US3853037A

US3853037A - Pneumatic holding device

Info

Publication number: US3853037A
Application number: US00239143A
Authority: US
Inventors: E Denzler; R Widmer
Original assignee: HA Schlatter AG
Current assignee: HA Schlatter AG
Priority date: 1971-04-06
Filing date: 1972-03-29
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10
Also published as: BE780994A; CA947590A; CH518158A; DE2211909A1; AU464983B2; AU4028472A; FR2132061B1; GB1352963A; SE382770B; IT960307B; FR2132061A1; NL7202788A

Abstract

A pneumatic holding device with at least one piston which can be impinged with a pressurized fluid medium at one face and displaceable in a cylinder against the action of a restoring force. The cylinder connection leading to the impinged face of the piston can be obturated by a valve mechanism which can be closed by the impinging fluid medium. The valve mechanism contains a valve body in which there is mounted a check or relief valve which opens in the direction of closing of the valve body. When open the valve mechanism communicates the impinged face of the piston with the face of the piston not impinged by the fluid medium.

Description

Denzler et a1.

14 1 Dec. 10, 1974 Ott et a1 92/151 X Potepalov et a1 137/525 FORElGN PATENTS OR APPLICATIONS 11/1950 Sweden 91/447 Primary Examiner-Irwin C. Cohen Attorney, Agent, or Firm-Ostro1enk, Faber, Gerb &

ABSTRACT A pneumatic holding device with at least one piston which can be impinged with a pressurized fluid medium at one face and displaceable in a cylinder against the action of a restoring force, The cylinder connection leading to the impinged face of the piston can be obturated by a valve mechanism which can be closed by the impinging fluid medium. The valve mechanism contains a valve body in which there is mounted a check or relief valve which opens in the direction of closing of the valve body. When open the valve mechanism communicates the impinged face of the piston with the face of the piston not impinged by the fluid 2 Claims, 2 Drawing Figures PNEUMATIC HOLDING DEVICE 3,485,141 12/1969 3,584,639 6/1971 [75] Inventors: Emil Denzler, Sprertenbach; Robert Widmer, Windisch, both of Switzerland 130 221 [73] Assignee: H. A. Schlatter A.G., Schlieren,

Switzerland [22] Filed: Mar. 29, 1972 soffen [21] Appl. No.: 239,143

[30] Foreign Application Priority Data Apr. 6, l97l Switzerland 5071/71 [52] U.S. C1 91/440, 91/442, 137/493.1 [51] Int. Cl. ..F1Sb 11/08, Fl5b 13/042 [58] Field of Search 91/440, 442, 268

[56] References Cited UNITED STATES PATENTS 1,441,759 1/1923 Schwennker 91/442 1,681,579 8/1928 Farmer 92/78 2,888,909 6/1959 Gratzmu1ler.... 9l/442 3,307,454 3/1967 Larsson 92/161 x medlum- 3,456,561 7/l969 Laikam, Jr 1. 91/440 3,464,321 9/1969 Piotrowski, Jr. 91/442 \I\ )KVX \IY \X 3 fi ze 9 "T a \LAL PNEUMATIC HOLDING DEVICE BACKGROUND TO THE INVENTION The present invention relates to a new and improved construction of pneumatic holding or supporting device with at least one piston which can be impinged by a pressurized fluid medium at one face and which is displaceable in a cylinder against the action of a restoring or return spring.

Such devices are especially used in the construction of equipment where, during a given time, it is desired to generate a certain holding force, such as for instance for fixedly supporting a workpiece upon the work table of a processing machine.

Among other things three requirements are placed upon such holding devices. Firstly, at the end of the work stroke the holding jaw connected with the piston rod should arrive at the workpiece as free as possible from impact and only thereafter should there be generated the complete holding force. Secondly, the holding force, when no longer required, should be reduced as quickly as possible and the holding jaw should participate as quickly as possible in the return stroke. Thirdly, there should be present as little noise as possible, especially during venting.

