneumatically operated tool, which is characterized in the two air tight chambers defined at the front and rear ends of the cylinder so that the air confined therein can produce reaction pressure respectively to reduce the operation speed of the piston when it approaches the dead ends of the cylinder and further to bounce back the same in a rapid manner whereby the impact of the moving piston can be effectively reduced at the dead ends and the noise and vibration generated as a result of high speed impact on the ends of the cylinder can also be minimized; moreover, the piston can be protected from being deformed and damaged due to constant direct impacts.

Abstract: Cylinders of the type used in fluid power systems are cushioned by a floating spear. The reciprocating piston is centrally bored to receive the spear. Accordingly, the spear and piston are movable independent of each other. A blind axial bore is formed in opposite ends of the spear and one or more diametrically extending bores are also formed in the spear in open fluid communication with those axial bores. Thus, when the spear enters the cushion cavity, the piston continues its motion and progressively blocks off the diametrically extending bores. Air in the cylinder cavity escapes into the atmosphere through the cushion cavity, but is constrained to enter the spear through one or more of the diametrically extending bores and hence through an axially extending blind bore. The length of the spear is variable, as is the length and diameter of the blind bore and the number, diameter, and spacing of the diametrically extending bores. Thus, the deceleration of the piston is programmable.

Abstract: An improved hydraulic door actuator comprising a hydraulic fluid pump having first and second ports; integral operating cylinder and fluid control apparatus including a barrel coupled at each end to the first and second ports of the hydraulic fluid pump; a piston fluidly sealed within the barrel; and means for controlling the flow of fluid of the hydraulic fluid pump to and from the barrel disposed between the barrel and the first and second ports such that the door automatically slows to a stop upon opening or closing wherein the fluid flow control means comprises a plurality of openings disposed along the length of the barrel for bypassing pressurized fluid from the barrel.

Abstract: A telescopic pneumatic hoist has a flexible stationary hollow probe on its base arranged to unseat a check ball in the piston of the lowest intermediate stage when the piston is near the base. When such a condition exists, the probe closely interfits with the piston and has a radial port communicating with the underside of the piston. The probe connects at the bottom with a supply and exhaust passage which also communicates with the underside of the piston via a check valve controlled secondary passage.

Abstract: A hydraulic control valve for a continuously-variable-ratio transmission (CVT), particularly one of the toroidal race rolling traction type. The transmission includes hydraulically-operated clutches (25,26) whose capacity to transmit torque varies with the operating pressure supplied to them. The transmitted ratio is related to the position of a hydraulic ram (35), which when it overshoots its normal stroke creates a pressure rise upstream of it in the circuit. This pressure rise first resists further overshoot, and then causes a reduction in the clutch operating pressure. Ram position is controlled by valves (56,57) which are located downstream of the ram, and which are themselves sensitive (via 58) to feedback from upstream circuit pressure: when that pressure rises, the valves open so as to depress the downstream circuit pressure by which the clutches are operated (via 68).

Abstract: A hydraulic ram unit for a transmission of the toroidal-race, rolling-traction type. The ram is connected to the rollers of the transmission so that the position of the ram within its stroke is related to the angular setting of the rollers and so to the transmitted ratio. The ram pistons move within cylinders the inlet and outlet ports of which are located in the cylinder end walls, with the outlet ports axially protruding of the inlet ports. If a piston overshoots its normal stroke it tends first to restrict flow through the outlet port and then to contact and obstruct it, so creating firstly hydraulic and then contact forces to resist further overshoot, without substantially restricting the inlet port. Novel construction for the ram itself, and for the ram cylinders and casing are also described.

Abstract: A hydraulic door opening or closing device comprises a hydraulic fluid pump motor having two ports connected to each end of integral dual manifold and operating cylinder apparatus by way of two branch fluid lines. One branch line is fluidly connected to a particular end of the operating cylinder by way of a directional flow valve. The other branch line to the same end of the cylinder is fluidly connected to the cylinder by way of an associated manifold. Fluid communication with the cylinder through the manifold is accomplished by providing a plurality of valved openings linearly disposed along the end of the cylinder between the manifold and the cylinder. As a piston of the operating cylinder passes these openings, a door coupled to the piston is automatically slowed as fluid on the drive side of the piston is returned through the openings to the hydraulic fluid pump.

