Title:
MULTI-WAY-VALVE
United States Patent 3559685


Abstract:
A multiway valve for connecting outlets leading to either end of a hydraulic cylinder, and at the same time connecting the other outlet to a return passage, includes a casing having a control member movable with clearance therein. This control member when shifting from one position to another is lifted up by the pressure of the fluid being controlled, then shifted to a different position, and then restored to sealing position by the application of pressure on its upper side.



Inventors:
DEFRIES JAN RICHARD PETER
Application Number:
04/834850
Publication Date:
02/02/1971
Filing Date:
06/19/1969
Assignee:
JAN RICHARD PETER DEFRIES
Primary Class:
Other Classes:
251/282
International Classes:
F15B13/12; F16K11/065; F16K11/074; (IPC1-7): F16K11/07
Field of Search:
137/625
View Patent Images:
US Patent References:
3396750Milking machine pulsatorAugust 1968Nilsson
3353557Distributor valveNovember 1967Faisandier
3227180Distributing systemJanuary 1966Tissot-DuPont
2946321Control system for fluid pressure-actuated reciprocating deviceJuly 1960Liesel
2747612Force-compensated flow valveMay 1956Lee



Primary Examiner:
Cline, William R.
Claims:
I claim

1. A multiway valve for control of a pressure medium which has a casing with an inlet and at least two outlets and a control member able to perform a control movement with the aid of which the inlet can be connected selectively with said outlets, said outlets being adapted for connection to a supply line for the pressure medium and with a relief line respectively, wherein means are provided to change the pressure on the control member before starting the control movement whereby the control member is lifted from the contact faces of the casing allotted thereto for sealing contact, wherein fluid pressure means are provided to act on the control member for performing its control movement in the course of which movement it is moved into a new valving position while being in a state of suspension by the medium and wherein the control member upon reaching its new valving position is again pressed against the contact face allotted thereto by again changing the pressure distribution.

2. The multiway valve set forth in claim 1, wherein the control member is a flat slide displaceable during the control movement across the inlet and outlets and fitting snugly in the respective valving positions under the influence of the pressure within the casing to perform a sealing effect, said slide standing in its slide case on its one flat side under the influence of the pressure medium coming from the inlet which influence is directed across the direction of the displacing movement, and on the opposite flat side and on its two axial ends under the influence of a pressure medium cushion which in its operative condition sealing presses the slide in its respective valving position against the face portions of the inner face of the casing surrounding the inlet and outlet, and means to change the pressure acting on the ends, whereby the effect of the pressure medium cushion can be neutralized and annulled partly and temporarily, whereby the slide lifts from the inner face of the casing until the full working state of the pressure medium cushion has been restored, and displaces into the valving position coordinated to the side on which the change of pressure has taking place so that the slide is displaceable within the casing to-and-fro in direction of its longitudinal axis between its two valving positions.

3. The multiway valve set forth in claim 1, wherein said valve casing has openings on one side thereof constituting the inlet and outlets, and said control member comprises at least one slide movable within the said casing and having slide channels on one side which interconnect said openings in said casing in different ways in dependence on their relative position with respect to the said openings and at least one auxiliary valve, and wherein the said slide is mounted within said casing with a clearance in a direction perpendicular to the direction of control movement and in a direction towards the side containing the said openings, and said fluid pressure means comprising a supply channel connecting the said clearance to a reservoir of medium the pressure of which within the casing is high enough for sealingly pressing the slide onto the side of the casing containing the said openings against the action of the pressure in the inlet and in the slide channels, and wherein auxiliary valve means are connected to the said clearance, said auxiliary valve means on being opened establishing a connection to a medium the pressure of which within the clearance is not high enough to press the slide sealingly onto the side wall of the casing containing the openings whereby, upon actuation of the auxiliary valve, the slide lifts from the face allotted thereto for sealing contact and occupies an intermediate position under the forces resulting from the openings and the incoming medium on the one hand and from the supply channel for a medium standing under higher pressure on the side of the clearance on the other hand, in which intermediate position it is easily movable in the direction of the control movement, and wherein, finally, upon closing the said auxiliary valve the said slide is again pressed against the openings.

