US3160682A

US3160682A - Carburetor

Info

Publication number: US3160682A
Application number: US192198A
Authority: US
Inventors: Harold A Carlson; Eldon A Johnson; Edward R Frey
Original assignee: ACF Industries Inc
Current assignee: ACF Industries Inc
Priority date: 1962-05-03
Filing date: 1962-05-03
Publication date: 1964-12-08
Anticipated expiration: 1981-12-08

Description

Dec. 8, 1964 H. A. CARLSON ETAL 3,160,632

CARBURETOR Filed May 3, 1962 2 Sheets-Sheet 1 INVENTORS HAROLD A. CARLSON ELDON A. JOHNSON AGENT,

1964 H. A. CARLSON ETAL 3,

' CARBURETOR Filed May 3, 1962 2 Sheets-Sheet 2 F '6 5 INVENTORS HAROLD A.CARLSON ELDON A.JOHN\S(ON United States Patent 3,160,682 (ZARBURETGR Harold A. Carlson, Brentwood, Eldon A. Johnson, Sunset Hills, and Edward R. Frey, Dellwood, Mo., assignors to ACE Industries, Incorporated, New York, NFL, a corporation of New Jersey Filed May 3, 1962, 521'. No. 192,193 4 Claims. (ill. 261-35) This invention is directed to a carburetor for small engines used with power tools. The application of carburetors of this type is with engine driven devices such as chain saws and other portable power tools as well as gocarts and outboard motors. In applications with engines used with portable power tools, as well as small vehicles, the carburetor is expected to be a rather simple device yet provide all of the advantages of a more sophisticated carburetor. The power tool is used in all positions and the carburetor must be one which can supply an optimum mixture of fuel and air to the engine under conditions varying fiom idle speeds to high speeds at wide open throttle. Carburetors of this type, because of the nature of their application, are provided with a built-in fuel pump, which supplies fuel under pressure to a fuel chamber from which the fuel is conducted to the air and fuel mixture conduit of the carburetor.

The fuel pump includes a thin diaphragm exposed to pulsating pressure of the engine to draw fuel from a source into a carburetor. The present demands on a carburetor used in gocarts or chain saws require the delivery of fuel to an engine operating at high speeds in the order of 10,000 rpm. This requires that the carburetor pump diaphragm and the inlet and outlet valves of the pump operate at this fiequency rate. It has been found the pump valve structures must be of a material and design to operate properly under conditions of high engine speed.

It is thus an object of this invention to provide a novel carburetor of the type described having a built-in fuel pumping system which will operate properly to supply the fuel demands of an engine under all conditions of operation.

It is another object of this invention to provide a novel carburetor structure having a built-in fuel pumping systern which will function at high frequency rates during high speed engine operation.

The invention is directed specifically to a carburetor having fuel pump and fuel chamber portions. The carburetor is provided with a fuel pump, one wall of which is movable and formed by a flexible diaphragm adapted to be operatively connected to an engine crankcase. The inlet and outlet valves of the fuel pump are formed from a thin polyester film which provides a flexibility which permits rapid operation of the valves at the frequencies required for high speed engine operation. 7

FIGURE 1 is an elevational view of the carburetor in accordance with this invention and connected to the intake manifold of an engine partly shown.

FIGURE 2 is atop plan view of the carburetor of FIG- URE 1.

FIGURE 3 is an enlarged longitudinal sectional view of the carburetor of FIGURES 1 and2 and taken on section line 33 of FIGURE 2. V I

FIGURE 4 is an enlarged sectional view of the carburetor of FIGURES 1 and 2 and taken on the section line 44 of FIGURE 2.

FIGURE 5 is an enlarged view of the valve diaphragm of the carburetor of FIGURES 1-4 and in accordance with this invention. I

FIGURE 6 is an expanded view of the pump valve "ice structure of the carburetor of FIGURES 1-4 and in accordance with the invention.

FIGURE 7 is a bottom plan view of the carburetor of FIGURES l-4 with the fuel chamber plate and diaphragm removed to show the interior of the fuel chamber.

The carburetor in accordance with the invention is indicated at 10 in FIGURES 1 to 4. It is connected to the intake manifold 12 of an engine 14, which may be a two cycle engine in which, during the intake cycle of the engine, air and fuel is drawn through the carburetor 10 into the crankcase of the engine. During the compression stroke of the engine, the mixture of gas and fuel is bled by a passageway from the engine crankcase into the engine cylinder. During the operation of engines of this type the pressure of the gases within the crankcase of the engine undergoes a change from sub-atmospheric to above atmospheric pressure. These pressure changes are conducted by an appropriate passage to a pumping portion of the carburetor 10 to operate the fuel pump of the carburetor.

