US3237641A

US3237641A - Preselective command device

Info

Publication number: US3237641A
Application number: US305423A
Authority: US
Inventors: Audemar Pierre
Original assignee: Alsacienne de Constructions Mecaniques SA
Current assignee: Alsacienne de Constructions Mecaniques SA
Priority date: 1962-09-19
Filing date: 1963-08-29
Publication date: 1966-03-01
Anticipated expiration: 1983-03-01
Also published as: FR1347038A

Description

March l, 1966 P, AUDEMAR 3,237,641

PRESELECTIVE COMMAND DEVICE Filed Aug. 29, 1963 4 Sheets-Sheet 1 l FIG. 2c:

6 @f "n 38 z l 4(l FIG 3 l |120 72 l 1 so 10k i 52 m so (7s 36l Sf'; 76

PIERRE AUDEMAR March 1, 1965 P. AUDEMAR 393%@ PRESELECTIVE COMMAND DEVICE Filed Aug. 29, 1963 4 Sheets-Sheet 2 FERRE AUDEMAR March 1, 1966 P, AUDEMAR 39237,

PREsELEcTIvE COMMAND DEVICE Filed Aug. 29, 1963 y 4 Sheets-Sheet S KEG/108 WERKE AUDEMAR P. AUDEMA 3,23%@

PRESELECTIE COMMAND DEVICE FIG. 7

PIERRE AUDEMAR bj M\ 5W United States Patent 3,237,641 PRESELECTIVE COMMAND DEVICE Pierre Audemar, Paris, France, assignor to Socit Alsacienne de Constructions Mcaniques, Paris,

France, a company of France Filed Aug. 29, 1963, Ser. No. 305,423 Claims priority, application France, Sept. 19, 1962, 909,826, Patent 1,347,038 Claims. (Cl. 137-596.15)

The instant invention concerns a iiuid pressure operated device for the preselective control or command of an apparatus including a pressure operated member moving between two limiting positions and more particularly preselectively operable means for the later and subsequent control of an hydraulic or pneumatic valve which directly causes operation of the pressure operated member.

The device according to the invention serves to maintain the valve member, for example, a valve slide, locked in either of the two positions it had previously been placed by the preselectively operable control means controlling its movement, so that said preselective means may be activated in advance but will only become operative (that is, actually move the Valve member component under command) after the device has received a momentary signal causing the unlocking of said valve member component. A device according to the invention is characterized in that this signal is in the form of a temporary or momentary lowering, or preferably, a complete cut-oi, of the iiuid pressure in at least that part of the pneumatic or hydraulic circuit controlled by the valve(s) preselectively under command.

In a device conforming to the invention for the preselective command of a two position valve controlling a pressurized fluid circuit, the mobile throttle component of said valve is mechanically linked to a piston running in a cylinder.

The cylinder is normally in communication with a source of iiuid under pressure, in such a manner as to hold the piston stationary in the cylinder at one or the other of the ends of the course of travel thereof under the elfect of the pressure exerted on one of the faces of said piston, whereby the throttle component of the valve is normally locked in one or the other of these positions.

f According to the invention, the fluid pressure and thev effective surface area of the piston are chosen so that the fluid locking action will not be overridden (with the resulting movement of the mobile throttle component to its other position) by the force exerted on said component of the valve by the command means, this arrangement allowing said command means to be preselectively activated without its having an immediate effect.

The device according to the invention includes as well means for temporarily reducing or cutting-off the normal pressure exerted by the fluid on the face of the abovementioned piston so as to unlock the throttle component of the valve and free it to respond to the means of command, if it has been previously activated.

In a preferred embodiment of the invention, the locking piston and the throttle component, rather than merely being linked together, are actually made an integral part of a piston slide which runs in the body of a valve, a part of which body serves as the above-mentioned cylinder. Following this embodiment, one or the other of the 3,237,641 Patented Mar. 1, 1966 lCe faces of the locking piston is normally subject to the iluid pressure prevailing in at least one of the parts of the circuit controlled by the valve so that the unlocking of the piston slide may simply be accomplished by temporarily venting all or part of the above circuit to a drain receptacle. The results of this combination are simple, economical preselective command valves, the invention of course contemplating as well the valves themselves.