4. The multiway valve set forth in claim 1, wherein the pressure effect of the medium to be controlled upon the slide causes the slide to bear against the walls surrounding the channels before and during the control movement without sealing effect, but sealingly presses against the walls surrounding the channels after the end of the control movement and under the influence of the pressure effect, wherein the fluid supply means to the pressure space serving to sealingly press the slide against the coordinated face of the casing includes a throttling means, and auxiliary valve means operative before starting the slide motion to relieve pressure in the pressure space whereby the slide no longer sealingly presses against the coordinated face, closing off the auxiliary valve means causing the pressure space to again be pressurized after the end of the slide motion.

5. The multiway valve set forth in claim 1, wherein the control member in its state of suspension is freely movable as a plate in its plane and establishes connections between the channels under the influence of controlling adjusting operations along several coordinates.

6. The multiway valve set forth in claim 1, wherein the said control member is constituted by a round plate changing its position by rotation.

7. The multiway valve set forth in claim 1, wherein the said control member in its state of suspension can be displaced by means of inductive electric fields into a new position.

8. The multiway valve set forth in claim 1, wherein the said control member can be displaced with the aid of exterior mechanical means, acting through a magnetic power gradient through a wall impermeable to liquids.

9. The multiway valve set forth in claim 1, wherein to the said control member there are coordinated two pressure chambers fed with pressure medium serving to produce the control movement of the said control member said pressure chambers being in connection with at least one of the other chambers containing the pressure medium cushion and in which the pressure medium exerts upon a wall of the said slide a control pressure directed approximately transverse to the direction of the control movement, the control pressures in the said two pressure chambers being directed oppositely to one another, and means for changing the pressure conditions and the pressure distribution includes means for reducing the pressure in one of the said two pressure chambers.

10. The multiway valve set forth in claim 9, wherein the pressure chamber serving to provide the sealing effect is constituted by a fluid pressure cushion, wherein between the throttling means and the chambers serving for the discharge of the medium out from the pressure chamber there is arranged a further throttle the cross section of which is reduced by releasing the sealing contact between the said slide and the said faces allotted thereto, the pressure cushion being situated on one side of the said slide and integral therewith, and being movable with the said slide.

11. The multiway valve set forth in claim 10, wherein the flat side of the said control member under the influence of the medium issuing from the supply line has a smaller effective surface than the opposite side.

12. The multiway valve set forth in claim 1, in which a said flat slide constitutes the control member and is guided within a groove of rectangular cross section of said casing, the height of which groove is slightly greater than that of the slide and the axial length of which groove is greater than that of the slide by such an amount that the slide is able to execute its movement between its different valving positions within the casing, wherein into the groove of the casing there open lines on the two front sides corresponding to the axial ends of the slide by means of which can be changed the pressure in the groove of the said casing, and on one of the flat sides of the flat slide, the inlet line and the outlet lines.

13. The multiway valve set forth in claim 12, wherein on the inner faces of the front walls limiting the groove on its two axial ends there are provided abutting cushions of resiliently elastic material.

14. The multiway valve set forth in claim 1, wherein the said control member comprises a slide in the shape of a longish flat body with rectangular cross section which has in the zone of its two axial ends on the side facing the opening of the inlet as well as on the side opposite thereto sealing projections directed rectangularly in outward direction, wherein the effective surface contained between the sealing projections on the side facing the supply line for the pressure medium is smaller than the effective surface on the side opposite thereto.

15. The multiway valve set forth in claim 14, wherein through the slide there passes at least one channel of small diameter, and constituting a throttle, which channel leads from the effective face facing the inlet to the effective face opposite thereto, and thereby interconnects the chambers surrounding these faces.

16. The multiway valve set forth in claim 15, wherein the inner face of the said groove is covered on the side facing the inlet by a layer of resiliently elastic material or the slide and the casing have on sides facing one another interengaging teeth, whereby the slide is released for lateral movement only after having performed a defined movement to the direction of control movement perpendicular and is otherwise prevented from displacement.

17. The multiway valve set forth in claim 16, wherein the said slide casing and slide are so constructed that energy fields in the form of fields of force must be overcome in order to initiate a change of position, that in order to maintain the position of the slide also when the sealing contact between the slide and the face allotted thereto is interrupted due to an interruption of the supply of pressure medium.