The carburetor shown in the figures of the drawing consists of a main body portion 16, to the underside or bottom of which is attached a fuel chamber cover plate 18 and to the upperside or top of which is attached a pumping chamber cap 20. The carburetor body portion has a flange section 22 which is connected directly to the intake manifold 12 of the engine in any appropriate manner, such as by bolts extending from the intake manifold through the flange 22 with retaining nuts 24 holding the carburetor to the manifold. The pump cap 20 is retained and held to the main body 16 by machine screws 26 threaded into the body 16. In a similar manner the fuel chamber cover plate 18 is fixed to the carburetor body 16 by threaded screws 27 extending through the plate 18 into threaded portions of the carburetor body.

As shown specifically in FIGURE 3, the carburetor has an air and fuel mixture passage 28 therethrough and in line with an opening into the intake manifold 12 of the engine 14. Mounted within the mixture conduit 28 is a choke valve 30 fixed for rotational movement on a choke shaft 32. Also mounted within the mixture conduit 28 of the carburetor between choke valve 30 and the intake manifold 12 is a throttle valve 34 fixed for movement therewith to a throttle shaft 36 journaled for rotation in the body 16 of the carburetor. Between the choke valve 39 and the throttle valve 34, the mixture conduit 28 is formed with a restriction or venturi portion 38. A reed valve plate structure 40 is mounted between the throttle 34 and the intake manifold 12. The reed valve prevents compressed gases within the crankcase from blowing back through the mixture conduit 28 when the engine exhausts. The intake cycle of the engine sucks air through the mixture conduit 28 of the carburetor and the valve 40 opens at this time.

To provide fuel to the engine, the carburetor 10 is formed with a fuel pump structure fixed between the pumping chamber cap 20 and the body 16 of the carburetor. As shown more clearly in FIGURE 4, the pumping chamber cap 20 and the carburetor. body 16 are both provided with oppositely disposed cavities or recesses which together form a hollow chamber 44. A pumping diaphragm 42 fixed across chamber 44 divides it into a pumping chamber 46 and a pulsation chamber 48. The attachment of the cap 20 to the carburetor body 16 by the screws 26 is sufiiciently tight to seal the diaphragm 42 around its peripheral edge between the cap 20 and the body portion 16. A fuel inlet passage 50 is formed in cap 20 extending from the fuel chamber 46 upwardly and outwardly to the outer surface of the cap. Within the inlet passage 50 is press fitted an inlet nipple structure 52 to which may be attached in any appropriate manner a flexible tubing 54 extending to a fuel tank represented schematically at 56 in FIGURE 1. Mounted within the nipple 52 is a tubular mesh structure 58 having an open end press-fitted into the free end of the nipple 52. The other end of the tubular filter 58 is closed to the passage of fuel. An outlet chamber 60 is formed within the pump cap 20 and above the pumping chamber 46, as viewed in FIGURE 4.

In accordance with the invention, there is provided a valve assembly 61 consisting of a flexible valve diaphragm 62 (FIGURES 4, and6) fixed between portions of the pumping cap and a retainer plate 64. The valve diaphragm is formed of a polyester film and has partially cutout portions forming a pair of

flap valves

66 and 68. Valve 66 is fitted over the inlet passage to provide an inlet check valve for fuel flowing into the pumping chamber 46, while the valve flap 68 is fitted over a short outlet passage 70 through retainer plate 64 between the pumping chamber 46 and the outlet chamber 60. A portion 72 of retainer plate 64 is offset from the surface of plate 64 and is aligned with inlet valve flap 66. Portion 72 provides a stop means for the movement of the inlet valve flap 66 in a downward direction as fuel passes into the pumping chamber 46. In a similar manner, an extension 74 of the cap 20 provides a'stop means for the valve flap 68, as it moves in an upward direction for the passage of fuel into the outlet chamber 68, and as viewed in FIG- URE 4.

Leading from the outlet chamber 68 is a passage 75 formed in the pumping cap 20 and extending into a second chamber 76 within the cap, which connects through an eyelet 81 with a fuel passage 78 extending downwardly, as viewed in FIGURE 4, to a fuel chamber 80. Press fitting of eyelet 81 into passage 78 seals the adjacent diaphragm portion around the entrance to passage 78.