Abstract: A railway car hydraulic cushioning unit prevents the mixing of gas and hydraulic fluid in chambers interiorly and exteriorly of a high pressure cylinder unit by strategic placing of metering ports through the cylinder wall at positions below the level of gas in the exterior chamber. The invention is furthermore directed to a method for converting hydraulic cushioning units adapted for connection to an external spring operated restoring mechanism to a self-contained gas return unit.

Abstract: The invention relates to a compressed fluid saving device positioned between the outlet of a distributor and the admission of a pneumatic jack. The device comprises a valve which is kept open, to allow the flow of driving fluid into one chamber of the jack from the start and right through the stroke, by the exhaust back-pressure escaping from the other chamber of the jack, and acting on the piston of said valve. When the back-pressure disappears, the valve closes under the action of a screw-adjustable spring.

Abstract: A neck ring mechanism for transferring a blank or parison from a blank mold section to a blow mold section of an I.S. glass forming machine includes a rock shaft and a pair of spaced cylinders reciprocable in opposition directions on the shaft. The rock shaft is provided with a plurality of longitudinal grooves, and a like plurality of followers are arranged in the grooves so as to contact at least one side wall of each groove. The followers are supported on each cylinder. One or more piston rings are seated in associated annular grooves in the rock shaft so as to preclude air leakage.

Abstract: A vacuum pump assembly which is driven by pulsating exhaust gases emanating from an internal combustion engine is disclosed. The pump assembly includes a double-acting pump means for pumping air from a vacuum source and having a reciprocable pumping member, an actuating means including a reciprocable actuating member drivingly connected to the pumping member and which is driven through first and second strokes to move the pumping member through first and second strokes, respectively, one side of the actuating member being in communication with the exhaust gases and with the actuating and pumping members being movable through their first strokes during the pressure increasing phase of each pressure pulsation and being moved through their second strokes by a nonlinear variable rate air spring means during each pressure decreasing phase of each pressure pulsation.

Abstract: An apparatus for converting pressure into motion includes a housing having a plurality of ports formed therein. Movably disposed within the housing is a piston having a first plurality of apertures communicating with a first chamber and a second plurality of apertures communicating with a second chamber therein. The piston is positioned within the housing so that the apertures can register with consecutive ones of the ports as the piston is moved in either of two directions within the housing. The movable member is moved by a pressurizing substance applied to a selectable one of the ports through an appropriate valve circuit. The valve circuit is operated by excitation signals from a control member. By operating the valve circuit in an appropriate sequence, the pressurizing substance is sequentially applied to consecutive ones of the ports to move the piston longitudinally through the housing.

Abstract: After the piston, in a piston/cylinder type fluid pressure motor, has moved past the fluid discharge port during termination of the stroke, fluid is forced to flow through a circuitous conduit formed into the outer surface of the piston. The rate of deceleration of the piston is proportional to the length, cross-sectional area, and surface finish of the channel forming the conduit.

Abstract: A hydraulic mine prop includes an inner piston-like prop guided within an outer cylinder-like prop, and a roof fall valve. The interior space of said inner prop communicates freely with the working chamber of the prop, and the roof fall valve is arranged outwardly on the prop and rigidly secured thereon, the valve being connected to the working chamber by an orifice provided in the prop and leading to the working chamber. The cross-sectional area of the roof fall valve in its open position.

Abstract: An air conditioner of a vehicle having a selectively controlled conditioned air blowing outlet system using a shift actuator (20) equipped with a number of negative pressure supplying ports (a, b, c, d), in which selection of the operation mode of the conditioner is represented by the supply of a negative pressure signal to any one of the supplying ports, which causes displacement of a piston (31) of the shift actuator (20). The displacement is conveyed to selected one or more of doors provided at the outlets via a link mechanism to control the outlets according to a predetermined program.

Abstract: A vibratory seismic energy source capable of generating significant energy over a broad frequency band. The vibrating baseplate and associated structure are designed to have minimum weight while still retaining sufficient structural integrity to permit the use of high actuator forces. This, coupled with a large reaction mass results in the generation of significant energy levels in the earth at high frequencies.