18. The multiway valve set forth in claim 17, wherein the said slide has the shape of a longish prismatic body with rectangular cross section which has on its side turned away from the channels to be interconnected two separated grooves serving to receive pressure cushions and extending in the longitudinal direction of the slide and being in connection with the inlet through channels and being open on their top, to which grooves there are coordinated relief channels extending in the longitudinal direction of the slide and serving to control said slide, of which relief channels one is provided in the middle region of the slide between the two grooves and is open in a direction towards one axial end thereof, whereas two further relief channels contain the two grooves between them and are open in the direction towards the other axial end of the slide.

19. The multiway valve set forth in claim 17, wherein the said slide is constructed as a disc mounted rotatably about a central axis having on the side of the slide turned away from the openings of the channels to be controlled two grooves for receiving pressure medium cushions which are in connection with the inlet by channels, whereas on the opposite flat side there are provided of shell like shape for establishing the connections between the channels to be controlled.

20. The multiway valve set forth in claim 15, wherein the said slide when in the end positions of its control movement neutralizes in one valving position in the channel of the relief valve of the pressure medium cushion the relief of the pressure cushion and thereby is pressed against its faces whereby the energy necessary for passing through this valving position can be taken from an accumulator.

21. The multiway valve set forth in claim 20, wherein the said slide casing and slide are provided with a small auxiliary piston displaceable under the influence of the pressure of the supply medium and against the tension of a spring, whereby upon the pressure of the supply medium sinking below a predetermined level said piston holds the slide in its position determined before the pressure has begun to sink.

Description:
The invention refers to a multiway valve and more particularly to a multiway valve which has a control member with the aid of which the line leading to a consuming point, for example, a working cylinder for liquid or gaseous media can be connected selectively with the supply line for the pressure medium or with a relief line leading to the free atmosphere or to a reservoir.

SUMMARY OF THE INVENTION

According to the invention the construction of the new multiway valve is such that, before starting the control movement, the slide is lifted from the contact faces allotted thereto for sealing contact by changing the distribution of the pressure, that further the control member is driven exclusively by fluid pressure for performing its control movement in the course of which movement it is brought or moved into a new valving position, whilst being in a state of suspension and floating so-to-say between two layers of the medium, and that, finally, the control member upon reaching its new valving position is again pressed against the contact faces allotted thereto by again changing the pressure distribution and this time conveniently in the opposite sense. The arrangement can, for instance, be such that the control member is constructed as a slide which is displaced during the control movement in the manner of a flat slide transverse to the channels to be controlled and fitting snugly in the respective valving positions under the influence of the pressure, for example, of the medium to be controlled with the walls surrounding the channels in order to perform a sealing effect, said slide standing in its slide case on one of its flat sides under the influence of the pressure medium coming from the supply line which influence is directed transversely to the direction of the displacing movement, and on the opposite flat side and on its front sides coordinated to its two axial ends under the influence of a pressure medium cushion which in its operative position sealingly presses the slide in its respective valving position against the face portions of the inner face of the slide case surround the lines to be connected with one another, and the effect of which pressure medium cushion can be temporarily and partly neutralized and annulled by short-time changes of the pressure on one of its front sides coordinated to the axial ends in such a manner that the slide lifts from the inner face of the slide case until the full working state of the pressure medium cushion has been restored, and displaces into the valving position coordinated to the side on which the change of pressure has taken place so that the slide is displaceable within the slide case to and fro in the direction of its longitudinal axis between its two valving positions.

With the arrangement according to the invention the control member is lifted from the contact faces by a change in the pressure distribution before the control movement begins, whereby it floats so-to-say or is suspended between two layers of the medium and when in this state can glide thus into a new position, whereafter a change in the pressure distribution follows and the control member is sealingly pressed again against the contact surfaces. No friction takes place during the control movement, after the end of the movement the slide is pressed against the surface by the pressure of the medium so that a good sealing against leakage is secured. During the control movement and change of position the cushion, consisting of the medium surrounding the slide prevents any direct contact between material and material so that practically there is no friction and almost no wear; if, however, wear occurs, the control member is automatically adjusted and maintains its sealing effect. The equal pressures of the liquid on both functional sides of the slide have the effect that the slide will float like an air cushioned vehicle, that state of floating or suspension being maintained by a steady and unsubstantial flow of the pressure medium and by the regulation of the cross sections of the throttle due to the variations in the distance. In this state of floating or suspension the slide is free from strong fraction, which, however, may occasionally appear with secondary guiding surfaces of the slide only. The construction is as uncomplicated as it can be with slide valves. The result therefore is that the device presented by the invention combines the advantage of a disc valve, namely that the control member performs its sealing function only when the control position is completely reached, with the advantages of the slide valve, the simple and reliable construction of the slide that moves across the channels to be controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the present invention will become further apparent from the following detailed description thereof, whereby in the drawings several embodiments of the invention are shown.