Fuel chamber is formed by a depression in the carburetor body 16 which is closed on one side by a flexible diaphragm 82 fastened and sealed between the body casting 16 and cover plate 18.

Fitting in the lower end of the fuel passage 78 is a valve assembly consisting of a sleeve 84 sealed by an O-ring 86 to the body casting 16. Within the sleeve 84 there is positioned a resilient valve seat 88 retained by a ring 90 press-fitted into sleeve 84. Valve seat 88 may be an annular synthetic rubber washer into the center of which is fitted one end of a needle valve 92. A threaded fitting 87 locks sleeve 84 within the body 16 and also retains a light spring 89 between its flanged end and the flange of the needle valve 92. The valve 92 has a tapered upper end 94 which has an extension, as shown in FIG- URE 4, extending through the annular rubber seat 88. The lower end of needle 92 has a headed end 95in which is positioned the forked end of a lever 96 pivoted on a shaft 98 journaled within the body casting 16. The other end of lever 96 is in operative contact with a metallic button 100 fixed to the center of the diaphragm 82. Button 100 consists substantially of a headed rivet, which is used to tightly hold a pair of

backing plates

102 and 104 on opposite sides of the diaphragm 82 for. retaining the center of the diaphragm substantially rigid.

A fuel well 108 (FIG. 7) extends from the fuel chamber 80 to a cross passage 110 extending from outside the carburetor body 16 and as shown in FIGURE 7. The cross passage 110 is internally threaded at its outer end to receive a threaded adjusting screw 126. The inner end of screw 126 has a sharp tapered point which extends axially along passage 110 and into a tapered portion 112 of the passage. The tapered passage portion 112 opens into a nozzle chamber 114 (FIG. 3) having a nozzle fitting 124 press-fitted through wall thereof into the venturi portion 38 of the air and fuel mixture conduit 28 of the carburetor. The nozzle chamber'114 is separated from the main fuel chamber 80 by a cross plug structure 115.

These portions of the carburetor, constitute the high speed fuel circuit of the carburetor. Fuel can flow from the chamber 80 through

passages

108, 110 and the restriction 112 into the nozzle chamber 114 from which fuel is drawn out through the nozzle 124. The metering of the fuel flow through the main fuel passages is controlled by the restriction 112 and the nozzle passage. Screw 126 can be adjusted to provide the desired speed of the engine at wide open throttle.

The low speed fuel circuit, or idle circuit, of the carburetor consists of a well structure 117 extending from the fuel chamber 80 into the carburetor body 16, as shown in FIGURES 3 and 7. A cross passage 119 intersects the fuel well 117 and is threaded at its outer end to receive a low speed adjustment screw 122. The low speed adjusting screw 122 has a tapered end 125 extending into a restriction 121 connecting the cross passage 119 with the low speed fuel chamber 116. A solid plug 123

separates chambers

116 and 80. As shown in FIGURE 3, idle fuel.

port 118 extends between the fuel chamber 116 and the mixture conduit 28 downstream of the throttle 34 in its closed position. Also, a pair of idle air ports 120 extend between the fuel chamber 116 and the mixture conduit 28 upstream of the throttle 34 in its closed position. The restricted portion 121 of the cross passage 119 has a tapered portion into which the end of adjustment screw 122 can be adjustably positioned. When the throttle 34 is closed and the engine is operating at a low speed or idle speed, fuel is drawn from the chamber 80 through

passages

117 and 119 past the adjustment screw end 125 and through the restricted passage 121 into the fuel chamber 116. Fuel is then drawn from the chamber 116 through'the idle port 118 to operate the engine. Screw 122 can be adjusted to provide the desired operation of the engine at closed throttle position.

In operation, cranking of the engine 14 pumps air through the mixture conduit 28 of the carburetor into the intake manifold 12 of the engine; the reed valve 40 being opened-under the pumping suction of the engine. Flow of air past the main fuel nozzle 124 with the throttle valve 34 open provides a subatmospheric pressure at the mouth of nozzle 124 due to the venturi effect of the restriction 38. This low pressure at the mouth of nozzle 124 is transferred back through

passages

114, 112, 110 and 108 to the fuel chamber 80. Lowering the pressure in chamber 80 causes atmospheric pressure on the outer surface of diaphragm 80 to press the diaphragm inwardly or upwardly, as viewed in FIGURE 4, and to rock the valve lever 96 in a clockwise direction. This positively pulls the needle valve 92 downwardly and the end of needle valve 94 elf of the resilient valve seat 88.

