US2376348A - Resuscitator - Google Patents

Description

May 22, 1945. y LE ROY G..Fox

RESUSCITATOR Fl'ed April 24, 1945 2 Sheets-Sheet 1 w 1p Z May 221945. LE ROY G. Fox 2,376,348

RESUSCITATOR Filed April 24, 1943 2 sheets-sheet 2 ll N f mum" mum Y- m 1| mulllll Imam/bow E Por 6. /Cx

Patented May 22, 1945 RESUSCITATOR Le Roy G. Fox, Los Angeles, Calif., assignor to Clarence N. Erickson, Glendale, Calif.

Application April 24, 1943, Serial No. 484,443

Claims. (Cl. 12S-29) This invention relates to articial respiration apparatus or resuscitators wherein a gaseous fluid operated mechanism controlled by the lung capacity of the patient alternately directs gaseous iluid into and withdraws it from the patients lungs to promot respiration and resuscitate the patient.

Heretofore in such resuscitators, the gas operated control mechanism has been directly supported by or mounted on a gas tank or other source of supply of gas under pressure or connected thereto by rigid fittings and mounted in a case or cabinet corresponding in size to a large suitcase or small trunk, with flexible hose lines for connecting the mechanism to a mask. In these machines the working mechanism includes diaphragm operated valves and a plurality of ports, passages and elements such that the machine constitutes a relatively large and heavyunit of considerable weight and bulk requiring the mounting thereof in a large case or cabinet and the direct connection ofthe gas tanks therewith, whereby the machine as a whole will be portable. Due to the construction and arrangement of such a machine it is not practicable and in many cases not possible to treat more than one patient at a time inasmuch as provision is made for the connection and operation of but one mask at a time per machine. Moreover, the weight, size and bulk of these machines make it diiiicult to transport them and serious delays are likely to occur in the application of the resuscitator to patients in field operations and in confined places and where access to the patient would be difcult with large and heavy equipment.

It is therefore an important object of my invention to provide a resuscitator wherein the gas operated mechanism is of such improved construction and arrangement that it is of minuscule proportions compared to resuscitation mechanisms heretofore used. and is actually smaller than the mask and supported thereby to form a complete unit subject to ready connection with a gastank or other source of supply of gas under pressure by means of a single flexible hose line.

Another object of my invention is to provide a resuscitator such as described which may be more conveniently shipped, stored and carried from place to place as well as applied to a patient, and is constructed so that a plurality thereof may be connected with a single source of supply of gas for independent or simultaneous operation in a v much more efficient and economical manner than suscitator units of the type heretofore used are ,a size which would accommodate but one machine of the type heretofore used, with any one or all of the units subject to a convenient and eilcient application in locations and under conditions where the type of machine heretofore used would A be difficult, if not impossible, of use.

A further object of my invention is to provide a gas operated resuscitator mechanism which is.

smaller, more compact, of less weight, size and bulk, cheaper to manufacture and more economical and efilcient in use than gas operated resuscitator mechanisms heretofore made, by reason of the use of a novel construction, arrangement and combination of comparatively few parts and elements including a housing having a gas chamber for communication with a mask, a Venturi tube carried by the housing with its suction port open to the chamber at al1 times and'its discharge portv subject to being opened to the atmosphere, a means for connecting the Venturi tube with a source of supply of gas, a diaphragm in the chamber, a valve for controlling the discharge port of the Venturi tube, and a means of operative connection between the valve and diaphragm for opening and closing the valve responsive to movement of the diaphragm so that when the valve is closed, gas under pressure will flow through the Venturi suction port. into the chamber for delivery to the mask and the lungs of the patient and when the valve is opened, said Venturi tube will evacuate the patients lungs through the mask, chamber and open discharge port.

Another object of my invention is to provide a resuscitator of the'character described having a valvular means mounted on the housing of the gas operated mechanism so as to be readily accessible and operable at will for rendering the mechanism inoperative as a resuscitator and operative as an insufflator or what is known in the art as an inhalator, and vice versa, this Valvular means also serving as a safety valve which will open responsive to a fluid pressure beyond safe limits, for example, beyond approximately four ounces (13 mm. of hg.) during the inhalation phase of aresuscitation operation of the machine.

Yet another and important object of my invenpossible where a plurality of independent retion is t0 provide a resuscitator of the character described which is constructed so that it may be conveniently held with one hand in the properly applied position with all controls readily accessible to the operator and the weight and pressure of the unit against thepatients face under control of the operator.