FIG. 1 shows an embodiment of the invention in a vertically sectioned schematical side view, wherein this embodiment is shown in a first stage of the control operation,

FIG. 2a shows the arrangement according to FIG. 1 in a second stage of the control operation,

FIG. 2b shows the arrangement according to FIG. 1 in a third stage of the control operation,

FIG. 3 shows the arrangement according to FIG. 1 in a fourth stage of the control operation,

FIG. 4 shows a modified embodiment of the invention in a side view in a vertical section in a schematical representation corresponding to that of FIG. 3,

FIG. 5 shows the slide of another variation of the device according to the invention in a perspective view as seen from above,

FIG. 6 shows another modified embodiment of the invention in a schematical side view and in a vertical section,

FIG. 7 shows a schematical representation of a fifth embodiment of the invention in a plan view, and

FIG. 8 shows the slide of the embodiment according to FIG. 7 as viewed from above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment of the device according to the invention and shown in the drawings is a four-way valve. This valve has a control member 1 by means of which the feeding line leading to a consumer, for instance, to a working cylinder, can be connected at will either with the supply line supplying the pressure medium--compressed air for instance--or with a relief line leading to a reservoir or into the open air. The control member 1 has the form of a flat slide which can be moved within the slide casing to and fro according to the arrow 3 in the direction of its longitudinal axis between its two valving positions. The slide is adapted and guided within the space 4 of the slide case which has a rectangular cross section. On its flat side 5 it is under the influence of the medium coming from the supply line 6, whereby the medium works or acts in accordance with the arrow 7, that is in a direction transverse to the displacing movement. On the opposite flat side 8 and the two front sides 9 and 10 the slide stands under the influence of a cushion consisting of pressure medium and pressing in its operative stage with sealing effect the flat slide in it respective valving position against those parts of the inner wall of the case which surround the lines to be connected with each other. The effect of the said cushion can thereby be temporarily and partly neutralized and annulled by changing for a short time the pressure at one of its front sides coordinated to its axial ends so that the flat slide is lifted from the inside of the case wall in order to glide into that valving position coordinated to that side, on which the change of pressure has taken place, until the full working or operating condition of the cushion of pressure medium has been restored.

The space or cavity 4 is higher than the slide 6, its axial length is greater than that of the slide by such an amount that the slide is able to move between its different valving positions within the case. Into the space 4 or cavity there open the following lines or connections: on the front sides 9 and 10 the lines 11 and 12, by means of which the pressure within the space or cavity of the slide case can be changed; on the lower side 5 the supply line 6 for the pressure medium, the connections 13 and 14 to the two sides of the cylinder and the connections 15 and 16 for the relief lines coordinated to the two sides of the cylinder. The arrangement is thereby such that the connection for a supply line 13 and 14 leading to a working cylinder is provided-- as seen in direction of the longitudinal axis of the slide (according to arrow 3)--between the supply line 6 for the pressure medium and the connection for the relief line 15 or 16 coordinated with the working cylinder. The lines 11 and 12 are coaxial to one another. The inside surfaces of the front walls limiting the space or cavity of the slide case at its two axial ends are provided with padlike abutment cushions 17 and 18 which are made of elastic resilient material, for instance of rubber or synthetic material with rubberlike qualities, and which abutment cushions serve to prevent the slide from abutting too intensively at the end of the shifting movement. The slide has the shape of a longish and flat body which has a rectangular cross section and which has in the region of its two axial ends the sealing projections 19, 20 on its side 5 facing the opening of the supply line for the pressure medium and 21, 22 on the opposite side whereby both pairs of projections 19, 20 and 21, 22 project rectangularly from their surface in outward direction and have rectangular cross sections. The effective surface lying between the sealing projections 19, 20 on the side 5 is smaller than the effective surface lying between the sealing projections 21, 22. On the side 5 coordinated to the supply line for the pressure medium there are provided between the two sealing projections 19, 20 two further sealing projections 23, 24 projecting rectangularly in outward direction which are coordinated each with one of the cylinder sides and which in the two valving positions of the slide separate the supply line of the coordinated side of the cylinder either from the corresponding relief line or from the supply line for pressure medium common to both sides of the cylinder. On the side opposite to the supply line for pressure medium there is provided about midway between the sealing projections 21, 22 the sealing projection 25 which stand outward almost rectangularly; on both sides of that projection 25 there are provided channels 26, 27 which are parallel to each other and have relatively small cross sections, and which lead from the surface 5 to the opposite side 8, representing so-to-say throttles. Eventually, a single channel may be sufficient; likewise, the throttles may be constituted by slide portions made of porous material.