Pulsations in the crankcase of the engine are transferred through a passage 49 (FIGURES 3 and 4) to the pulsation chamber 48. The pumping diaphragm 42 flexes back and forthunder the elfect of the engine pulsations transferred into pulsation chamber 48. This causes a pumping action in the pumping chamber 46 which sucks fuel from tank 56 through the conduit 54 into the inlet chamber 50 of the carburetor cap 20. Fuel passes into the pumping chamber 46 and out past the outlet check valve 68 into the

passages

60, 76 and 78. Continual pumping forces fuel down past the open valve 92 into the fuel chamber 80 and out through the

fuel passages

108, 110 and 114 to the nozzle 124. The capacity of the pump section of the carburetor supplies fuel at a higher rate than used by the engine. Accordingly, fuel accumulates in the fuel chamber 80- to fill it and the fuel reacts against the diaphragm 82 to move it outwardly against atmospheric pressure. The fuel pressure in chamber 80 is aided by the valve spring 89 which, as the diaphragm moves away from lever 96, forces the needle upwardly into a closed position in seat 88. In fuel chamber 80, the fuel pressure within the chamber and the valve spring 88 work together against the atmospheric pressure on the outer surface of the diaphragm 82. The fuel pressure in the fuel chamber 80 varies within a small range of values to open and close the needle valve 92.

An idling or low speed operation of the engine takes place when the throttle 34 is closed. At this time, there is insufficient air flow through the carburetor conduit 28 to pull fuel from chamber 80 through the nozzle 124. However, the manifold pressure downstream of throttle 34 is at a subatmospheric pressure and a large pressure depression is created at the idle jet opening 118, which pulls fuel from the fuel chamber 80 through

passages

108, 110 and the idle chamber 116. Simultaneously sufficient air for mixing with this fuel and to operate the engine at low speed is sucked through the idle ports 120 upstream of the closed throttle 34. This air is pulled into the idle fuel chamber 116 to mix with the fuel coming from the fuel chamber 80. Adjustment of screw 122 is used to provide the optimum fuel and air mixture for idling or low speed conditions.

Carburetors of the type described above and as shown in the figures are used in small engine applications as chain saws and in gocarts. Engines used with such devices should provide an rpm. up to 10,000 rpm. Engines used on gocarts on test tracks operate between 9200 and 9500 rpm. Engines operating at this high speed require a carburetor which can supply the needed fuel at all times. Such high speeds of the engines put considerable demands on the pumping portion of the carburetor and particularly on the inlet and outlet valves of the pumping section.

In accordance with the invention, the valve assembly of the pumping section, shown in an exploded view in FIGURE 6 and in sectional views in FIGURES 3 and 4, is one which provides an efiicient pumping action during high speed operation of the engine. As described above, the valve diaphragm 62 is formed from a thin plate of a polyester film. The film is one having a thickness of around 0.005 inch. The polyester film from which the valve assembly 62 is formed is a material, which is resistant to chemical attack by such fuels with which it is to come in contact. The material should have substantially no permeability to gasoline, or to fuels consisting of up to 20% alcohol, or to fuels containing water, oil and such other contaminants that might be present in fuels used in the engines with which the carburetor is used. The polyester furthermore should be able to withstand a temperature range from 300 Fahrenheit to a minus 40 Fahrenheit. The material should be one which can maintain its characteristics substantially the same under immersion in liquids of the type described for long periods of time. For example, 90% of its original tensile strength should remain after immersion of the material in any of the above mentioned liquids for a period of one month.

It has been found that a polyester film of this type has an inherent resiliency which causes the valve flaps 66 and 68 to snap back into place when pressure is released. For example, the valve 66 will close against its valve seat consisting of the lower end of passage 50 at the beginning of a pumping stroke before the liquid pressure in the pumping chamber 46 forces it back into position. Also, the outlet valve flap 68 will snap back into a closed position against its valve seat 70 when the pump is producing a suction stroke and before fluid flow closes the valve. These valve flaps will close more rapidly than those which might otherwise depend upon the movement of fuel in the pumping chamber to press them into their closed position. A polyester material which has been found to have the desired properties for the valve diaphragm 62 is that known by the trade name of Mylar.