The first requirement has attempted to be previously fulfilled in that the build-up of pressure in the cylinder during the work stroke has been controlled, for instance, by supplying same via a throttle location or throttle valve. Owing to the foregoing the second and third requirements could not be previously simultaneously and optimally fulfilled. In the interest of achieving a rapid return stroke the cylinder was either suddenly vented, while taking into account considerable noise, or attempts were made to reduce the development of noise by slowly venting the cylinder, but ,in such case there had to be taken into account the drawback that pressure reduction only took place very slowly. I

SUMMARY OF THE INVENTION and is not associated with the aforementioned drawbacks and limitations of the prior art proposals.

Another objective of the present invention relates to an improved holding device or holding unit of the aforementioned type wherein all three of the previously discussed requirements can be optimally fulfilled.

Yet a further significant object of the present invention relates to a new and improved construction of pneumatic holding device which is relatively simple in design, economical to manufacture, not readily subject to breakdown, requires a minimum of maintenance and servicing, and enables the holding force to be both producedin a controlled manner and quickly reduced, and affords relatively quiet operation of the system.

To implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the invention is directed at designing the holding device in such a manner that the return force can be immediately effective independently of the pressure conditions prevailing at the cylin der, that is to say, independently of the momentary degree of venting, and as soon as the'device is cut-off from the pressure source and vented.

In order to carry out the objectives of the invention the proposed holding device as contemplated by this development is manifested by the features that the cylinder connection leading to the face or side of the piston which is impinged by the pressurized fluid medium can be operated by means of a valve mechanism which can be closed by the impinging fluid medium. This valve mechanism has a valve body at which there is mounted a check or relief valve which opens in the closing direction of the valve body. The valve mechanism in its open position communicates the impinged face of the piston with the non-impinged face thereof.

Owing to the above-described construction as soon as the impinging fluid medium is no longer present the valve mechanism is opened by the pressure still present in the cyliner. Consequently, there is obtained an immediate pressure equalization between the impinged and the non-impinged faces of the piston, enabling the restoring force to become immediately effective.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a schematic longitudinal sectional view through a preferred constructional form of holding device or holding unit as designed according to the teachings of this invention; and

FIG. 2 is a fragmentary sectional view through a portion of a modified embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, the exemplary illustrated embodiment of holding device or holding unit 1 depicted in FIG. 1 will be understood to comprise a cylindrical housing 2, at one end or end face 3 of which there is formed a guide opening 5 equipped with a seal 4, this guide opening 5 guiding a piston rod 6 which extends towards the outside. A cylinder 8 is arranged internally of the housing 2 while maintaining free therebetween a jacket space or outer compartment 7. In the embodiment under consideration the cylinder 8 possesses a so-called tandem construction, that is to say, it contains two axially aligned cylinder compartments 9 and 10 separated from one another by a partition of separation wall 11.

At the center of the partition wall 11 there is formed a substantially hub-shaped contact or impact support 12 which, in turn, possesses a further guide bore 14 for the piston rod 6, guide bore 14 being equipped with a seal 13, as shown.

The tandem construction of the cylinder 8 automatically leads to the same type of construction for the piston 70. Specifically, in each of the cylinder compartments 9 and 10 there is mounted a piston plate 15 and 16 respectively so as to be movable to-and-fro. As is standard practice at the periphery of each piston plate 15 and 16 there is provided a circumferential seal 17 by means of which, together with the associated piston plate, each cylinder compartment 9 and 10 is subdivided into a chamber or

section

9a and 10a respectively which is impinged by pressurized fluid medium and a chamber or section 9b and 10b respectively which is not impinged by such fluid medium.

The piston plates and 16 are seated upon the common piston rod 6 in which between both piston plates 15 and 16, there is formed an axial bore 18 which at one end has ports or throughflow openings 19 leading radially out of thepiston rod 6, as shown. Bore 18 and ports 19 thus always flow communicate with one another the

chambers

9a and 10a of the cylinder compartments 9 and 10 respectively which are impinged by the pressurized fluid medium.

Between the partition wall 11 and the non-impinged face 16a of the piston plate 16 there is arranged a pressure or compression spring 20 which in the pressureless condition of the system retains the piston 70 in the position depicted in FIG. 1.