Generally speaking, the arrangement is such that the slide sealingly rests in both its valving positions on the corresponding inside of the slide case on the side facing the supply line for pressure medium and is separated during its axial displacement from the inner sides of the slide case facing its two flat sides by means of pressure cushions produced by the pressure medium. The distribution of the pressure coming from the supply line for pressure medium by means of a layer of medium on the opposite sides of the control member directed in the opposite direction to the above mentioned pressure, and by making the resulting force greater than the forces produced by the pressure air coming from the supply line at least by the sealing pressure.

The pressures exerted are counterbalanced by a cushion of medium, the pressure of which is automatically regulated by the cross section on the periphery and the magnitude of the opening of the supply line in such a way that the control member is kept in suspense. In FIG. 1 of the drawings there is shown the valving position of the slide in which the supply line 6 for the pressure medium is connected with the supply line 13 feeding the one side of the cylinder, whereas the supply line feeding the other side of the cylinder is in connection with the relief line 16. The sealing projections 19 and 20 bear against the corresponding surface of the slide sealing thereby the different lines and connections in the outward direction. To get a sealing that is still better, the surface 23 of the slide case can be fitted out with a layer 30 consisting of synthetics or rubber, i.e. of a material with a high sealing quality and a high coefficient of friction. The slide and the surface of the slide case facing it may also be equipped with fine teeth or notches by means of which the slide is released for a lateral movement only after having performed a certain motion corresponding to the depth of the teeth or notches, but which otherwise blocks or prevents any displacement of the slide. If now the pressure in the line 12 is changed, the pressure above the slide will diminish likewise so that the pressure coming from the supply line 6 for the pressure medium lifts the slide. With the pressure being higher on the side 11 than that on the side 12, the slide is displaced at the same time to the right beyond the position according to FIG. 2b into the position according to FIG. 3 in which its front side 10 abuts against the resilient pad 18.

If thereafter the pressure in the line 12 is suitably changed again, the slide is pressed down until it comes to sit on the surface 29 so as to fulfill an effective sealing action. In that case the supply line 6 is connected with the supply line that feeds the other side 14 of the cylinder; at that moment the supply line 13 for feeding the one side of the cylinder is connected with the relief line 15 coordinated to it. By such an arrangement the pressure within the pressure space which has been reduced by the auxiliary valve, will rise again upon lifting of the slide, until the balance between the pressure in the pressure space and the pressing effect of the controlled canals is established.

The invention can also be applied to a three-way valve. The slide can, moreover, be combined with a greater number of connecting channels and must then have a correspondingly greater number of control and intermediate positions, whereby the different connecting channels can be combined with each other ad libitum by interrupting the condition of suspension of the slide.