An additional object of my invention is to provide a small, compact, gas operated working mechanism for a resuscitator which may be directly mounted on top of the mask o r supported close thereto on rigid tubing with said tubing serving as a convenient handle and affording a controlled application of the mask whereby the I currect pressure and contacto! the mask against the patients face is assured. I

Another object of my invention is to provide a resuscitator Working mechanism wherein a Venturi tube, a single pressure operated control valve and a toggle device operatively connecting the control valve with a diaphragm, are/of such novel construction, relative arrangement and simplied design that the working mechanism as a whole consists of fewer parts, is less expensive to manufacture, smaller and more compact, lighter as to weight, and more reliable in operation than working mechanisms heretofore employed in resuscitators, and also subject to being mounted on a gas tank or other source' of supply of operating fluid, or supported by and adjacent the mask or between the mask and source of supply of operating fluid and in all cases will constitute an improvement in the art.

Yet another object is to provide a resuscitator of the character described which is provided with an anti-contamination valve which may be opened to the atmosphere between the mask and working mechanism should the patient vomit or cough up sputum, thereby preventing contamination of the working mechanism.

Another object of my invention is to provide a resuscitator mechanism wherein an appreciable saving in strategic materials and a decided reduction in the size, weight and bulk of the mechanism as well as a considerable reduction of the number of parts employed and a more reliable performance are afforded by the use of a particular construction and relative arrangement of a Venturi tube and a control valve in which the valve is mounted in the tube and operated by a pressure responsive diaphragm so that when closed the Venturi tube will discharge gas under pressure for introduction through a mask into the lungs of a patient and when opened will cause the Venturi tube to operate for evacuating the lungs of the patient.

Another object of my invention is to provide a resuscitator of the character described which is designed to be operated from a tank of oxygen or similar gas under pressure, or by means of a simple manually operable air pump or other source of supply of air under pressure, and is particularly adapted for use and transportation in aircraft, submarines and other vehicles having limited space and facilities. Y

With the foregoing objects in view, together with such other objects and advantages as may subsequently appear, theinvention resides in the parts and in the combination, construction and arrangement of the parts hereinafter described and claimed, and illustrated by way of example in the accompanying drawings, in which:

Fig. 1 is a side elevation of a resuscitator embodying my invention as connected to a source of supplyA of gas under pressure Fig. 2 is an enlarged horizontal sectional view taken on the line 2 2 of Fig. 1;

Fig. 3 is a vertical sectional view taken on the line 3-3 of Fig. 2; showing the control valve in open position as when evacuating the lungs` of a patient;

Fig. 4 is a sectional View corresponding to Fig. 3 but showing the control valve in closed position as when introducing gas into the lungs of a patient;

Fig. 5 is a fragmentary side elevational view of a modified form of resuscitator embodying my invention;

Fig. 6 is an elevational view of another modied form of my invention;

Fig. 7 is an elevational view of a third modified form of this invention.

Referring to the drawings more specifically, it is seen that one embodiment of my invention generally includes a mask A for the most part made of transparent material and adapted to be applied over the nose and-mouth of a patient, an enclosed working mechanism B supported by the mask and operable for introducing gas into and withdrawing it from the lungs of a patient responsive to the'lung capacity of the patient, a single flexible hose line C, connecting the working mechanism with a source of supply D of gaseous uid under pressure, a pressure regulator E, a pressure gage F and an intake valve G operable on the exterior of said working mechanism for controlling the flow of gaseous iluid thereto.

As shown in Fig. 1 the enclosed working mechanism B is disposed on top of the mask A and serves as handle for applying the mask and holding it in proper position on the face of thaf "J tient, said mechanism being of considerably smaller diameter than the mask and affording ready access to the gas supply valve G as well as making it possible for the operator to clearly .see the patients face through -the transparent mask to note any reaction so that the mask or the mechanism may be quickly and properly manipulated or regulated to best suit the condition of the patient.

In accordance with my invention the working mechanism B is contained in a cylindrical housing l formed of telescopically joined sections la and Ib and provided with a cylindrical wall 2, an inner wall 3 and an outer wall 4, said housing being of considerably less diameter and of less height than the diameter and height of the mask for the purposes hereinbefore noted.

Removably screwed into the Vsmaller section la of the housing l is an annular supporting member 5 for a diaphragm 6 and a Venturi tube assembly 1. The diaphragm 6 is held on a flange 8 on the supporting member 5, by means of a ring 9 adapted to be engaged with the outer wall 4 and the marginal portion of the diaphragm so 'the operator grasps the housing to apply the mask.