One end of the cylinder 8 is secured in any convenient manner to the end face 3 of the housing 2, whereas the cylinder 8 carries at its opposite end a closure flange 21, at the center of which there is formed a connection port or opening 22. The peripheral edge of this connection opening 22 which protrudes past the closure flange 21 is constructed as a valve seat 23 for a valve plate 24 ofa valve mechanism or unit 71. At the flat face 24a of the valve plate 24 confronting the valve seat 23 there is mounted a suitable sealing ring 25. Valve plate 24 also carries a seal 29 at its periphery and, similar to the piston plates, is mounted to be displaceable longitudinally a valve compartment 27 formed at the other end face 26 of the housing 2. A connection opening or port 28 leads to the valve compartment 27 and by means of which the illustrated holding device or unit 1 can be connected via a schematically illustrated compressed air conduit 31 and a suitable valve, such as the electromagnetic 3/2-way valve 32 with a source of pressurized medium e.g. compressed air source 33.

Whereas the fluid medium-impinged

chambers

9a and 10a of both cylinder compartments 9 and 10 respectively, as mentioned, are always in flow communication via the bore 18 and the throughflow openings or ports 19 at the piston rod 6, the non-impinged chambers or sections 9b and 10b of both cylinder compartments 9 and 10 respectively, are likewise continuously in flow communication with one another. This is accomplished in that there are provided at the walls of the cylinder compartment 9 and cylinder compartment 10, at the region of the dead-center points of the piston plates 15 and 16 respectively appearing at the left of the drawing, the openings or ports 34 and 35 which connect the associated cylinder compartments 9 and 10 directly with the jacket or outer compartment 7. Finally, the jacket compartment 7 is continuously connected via a small opening 36 with the ambient air.

The mode of operation of the illustrated embodiment of holder device or holder unit is as follows: If the valve 32 is moved out of its illustrated position, then there is connected the compressed air source 33. Thus initially the valve plate 24, under the action of the incoming compressed air, is displaced towards the left in its valve closing or closure position upon the valve seat 23. Consequently, the connection 22 is cut-off from the jacket 4 or outer compartment 7. The check or relief valve opens and in accordance with its throughflow capacity compressed air flows to the impinged

chambers

9a and 10a of the cylinder compartments 9 and 10 respectively. The thus occuring pressure build-up, after overcoming the force of the spring 20, displaces the piston plates 15 and 16 towards the left until the piston plate 16 comes to bear against the free end face of the contact piece or stud 12. When this condition has been reached then the pressure in the fluid mediumimpinged chambers of the cylinder compartments 9 and 10 corresponds approximately to the pressure delivered by the compressed air source 33.

In this condition it would be possible to switch-off the compressed ait source 33 by closing the conduit 31 or the throughflow opening 28. If there is not taken into account possible leakage losses past the piston seals 17 the holding unit will remain with the piston rod 6 in extended position because the valve mechanism 71 with the valve components 23-24-25 remains closed. The reason for this resides in the fact that he surface of the face 24b of the valve plate 24 confronting the compartment 27 is greater than the surface of the other face 24a of the valve plate 24 circumscribed by the ring seal 25.

Since both faces of the valve plate 24, that is to say, the face 24b confronting the compartment 27 and the face 24a confronting the connection 22 are impinged by the same pressure there is provided for the valve plate 24 a resultant force effective towards the left of the drawing.

Even with smaller leakage losses past the piston seals 17, i.e. with a slight pressure loss in the cylinder compartments, the check valve 30 opens for pressure equalization between both faces of the valve plate 24.

In the event that the return stroke should be initiated, then it is sufficient to withdraw the valve 32 back into the illustrated solid line position. In so doing only the compartment 27, which possesses a considerably smaller volume than the stroke volume or swept capacity of the cylinder compartments 9 and 10, is vented. The check valve 30 instantly closes and the valve plate 24 immediately shifts towards the right, so that the valve mechanism 71 with the valve components 23-2- 4-25 is opened. As a result, however, there immediately takes place a pressure equalization in the cylinder compartments 9 and 10 to both sides or faces of the piston plates 15 and 16 owing to the jacket compartment 7 and the openings 34 and 35, so that the spring 20 immediately comes into play even if the total pressure prevailing in the housing 2 is still considerably higher than theatmospheric pressure of the surroundings.

Independent of the return stroke of the pistons 15 and 16, with the opening of the plate valve unit 71 there begins the venting of the holder device 1 via the opening 36. Since the throughflow capacity of this opening 36 is however limited the quantity of air located in the holder unit is not suddenly expanded, which otherwise could lead to the heretofore known and experienced undesired noise. Quite to the contrary, venting of the device takes place slowly, which in the most favorable situation is accompanied by a hissing sound which can be readily tolerated. Additionally, those skilled in the art will recognize that even when venting of the device has not yet been completed it is possible to initiate the next work stroke. In practice the volume content of the jacket compartment 7 with regard to the inner volume or swept capacity of the cylinder 2 and with regard to the throughflow-capacity of the opening 36 are accommodated to one another in such a manner that presupposing a periodic work stroke the jacket compartment 7 so to speak acts like an expansion chamber or surge tank and venting occurs continuously via the opening 36.

The illustrated and described construction of holder unit or holder device of this invention possesses a still further advantage. Since the return stroke of the piston 70 embodying the piston plates 15, 16 takes place at a higher pressure than the atmospheric pressure of the surroundings, during the return stroke there does not occur any suction action upon the non-impinged face of the piston plates 15, 16. Accordingly, measures are also provided which ensure that no contaminants are sucked-up from the surroundings which, as is well known, could considerably reduce the longevity of the seals, in this case the seals 4, 13 and 17. i

It should be understood that the invention is not limited to the exemplary illustrated tandem construction. If it is imagined for instance for the illustrated embodiment of holder device 1 that the opening 35 is closed, the bore 18 closed, there is omitted the piston plate and the partition wall 11 is displaced to the left and coincides with the end wall 3, then there is realized a construction of holder device which as far as its external dimensions are concerned is approximately of the same size, however, has approximately twice the stoke with approximately half the force.

Continuing, in FIG. 2 of the drawings there is illustrated a variant embodiment of inventive holder device or unit in which the valve mechanism 71 embodying the components 23, 24, is indirectly controlled by the impinging fluid medium, i.e. is servo-controlled. By referring now to FIG. 2 more specifically there will be recognizeda portion of the housing 2 in which there is arranged the cylinder 8 while again maintaining free therebetween the jacket or outer compartment 7. The closure flange 21 of the cylinder 8 is constructed in the same manner as for the embodiment of FIG. 1. The valve plate 24 on the other hand is not only mounted so as to be displaceable to-and-fro within the valve compartment 27, rather additionally is subjected to the action of compression or pressure springs which strive to displace valve plate 24 to the right of FIG. 2, that is into its open position. Furthermore, a piston extension or projection 41 is formed at the valve plate 24, which, in turn, is displaceably mounted in a piston compartment 42 and leads to the check or relief valve 30 via the onethroughflow opening 43 communicating with such check valve. The piston projection 41 carries at one end a seal 44 which is destined to cooperate with the throughflow opening 46 at the piston compartment 42, which throughflow opening 46 was a valve seat 45. The throughflow opening 46 opens into the inlet 47 to the holder device which is directly connected with a compressed air network.

A further throughflow opening 48 leads from this inlet 47 into the valve compartment 49 of a solenoid valve 50. From this valve compartment 49 there leads a further continuously open throughflow opening 51 into the valve compartment 27 as well as past the plunger-type armature 52 of the solenoid valve which is subjected to the action of a compression or pressure spring 53, to a throughflow opening or channel 54 which opens into the jacket or outer compartment 7. The plunger-typearmature 52 is provided at both' end faces with the seals SSwhich serve to close the mouths of the throughflow openings 48 and 54 depending upon the position of such armature 52.

The mode of operation of this embodiment of the invention is as follows: It is assumed that the inlet 47 is directly connected to a compressed air source and that the coil of the solenoid valve 50 is not excited. Accordingly, the plunger-type armature 52 is in its extended position and closes by means of its seal 55 the mouth of the throughflow opening 48. The throughflow openings 51 and 54 are in communication with one another and therefore also the face 24b of the valve plate 24 facing away from the cylinder 8 with the face 24a of the valve plate 24 confronting the cylinder 8. Thus at both sides of the valve plate 24 there prevails the same pressure, causing the compression springs 40 to raise the valve plate 24 from the valve seat 23 and the therewith connected piston 41 to shift until the throughflow opening 46 is closed by the seal 44. At this point it is to be mentioned that the compression or pressure springs 40 are designed such that their force overcomes the force of the pressure at the inlet 47 upon the surface circumscribed by the seal 44 of the piston extension 41. If however the inlet 46 to the piston compartment 42 is closed then no compressed air arrives at the throughflow opening 43 and therefore at the cylinder 8. The holder unit remains in its retracted position.

Now if the coil of the solenoid valve 50 is excited or energized, then the plunger-type armature 52 is pulledin and therefore the throughflow opening 48 is freed, whereas on the other hand the throughflow opening 54 is closed-off. Now compressed air flows via the throughflow opening 48, the valve compartment 49 and the throughflow opening 51 into the valve compartment 27 of the valve plate 24, in which compartment pressure builds up, the action of which upon the much larger free surface of the valve plate 24 (in comparison to the surface at the piston extension 41 circumscribed by the seal 44) is capable of overcoming the force of the compression or pressure springs 40. Hence the valve plate 24 in FIG. 2 is thus displaced towards the left, that is to say, by means of the seal 25 is pressed onto the valve seat 23. At the same time, however, the piston extension 41 is lifted off of the valve seat 45 and thus compressed air flows without obstruction through the throughflow opening 43 from the inlet 47. As a result the throttlecheck valve 30 is opened and at the cylinder 8 there takes place the build up of pressure which displaces the piston (as the pistons 15,16 in FIG. 1) to the left has already been described in conjunction with the embodiment of FIG. 1. This condition is maintained for such time as the coil of the solenoid valve 50 is energized, that is, for such time as the through flow opening 48 is connected via the compartment or chamber 49 with the throughflow opening 51.

As soon as however the coil of the solenoid 50 is deenergized then the throughflow opening 48 is closed and the throughflow opening 54 is opened. Consequently, there occurs a pressure equalization between the face 24a of the valve plate 24 confronting the cylinder 8 and the face 24b thereof which faces away therefrom. Consequently, the compression springs 40 again comes into play which then raise the valve plate 24 away from the valve seat 23 and, on the other hand,

again close the inlet 46. Hence, as already described in conjunction with the embodiment of FIG. 1, there now however also takes place via the jacket compartment 7 an immediate pressure equalization between both faces of the work piston of the holding devices which pistonthus immediately undertakes its return stroke retracting into cylinder 21.

In contrast to the embodiment of FIG. 1, with this embodiment of FIG. 2 for initiating the return stroke of the work piston there is not even directly vented to the surroundings the already relatively small compartment volume of the valve compartment 27, rather the return stroke of the valve plate 24 is initiated by bringing about a pressure equalization to both faces or sides. Furthermore, with the construction as described in FIG. 2 only a very small control valve is required. Whereas for the embodiment of FIG. 1 the valve 32 must possess a sufficiently great throughflow capacity in order to satisfy the take-up capacity of the unit within an acceptable time, the solenoid valve 50 of the embodiment of FIG. 2 need only possess a nominal width of its throughflow of a few millimeters. Accordingly the solenoid valve 50 can be selected to be so small that it can be integrated as a unit in the end wall 26 of the housing.

According to a further feature of this development the reduction in noise realized with both embodiments, and particularly that of FIG. 2 can be even further increased. Instead of the aeration of vent opening 36 which connects the jacket or outer compartment 7 functioning as the expansion chamber with the external air, it is possible to form the cylindrical wall of the housing 2 entirely or partially from a limited air permeable material, for instance by a felt supported by ribs, from a glass fiber structure or from a single or multiple layer wire mesh with very narrow mesh size. This has been conveniently schematically indicated in FIG. 2 by reference character 2a. Consequently, all of the pressure surges which arise at the moment of pressure equalization between both faces of the piston plates 15, 16 and the valve plate 24 at the jacket or outer compartment 7 are not directly vented to the surrounding air, rather only gradually as a function of the throughflow capacity of the vent opening 36 and the limited throughflow capacity of the pervious housing wall 2a as above described.

The described holding device or holding unit of this development therefore will be recognized to simultaneously fulfill in an ideal manner all of the previously mentioned three requirements.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,

What is claimed is:

l. A pneumatic holding device, comprising: a cylinder having a first and an opposite second end;

a partition intermediate the ends of said cylinder dividing said cylinder into separate first and second piston compartments with said first compartment being the closer one to said cylinder first end;

a piston rod for supporting and guiding pistons, said piston rod extending through both said piston compartments toward said cylinder first and second ends;

a first and a second piston supported upon said piston rod andlocated, respectively, in said first and said second piston compartments of said cyliner; both said pistons being sealingly movable through the respective said compartments and each said piston thereby divides its respective said compartment; said pistons being spaced apart on said rod and being simultaneously movable by said rod; said pistons and said piston rod being shiftable axially through said cylinder toward said cylinder ends; both said pistons having a respective first face facing toward said cylinder first end and having a respective second face facing toward said cylinder second end; means normally biasing said pistons toward said cylinder first end;

pressurized fluid inlet having a first cross section and being connected to said cylinder; a valve located between said pressurized fluid inlet and said cylinder; said valve having an inlet communicating with said fluid inlet and an outlet communicating with said cylinder; said valve outlet communicating into said cylinder first compartment at a location such that pressure may be applied through said fluid inlet to the said first face of said first piston; a pressure transmitting conduit communicating between said valve outlet and said cylinder second compartment at a location such that pressure may be applied through said fluid inlet to said first face of said second piston;

said valve comprising: a valve element compartment ofa second cross section larger than said first cross section of said pressurized fluid inlet; a movable valve element in said valve element compartment, said valve element having a cross section such that it is sealably movable through said valve element compartment and being movable in said valve element compartment toward and away from said cylinder under the influence of pressure in said valve element compartment and in said cylinder; said valve element having a pressure inlet side facing toward said valve inlet and said fluid inlet and having a pressure outlet side facing toward said valve outlet and said cylinder;

narrowed passage through said valve element extending across said valve element compartment to join said fluid inlet with said cylinder; a one-way check valve in said narrowed passage permitting only inlet to said cylinder through said narrowed passage;

said cylinder carrying a valve seat for said valve element against which said valve element pressure outlet side is scalable; when said valve element pressure outlet side, which said section has a third cross-section which is smaller than said valve element second cross-section and which said valve element section is exposed to the sections of said first and said second compartments and thereby is exposed to the cylinder pressure at said first side of both said pistons; with said valve element moved through its said compartment onto said valve seat, the entire said pressure inlet side of said valve element is exposed to the inlet pressure in said fluid inlet and in said valve element compartment;

pressure equalization conduit connected to both said piston compartments in said cylinder at respective locations in said compartments such that said pressure equalization conduit is always at the pressure at both said piston second faces; said pressure equalization conduit also communicating with said piston compartments at respective locations so that it is in communication with said first sides of therefor;

