US3018777A - Anesthetic vaporizer and administering apparatus - Google Patents

Description

Jan. 30, 1962 H. A. DIETRICH 3,018,777

ANESTHETIC VAPORIZER AND ADMINISTERING APPARATUS Filed Dec. 17, 1958 2 Sheets-Sheet a INVENTOR. HAROLD A. DIETRICH BY W 3 f ATTORNEY-6. AG T United States Patent 3,018,777 ANESTHETIC VAPORIZER AND ADMINISTERING APPARATUS Harold A. Dietrich, Madison, Wis., assignor to Air Reduction Company, Incorporated, New York, N.Y., a

corporation of New York Filed Dec. 17, 1958, Ser. No. 781,013 Claims. (Cl. 128-188) This invention relates to apparatus for vaporizing and administering volatile anesthetic agents during anesthesia and particularly to improvements in such apparatus adapted to facilitate rapid increases in the flow of carrier gas employed for the entrainment of such anesthetlc vapors without the attending surge of anesthetic vapors which occurs in conventional anesthetic vaporizer apparatus heretofore in use.

It is customary, in certain techniques for the administration of inhalant anesthetics derived from volatile liquid anesthetic agents, for example, such as ether or trichloroethylene to provide a vaporizer device which holds a supply of the liquid agent and to deliver and pass therethrough a suitable carrier gas usual-1y oxygen or an oxygen-containing gas mixture with which the anesthetic vapors are entrained and thence carried to conventional administering devices for inhalation by the breather. The desired relative proportions of the oxygen to supply the need to the patient and of the anesthetic vapors to sustain a desired depth of anesthesia is achieved by proportioning in some suitable fashion the rate at which the anesthetic vapors are entrained in the carrier stream. In one conventional type of apparatus that is widely used, the oxygen stream is divided so that a portion thereof passes in contact with the liquid agent undergoing vaporization which is then recombined with the main stream and thence delivered to the patient. The concentration of the anes thetic vapors, of course, will vary depending upon the adjustment of the flow of the divided portion for picking up the anesthetic vapors as well as by the adjustment of the total flow rate.

Under certain circumstances during the period of the anesthesia, it occasionally arises that the patient requires the rapid administration of a higher concentration of oxygen. Such requirement may be brought about, for example, by an undesired deepening of anesthesia to a hazardous degree or by any relapse or apparent defection in the pulmonary or cardiac conditions of the patient.

' The rapid administration of highly concentrated oxygen for breathing by the patient will then ordinarily be immediately ordered by the surgeon or anesthetist supervising the condition of the patient.

With the conventional type of vaporizer device as described above, such rapid increase in the delivery of oxygen incurs inherently the concurrent entrainment of additional quantities of the anesthetic vapors which also are carried to the patient. Such an occurrence is objectionable especially under circumstances where high oxygen concentrations are desired. Consequently, in order to satisfactorily meet such emergencies when they arise, it is necessary to resort to an alternate mode of introduction of such oxygen and to make necessary adjustments which will obviate the simultaneous delivery of excessive anesthetic vapors. Obviously, such manipulations and adjustments require additional efiort and attention on the part of the anesthetist and, thus, impose an additional burden on carrying out the anesthesia.

It is an object of the present invention to provide an improved apparatus for vaporizing and administering anesthetic vapors wherein a suitable carrier gas for the entrainment of the anesthetic vapors may flow in a normal range required forthe maintenance of normal levels.

of anesthesia and which may be increased abruptly to substantially greater flows without the attendant delivery of correspondingly greater amounts of anesthetic vapors.

It is a further object of the present invention to provide an improved vaporizer for liquid anesthetic agents adapted for such application having means for dividing the flow of the carrier gas such that a part thereof is passed in contact with the anesthetic liquid to be vaporized and a second part is maintained separately therefrom such that the recombination of said divided parts affords a controllably diluted anesthetic-containing mixture and wherein valve means are arranged to close off the divided part of said carrier gas stream when the flow rate of said carrier gas is raised substantially above its normal range of flow.

It is a still further object of the invention to provide such an improved anesthetic vaporizer having a valve means for effecting the closing ofi of said divided part of the carrier gas stream which is responsive to a pressure diiferential produced by the carrier gas stream and effective and responsive thereto to prevent the delivery of anesthetic vapors for entrainment in said main stream.