The inner end portion of the supporting member 5 has a close t in the section Ib of the housing and supports the Venturi tube unit 1 between the diaphragm and the inner wall 3, with said diaphragm exposed to the gas chamber I3 which is constituted in that part of the housingbetween the diaphragm and said inner wall. The Venturi tube assembly 1 as here provided consists of a Venturi tube I4 formed integral at its ends with the annular supporting member 5 and extending transversely thereof. The intake end of the Venturi tube I4 abuts the wall 2 of the housing and registers with an opening I5 inV said wall so that a tting I6 may be extended through said opening and screwed into said end of the tube for introducing gaseous uid into the tube. The outer end of the fitting serves as a hose connection for the hose line C leading from the supply D of gaseous iluid. The intake valve G is mounted intermediate the ends of the fitting I6 and together with associated parts constitute a valved intake means for gaseous fluid under pressure.

The Venturi tube I4 has its outlet end in registration with a discharge port or opening I8 in said Wall 2 of the housing. Threaded into the opening I8 is a muffler I1 comprising a small perforated casing I9 having felt or like porous muffler elements therein between the apertures 2| thereof and the opening I8, to reduce the noise of the fluid as it discharges to the atmosphere. The fitting I6 in being screwed Vinto the intake end of the Venturi tube I4 holds the tube A suction port 24 is provided in the tube I4 for discharging fluid `under pressure into the gas chamber I3 as well as for evacuating said chamber throughj the Venturi tube assembly to the atmosphere. The port 24 opens into an annular space 25 in the tube I4 Aformed between the reduced portion 26 0f the nozzle member 22 and the wall of the bore of said t be. This annular space is communicated with t e bore of the tubular nozzle member 22 by means of a transverse opening 21 in said nozzle member. In this connection it will be noted, as shown in Figs. 2 and 3, that the nozzle member 22 has one nozzle 28 arranged to discharge a jet of i/luid across the transverse opening 21 into -and through a conical nozzle 29 which latter discharg/es a jetof iiuid into the conical constriction or mouth 30 of the Venturi member 23, thus forming in combinationl ak species of jet pump. As shown in Fig. 3 the nozzle 29 is spaced somewhat from the mouth 3l!v to define a conical extension of the ,space 25. However, the nozzle member 22 maybe axially adjusted to regulate the width or size of this exT tension or to cause the nozzle 29 to seat in the mouth 30 for regulating the suction action through the port 24.

A valve bore 3| extends transversely through the tube I4 between the discharge end of the Venturi member 23 and the discharge end of the tube I4 at which latter a discharge port 32 is l provided in registration with the outlet opening I8 in the housing. A valve member 33 is slideble in the bore 3I to bring a transverse valve port 33' therein into and out of registration with the bore of the member 23 and discharge port 32. 1 When the valve member 33 is closed, as shown in Fig. 4, pressure fluid will be discharged from the nozzle member 22, through the opening 21, space 25 (see Fig. 2) and port 24 into the gas chamber I3. When the valve member 33 is opened, as shown in Fig. 3, the pressure vfluid discharges through the Venturi tube discharge port 32, opening I8 and the muiiler I1 to the atmosphere, thereby producing a suction action through the port 24 and evacuating the gas chamber.

` A toggle device is provided for operating the control valve 33 responsive to movement of the diaphragm 6 and includes a pair of arms 34 xed to the diaphragm and arranged to str-addle the tube I4. These arms are pivoted as at 35 to a pair of like toggle levers 36 at points between the ends of the toggle levers while certain corresponding ends of said levers are pivoted as at 31 to ears 38 on the tube I4. The other ends of the levers 36 are pivotally connected with one end of a valve-connected toggle lever 39, by means of a pin supported by and extended between the levers 36, withspacer sleeves 4I thereon to center the lever 39 as shown in Fig. 2. The lever 39 extends loosely through a slot 42 in the steam 43 of the valve 33, said slot being of sutiicient length to permit of necessary movement of the lever 39 relative thereto as shown in Figs 3 and 4,

Retractile springs 44 are connected at their ends to pins 45 and 46 carried by the pair of levers 36 and the single lever 39 respectively to provide a quick action of the toggle device for opening and closing the valve 33 as Well as for holding the valve in opened and closed positions. As shown in Fig.,3 the levers 36 will engage the tube I4 to limit the movement of the toggle levers to a position in which the valve 33 is opened and held open, while Fig. 4 shows how the toggle movement is limited by means of hook members 41 when the toggle is operated to close the valve,

said hook members being fastened to the tube I4 and arranged to engage the pin 4B on the lever 39.