Moreover, the arrangement can be such that the slide automatically neutralizes and annuls in the end positions of its movement the relief of the pressure cushion due to its geometrical position in a control point provided in the channel of the valve that has to relieve the pressure cushion, so that it is again pressed against the coordinated surface, whereby the energy necessary for passing through this control point may be taken from a mechanical, hydraulical or pneumatical accumulator. The slide can thereby be so designed that it can be brought into a great number of intermediate positions also with a greater number of connecting channels which may be functionally connected by the connections on the side of the slide whenever the state of suspense is interrupted at the desired point. In addition to that, it is also possible to provide that the slide in its state of suspension be freely movable as a plate in its plane and effectuate connections between different channels under the influence of the above-mentioned controlling operations, for instance in the form of a crossbar selection system. Further, it can be provided that the slide has no preferential position dependent on, and due to, gravitation, it being designed for instance, as a round plate that changes its position by a rotary movement and/or as a system in which the masses are balanced. Moreover, the slide in its suspended state may be brought into a new position by inductive electric fields as is the case with the rotor of a motor, in particular as the movable part of a linear motor, or that it can be displaced by mechanical exterior means which work by means of a magnetic power gradient through a wall impermeable for liquids, whereby conveniently the slide yields to the actuating exterior powers which produce the power gradient only when the contact with the channel face is interrupted by the relief of the pressure space, in that sense that only the coincidence of both states brings about a control operation. With another modified embodiment of the invention the slide case or the slide are so constructed that energy fields in the form of fields of spring tensions or of magnetic energies must be overcome for starting a changing in position, and this with the intention hereby to maintain the position even in the case that due to an interruption of the pressure supply the slide no longer bears against the surfaces allotted thereto. The arrangement may be also such that the slide case or the slide are provided with a little auxiliary piston which is displaceable under the influence of the supply pressure and against the action of the spring tension and which serves to hold the slide, upon the supply pressure sinking under a predetermined level, in the position given before the diminishing of the pressure.

FIG. 4 shows an arrangement in which the relief lines 35 and 36 supplying the pressure medium serving to produce the control movement to the control spaces 37 and 38 of the slide case in the zone of the two axial ends of the slide 39 open into the slide case on the same side as the supply line 40 containing the control medium. This arrangement allows the slide to be controlled via the relief lines 35 and 36, whereby the operations of lifting or sinking down of the slide take place automatically because near the end positions to the left and right the slide closes automatically the respective relief line. The pressure supplies 41 and 42 allow the slide to fully perform its movement even after the relief channels have been closed.

With a modified embodiment of the invention the slide is constructed according to FIG. 5. Thereby, the slide has the shape of a longish prismatic body with a rectangular cross section and with two spaces or grooves 44 and 45 on the side of the slide turned away from the channels to be connected with each other, said spaces or grooves 44 and 45 serving to receive the cushions of the pressure medium and being separated from one another whereby they are open towards the top side. These spaces or grooves 44, 45 extending in the longitudinal direction of the slide are connected with the supply line for the pressure medium by means of corresponding and suitable channels 46 and 47. For controlling the slide, to these spaces or grooves there are allotted or coordinated relief channels extending in the longitudinal direction of the slide. The relief channel 48 is provided in the middle zone of the slide and between the two spaces 44 and 45; it extends in the longitudinal direction of the slide and is open towards the one of the axial ends at 48a. Two further relief channels 49 and 50 enclose the two spaces 44 and 45 between them and are open towards the other axial end of the slide at 49a and 50a. This arrangement has the advantage that the slide does not show any tendency for tilting and that it is stable about the axis A-A; moreover the manufacture is much simplified. An impediment or obstacle for the flow is found between the spaces B and C.

To diminish or reduce the losses, the path of the flow may be designed according to FIG. 6. The channels for the incoming streams 51, 52a, 52b, 53a, 53b have the shape of shells, the curvature of which becomes steadily wider and wider up to the vortex, whereby the ratio of the inside diameters x, y of the channels coordinated to one another is approximately 1,0 : 1,2 and whereby there is a whirl or vortex forming at the point 54.

In accordance with FIG. 7 the slide can also have the form of a disclike or platelike body 56 rotatable about a central axis 55 and provided on its side turned away from the openings of the channels for the incoming medium with two spaces or grooves 57, 58 to receive the pressure medium which are connected with the supply line for the pressure medium via the throttling channels 57a, 58a. On the opposite flat side of the slide there are provided the spaces or grooves having, for instance, a shell-like shape which serve to furnish the connections between the channels for the incoming medium. 59 designates a member rigid with the slide that is under the influence of the control pressure which is introduced into the control spaces 60 and 61 to produce the control movement. 62a and 62b indicate the supply lines that bring the compressed medium to the diverse consuming points. 63a and 63b represent the relief lines coordinated to the said consuming points, whereas 64 is the supply line for feeding the pressure medium. The shell like connecting channels within the slide are indicated at 65, 66, 67; 68 is a counterbalance pocket within the slide. All this taken together gives a compact construction well balanced with respect to the weights and to the pressures.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is: