US3671024A

US3671024A - Expansion temperature sensing means, in particular for medical apparatus

Info

Publication number: US3671024A
Application number: US33361A
Authority: US
Inventors: Hans Georg Breiling
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1969-05-02
Filing date: 1970-04-30
Publication date: 1972-06-20
Anticipated expiration: 1989-06-20

Abstract

A temperature responsive device for controlling the flow of fluid particularly for medical devices, such as a breathing apparatus and a vaporizer for anaesthetics, comprises a housing which has a supply inlet for the gas and includes a chamber at its lower end which is adapted to contain a liquid such as an anaesthetic. The interior of the housing defines a first pressure compensating passage for the gas in which a part of the inflow of the gas flows through a spiral around a top portion of the housing and then down to a lower spiral defined around the fluid chamber for the liquid, such as the anaesthetic. A second partial gas flow passage extends in the form of a by-pass from the inlet through a valve passage to the outlet. Flow from the fluid chamber to the discharge are regulated by means of two concentric rearranged movable valve members, the first valve member containing the expansible means which is located in the anaesthetic material includes a surface which is spaced from a valve surface of the second movable member and which defines the flow passage from the fluid chamber to the outlet. The second movable member defines a flow passage with a fixed portion of the housing and it is biased in a downward direction against the housing but is movable against this biasing pressure to vary the passage in the by-pass line. In addition, this same second movable member defines a surface which, together with the first movable member, defines the control passage from the fluid chamber to the outlet.

Description

United States Patent Brellmg [451 June 20,1972

I EXPANSION TEMPERATURE SENSING Manet-Tun Miles MEANS, IN PARTICULAR FOR MOWPMCGIMMTOM MEDICAL APPARATUS I V [57 AISTRACT ll2l Inventor: lllnn Georg Breillng, Gross Gronau, Ger- 1 a y A temperature responsive device for controlling the flow of [73] Assignee: Dmgerwerke Akflengeseuschafl Lubeck fluid particularly for medical devices, such as a breathing ap- Germany paratus and a vaporizer for anaesthetics, comprises a housing which has a supply inlet for the gas and includes a chamber at [22] Filed: April 30, 1970 its lower end which is adapted to contain a liquid such as an anaesthetic. The interior of the housing defines a first pressure [21] Appl' 33361 compensating passage for the gas in which a part of the inflow of the gas flows through a spiral around a top portion of the [30] Foreign Application Priority Data housing and then down to a lower spiral defined around the fluid chamber for the liquid, such as the anaesthetic. A second $2 5' germany partial gas flow passage extends in the form of a by-pass from y emany the inlet through a valve passage to the outlet. Flow from the [52] U S Cl 261/39 R 128/188 261/63 fluid chamber to the discharge are regulated by means of two 261/1O7 concentric rearranged movable valve members, the first valve [51] In Cl B 3/04 A61m 17/00 member containing the expansible means which is located in [58] Fie'ld R 65 63 the anaesthetic material includes a surface which is spaced from a valve surface of the second movable member and which defines the flow passage from the fluid chamber to the 56 R i cud outlet. The second movable member defines a flow passage 1 e erences l with a fixed portion of the housing and it is biased in a UNITED STATES PATENTS downward direction against the housing but is movable against this biasing pressure to vary the passage in the by-pass line. In 3,162,192 12/1964 Gardner et al "128/188 addition, this Same second movable member defines a surface 3 3 which, together with the first movable member, defines the 3 3 4 969 TI control passage from the fluid chamber to the outlet. 3:192:92: 7 1965 Ed d t l. U 261 39 mon Son e 3 I 6 Claims, 3 Drawing Figures FOREIGN PATENTS OR APPLICATIONS 648,191 l/195l Great Britain ..l28/188 26 Z 28 r i 1 i 48 4 V 22 46 I 1 I 7 47 37 [ii 4 1 l6 2T 40 1,; /a 2? if l h l 6 W t if j t ,3 gr f & t v r I] r 9M2 g/ 5 l 4 a I Q 10 E ll 2 e if-f I e l i 5 7" i7 l W 1 t EXPANSION TEMPERATURE SENSING MEANS, IN PARTICULAR FOR MEDICAL APPARATUS SUMMARY OF THE INVENTION This invention relates in general to a breathing apparatus and in particular to a new and useful flow control for regulating the flow of a fluid, such as an anesthesia to a breathing apparatus or a vaporizer.

BACKGROUND INFORMATION AND PRIOR ART In known vaporizers for anesthetic agents which are liquid at ordinary temperature, the disadvantage exists that the operation is temperature dependent to a relatively large extent. When the temperature of the device increases, the vapor pressure of the anesthetic increases relatively quickly. In dependence on the magnitude of the vapor pressure, the saturation degree of the airflow, which is guided above the anesthetic, is then reached. Since the vapor pressure, however, is temperature dependent to a relatively large degree, the danger exists that even with relatively small temperature changes of a few degrees only, a change of several percent by volume of anesthetic in the airflow may take place.

In order to prevent this disadvantage, it is known to measure the temperature of vaporizers for anesthetic by means of a thermometer. The anesthetic is then provided with a table and by interpretation of the tables the anesthesist, in dependence on the temperature which is shown by the thermometer, can then set the valves in the various conduits. This, of course, presupposes a continuous exact observation of the thermometer, and moreover, it requires constant adjustment of the settings. Moreover, the calibration of the device, which gives rise to a whole set or groups of graphs for different temperatures and concentrations is, of course, extremely cumbersome. Further, the anesthetic must follow and observe not only the temperature but he must also be able to read the calibration graph.

Vaporizers for anesthetic are also known which are provided with a so-called automatic temperature equalization device. This temperature equalization device consists of an opening which is arranged in the gas flow, which opening is covered more or less entirely by a thermo-bimetal strip in dependence on the prevailing temperature. In this manner temperature fluctuations are supposed to be equalized by changes in the flow resistance. However, in using thermo-bimetal strips, the danger of aging has to be considered since the life of the strips is limited; Moreover, due to inadvertent or undesired bending of the bimetal strip, the desired adjustment may not be accomplished but a distorted adjustment may take place. This known control device otherwise acts in such a manner that the setting adjustment range at a predetermined temperature difl'erential will always be the same and does not change in dependence on the concentration. This, of course, results in the disadvantage that temperature fluctuation cannot be compensated to the same extent in all the different concentration ranges.

Furthermore, an anesthen'c vaporizer of the above-indicated construction is known in which flow meters are arranged in the by-pass conduit and also in the conduit which leads through'the vaporizer. In this case the anesthetic must measure the temperature and must also continuously observe the measurement of the temperature and must by means of tables adjust the desired mixing ratio by changing the flow speed of the two conduits. This is accomplished by proper setting of valves.

Moreover, vaporizers for anesthetic have been proposed which are provided with temperature equalization devices of different kinds. It has thus been proposed to provide the vaporizers for anesthetic with expansion temperature sensing means so that the valves, throttles and the like are controlled in dependence on temperature fluctuations in such a manner that changes in temperature do not cause flow resistance, changes in the concentration of the anesthetic and the like. In these prior art constructions the setting, which is caused by the temperature sensing means at a predetermined temperature change, does not coincide with the desired control setting which would be necessary for unobjcctionable compensation of the temperature change. This may be due to the reason that the expansion coefficient of the temperature sensing means changes in dependence on the temperature in a different manner than the change of the vapor tension, that, for example, the temperature changing means in. the respective temperature range has a substantially constant expansion coefficient while, however, the vapor pressure of a certain anesthetic does not change linearly in the respective temperature range in dependence on a temperature change. Generally, the expansion coefficient of expansion temperature sensing means in the respective range in which the means is used, is approximately constant so that the control path of the expansion temperature sensing means changes practically linearly with the temperature. By contrast, the vapor pressure graph of anesthetic at the respective temperature ranges extends, generally, in a bent or curved manner.

The invention provides a simple anesthesia which operates so that upon occurring temperature fluctuations no or negligible changes in the composition of the anesthetic gas delivered by the anesthesia device occur. The anesthesia device includes a housing bearing a pressure compensated passage and a bypass which is switched or arranged in parallel and which includes control valves arranged in each passage. An adjusting wheel is connected with the movable valve member of the control valve or by-pass valve and at this movable valve member or at a member which performs the same movement as the movable valve member, the by-pass valve or control valve is arranged which is controlled by the temperature of the anesthetic agent. The inventive construction has the advantage of a very simple construction for the entire device, wherein either the control valve or the by-pass valve serves to adjust the concentration of the gas mixture, while the other valve is temperature controlled and ensures that no changes in concentration occur even if there are fluctuations in temperature. The amount or content of anesthetic contained in the gas which leaves the device may be adjusted solely by a manual wheel adjustment and is otherwise independent from temperature fluctuations.

A very simple embodiment resides in that the control valve and the by-pass valve are arranged concentrically relative to each other and that the movable valve member of the by-pass valve or control valve at the same time carries the valve seat of the control valve or by-pass valve. In doing so the temperature sensing means may be secured at the valve member which is connected with the adjusting wheel and the temperature sensing means is situated in the region of the liquid anesthetic.

In order to be able to obtain the inventive effect even if anesthetics are used, in which the vapor pressure curve in the respective temperature range is strongly bent or curved, the invention, according to a further modification, provides that between the expansion temperature sensing means and the control means there is interposed a transmission path which translates a linear adjusting path change in dependence on the absolute adjusting path length into a non-linear adjusting path change in dependence on the same absolute adjusting path length. In this manner, also with an expansion temperature sensing means, whose expansion occurs about linearly to the temperature change, a control of the temperature controlled valve is obtained which corresponds to the non-linear temperature dependency of the vapor pressure of the respective anesthetic employed. In other words, a linear adjusting path, which is produced by the expansion temperature sensing means in dependence on the temperature change is transformed into a progressively changing adjusting path.

The invention provides an expansion temperature sensing means, particularly for the control of valves, throttles or the like for medical purposes such as breathing devices, vaporizers for anesthetics, or the like, in which the control setting which is determined in dependence on the temperature, is changed into another control setting and results in the desired adjustment corresponding to the prevailing condi tions.

The invention provides that between the expansion temperature sensing means and the control means there is inter posed a transmission mechanism which translates a linear adjusting path change in dependence on the absolute adjusting path length into a nonlinear adjusting path change in dependence on the absolute adjusting path length. I

The invention has the advantage that, for example, a linear adjusting path, which is produced by the expansion temperature sensing means, in dependence on the temperature change, can be transformed into an adjusting path which changes, for example, progressively.

Accordingly, it is an object of the invention to provide an improved device for controlling the flow of fluid, such as anesthetic, to a breathing apparatus.

A further object of the invention is to provide a device for providing a uniform fluid flow irrespective of temperature variations which includes a movable valve member having a temperature sensitive element which is located in a fluid chamber for the fluid to be controlled and which is displaceable in accordance with temperature variations thereof for regulating a flow valve from the chamber to a discharge and also for regulating a flow valve between an inlet to the device for the fluid through a by-pass to the discharge of the device.

A further object of the invention is to provide a controlling device particularly for anesthetic devices and breathing devices which is simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a vertical sectional view through a control device for anesthetics constructed in accordance with the invention;

FIG. 2 is a section taken on the line 2,2 of FIG. 1; and

FIG. 3 is an enlarged sectional view of another embodiment of sensing control for the apparatus shown in FIG. I.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to the drawings in particular, the invention embodied therein as indicated in FIGS. 1 and 2 comprises a flow controlling device for regulating the flow of a fluid such as an anesthetic to a breathing apparatus or a vaporizer for anesthetics. A gas supply line (not shown) is connected to a housing 50 having a gas inlet opening 1. The gas flow divides itself at the point 2 and a portion of the gas flows through a passage or bore 3 into a premure compensating spiral 4 and through the line 5 and into the cylinder jacket space 6 of the vaporizer. Both sides of the space 6 are limited or restricted by the wick jackets 7 and 8. Between the wick jackets 7 and 8 there is arranged a gas conducting spiral 9 so that the anesthetic gas is guided around the outside of the spiral 9 downwardly in the cylinder jacket space in a helical path in a downward direction in order to enter a vaporizing chamber 12 at a location through bores (not shown) defined in the inner casing wall 11. During the travel of the gas, the gas becomes saturated with the vapor of the anesthetic. The gas flows then through the control valve 15 into the space 16.

A second part flow or by-pass flow enters through a by-pass valve 17 also into the space 16 and mixes there with the first part flow. The gas mixture leaves the device at a gas discharge opening 18.

The by-pass valve 17 is formed by a conical valve seat 19 which is rigidly connected with the casing, and by a first movable valve member 20, whose outer surface 21 is also conical. The first movable valve member 20 is movably mounted in the opening 22 of the casing. On its outer side it is provided with a groove 23 which extends perpendicular. A set screw 24 engages into groove 23 in order to prevent turning of the member 20. For adjustment, the movable valve member 20 is provided with a thread 25 which engages with a corresponding thread 26 of the adjusting wheel 27. The movable valve member 20 is otherwise under the influence of a compression spring 28 in order to make sure an unobjectionable adjustment of the valve 17.

At its lower end, removable valve member 20 is provided with a supporting stirrup 29 which extends downwardly and which includes an opening or bore 29 therethrough for the passage of gas from the chamber 12 through the valve 15 into the space 16. This stirrup carries the temperature responsive sensing means 31 which dips into the anesthetic. This sensing means contains a liquid 32 which is closed by a folded expansi ble and contractable bellows 33. A spindle 35 engages against the closure piece 34 of the bellows. The spindle 35 also engages with an adjusting thread 36 into a second movable valve member 37 which is provided with a meshing thread. This second valve member 37 is situated in a bore of the movable valve member 20 and engages the latter by means of the compression spring 38. The second movable valve member 37 has at its lower end a conical valve surface 39 which, together with the conical valve seat 40, forms the control valve 15.

The adjustment of the concentration is accomplished by means of the adjustment wheel 27, with which the opening of the by-pass valve 17 is adjusted or set.

The control valve 15 is adjusted by the temperature of the anesthetic means 30 in such a manner that the gas mixture which leaves the vaporizer, does not change its content of anesthetic even if the temperature changes. Upon cooling or heating of the anesthetic the temperature sensing means 31 thus increases or decreases the cross section of the control valve 15.

In the invention device one of the valves, the by-pass valve 17, takes over the adjustment of the concentration; while the other valve, in the embodiment shown the control valve 15, takes over the temperature compensation.

The spring 38 serves to prevent disturbing play between the temperature sensing means 31, the spindle 35 and the second valve member 37.

So that the device as shown can work in perfect manner, also if anesthetics are used which exhibit in the respective temperature range, a strong bending of their vapor pressure graph, the generally linear adjusting path change of the temperature sensing means in dependence on the temperature, can be changed or converted into a progressive cross section change of control valve by the embodiment of FIG. 3. For this purpose, a spindle 35 is divided into an upper part 43 and a lower part 40. The lower part 40 engages the closure piece 34 at its lower end and the other end engages a lever 41 which lever is articulated at 42 to the supporting stirrup 29 of the temperature sensing means 31. The upper part 43 of the spindle 35 is secured at a pressure plate 44 which is provided with a bent portion which engages over the lever 41, the curvature of the bent portion extending in direction of the lever 41. The lever 41, consequently, engages upon tilting in the directions of the double arrow at different areas of the curved surface.

The inventive device may also be provided with a special blocking or check valve 46 which upon operation of the device is in the position shown in FIG. I. This valve consists of a piston 47 which with its upper end face bears against the lower end face 48 of the adjusting wheel 27. The adjusting wheel 27 is provided with a projection (not shown) through which, upon switching 05 the vaporizer, the valve piston 47 in the switch off position is pressed into an upper position. In this upper position (not shown) the piston part 48 closes the gas inlet opening I in the by-pass valve 17 and pressure compensation spiral 4. At the same time the constriction 49 of the piston frees in this position the opening 51a to the annular line 51 shown in FIG. 2 which line, behind the space 16, merges into the line which leads to the exit 18. Finally, the lower piston portion 52 clears or frees the venting bore 53 of the vaporizer space 12 so that this space is now in communication with the ambient atmosphere. The pressure piston is maintained in the indicated position by means of the compression spring 54.

Upon switching off the device as shown, the entire gas flow is thus moved past the evaporation chamber and the by-pass valve through the branch line 51 so that the resistance can be reduced to any desired value. In the switched off condition the entry from the gas supply line 1 to the evaporation chamber 12 is thus blocked and the latter is vented.

The venting bore 53 is situated below the level of the valves 15 and 17 so that an anesthetic system, which may possibly be connected, can only be supplied with those concentrations which are desired and have been positively and intentionally adjusted.

In the embodiment as shown, an adjustment of the movable valve member 20 and thus adjustment of the by-pass valve 17 does not cause any adjustment of the control valve 15 when there prevails temperature uniformity since the element 37 is adjusted in a level equalizing manner by means of the member 20 through the stirrup 29.

What is claimed is:

1. An expansion temperature sensing device particularly for the control of valves of medical devices, such as breathing apparatus and Vaporizers for anesthetics, comprising a housing defining a fluid chamber, inlet passage means connected into said fluid chamber and discharge passage means connected from said fluid chamber to the exterior of said housing, an expansionable temperature sensing means in said fluid chamber, control means connected to said sensing means and being movable thereby for regulating the flow from said inlet to said discharge, a transmission mechanism connected between said sensing means and said control means for translating a linear adjustable movement of said sensing means in dependence on the absolute adjusting movement thereof into a non-linear adjusting movement length in dependence on the absolute adjusting movement change, said transmission mechanism including a movable member connected to said sensing means, said sensing means being movable in accordance with temperature changes, said movable member including an upper portion adapted to be connected to flow control means and a lower portion, a lever member pivotally mounted at one end being connected to said lower portion, and a pressure surface plate member connected to said upper portion and having a curved portion engaged over said lever member.

2, A temperature responsive device for controlling the flow of fluid particularly for the control of fluid in medical devices, such as breathing apparatus and a vaporizer for anesthetics, comprising a housing defining a fluid chamber for a fluid, suchas an anesthetic, said housing having an inlet for the inflow of fluid and an outlet for the outflow of fluid, a pressure compensating passage for the fluid defined in said housing from said inlet into said fluid chamber, a first movable valve defining a first valve flow surface having an expansible temperature responsive portion supported in said fluid chamber and being expansible and contractable with temperature and pressure changes to shift said movable first valve member correspondingly, a second movable -valve member defining a second valve flow surface spaced from said first flow surface and defining a flow passage from said fluid chamber to said outlet between said second flow surface and said first flow surface, said second valve member also defining a third flow surface which is spaced from a portion of said housing and defining a by-pass passage from said inlet to said discharge between said third flow surface and said portion of said housing, said first movable valve member including a rod portion terminating in an end which is connected to a bellows and is movable by said bellows upon expansion and contraction thereof, said bellows comprising said temperature responsive portion, said rod member including an upper portion and a lower portion, a lever pivotally mounted at one end and being connected intermediate its length to said lower portion and a curved plate connected to said upper portion and engaged over said lever, said plate and said lever constituting a transmission for translating a linear adjusting path change in dependence on the absolute adjusting path length into a non-linear adjusting path change in dependence on the absolute adjusting path length.

3. A temperature responsive device for controlling the flow of fluid particularly for the control of fluid in medical devices,

such as breathing apparatus and a vaporizer for anesthetics,-

comprising a housing defining a fluid chamber for a fluid, such as an anesthetic, said housing having an inlet for the inflow of fluid and an outlet for the outflow of fluid, a pressure compensating passage for the fluid defined in said housing from said inlet into said fluid chamber, a first movable valve defining a first valve flow surface having an expansible temperature responsive portion supported in said fluid chamber and being expansible and contractable with temperature and pressure changes to shift said movable first valve member cor respondingly, a second movable valve member defining a second valve flow surface spaced from said first flow surface and defining a flow passage from said fluid chamber to said outlet between said second flow surface and said first flow surface, said second valve member also defining a third flow surface which is spaced from a portion of said housing and defining a by-pass passage from said inlet to said discharge between said third flow surface and said portion of said housing, a second by-pass passage in said housing for the flow of fluid from said inlet to said discharge, means for selectively opening and closing first passage in order to selectively permit substantially complete or partial flow through said by-pass, a slide valve member mounted in said housing for slide movement between a position in which it blocks said by-pass passage and a position in which it opens said by-pass passage, and a handwheel connected to said second movable valve member and being rotatable thereon to shift said slide valve between an opened and closed position.

4. An expansion temperature sensing device particularly for the control of valves of medical devices, such as breathing apparatus and Vaporizers for anesthetics, comprising a housing defining a fluid chamber, inlet passage means connected into said fluid chamber and discharge passage means connected from said fluid chamber to the exterior of said housing, an expansionable temperature sensing means in said fluid chamber, control means connected to said sensing means and being movable thereby for regulating the flow from said inlet to said discharge, a transmission mechanism connected between said sensing means and said control means for translating a linear adjustable movement of said sensing means in dependence on the absolute adjusting movement thereof into a non-linear adjusting movement length in dependence on the absolute adjusting movement changes, said transmission mechanism including a first movable rod terminating in an end which is connected to said sensing means and is movable upon expansion and contraction thereof, said rod including an upper portion and a lower portion, a lever pivotally mounted at one end and being connected intermediate its length to said lower portion, and a curved plate connected to said upper portion and engaged over said lever, said plate and said lever constituting said transmission mechanism for translating a linear adjusting path change of said sensing means into a non-linear adjusting path change.

5. A device, according to claim 4, wherein said slide valve is a double valve and in an end position may close off at least a portion of said pressure compensating passage and said bypass passage.

6. A device, according to claim 5, wherein said valve also includes means for venting said fluid chamber to the atmosphere.

Claims

2. A temperature responsive device for controlling the flow of fluid particularly for the control of fluid in medical devices, such as breathing apparatus and a vaporizer for anesthetics, comprising a housing defining a fluid chamber for a fluid, such as an anesthetic, said housing having an inlet for the inflow of fluid and an outlet for the outflow of fluid, a pressure compensating passage for the fluid defined in said housing from said inlet into said fluid chamber, a first movable valve defining a first valve flow surface having an expansible temperature responsive portion supported in said fluid chamber and being expansible and contractable with temperature and pressure changes to shift said movable first valve member correspondingly, a second movable valve member defining a second valve flow surface spaced from said first flow surface and defining a flow passage from said fluid chamber to said outlet between said second flow surface and said first flow surface, said second valve member also defining a third flow surface which is spaced from a portion of said housing and defining a by-pass passage from said inlet to said discharge between said third flow surface and said portion of said housing, said first movable valve member including a rod portion terminating in an end which is connected to a bellows and is movable by said bellows upon expansion and contraction thereof, said bellows comprising said temperature responsive portion, said rod member including an upper portion and a lower portion, a lever pivotally mounted at one end and being connected intermediate its length to said lower portion and a curved plate connected to said upper portion and engaged over said lever, said plate and said lever constituting a transmission for translating a linear adjusting path change in dependence on the absolute adjusting path length into a non-linear adjusting path change in dependence on the absolute adjusting path length.

3. A temperature responsive device for controlling the flow of fluid particularly for the control of fluid in medical devices, such as breathing apparatus and a vaporizer for anesthetics, comprising a housing defining a fluid chamber for a fluid, such as an anesthetic, said housing having an inlet for the inflow of fluid and an outlet for the outflow of fluid, a pressure compensating passage for the fluid defined in said housing from said inlet into said fluid chamber, a first movable valve defining a first valve flow surface having an expansible temperature responsive portion supported in said fluid chamber and being expansible and contrActable with temperature and pressure changes to shift said movable first valve member correspondingly, a second movable valve member defining a second valve flow surface spaced from said first flow surface and defining a flow passage from said fluid chamber to said outlet between said second flow surface and said first flow surface, said second valve member also defining a third flow surface which is spaced from a portion of said housing and defining a by-pass passage from said inlet to said discharge between said third flow surface and said portion of said housing, a second by-pass passage in said housing for the flow of fluid from said inlet to said discharge, means for selectively opening and closing first passage in order to selectively permit substantially complete or partial flow through said by-pass, a slide valve member mounted in said housing for slide movement between a position in which it blocks said by-pass passage and a position in which it opens said by-pass passage, and a hand-wheel connected to said second movable valve member and being rotatable thereon to shift said slide valve between an opened and closed position.

5. A device, according to claim 4, wherein said slide valve is a double valve and in an end position may close off at least a portion of said pressure compensating passage and said by-pass passage.