It is important to note that upon removing the tting- I6 the entire working mechanism may be lifted out of the section I b of the housing with the removal of the housing section Ia from section Ib. .This arrangement makes for ease of assembling and disassembling the unit as well as ready inspection and replacement and repair of parts thereof.

Asbest shown in Fig. 2, a suction or vacuum relief valve unit 48 is mounted on the exterior of the housing I and comprises a small valve casing 49 screwed into an opening 50 in the housing wall 2 and provided with an inwardly opening spring loaded disk check valve 5I normally closing a vent opening 52 and operating when a predetermined sub-atmospheric pressure is developed in the chamber I3 such as might injure the patient (say beyond four ounces of vacuum) to open said chamber to the atmosphere.

A combined insuillator and pressure relief valve 54 is, mounted on thefhousing I and includes a small valve casing 55 having a threaded nipple 56 screwed into an opening 51 in the wall 2 and affording communication between said casing and the gas chamber I3. mounted in the casing 55 and is' urged inwardly against a seat 59 therefor byy a spring 60. The force of this spring is controlled by turning a screw cap 6I on the casing 55. When lthe cap 6I is screwed in to its limit-the spring will be so tensioned that it will yield and allow the valvev 58 to open and discharge gas to the atmosphere through vents 62 in the casing 65 when a posi- A disk valve 58 is` tive pressure beyond safe limits, for example beyond four ounces, is attained in the gas chamber I3, thereby preventing injury of the patient. When the screw cap 6I is screwed out to its limit, the tension of the spring 60 is lessened to the extent that. the valve 58 will open responsive to a positive pressure less than the positive pressure required to move the diaphragm and open the valve 32. Thus the valve 32 remains closed and a steady flow of gas passes from the Venturi Vsuction port 24 into the chamber I3 for insulation purposes, as will be hereinafter more fully described.

The inner wall 3 of the housing I is provided with an opening or port 63 affording communication of the gas chamber I3 in said housing with a mask such as the mask A shown in Fig. 1, it being noted that this mask has the customary pneumatic marginal cushion 64 thereon provided with a valved inilation stem 65.

As shown in Fig. 1 the opening 63 in the housing is directly connected with the interior of the mask by means of a short tubular fitting 66 bringing the working mechanism and the mask close together, the working mechanism being literally supported on top of the center of the mask. The fitting 66 extends through an opening 61 in the mask and has a flange 68 engaged with the outer surface of the mask while a nut 68 is screwed onto the inner end of the tting within the mask to hold the tting in place. The outer end of the tting 66 has a tight frictional fit in a socket member 69 extended into the chamber I3 from the opening 61. This means of connection provides for detachably connecting the working mechanism B (housing) with the mask.

Instead of connecting the Working mechanism B close to the mask A as shown in Fig. l, I may, as shown in Fig. 5, connect said mechanism to the outer end of a horizontally disposed piece of rigid tubing or conduit 'I0 which is connected with the mask by means of a fitting 'II similar to the fitting 66 and adapted to extend into a socket 'I2 in the side of thetubing I0 near the closed end 'I3 thereof. The tube I0 serves as a convenient handle and permits the operator to regulate the weight and pressure of the unit against the face of the patient and affords good visibility of the face of the patient through the transparent body of the mask. This arrangement, disposing the working mechanism to one side of the mask may be preferable in some instances to the overhead arrangement of Fig. l. It affords ready access to the valves on the housing and it is seen that aside from the manner of mounting the working mechanism on the mask the construction and operation of this modied unit is the same as that of the form of my invention shown in Figs. 1 t0 4 inclusive.

I may employ, as shown in Fig. 5, an anticontamination butterfly type of valve 'I5 for controlling a vent opening I6 in the tubing 10. A spring 11 normally holds the valve in position closing the opening I6. Should the patient commence to vomit or cough up sputum, the operator by manipulating the lever "I8 may move the valve to position shutting olf the passage through the tube 'I0 to the working mechanism and opening the vent I6 so that foreign mattermay be discharged through said opening and does not reach 'and contaminate the working mechanism.