The valve flaps 66 and 68 are partially cut out of the round polyester diaphragm 62, as indicated in FIG- URE 5. Valve flaps 66 and 68 project as arcuate extensions from the center portion of diaphragm 62. The particular arrangement in the carburetor described above provides the

flaps

66 and 68 in alignment and extending in opposite directions from the center of diaphragm 62. Because of the symmetry of the design of diaphragm 62, there is no difiiculty in orienting diaphragm 62 during its assembly. Valve flaps 66 and 68 are identical and symmetrically arranged.

The formation of the inlet and outlet flaps out of an integral piece of polyester film constituting the valve diaphragm 62 provides a relatively simple means for providing valve structures of small dimensions. In carburetors of the type described, the diameter of the valve diaphragm 62 is in the order of A of an inch. Accordingly, then, the valve flaps themselves which have a radius in the order of of an inch would be difiicult to handle and assemble if separately formed and retained by other means.

The valve diaphragm 62 and the retainer plate 64 are held onto the pumping cap 20 by a pair of machine screws 65 on which are mounted a pair of washers 67. As shown in FIG. 3, the screws 65 are threaded into the carburetor cap portion 20 to tightly hold the retainer plate 64, the valve diaphragm 62 against the upper surface of the valve chamber 46. The screw 65 together with the washers provide a stop means sulficiently spaced from the surface of the valve diaphragm 62 so as to prevent the diaphragm 42 from pressing against the valve assembly 61. If diaphragm 42 became sufiiciently stretched during operation it will come into contact with the valve assembly 61 and on the pumping stroke will close off the outlet passage and cut down complete flow of fuel out of the pumping chamber 46. The heads of screws 65 are sufiiciently spaced from theretainer plate 64 by the washers 67 to serve as a stop means to prevent diaphragm 42 from interfering with the operation of the valve assembly 61.

The choke shaft has fixed thereto a manual choke operating lever 33, as shown in FIGURE 2. By the use of this lever, the choke may be closed during cold starting of the engine to provide an enriched mixture of fuel and air. When the engine has started, the choke valve is moved to an open position, as shown in FIG- URE 3. Also, the throttle valve 34 is operated by means of an manually operable throttle lever 37 (FIGURE 1) fixed to the throttle shaft 36. Normally, the throttle lever 37 is attached to a Bowden cable or operative linkage through an aperature 39 in the lever 37. An adjustment screw 41 is, threaded through an embodiment of the carburetor body 16 to provide at its threaded end a stop for lever 37. In this manner the amount of closing of the throttle can be controlled to provide a slightly open throttle under certain conditions of low engine speed.

We claim:

1. A carburetor comprising a body formed with a fuel and air mixture conduit through said body, a fuel chamber and a fuel passage connecting said fuel chamber with said mixture conduit, a cap forming a pumping chamber with said body, means removably securing said cap to said body, a movable pump diaphragm fixed between said cap and said body and forming a portion of said pumping chamber, means forming a fuel inlet passage into said pumping chamber and a fuel outlet passage connecting said pumping chamber with said fuel chamber, a valve assembly mounted within said pumping chamber and spaced from said movable diaphragm, said valve assembly including a resilient valve diaphragm with one surface against said cap and having integral inlet and outlet valve flaps closing said inlet and outlet passages respectively and a retainer plate against the other surface of said valve diaphragm and having a portion spaced from said inlet valve flap to provide a stop therefor and a portion in contact with said outlet valve flap having a passage therethrough forming an outlet valve seat aligned with said outlet passage, and mounting means for removably fixing said valve diaphragm and said retainer plate to said cap, said mounting means having portions thereof extending between said valve diaphragm and said pump diaphragm to prevent said pump diaphragm contacting said valve assembly during pumping operation.

2. A carburetor comprising a body formed with a fuel and air mixture conduit therethrough, a fuel chamber and a fuel passage connecting said fuel chamber with said mixture conduit, a cap forming a pumping chamber with said body, said cap including an inwardly facing recess, means removably securing said cap to said body, a movable diaphragm fixed between said cap and said body and forming a portion of said pumping chamber,

means forming a fuel inlet passage through said cap into said pumping chamber and a fuel outlet passage connecting said pumping chamber with said fuel chamber, a valve assembly mounted on said cap Within said recess, said valve assembly including a resilient valve diaphragm fixed with one surface against said cap and having integral inlet and outlet valve flaps closing said inlet and outlet passages respectively and a retainer plate fixed against the other surface of said valve diaphragm and having a portion spaced from said inlet valve flap to provide a stop therefor and a portion in contact with said outlet valve flap and having a passage therethrough forming an outlet valve seat aligned with said outlet passage, whereby said valve flaps open by movement in opposite directions, and means removably securing said valve assembly to said cap within said recess.