The preselective valves conforming to the invention find a particularly interesting application in the control of gear boxes, as for example those found in machine tools or vehicles, with each of the said valves controlling the feeding or draining of iuid under pressure of an hydraulic jack which in turn activates the shifter device or analoguous selector device of the gear box. The simultaneous unlocking of all of the valves may be realized by opening a single unlock valve which operates all of the valves and allows them to respond to what ever command signals may have been preselectively applied.

The invention will be better understood from a study of the following detailed description in Iconjunction with the annexed drawings which represent, by way of example only, certain embodiments of the invention.

On the drawings:

FIGURES 1 and 1a are schematic representations of a preselective control or command device in accordance with the invention as applied to a rotating control Valve.

FIGURES 2 and 2a show a longitudinal cut-away of an embodiment as applied to a slide valve with electromagnetic command means.

FIGURE 3 is a cut-away view of another variant in construction.

FIGURES 4, 4a and 5 represent another embodiment of a preselective valve according to the invention with hydraulic command means, in several of its operating positions.

FIGURE 6 is an hydraulic schematic representation of the preselective command means of a gear box including automatic command of the couplings associated with said box by means of a plurality of valves conforming to the invention.

FIGURE 7 represents a cross-section of a command block which groups four preselecting valves in the same valve body.

FIGURE l illustrates the fact that the invention is applicable to all types of valves, be they hydraulic or pneumatic, although the most advantageous applications concern those valvesin which the valve member moves axially. In the following description, the invention will be described as it applies to hydraulic circuits, for purposes of simplification, although it is to be understood that it is equally applicable to all pressurized fluid circuits.

A rotary three-way valve 2 is shown arranged to con, neet a hydraulic jack 3, either with a pipe 6 carrying fluid under pressure or a discharge pipe S. The valve 2 is mechanically linked to a piston 10 by a transmission system comprising a piston rod 12 provided with a rack 14 engaging a pinion (not shown) connected to the valve 2 for rotation therewith. The Ipiston 10 is slidable in `a cylinder 16 which is normally in communication with a source (not shown) of pressure fluid through a pipe 18-18" through a valve 20, called the unlock valve, which allows this communication to be momentarily interrupted whileY simltaneously providing free commnication between the two

end chambers

36 and 34 at opposite sides of the piston through pipes 22 and 24.

The preselectively operable control means acting on the valve 2 is i'llustratively shown as a manually operable push button 26 linked through a helical spring 28 to a piston rod 30 extending from the piston 10.

In the position as shown in FIGURE 1, the jack 4 is under pressure and the valve 2 remains locked in a position which supplies pressure fluid to the jack due to the fact that the piston is positively held at Ione end of the cylinder 16 'by pressure uid admitted lthrough the valve 20 and the pipes 18, 18'. In order to preselectively actuate valve 2, the button 26 is held continuously pressed in the direction indicated 'by the arrow 32 Ibut the valve is held against operation by the locking action of the piston 10, and the sole result of pressing the button 26 is the compression of spring 2S. Of course, as already mentioned, the pressure of the fluid admitted into cylinder 16 and the surface area of the piston 10 are chosen in such a way as to insure that the hydraulic locking of the piston 10 will not ybe overcome by the vforce exerted by the button 26 through the spring 28.

The operation or non-operation of the jack 4 may thus -be preselected at any time lby appropriate positioning of the button 26, which is held in the preselected position by conventional means (not shown) and the preselected operation or non-operation will beco-me effective only when the locking valve 20 is momentarily rotated 90 to the position shown in FIG. 1a. At that moment, the piston 10 is unlocked, then, due to tthe force of the compressed spring 28 and/or the force exerted on the button 26 it slides freely to the right of the diagram, and the flu-id contained in chamber 34 of the cylinder is forced to the opposite chamber 36 'by the piston through pipe 24, valve 20 and pipe 22. The valve 2 is thus rotated to the position as indicated in FIGURE la and jack 4 drains through pipe 8.