Another modified form of my invention as shown in Fig. 6 is identical with that form of the invention shown in Figs. 1 to 4 inclusive except that a rigid upright tube is employed to connect the working mechanism B with the mask A and is of such length as to constitute a handle. The tube 80 may beI provided with an anti-contamination valve 8l identical with the one shown in Fig. 5. In all other respects this form of my invention is identical as to construction and mode of operation with the device shown in Figs. 1 to 4 and the identical parts shown are designated by the same reference characters as employed in Figs. 1 to 4.

The vertical handle provided by the tube 80 disposes the controls on the working mechanism within convenient reach of the operator, affords a ready application of the mask and an effective control of the weight and pressure of the'mask on the face of the patient also makes for greater visibility of the mask covered portions of the patients face.

Another modified form of the invention as shown in Fig. 7 takes into consideration the same mounting of the mechanism B on the mask A as shownin Fig. 1 but provides a rigid horizontal tube 82 as a connection between the fitting I6 and the hose line, whereby a handle is aiorded on one side of the mask and working mechanism.

' In all forms of the invention as here shown the working mechanism B is of the same construction and follows the same mode of operation.

When a resuscitation operation is desired the screw cap 6I is screwed in to its limit to set the valve 58 to operate as a safety valve. Upon now opening the intake valve G, fluid pressure will flow into the Venturi tube I4 and with the control valve 33 closed the diaphragm 6 bowed inwardly as shown in Fig. 4, the pressure fluid will pass out through the Venturi port 24 intothe chamber I0 and thence to mask A and into the lungs `of the patient. When the pressure in the patients lungs and in the chamber I 3 reaches approximately four ounces, the diaphragm 6 will be bowed outward so that the toggle levers 36 and 39 will be moved to open and hold open the control valve 33 as shown in Fig. 3, whereupon the exhalation cycle of the machine takes place inasmuch as the Venturi tube I4 is then open to atmosphere through the valve 33 and operates to evacuate the lungs of the patient through the mask, chamber I3 and Venturi tube port 24 vand Venturi tube I 4. When a negative pressure of say approximately four ounces is produced by the Venturi tube in the chamber I3 and patients lungs, the diaphragm 6 will respond to atmospheric pressure in chamber I6 and be bowed inwardly into position shown in Fig. 4, whereby the valve 33 will again be closed and gas under pressure will ow into-the patients lungs. These inhalation and exhalation cycles are repeated and controlled by the lung capacity of the patient and the rate of the resuscitation operation may be regulated by adjusting the intake valve G which is readily accessible to the operator in all forms of the invention.

When the machine is to. operate as an insufllator the operator unscrews the cap 6I and reduces the tension on the spring 6I) to the point that the valve 58 will open lthe chamber I3 to the atmosphere responsive to a pressure below that required to open the valve 33. With the valve 33 maintained in closed position a steady ow of oxygen passes from the Venturi tube I4 through the port 24 into the chamber I3 and thence to thetient. When the patient exhales the valve 58 will open and allow the exhaled gas to pass to the atmosphere. When the patient inhales kthe valve 58 will be closed whereby gas Vwill flow to the patient. During this insuiilation operation the flow to Venturi tube may be reduced as desired by regulating the intake valve G.

It is important to note that the housing and working mechanism therein are of minuscule proportions compared to housings and working mechanisms as heretofore employed and that the working mechanism itself consists of fewer parts and is much more simple as to construction and operation than any resuscitation mechanism heretofore produced and at the same time is reliable in performance'and subject to a nicety of control, Wherefore the objects and advantages of my invention as hereinbefore set forth are achieved in a. particularly efcacious manner.

It is also important to note that my improved resuscitator is particularly well suited for use in aircraft operating in the substratosphere in thatthe machine may be operated as an insuiiiator to take the place of the oxygen mask as now used inairplanes, and when extremely high altitudes are reached and respiration of the occupants of the airplane becomes diiiicult it only being necessary to' make a simple adjustment of the insulator-safety valve to render the machine operable as a resuscitator and thereby promote normal or satisfactory breathing. The practicability of this use of my resuscitator is readily seen in consideration of its small size, lightness in weight, convenience of application, the provision for the operation of a plurality of the units from a single source of supply of oxygenor other suite able gaseous fluid, and in view of the selective operation of the machine as an insuiiiator and a resuscitator while the mask is applied to the userN While I have shown and described specific embodiments of my invention I do not limit myself to the exact details of construction set forth, and the invention embraces such changes, modifications and equivalents'of the parts and their formation and arrangement as come within the purview of the appended claims.