3. A carburetor comprising a body formed with a fuel and air mixture conduit therethrough, a fuel, chamber and a fuel passage connecting said fuel chamber with sair mixture conduit, a cap fixed to and forming a pumping chamber with said body, conduit means connecting said pumping chamber to said fuel chamber, a movable diaphragm fixed between said cap and said body and forming a portion of said pumping'ehamber, means forming a fuel inlet passage through said cap into said pumping chamber and a fuel outlet passage connected to said conduit means, and a valve assembly mounted on said cap within said pumping chamber, said valve assembly including a resilient valve diaphragm fixed with one surface against said cap and having integral inlet and outlet valve flaps closing said inlet and outlet passages respectively and a retainer plate fixed against the other surface of said valve diaphragm and having a portion spaced from said inlet valve flap to provide'a stop therefor and a portion in contact with said outlet valve flap and having a passage therethrough forming an outlet valve seat aligned with said outlet passage, whereby said valve flaps open by movement in opposite directions, 50

said cap having a portion thereof positioned within said outlet passage adjacent to said outlet valve flap to provide a stop to limit opening movement of said outlet valve flap and a pair of spaced securing means terminating at one end in said pumping chamber and extending through said retainer plate and valve diaphragm and securing same to said cap.

4. A carburetor comprising a body formed with a fuel and air mixture conduit therethrough, a fuel chamber and a fuel passage connecting said fuel chamber with said mixture conduit, a cap fixed to and forming a pumping chamber with said body, conduit means connecting said pumping chamber to said fuel chamber, a movable diaphragm fixed between said cap and said body and forming a portion of said pumping chamber, means forming through said cap a fuel inlet passage into said pumping chamber and a fuel outlet passage connected to said conduit means, and a valve assembly mounted on said cap within said pumping chamber, said valve assembly including a resilient valve diaphragm fixed with one surface against said cap and having integral inlet and outlet valve flaps closing said inlet and outlet passages respectively and a retainer plate fixed against the other surface of said valve diaphragm and having a portion spaced from said inlet valve flap to provide a stop therefor and a portion in contact with said outlet valve flap and having a passage therethrough forming an outlet valve seat aligned with said outletpassage, whereby said valve flaps open by movement in opposite directions, said cap having a portion thereof positioned within said outlet passage adjacent to said outlet valve flap to provide a stop to limit opening movement of said outlet valve flap, said valve diaphragm being formed of a polyester film and said inlet and outlet valve flaps being formed as arcuate portions of said valve diaphragm and extend in alignment in opposite directions from the center of said valve diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS 1,956,691 McCune May 1, 1934 2,095,842 Steenstrup Oct. 12, 1937 2,841,372 Phillips July 1, 1958 2,903,250 Phillips Sept. 8, 1959 2,905,188 Loew Sept. 22, 1959 2,908,287 Augustin Oct. 13, 1959 2,926,894 Price Mar. 1, 1960 3,056,353 Peters Oct. 2, 1962 FOREIGN PATENTS 561,591 Germany Oct. 15, 1932

Claims

2. A CARBURETOR COMPRISING A BODY FORMED WITH A FUEL AND AIR MIXTURE CONDUIT THERETHROUGH, A FUEL CHAMBER AND A FUEL PASSAGE CONNECTING SAID FUEL CHAMBER WITH SAID MIXTURE CONDUIT, A CAP FORMING A PUMPING CHAMBER WITH SAID BODY, SAID CAP INCLUDING AN INWARDLY FACING RECESS, MEANS REMOVABLE SECURING SAID CAP TO SAID BODY, A MOVABLE DIAPHRAGM FIXED BETWEEN SAID CAP AND SAID BODY AND FORMING A PORTION OF SAID PUMPING CHAMBER, MEANS FORMING A FUEL INLET PASSAGE THROUGH SAID CAP INTO SAID PUMPING CHAMBER AND A FUEL OUTLET PASSAGE CONNECTING SAID PUMPING CHAMBER WITH SAID FUEL CHAMBER, A VALVE ASSEMBLY MOUNTED ON SAID CAP WITHIN SAID RECESS, SAID VALVE ASSEMBLY INCLUDING A RESILIENT VALVE DIAPHRAGM FIXED WITH ONE SURFACE AGAINST SAID CAP AND HAVING INTEGRAL