The locking valve 20 can then be returned to its initial position thus locking the piston 10 in place at the other end of the course of travel thereof and permitting another preselective inverse command of valve 2 by pulling on the button 26 in a direction contrary to arrow 32, which action will only take effect at the time of the momentary manipulation of locking valve 20.

Of course, it is preferable to employ a pressurized fluid source common to the device(s) under command 4 and the locking cylinder 16. Thus pipe 6 may be joined to

pipes

18 and 18.

In the embodiment as represented in FIGURE 2, a locking piston 10 sliding in a cylinder 16 is directly coupled, by its rod 12', to the slide 38 of a sliding valve. The cylinder 16', which is closed by

ends

40 and 42, is the prolongation of the valve body 44 which can be a cylinder open at one end.

In the position of the slide 38 as shown in the diagram, the

shoulders

46, 48 and 50 of said slide put a pressurized oil feed pipe 52 into communication with the drain pipe 54 which leads to one of the two ends of a double acting jack 4', which is the apparatus under command. At the same time, the slide puts a drain pipe 56 into communication with the conduit 58 at the other end of the jack 4.

The two

chambers

34 and 36 as delimited in the locking cylinder 16 lby the piston 10 are connected respectively -by

pipes

60 and 62 to

pipes

54 and 58. As a result, in the position as shown in FIGURE la, the slidepiston combination is kept hydraulically locked to the left end of the course of travel by the oil pressure in chamber 34 so that the means of com-mand may be preselectively activated without their having any immediate eifect. By way of example electro-magnetic command means have been represented in FIGURE 2 consisting of an armature 64 linked to the slide :by a rod 66 4- controlled by one or "the other of the two solenoids 68 and 70. All other known means for controlling electrovalves may be used.

If the solenoid 70 is preselectively activated, thereby tending to urge the slide to the right, the pressure applied to the locking piston 10 prevents the slide from moving. The operation only becomes effective when the unlock valve 20 is moved to the position shown in FIGURE 2a such that pipe 52 is linked to drain pipe 72. Chamber 34 is thereby drained through pipes 60-54 and the slide is then `free to move under the influence of the command means, that is to the right end of the course of travel, the piston finally coming to rest against stop 42. In this position of the. slide, the shoulders 46- 48 establish a connection between

pipes

58 and 52 as well as `between

pipes

54 and 56.

As soon as the unlock valve 20 is returned to its initial position (FIGURE 2), the pressurized oil again flows through pipe 52, the central portion of the valve body, pipe 58 and the right extremity of the jack 4' thereby forcing the piston to the left. The oil forced out by the jack piston drains through pipes 54 and 56'. The oil pressure equalizes in chamber 36' through pipe `62 so as to maintain the slide locked in its new position. At this moment, the command means may be de-activated, that is, the solenoid 70 may Ibe de-energized (this operation being accomplished manually or automatically) and the valve is then ready to preselectively receive a new order.

FIGURE 3 represents a variant of the embodiment as revealed in FIGURE 2. According to this variant, the locking piston 10' does not function as a double-acting jack, that is the locking pressure is not alternately applied to rst one piston face and then the other. Rather, to obtain the locking effect, the pressure is applied to the I exterior face of one or the other of the

end pistons

10 and 50 of slide 38, the body 44 of the valve, following this variant, being closed at its two extremities by end walls 40 and 74 which determine the two locking

chambers

36 and 76. In effect, this modification eliminates the intermediary closure element 42 as shown in FIGURE 2 and replaces i-t with a closure element at the extremity of the valve body. It will be observed that chamber 76- in FIG- URE 3 plays the same role as chamber 34 in FIGURE 2 and that it is connected by pipe 60 (analogous to pipe 60) to conduit 54 which leads to the apparatus under command (not represented).

The valve command means as indicated in FIGURE 3 are electro-magnetic and elastic: a solenoid 70, when energized, tends to urge the armature 64, which is fixed to the slide, to the right while a helical compression spring 78 tends to urge the slide 38 to the left.

In the position as shown in the diagram, the pressurized fluid admitted through pipe 54 from the apparatus under command and into chamber 76 by pipe 60 locks the slide so that solenoid 70- may be preselectively energized but will only operate when the locking valve 20r momentarily drains the circuit.

In the opposite position of the slide, the fluid pressure in chamber 36 locks the valve and holds it stationary against the action of the spring 78 which cannot move it to the left until the unlock valve 20 has been momentarily activated.

FIGURES 4, 4a and 5 reveal several positions of an alternate embodiment of a preselective command valve: conforming to the invention in which are combined, in. the interior of the same valve body 44', a hollow, dis-v tributor slide 38", a locking piston 10 and valve command means which are preferably of an hydraulic type, and include a movable piston 80 running in a cylinder 82, which cylinder is integral with the valve body. The distributor slide 38 is, as in the variant as shown in FIG- URE 3, urged to the position represented in FIGURE 4 by a spring 78.

. The preselective command valve controls the flow of pressurized oil into (FIGURE 4) or out of (FIGURE,

5) chamber 84 of one or several jacks 4 (or other apparatus under command), in which jacks the opposing charnber 84' can normally be subject to the oil pressure through pipe 90 (as in the case of a differential jack piston as shown in FIGURES 4 and 5).

The operation of the device is similar to that of the embodiments already described and it is sufficient to mention that in the position as represented in FIGURE 4, the pressurized fluid preferably oil, flows from its source via pipes 52-52 to the interior of the distributor slide 38 through orifices 92 and then to the jack 4 through pipe 86. The drain pipe 94 is closed olf by the cylindrical portion 96 of the slide-distributor and the high pressure found in the body of the valve is applied against the right face of piston in order to maintain the slide locked. The valve may therefore be preselectively commanded by admitting command pressure into chamber 82 through pipe 98. This command pressure and the crosssection of the piston face being chosen to insure that the force exerted to the right be less than the locking force which is applied in the opposite sense, the slide remains in position until its unlocking is effected by turning valve momentarily to the position as shown in FIGURE 4a in which the pressurized lluid feed through pipe 52' is temporarily interrupted while pipe 52 is linked to drain pipe 72. The locking pressure on the piston falls as a consequence and the distributor slide is free to respond to the command means, that is to the pressure exerted on piston 80. Said piston then moves to the position as indicated in FIGURE 5 in which the drain pipe 94 is opened and put int-o communication with pipe 86 of the jack 4 through orifices 92 and the interior of the slide.

As soon as the unlock valve is returned to its initial position, the pressurized fluid is again admitted into pipes 52-90 and into chamber 84 of jack 4 in which piston 88 is forced to the left (FIGURE 5) while the fluid which had been in chamber 84 is drained out through pipe 94.

At the same time, pressure is applied to the left face of piston 10 which serves to hold the slide locked in its new position against the action of spring 78 even when the command pressure is no longer applied in chamber 82.

The combination of many valves conforming to those already described adapts particularly Well to the preselective command of 4gear boxes combined, with the command of a clutch which has -been represented in FIG- URES 4 and 5 in dotted lines. A clutch 100 can be activated by a jack 102 supplied with uid by pipe 104 branched onto pipe 52.

While the unlock valve 20' is in its normal position, the clutch is engaged but disengages when valve 20 Iis momentarily turned to the unlock Iposition as shown in FIGURE 4a by draining through

pipes

72 and 104. The clutch disengages during the intermediate phase of the distributor slide displacement, that is during the time the gears are disengaging or engaging, as dictated by the movements of the command jack 4, and a delay in the clutch action may be introduced if necessary, as follows.