Other objects and advantages of the present invention may be more fully understood by reference to the following description of advantageous embodiments thereof and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an anesthetic administering system showing the manner in which an improved vaporizer device, in accordance with the present invention, may be employed so as to aiford an anesthetic administering system having the advantages in accordance with the objects of this invention.

FIG. 2 is an enlarged sectional view of the anesthetic vaporizer illustratedschematically in FIG. 1 and including the valve means for effecting closure of the divided vapor entraining portion of the carrier gas stream in accordance with the objectives of the invention.

FIG. 3 is an enlarged sectional view illustrating in greater detail the pressure responsive valve means of the vaporizer seen in FIG. 2; and

FIG. 4 is an enlarged sectional view of a vaporizer showing an alternative pressure responsive valve means.

Referring now to the drawings, a typical anesthetic administering system for anesthetizing the patient is referred to generally by the numeral it). Such a system includes a suitable source of the carrier gas such as oxygen, for example, in an oxygen cylinder '12 whose delivery may be adjusted by means of a valve 14 and the rate thereof indicated on a gauge 16. It will be understood that the cylinder will normally have its own closing valve and that the control valve 14 is desirably situated on the anesthetic apparatus for convenient access by the operator. A suitable pressure regulator device Will preferably be included upstream of the valve 14 to maintain a substantially constant delivery pressure at the inlet to the valve 14. The metered oxygen may be delivered by a conduit 18 to the inlet 20 of anesthetic vaporizer 22. wherein the liquid anesthetic agent contained therein is vaporized and entrained as will be more fully described hereinafter in controllable concentrations in the oxygen stream which is thence discharged through the vaporizer delivery outlet 24. A conduit 25 leads to an inlet valve fixture 26 attached to a conventional anesthetic face mask 28 that is placed over the nose and mouth of the patient indicated at P. The administering system shown constitutes a socalled partial rebreathing or semi-closed system which Will be well understood by those skilled in the art. In this system, the fixture 26 connects to the mask 28 through a valve body 3%. Also connecting with the valve fixture 2 6 and in direct communication with the valve body 30 and face mask 28 is a rebreathing bag 32.

It is conventional in this particular type of administering apparatus that the valve body 30 be provided with an exhalation check valve arranged such that upon inhalation the valve closes but upon exhalation opens permitting the venting of exhalation gases directly to the atmosphere. The designation of this method of administration, i.e., partial rebreathing, derives its name from the fact that the initial portion of the exhalation gases are passed back to the rebreathing bag 32 which when substantially fully distended causes the remainder of the patients exhalation to pass through the exhalation check valve of the valve body 30 to the atmosphere. Subsequently, upon the inhalation phase, the gases from the bag 32 are first inspired together with the additional gases which are continuously fed through the delivery conduit 25. It will be understood that the delivery means illustrated in the present embodiment by the conduit 25 through which the oxygen an anesthetic vapors are conducted for administration to the patient may be employed with any of the various conventional systems for administering inhalant anesthetics to patients. Thus, for example, the conduit 25 might instead be connected to a conventional closed circuit system in which the gases breathed by the patients are continuously recirculated. The recirculation gases in such systems are passed through a carbon dioxide absorber for the removal of carbon dioxide expired by the patient and the oxygen and additional anesthetic vapors required would then be supplied by the delivery means shown at 25 in the present drawings. The anesthetic-oxygen delivery means shown also might be employed in connection with nonrebreathing or semi-open inhalation anesthesia which diflers from the system hereinabove described in that all of the patients exhalation gases are discharged to the atmosphere and none are rebreathed. The arrangement and operation of such specific methods and devices for administration are well known and need not be described in any further detail.

Referring again to the present drawings, and particularly to FIGS. 2 and 3, an advantageous construction of the anesthetic vaporizer, in accordance with the present invention, is illustrated in greater detail. The vaporizer 22 has an upper body or housing portion 35 in which the inlet and outlet fittings are arranged. In practice, the body 35 is usually attached to a suitable supporting fixture such as on the anesthetic machine which also houses other accessory equipment within the immediate vicinity and accessible to the anesthetist. A jar 36 is threadedly received on the bottom of the vaporizer housing. The threaded connection may be afforded by means of a connector ring 38 threaded into the housing and provided with a sealing gasket 40. The jar may be provided with a Mason type neck having CGA threads in accordance with the standards of the Glass Container Association by which the jar may be threaded into the connecting ring 38. The connecting ring protects the fragile lip of the jar and facilitates the manipulation of the jar when it is removed and replaced for refilling. A suitable quantity of a volatile liquid agent, such as indicated by the line L, is placed in the jar to be vaporized.

The gas inlet communicates with a transversely extending inlet passage 42 in the vaporizer body which is intersected by a downwardly extending conduit 44 that feeds a down tube 46 carrying a porous distributor block 48 at its lower end. The intersection of the passages 42 and 44 forms a valve seat 50 against which the tapered end of a needle valve stem 52 is arranged to bear. A threaded portion 54 of the valve stem causes the valve stem to move vertically upon rotation to open or close the opening through valve seat 58 in varying amounts depending on the setting of the valve stem. Rotational adjustment of the needle valve is accomplished by rotation of a knob 55 arranged at the top of the vaporizer which carries a pinion 56 operatively meshed with a gear 58 carried at the upper end of the valve stem. A pointer 60 is carried by the valve stem on an upper protruding end portion and may be calibrated with respect to a dial face 62 arranged at the top of the vaporizer to indicate the various seatings of the needle valve. Depending upon the seating of the needle valve, varying proportions of the inlet gas fiow are diverted from the passage 42 through the passage 44 and down to 46. The distributor block 48 may be of a porous construction such as a block of sintered porous bronze which causes the gas conducted through the down tube to pass in a relatively uniform manner throughout the sections of the distributor block and to emanate into the body of liquid anesthetic as minute bubbles which then rise to the surface L of the liquid and pass outwardly from the vaporizing chamber 64 through a discharge opening 66, FIG. 3, as will be hereinafter more fully described. The intimate contact of the gas passing through the liquid assists in the vaporization of the liquid and a quantity of the anesthetic vapors is carried with the gas from the vaporizing chamber.

The remainder of the inlet gas flow is conducted through a bypass route to the vaporizer outlet 24. The bypass includes a passage 68 intersecting with the transverse passage 42 which opens into a cavity 76. A ball valve element 72 arranged within the cavity is adapted to sit against the upper end of the passage 68 under the influence of the marginal spring 74 which is compressed thereagainst by the threaded cap 76 forming an end closure for the valve cavity. The valve element 72 affords a differential-pressure check valve and the spring 74 is of predetermined strength to allow a portion or all of the inlet gas flow to pass therethrough depending upon the total flow rate and/ or the setting of needle valve 52 as will be hereinafter more fully described. The gas flowing into the chamber 70 is delivered thence to the outlet fitting 24 of the vaporizer by a connecting conduit 78.

The discharge opening 66 of the vaporizing chamber is formed in the stem portion of a cage 80 that is threadedly seated in an enlarged bushing 82. The bushing 82 is threaded into a bore formed in the bottom of the vaporizer housing which connects at its upper end with the transverse passage 42. The bore is closed 01f from the passage 42 by a pressure responsive diaphragm 84 which is sealed around its edges against an annular shoulder 86 by the engagement of the inner end of the threaded busing 82. A thin backing plate 88 is disposed underneath the diaphragm against which a compressed spring 90 is adapted to act to provide a predetermined upward force against the diaphragm, A ball element 92 is disposed within the valve cage 80 and acts as a check valve preventing backward flow of gases from the delivery outlet of the vaporizer to the vaporizing chamber. Within the normal range of carrier gas flow rates at which anesthetic vapors are dispensed therewith carrier gas conducted through the vaporizing chamber through the open needle valve 52 possesses sufiicient pressure to overcome the weight of the ball element so that it is raised to open the discharge opening 66.

A series of radial openings 94 connect the outlet chamber formed within busing 82 with an annular cavity 96. The gas and anesthetic vapors which are delivered through the discharge opening 66 past the ball element 92 are, thus, conducted to the annular cavity 96 and from thence by means of a connecting passage 98 to the delivery outlet 24 of the vaporizer.

The development of gas pressure within the vaporizing chamber sufficient to open the check element 92 is related to the pressure differential produced by the bypass valve 72. Thus, the spring loading of the spring 74 against the bypass valve is such that the back pressure in the passage 42 required to open the valve 72 exceeds the back pressure required to overcome the resistance to gas flow through the vaporizing chamber. Such flow resistance includes the head of the liquid anesthetic in the vaporizing chamber and the pressure required to raise the ball check element 92. To alford a control of the proportioning of the gas flow through the vaporizing chamber, it is desirable that within a normal range of flow rates the bypass valve be sufiiciently biased that, with the needle valve 52 fully open, all of the gas delivered to the vaporizer be conducted to the delivery outlet through the vaporizing chamber. In apparatus such as in the type herein described the normal flow ranges under which anesthetic vapors may be controllably administered extend in most instances from to about liters per minute and sometimes up to about liters per minute. Thus, in a preferred embodiment, the bypass valve 72 may be arranged to remain seated with the needle valve fully open for carrier gas flows up to approximately 10 liters per minute. It will be seen that as the needle valve is progressively closed, a resultant increase in back pressure is produced in the conduit 42 which will open then progressively increase the opening of the bypass valve 72 allowing correspondingly greater proportions of the carrier gas to bypass the vaporizing jar. When the needle valve is completely closed, of course, all of the gas received at the vaporizer inlet will be conducted through the bypass to the delivery outlet. In this manner, the varying adjustments of the needle valve permit a fine degree of control of the carrier gas fiow through the vaporizing jar and, consequently, of the amounts of anesthetic vapors entrained therein and dispensed with the total carrier gas ilow through the delivery outlet of the vaporizer.

The diaphragm 88 is so arranged that with an increase in the pressure of the carrier gas delivered to the vaporizer suflicient to produce a flow of the carrier gas therethrough which is substantially above the normal fiow range, the diaphragm moves inwardly against the opposing action of the marginal spring 90 to bear against and hold the ball element 92 in closed position against the discharge opening 66. Such relatively high gas flow rates are conventionally desired for purposes other than administering the anesthetic vapors and, indeed, at such flows it is normally desired or necessary that the administration of the anesthetic vapors be discontinued. Such flows may be desired, for example, to flush the patients respiratory system and displace these gases with a fresh supply of oxygen. As an example, devices such as the vaporizer herein described, may be arranged such that the described action of the diaphragm 88 occurs at a carrier gas flow rate above liters per minute which it will be seen exceeds the normal range by a substantial margin. patient administering circuit which Will prevail at the vaporizer delivery outlet 24 does not vary substantially from atmospheric pressure under ordinary circumstances. In a vaporizer embodying the present invention, the back pressure or inlet pressure to the vaporizer necessary to produce flow through the vaporizing jar with controllable adjustment thereof in the normal range of administering flows up to about 10 liters per minute may vary from 0 to about 0.5 psi In such a construction, the back pres sure at the vaporizer inlet corresponding to a flush flow rate of about 25 liters per minute may be slightly greater than 1 p.s.i. and will increase up to about 3 p.s.i. at a flush flow of about 60 liters per minute. It can be seen that, in the range of flush flows, a substantially greater back pressure exists at the vaporizer inlet than prevails within the range of normal flow rates. Preferably, the size of the diaphragm 88 and the spring 90 acting thereagainst are selected such that the diaphragm does not interfere in any way with the vaporizing chamber opening within the range of normal flow rates. However, upon the occurrence of an increased differential pressure thereon corresponding to flush flows, the diaphragm is capable of overcoming the resistance of the spring to close the opening.

It may be seen, by reference to the illustrative administering system shown in FIG. 1, that the carrier gas flow is adjusted by manipulation of the flow valve 14. Supposing that the vaporizer is being employed in a normal range for administering an anesthetic mixture the valve It will be understood that the pressure in the may be set to deliver, for example, 7 liters per minute as shown on the flow gauge 16. The adjusting knob 55 of the vaporizer is set at that flow rate to give a desired concentration of the anesthetic vapors which are dispensed through the line 25 to the respiratory apparatus. In the event that a substantially high flush flow rate is subsequently desired, the anesthetist need only turn the control valve 14 to the desired flow. The attendant increase in the inlet pressure to the vaporizer sufiicient to deliver this flow through the vaporizer acts immediately on the diaphragm 88 as hereinabove described closing the vaporizer chamber and causing all of the carrier gas to flow directly to the vaporizer outlet. Thus, the high flow of oxygen or other carrier gas is immediately produced without any attendant increase in the amount of anesthetic vapors and without the necessity of any separate adjustments to prevent the delivery of anesthetic vapors therewith.

An alternative embodiment of the invention is illustrated in FIG. 4 wherein the identical elements shown in the above described figures of the drawing are designated with the same numeral. In this embodiment the discharge opening 66 of the vaporizing chamber is provided with a positively acting closing means in place of the weighted ball check element 92 shown in FIG. 3. As shown in this figure, a cylindrical plate or disc rests on the upper side of the diaphragm 83. The diameter of the disc is slightly less than the diameter of the bore in which it is disposed to allow access of gas pressure within the transverse passage 42 to the upper side of the diaphragm. A threaded stern 102 is arranged for longitudinal movement and has a rounded lower end which is received in a recess 104 of the disc wherein the stem is adapted to bear downwardly on the disc. An O-ring 106 is arranged around the stem to afford a gas-tight seal. The upper end of the stem carries a gear member Hi8 which is in mesh with the gear 58 carried by the adjustable needle valve 52. The thickness of the gears 198 and 58, as in the case of gears 56 and 53, is such that engagement is maintained during relative vertical displacement. The threads 110 of the stem 102 are opposite with respect to the threads of the needle valve and are of a predetermined pitch. Thus, the pitch of the threads on stem 102 is larger than the pitch of the threads on the needle valve so that the outlet is opened more rapidly than the needle valve. The respective valve stems are preadjusted so that the outlet valve, through the stem 102, and the needle valve close simultaneously. In closed position, the stern acting through the disc 100 presses downwardly on the diaphragm and causes it to seat on the upper lip of the cage member 80. It will be seen that in this embodiment the diaphragm is arranged to cooperate directly with the cylindrical cage 80 to positively close the discharge opening 66 of the vaporizing chamber without the necessity of an interposed ball check element. While this embodiment dose not incorporate a check valve feature, it furnishes a positive sealing of the vaporizing chamber. The automatic closing action of the diaphragm 88 to seal the discharge opening 66 of the vaporizing chamber 64 operates substantially as before except that in this embodiment the diaphragm is urged downwardly in response to the predetermined actuating diflerential pressure to close the vaporizing chamber outlet by seating against the upper lip of the cage 86 The spring iii in this embodiment is arranged to compensate for the additional weight of the disc 10!) so that the diaphragm 88 will operate as previously described upon the occurrence of a predetermined pressure differential created by thedelivery of flush flow rates of the carrier gas.

In this figure, the bypass valve cavity 7th and ball 72 are ofiset from the plane in which they are shown in FIG. 3, and are shown, together with the bypass spring 68 conmeeting the cavity with the passage 42, in dotted lines in the drawing. Otherwise, the general arrangement and construction of the apparatus is substantially the same: as that described in connection with the other figures.

The invention, of course, is not limited specifically to the described embodiments but may be used or carried. out in other ways which will be obvious to those skilled. in the art without departing from the scope of the in--- vention as set forth in the following claims.

I claim:

1. An anesthetic vaporizer apparatus having an inlet adapted to receive varying flows of a carrier gas, a vaporizing chamber adapted to contain a liquid anesthetic agent to be volatilized, a delivery outlet, means for dividing: the carrier gas delivered to the vaporizer inlet such that. a portion thereof is passed through said vaporizing cham-- her and subsequently recombined with the remainder of' the carrier gas for discharge from said delivery outlet,. and means in communication With the carrier gas inlet, and including a member actuated by gas pressure difierential acting thereon, operative in response to the delivery of a predetermined flow rate of the carrier gas to said. vaporizer to prevent the passage of carrier gas through: said vaporizing chamber to said delivery outlet.

2. An anesthetic vaporizer apparatus adapted to re-- ceive varying flows of a carrier gas having a gas inlet and a delivery outlet, a vaporizing chamber adapted to contain a liquid anesthetic agent to be volatilized, meansv for dividing a portion of the carrier gas delivered to the vaporizer inlet and conducting said portion through said vaporizing chamber to said delivery outlet, bypass passage means for conducting the remainder of the carrier gas from said inlet to said outlet independently of said vaporizing chamber and pressure responsive valve means in communication with the carrier gas inlet, and including a member actuated by gas pressure differential acting thereon, responsive to the differential pressure between the inlet and outlet of said vaporizer to prevent the passage of said divided portion of the carrier gas stream through said vaporizing chamber to said delivery outlet.

3. An anesthetic vaporizer apparatus in accordance with claim 2 including means forming a discharge opening for said vaporizing chamber and means connecting said opening with said delivery outlet of said vaporizer and said pressure responsive means is arranged to close said vaporizing chamber discharge opening.

4. An anesthetic vaporizer in accordance with claim 2 having check valve means in said bypass passage means effective to produce a back pressure at the vaporizer inlet at least suflicient to produce a flow of the carrier gas through said vaporizing chamber and adjustable valve means for controllably varying the proportion of the carrier gas stream divided and conducted through said vaporizing chamber to said delivery outlet.

5. An anesthetic vaporizer having an inlet adapted to receive a carrier gas and a delivery outlet, bypass passage means connecting said inlet and delivery outlet, a vaporizing chamber adapted to hold a supply of a volatile liquid anesthetic agent, second passage means connecting said vaporizing chamber respectively with said vaporizer inlet and said delivery outlet through which a divided portion of the carrier gas is adapted to be conveyed from said inlet to said delivery outlet through said vaporizing chamber for the entrainment of anesthetic vapors therein, adjustable valve means forming a part of said second passage means operative to vary the proportion of the carrier gas stream conducted through said vaporizing chamber and pressure responsive valve means in communication with the carrier gas inlet, and including a member actuated by gas pressure difierential acting thereon, forming a part of said second passage means operauve to close said second passage means and prevent the flow of carrier gas through said vaporizing chamber to said delivery outlet.

6. An anesthetic vaporizer having an linet adapted to receive a carrier gas and a delivery outlet, bypass passage means connecting said inlet and delivery outlet, a vaporizing chamber adapted to hold a supply of a volatile liquid anesthetic agent, second passage means connecting said vaporizer inlet with said varporizing chamber, means forming a discharge opening from said vaporizing chamber, mean connecting said discharge opening with said vaporizer delivery outlet, adjustable valve means for varying the flow of carrier gas from said inlet to said vaporizing chamber, valve means operatively disposed to close said vaporizing chamber discharge opening and pressure responsive diaphragm means in communication with said carrier gas inlet for actuating said valve means, said pressure responsive diaphragm means being subjected at one side thereof substantially to the gas pressure at said vaporizer inlet and being subjected at the other side thereof substantially to the pressure of the gas at said vaporizer delivery outlet.

7. An anesthetic vaporizer apparatus in accordance with claim 6 wherein said valve means for said vaporizing chamber discharge opening comprises a gravityloaded valve element and said pressure responsive diaphragm is arranged to engage and hold said element in closed position against said discharge opening of said vaporizing chamber.

8. An anesthetic vaporizer apparatus in accordance with claim 6 including means for closing said vaporizer discharge opening independently of the gas pressure acting on said pressure responsive diaphragm, said means being mechanically connected with said adjustable valve :means in said second passage means such that said discharge opening of said vaporizing chamber is mechanically closed when said second passage means is closed by said adjustable valve means.

9. An anesthetic vaporizer apparatus comprising a vaporizer housing having an inlet adapted to receive a carrier gas stream and a delivery outlet, bypass passage means in said housing connecting said inlet and said delivery outlet, a second passage means connecting with said vaporizer inlet and terminating in a delivery tube extending downwardly from a lower face of said housng, a discharge opening in said lower face of said housing means connecting said discharge opening with said delivery outlet, seating means encompassing said delivery tubeand said discharge opening in the lower face of said housing, a removable anesthetic container removably received against said seating means adapted to hold a supply of a volatile liquid anesthetic agent and forming a vaporizing chamber in communication with said delivery tube and said discharge opening, and pressure responsive valve means arranged to close said discharge opening, said pressure responsive valve means including a diaphragm in communication with said carrier gas inlet and subjected at one side substantially to the pressure of the gas at the vaporizer inlet and subjected at the other side substantially to the pressure of the gas existing at the delivery outlet.

10. An anesthetic apparatus in accordance with claim 9 wherein said second passage means includes an adjustable needle valve for varying the proportion of the carrier gas conducted therethrough and having externally accessible means disposed at the top of said housing to permit the ad ustment of said needle valve.

References Cited in the file of this patent UNITED STATES PATENTS

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