Abstract: A slide valve has a spool valve element that is moved unidirectionally to a sequence of three positions during its operating cycle. The valve structure and unidirectional motion of the spool provide a precompression of the fluid being handled. The valve structure also permits relief of excess downstream pressure. Preferably hydraulic liquid is used to drive, position, and reset the spool valve. The spool valve itself has a hollow body with one groove on its outside surface and a valve body with a port at one end that is always in communication with the hollow portion of the spool valve. The slide valve is especially designed for and preferably used in a liquid reaction molding system to direct a reagent between a source (e.g. reservoir) and a destination (e.g. a mixing head). When applied to such a reaction molding system each slide valve replaces three conventional ball valves and one check valve and yet provides the additional features of precompression and relief of excess pressure.

Abstract: A piston ring for use in hydraulic cylinder cushions wherein advantage is made of the typical imperfect seal characteristics of a conventional metallic piston ring to effect a cushion exhaust fluid metering action near the piston stroke end; the piston ring then uniquely allowing major fluid bypass in the reverse stroke or input fluid pressure direction for instant, full reverse stroke piston velocity response wherein the invention includes a piston ring having a notched pattern in one ring edge surface, which surface is adjacent a piston ring groove side wall, thereby eliminating the prior art need for added secondary flow circuits to accomplish the same instant out of cushion full piston velocity result.

Abstract: Apparatus is disclosed for an improved hydraulic piston and cylinder design wherein grooves in the piston surface create a dashpot effect at the respective ends of piston stroke and assist hydraulic oil porting into the cylinder for improved response during stroke reversal, where the piston at least partially covers the cylinder oil flow port.

Abstract: A compact, double-acting piston-type fluid activated device having an axially reciprocable piston for controlled, predetermined deceleration of the piston as it approaches the limit at each end of its travel within a cylindrical bore. The cylindrical bore is sealed at each end by end walls removably retained in the bore. Each end wall is provided with a central counterbore in its inner surface which in cooperation with the piston provides a cushioning chamber. The area of the counterbore central surface is critically related to the circular cross-sectional area of the cylindrical bore in which the end wall is to be secured, being in the range from about 60% to about 85% thereof. A vent passage places the cushioning chamber in preselectedly restricted flow communication with porting means in the wall of the device, each port being located intermediate the end walls. A method is provided for removably circumferentially locking each end wall in the operating cylinder with a wire snap ring having a hooked end.

Abstract: A fluid motor or vacuum break for use with the carburetor of an internal combustion engine in which an output plunger of the motor moves in two stages and at different rates in each of the stages through means of an auxiliary housing supported within the main housing. Upon admission of vacuum pressure to the primary housing and output plunger moves in a first stage at the end of which vacuum pressure is admitted to the auxiliary housing causing it to collapse and move the plunger in a second stage.

Abstract: A pneumatic adjusting mechanism, especially for application in motor vehicles, which consists of a suction-air servo-motor that includes a working cylinder with a diaphragm piston whose piston rod is stressed by a spring against the action of the suction-air; to provide an adjustment to different adjusting path steps, individual control lines are connected to the working cylinder in places which correspond to the adjusting path steps; all control lines lead to a control switch connected with a suction-air reservoir line while each individual control line is adapted to be selectively connected with this suction-air reservoir line, after previous venting of all control lines, by means of the control switch.

Abstract: Step by step controlled servomechanism of the cylinder-type comprising a drive element movable in a case which it divides into two chambers and provided with a plurality of receiver ports, a distributor adapted to be put in communication with the high pressure and the low pressure and to supply said receiver ports, wherein said distributor is fixed and provided with a number of supply or transmitter ports at least equal to three but independent of the number of receiver ports, the transmitter ports being capable of being connected by permutation, in succession and in pairs, respectively to the low pressure and to the high pressure, the distance between the receiver ports and their length, on the one hand, the distance between the transmitter ports and their length, on the other hand, being such that, by the step by step displacement in one direction of the drive element, on one hand, it is possible to bring each time at least one receiver port between the two transmitter ports of a pair in such position that