FIGURE 6 is a schematic representation of a hydraulic preselective command circuit conforming to the invention as applied to a three speed gear box 106 in which the chan-ges in ratios are effected by three jacks 41-42-43. The three valves 441-442-443-contro11ing the operation of these jacks are, for example, of the type as shown in FIGURES 4 and 5 and the Ipipes associated with them carry the same reference numbers, with the indices 1-2-3 as in the diagram.

A single unlock valve 20 is connected to the three valves by pipe 52 which branches out into three directions 521-522-5211.

The combination is supplied with pressurized oil by a pump 108 which draws the oil from a tank 110 and charges an oleo-pneumatic accumulator 112. The pressurized oil fed by pipe 114 serves generally to supply the preselective command means of the valves (pistons 6 and cylinders -82 in (FIGURE 5') through a selector 116 interposed between pipe 118 and the three pipes 98-98-98, feeding the command pressure to the valves 44. The drain pipes 72 and 94 (identical to those indicated in FIGURES 4 and 5) return the oil to the tank 110.

The function of the valves has been suticiently described in connection with the preceding embodiments so that it suices to mention that the sole momentary operation of the unlock valve 20 brings labout a change in position in all valves having received a preselective pressure signal opposing the respective position they Occupied at the time and the automatic return (due to the eifect of spring 78) to the position as lshown in FIG- URE 4 of the valves which have received nopressure signal and which previously occupied the position as indicated in FIGURE 5. The selector 116 can be disposed in the form of a combiner to control the movements of the gear trains and successively change the gear ratios. The simultaneous operation of clutch is identical to that described in connection with FIGURES 4 and 5, but an elastic accumulator 120 :and a calibrated throttle 122 are preferably inserted in the circuit to delay the clutching action during engage and disengage of the gear trains. A jack 124 controlling a braking device 126 for the gear box may be branched onto pipe 104 of the clutch jack 102. Normally, the oil pressure in jack 124 holds the brake open but, during the momentary manipulation of the unlock valve 20', the oil drains thro-ugh

pipes

104 and 52 thereby freeing the brake which is moved to its braking position by return spring 128.

FIGURE 7 is a cross-section view of a block of four preselective command valves conforming to the invention and capable of controlling, for example, a four-speed gear box.

Each of the valves may include a hollow, distributor slide 381 38', the whole central portion of which 101 constitutes the locking piston.

According to their respective positions, the slides connect control pipes 861, 862, with either the oil feed line 52 or the dra-in pipe 56. In the case indicated in the diagram, the jack controlled by the first and fourth valves are in the drain position while the jacks controlled by the second and third valves are under pressure.

The control of the valves is accomplished hydraulically, as in FIGURES 4 and 5 Where the piston plungers 801, 802-which run in the command cylinders 821, S22-themselves are fed with pressurized oil by pipes 981, 982. The piston rods 1301, 1302 can act on slides 381', 382 simply by pushing aginst them in opposition to the force of springs '781, 782 .thus avoiding any problems in centering the slides or piston guides 801, 802 Such a valve block may be economically realized in three parts. A principal valve casing fitted with the oil feed 52 and 4drain 56-56 lines, an attached piece 134 grouping the command pipes 861, 862

and a control block 136 on which are grouped the hydraulic command means 801-821-981, the three parts being assembled in a convenient manner and joined with oil-tight ring seals such as 13S-140.

Of course, the invention is not limited to the examples described and represented and is susceptible to numerous variations accessible to men skilled in the art without departing from the spirit of the invention.

Accordingly, the closing component of the preselective valve following the invention may take a form other than the slides shown and may be, for example, a doubleseated valve, a rotating plug, etc.

What is claimed is:

1. A two-position valve, with preselective command, for the control of a pressurized fluid circuit, comprising .at least a piston running in a cylinder, said piston being mechanically linked to the movable selector component of said valve, said cylinder being normally in communication with a pressurized fluid source which selectively acts on one of the faces of said piston to hold it in one of the two positions at the ends of its course of travel where said piston locks said movable component in one of its two positions against the force of command means controlling said movable component, said valve including releasing means for freeing said movable component in response to the interruption of the above-mentioned communication between the fluid source and the face of said piston subjected to pressure and for re-establishing the communication between said source and the other face of said piston when said movable component has changed position un-der the effect of said command means. so as to lock said movable component in its new position.

2. A valve as claimed in claim l wherein the movable selector component `consists of a slide running in a valve casing, said slide being an integral part of at least a piston sliding in a part of said valve casing constituting a locking cylinder for said piston.

3. A valve as claimed in claim 2 for the preselective control of the dow :and draining of pressurized lluid to and from at least an apparatus under command, more especially a jack, wherein the part of the valve casing constituting a locking cylinder for the above-mentioned piston is normally in communication with the same pressurized fluid source as that leading to the apparatus under command.

4. A valve as claimed in claim l, wherein the command means of the movable selector component are electro-magnetic.

5. A valve as claimed in claim 2 wherein the command means of the closing component are hydraulic or pneumatic, said means including an additional piston integral with the above-mentioned slide and running in another part of the valve casing in which the command pressure may be preselectively established or interrupted.

6. A valve as claimed in claim 5 wherein the abovementioned command pressure and the effective diameter of the additional piston are such that the command force exerted on the slide is less than the locking force exerted on said slide.

7. A preselective valve according to claim 1, wherein .the above-mentioned rele-asing means consist of a three port Valve which normally establishes communication between the pressurized fluid source and said preselective valve but can selectively connect said preselective valve to exhaust to free the selector slide from the locking action of said pressurized iluid on one of the faces of the locking piston.

8. A preselective valve according to claim 1, which includes elastic means for returning the mov-able selector component to one of its two positions.

9. A preselective command valve having control over a hydraulically activated apparatus, comprising a piston running in a valve casing, said piston being normally `locked in one of two positions by uid pressure on one of its faces, said uid pressure being sufficient to overcome in the said pistons initial position, a hydraulic, preselective command signal on the opposite end of said piston; a two-position releasing valve in the feed line of said fluid which may .be momentarily manipulated so as to cut-off the source of `fluid pressure on the initial locking face of said piston and temporarily vent the chamber associated with said face to a drain pipe thereby freeing the piston to respond Vto the preselective command signal; a spring tending to urge the piston back to its original position against the greater hydraulic locking force exerted on the reverse face of said piston by the fluid pressure which is newly established in said chamber by returning said two-position valve to its initial position, thereby holding said piston in its alternate position; and a hollow, distributor slide, being the prolongment of said piston, fitted with orilices which, in said slides initial position connect said apparatus to said fluid source and connect, in said slides alternate position, said apparatus to a drain line.

10. A preselective fluid pressure control device comprising: a control valve including a control element movable between two limiting positions; duct means connected to supply pressure uid to said control valve, said control valve including means for continuously applying said pressure uid to said control element to hold said control element positively in either of said two limiting positions; utilization means connected to said control valve to receive said pressure fluid therefrom, movement of said control element from one of said limiting positions to the other selectively controlling the supply of pressure fluid to said utilization means; locking valve means serially included in said duct means, said locking valve means normally permitting said pressure fluid to be continuously supplied to said control valve, actuation of said locking valve means interrupting said supply whereby said control element is freed to move between said limiting positions and said supply is shut olf from said utilization means; and preselective means acting on said control element and selectively operable with said locking valve in its normal position continuously to urge said control element to move from one of said limiting positions to the other or to cause the same to remain stationary in either of said limiting positions, whereby momentary actuation of said locking valve means permits said control element to move between said limiting positions or to remain stationary in accordance with the operation of said preselective means, restoration of said locking valve means to its normal position causing said pressure fluid to be re-supplied to said utilization means in accordance with the preselective operation of said preselective means.