means communicating said equalization conduit di- 10 compartment toward and away from said cylinder under the influence of pressure in said valve element compartment and in said cylinder; said valve element having a pressure inlet side facing toward both said pistons; on the path between the piston said fluid inlet and a pressure outlet side facing tocompartment sides facing said second piston sides ward said cylinder; and the piston compartment sides facing said first a narrowed passage through said valve element expiston sides, said equalization conduit passes said tending across said valve element compartment to valve element and said valve seat, such that with join said fluid inlet with said cyliner; a one-way said valve element on said valve seat, said equalizacheck valve in said narrowed passage permitting tion conduit is blocked, and with said valve eleonly inlet to said cylinder through said narrowed ment off said valve seat, said equalization conduit passage; is open; said cylinder carrying a valve seat for said valve elecylinder housing surrounding and spaced from said ment against which said valve element pressure cylinder and in which said cylinder is mounted and outlet side is scalable; when said valve element is defining, between said cylinder and said cylinder on said seat, said seat defines a section of said valve housing, said equalization conduit in the form of a element pressure outlet side, which said section has jacket compartment around the exterior of said a third cross-section which is smaller than said cylinder; valve element second cross-section and which said said cylinder housing having opposed end faces; said valve element section is exposed to the cylinder valve means being in a valve housing formed at one pressure at said first face of said piston; with said end face of said cylinder housing surrounding said valve element moved through its said compartment cylinder; the other end face of said cylinder housonto said valve seat, the entire said pressure inlet ing having a guide opening for said piston rod and side of said valve element is exposed to inlet pressaid piston rod passing through said guide opening sure in said fluid inlet and in said valve element compartment;

pressure equalization conduit connected to said cylinder at a location such that said pressure equalization conduit is always at the pressure at said piston second face; said pressure equalization conduit also communicating with said cylinder at the side of said cylinder which faces said piston first 2. A pneumatic holding device, comprising: a cylinder having a first and an opposite second end;

at least one piston in said cylinder and shiftable therethrough axially thereof toward said cylinder ends; said piston having a first face facing toward side and so communicating with said cylinder past said valve element and said valve seat such that said cylinder first end and a second face facing towith said valve element on said valve seat, said ward said cylinder second end; means normally biequalization conduit is blocked and with said valve asing said piston toward said cylinder first end; element off said valve seat, said equalization cona pressurized fluid inlet of a first cross section conduit is open;

nected to said cylinder at a location such that presmeans for venting said equalization conduit for relief sure may be applied through said fluid inlet to said 40 of pressure in that said conduit; said equalization piston first face; conduit being in the form of ajacket compartment avalve between said fluid inlet and said cylinder; said on the exterior of said cylinder and said jacket valve comprising: compartment being enclosed by an outer wall; said a valve element compartment of a second crossventing means comprising at least a portion of said section larger than said first cross-section of said jacket compartment outer wall being formed of a inlet; material having limited air permeability, whereby a movable valve element in said valve element comsaid equalization conduit is gradually vented partment and having a cross-section such that it is through said outer wall portion of limited air persealably movable through said valve element commeability. partment and being movable in said valve element

Claims

1. A pneumatic holding device, comprising: a cylinder having a first and an opposite second end; a partition intermediate the ends of said cylinder dividing said cylinder into separate first and second piston compartments with said first compartment being the closer one to said cylinder first end; a piston rod for supporting and guiding pistons, said piston rod extending through both said piston compartments toward said cylinder first and second ends; a first and a second piston supported upon said piston rod and located, respectively, in said first and said second piston compartments of said cyliner; both said pistons being sealingly movable through the respective said compartments and each said piston thereby divides its respective said compartment; said pistons being spaced apart on said rod and being simultaneously movable by said rod; said pistons and said piston rod being shiftable axially through said cylinder toward said cylinder ends; both said pistons having a respective first face facing toward said cylinder first end and having a respective second face facing toward said cylinder second end; means normally biasing said pistons toward said cylinder first end; a pressurized fluid inlet having a first cross section and being connected to said cylinder; a valve located between said pressurized fluid inlet and said cylinder; said valve having an inlet communicating with said fluid inlet and an outlet communicating with said cylinder; said valve outlet communicating into said cylinder first compartment at a location such that pressure may be applied through said fluid inlet to the said first face of said first piston; a pressure transmitting conduit communicating between said valve outlet and said cylinder second compartment at a location such that pressure may be applied through said fluid inlet to said first face of said second piston; said valve comprising: a valve element compartment of a second cross section larger than said first cross section of said pressurized fluid inlet; a movable valve element in said valve element compartment, said valve element having a cross section such that it is sealably movable through said valve element compartment and being movable in said valve element compartment toward and away from said cylinder under the influence of pressure in said valve element compartment and in said cylinder; said valve element having a pressure inlet side facing toward said valve inlet and said fluid inlet and having a pressure outlet side facing toward said valve outlet and said cylinder; a narrowed passage through said valve element extending across said valve element compartment to join said fluid inlet with said cylinder; a one-way check valve in said narrowed passage permitting only inlet to said cylinder through said narrowed passage; said cylinder carrying a valve seat for said valve element against which said valve element pressure outlet side is sealable; when said valve element pressure outlet side, which said section has a third cross-section which is smaller than said valve element second cross-section anD which said valve element section is exposed to the sections of said first and said second compartments and thereby is exposed to the cylinder pressure at said first side of both said pistons; with said valve element moved through its said compartment onto said valve seat, the entire said pressure inlet side of said valve element is exposed to the inlet pressure in said fluid inlet and in said valve element compartment; a pressure equalization conduit connected to both said piston compartments in said cylinder at respective locations in said compartments such that said pressure equalization conduit is always at the pressure at both said piston second faces; said pressure equalization conduit also communicating with said piston compartments at respective locations so that it is in communication with said first sides of both said pistons; on the path between the piston compartment sides facing said second piston sides and the piston compartment sides facing said first piston sides, said equalization conduit passes said valve element and said valve seat, such that with said valve element on said valve seat, said equalization conduit is blocked, and with said valve element off said valve seat, said equalization conduit is open; a cylinder housing surrounding and spaced from said cylinder and in which said cylinder is mounted and defining, between said cylinder and said cylinder housing, said equalization conduit in the form of a jacket compartment around the exterior of said cylinder; said cylinder housing having opposed end faces; said valve means being in a valve housing formed at one end face of said cylinder housing surrounding said cylinder; the other end face of said cylinder housing having a guide opening for said piston rod and said piston rod passing through said guide opening therefor; means communicating said equalization conduit directly with the ambient air for relief of pressure in that said conduit.

2. A pneumatic holding device, comprising: a cylinder having a first and an opposite second end; at least one piston in said cylinder and shiftable therethrough axially thereof toward said cylinder ends; said piston having a first face facing toward said cylinder first end and a second face facing toward said cylinder second end; means normally biasing said piston toward said cylinder first end; a pressurized fluid inlet of a first cross section connected to said cylinder at a location such that pressure may be applied through said fluid inlet to said piston first face; a valve between said fluid inlet and said cylinder; said valve comprising: a valve element compartment of a second cross-section larger than said first cross-section of said inlet; a movable valve element in said valve element compartment and having a cross-section such that it is sealably movable through said valve element compartment and being movable in said valve element compartment toward and away from said cylinder under the influence of pressure in said valve element compartment and in said cylinder; said valve element having a pressure inlet side facing toward said fluid inlet and a pressure outlet side facing toward said cylinder; a narrowed passage through said valve element extending across said valve element compartment to join said fluid inlet with said cyliner; a one-way check valve in said narrowed passage permitting only inlet to said cylinder through said narrowed passage; said cylinder carrying a valve seat for said valve element against which said valve element pressure outlet side is sealable; when said valve element is on said seat, said seat defines a section of said valve element pressure outlet side, which said section has a third cross-section which is smaller than said valve element second cross-section and which said valve element section is exposed to the cylinder pressure at said first face of said piston; with said valve element moved through its said compartment onto said valve seat, the entire said pressure inlet Side of said valve element is exposed to inlet pressure in said fluid inlet and in said valve element compartment; a pressure equalization conduit connected to said cylinder at a location such that said pressure equalization conduit is always at the pressure at said piston second face; said pressure equalization conduit also communicating with said cylinder at the side of said cylinder which faces said piston first side and so communicating with said cylinder past said valve element and said valve seat such that with said valve element on said valve seat, said equalization conduit is blocked and with said valve element off said valve seat, said equalization conduit is open; means for venting said equalization conduit for relief of pressure in that said conduit; said equalization conduit being in the form of a jacket compartment on the exterior of said cylinder and said jacket compartment being enclosed by an outer wall; said venting means comprising at least a portion of said jacket compartment outer wall being formed of a material having limited air permeability, whereby said equalization conduit is gradually vented through said outer wall portion of limited air permeability.