I claim:

.1.' A resuscitator comprising,` in combination, a housing dening a gas-receiving chamber, said housing being provided with a port adapted for connection with a mask, conduit means traversing said chamber, said conduit means being fitted at one end for attachment to a source of gas under pressure and the other end thereof defining a discharge port open to the outer atmosphere, jet pump means mounted within said conduit and comprising a, nozzle and constriction, valve means positioned between said constriction and said'discharge port for opening and closing said discharge port, means responsive to changes in pressure within said chamber for operating said valve means, and port means in the side of said conduit communicating with said chamber, said port means being positioned at a point between said nozzle and said constriction so that suction is created therethrough when said valve means is open, said'port means introducing gas from said conduit into said chamber when said valve means is closed and withdrawing gas from said chamber into said conduit when said valve means is open.

connection with a mask and a second port communicating with the atmosphere, diaphragm means separating said chamber from said secondnamed port, conduit meanstraversing said housing and chamber, said conduit means being fitted at one end for attachment'to a source of gas under pressure and the other end thereof defining a discharge port open to the outer atmosphere, jet pumpmeans mounted within said conduit, and comprising a nozzle and constriction, valve means positioned between said constriction and said discharge port for opening and closing said discharge port, means mounted within said housing for controlling said valve means, said last-named means Vbeing operated by said diaphragm in response to changes in pressure within said chamber, and port means in the side of said conduit communicating with said chamber, said port means being positioned at a point between said nozzle and said'constriction so that suction is created therethrough when said valve means is open, said port means introducing gas from said conduit .into said chamber when said valve means is closed and withdrawing gas from said chamber into said conduit when said'valve means is open.

3. A resuscitator comprising, in combination, ahousing defining a gas-receiving chamber, said housing being provided with a port adapted for connection with a mask and a second port communicating with the atmosphere, diaphragm means separating said chamber from said second-named' port, conduit means traversing said housing and chamber, said conduit means being fittedat one `end for attachment to a source of gas under pressure and the other end thereof defining a discharge port open to the outer atmosphere, jet pump means mounted within said conduit and comprising a nozzle and a constriction, valve means slidably mounted in said conduit adjacent said discharge port for opening and closing said discharge port, toggle means Y mounted within said housing for controlling `said valve means, rsaid toggle means being operated f by said diaphragm in response to changes in pressure within said chamber, and port means in the side of said conduit communicating with said chamber, said portmeans being positioned l at a point between said nozzle and said constric- Y housing being provided with a port adapted for connection with a mask, conduit means traversing said chamber, said conduit means being tted at one end for attachment to a source of gas under pressure and the other end thereof defining a discharge port open to the outer atmosphere, jet pump means mounted within said conduit and comprising a nozzle and constriction, valve means positioned between said constriction and said discharge port for opening and closing said discharge port, means responsive to changes in pressure within said chamber for operating said valve means, port means in the side of said conduit communicating with said chamber, said port means being positioned at a point between said nozzle and said constriction so that suction is created therethrough, when said valve means is open, said port means introducing gas from said conduit into said chamber when said valve means is closed and withdrawing gas from said chamber into said conduit when said valve means is open, means providing a. further port in said housing between said gas receiving chamber andl the atmosphere, and valve means controlling said port for converting said resuscitator to use as an insuiiator.

5. A resuscitator comprising, in combination, a housing defining a gas-receiving chamber, said housing being provided with a port adapted for connection with a mask and a second port communicating with the atmosphere, diaphragm means separating said chamber from said second-named port, conduit means traversing said housing and chamber, said conduit means being iitted at one. end for attachment to a source of gas under pressure and the other end thereof dening a discharge port vopen to the outer atmosphere, jet pump means mounted within said conduit and comprising a nozzle and a constriction, valve means positioned between said constrictionl and said discharge port for opening and closing said discharge port, means mounted within said housing for controlling said valve means, said last-named meansbeing operated by said diaphragm in response to changes in pressure within said chamber, port means in drawing gas from said chamber into said conduit when said valve means is open, means providing a further port in said housing between said gas receiving chamber and the atmosphere, valve means controlling said port, spring means urging said valve means to closed position, and manually operated means for controlling the pressure of said spring between a predetermined maximum and a predetermined minimum, said minimum being less than the pressure necessary to cause said diaphragm to openl said rst-named valve means, said maximum being substantially equal to the limit of safe pressure within said chamber in excess of atmospheric pressure.

LE ROY G. FOX.

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