11. A preselectively controllable fluid pressure operated device comprising: a plurality of Huid pressure operated jacks; a separate control valve connected to supply pressure fluid to each of said jacks, each control valve comprising a control element movable between two limiting positions; duct means connected to supply pressure fluid simultaneously to all of said control valves, each control valve including means for continuously applying said pressure fluid to its control element to hold said control element positively in either of said two limiting positions, the operation of each jack being selectively controlled by the position of the control element within the control valve to which it is connected; locking valve means serially included in said duct means, said locking valve means normally permitting said pressure uid to be supplied continuously to all of said control valves, actuation of said locking valve means interrupting said supply whereby every control element is freed to move between said limiting positions and said supply is shut ofic from all of said jacks; and preselective lmeans operable with said locking valve in its normal position and acting on said control elements to urge preselected ones of said elements continuously to move from one of said limiting positions to the other and to cause preselected others of said elements to remain stationary in either of said limiting positions, whereby momentary actuation of said locking valve means permits said preselected ones of said control elements to move between said limiting positions, said preselected others of said elements remaining stationary, restoration of said locking valve means to its normal position causing said vpressure fluid `to be resupplied to said jacks in vaccordance with the operation of said preselective means.

12. A device according to claim 11, further comprising a gear box controlled by said jacks.

13. A device according to claim 11, further comprising: a gear box controlled by said jacks; a clutch connected to said gear box; and fluid pressure operated clutch control means connected to said duct means intermediate said locking valve means and said control valves, said clutch control means continuously holding said clutch engaged with said locking valve means in its normal position, said clutch being disengaged during actuation of said locking valve means.

14. A device according to claim 13, further comprising uid ow restricting means interposed between said Clutch control means and said duct means for delaying re-engagement of said clutch upon restoration of said locking valve means to its normal position.

15. A device according to claim 13, further comprising uid pressure operated brake means connected to said duct means intermediate said locking Vaive means and said control valves, said brake means braking said gear box during disengagement of said clutch.

References Cited by the Examiner UNITED STATES PATENTS M. CARY NELSON, Primary Examiner.

lo HENRY T. KLINKSIEK, Examiner.

Claims

1. A TWO-POSITION VALVE, WITH PRESELECTIVE COMMAND, FOR THE CONTROL OF A PRESSURIZED FLUID CIRCUIT, COMPRISING AT LEAST A PISTON RUNNING IN A CYLINDER, SAID PISTON BEING MECHANICALLY LINKED TO THE MOVABLE SELECTOR COMPONENT OF SAID VALVE, SAID CYLINDER BEING NORMALLY IN COMMUNICATION WITH A PRESSURIZED FLUID SOURCE WHICH SELECTIVELY ACTS ON ONE OF THE FACES OF SAID PISTON TO HOLD IT IN ONE OF THE TWO POSITIONS AT THE ENDS OF ITS COURSE OF TRAVEL WHERE SAID PISTON LOCKS SAID MOVABLE COMPONENT IN ONE OF ITS TWO POSITIONS AGAINST THE FORCE OF COMMAND MEANS CONTROLLING SAID MOVABLE COMPONENT, SAID VALVE INCLUDING RELEASING MEANS FOR FREEING SAID MOVABLE COMPONENT IN RESPONSE TO THE INTERRUPTION OF THE ABOVE-MENTIONED COMMUNICATION BETWEEN SAID SOURCE AND THE OTHER SAID PISTON SUBJECTED TO PRESSURE AND FOR RE-STABLISHING THE COMMUNICATION BETWEEN SAID SOURCE AND THE OTHER FACE OF SAID PISTON WHEN SAID MOVABLE COMPONENT HAS CHANGED POSITION UNDER THE EFFECT OF SAID COMMAND MEANS. SO AS TO LOCK SAID MOVABLE COMPONENT IN ITS NEW POSITION.