US3765803A

US3765803A - Air dome construction for pressure venting fuel pumps

Info

Publication number: US3765803A
Application number: US00239426A
Authority: US
Inventors: R Parrent
Original assignee: Airtex Products Inc; UNITED IND SYNDICATE
Current assignee: UIS Inc; Airtex Products Inc
Priority date: 1972-03-30
Filing date: 1972-03-30
Publication date: 1973-10-16
Anticipated expiration: 1990-10-16
Also published as: CA975611A

Abstract

In bleed back or vent type fuel pumps pressure in the flow line from the pump to the carburetor is relieved when the engine is not operating. Such vents, however, cause loss of pump outlet pressure, so called shut off pressure, when the engine is operating but the pump, although under power, is delivering no fuel because the carburetor is full and the float valve is closed. An air dome construction is provided to prevent air in the air dome from leaking into the fuel in the pump during this time of pump shut off while the engine is running. Air in the fuel is avoided which otherwise would be circulated inside the pump resulting in delay in building up pressure when the carburetor requires more fuel. The air dome also maintains a suitable pressure at the pump outlet during such periods of shut off. These advantages are brought about by providing an air dome having a passageway which rises from the fuel chamber into the air dome beyond the open end and prevents air in the dome from leaking back into the fuel when the pump is not actually providing fuel flow but permits the air pressure built up in the air dome to maintain a high shut off pressure for a considerable length of time so as to be immediately available when the carburetor float valve opens.

Description

United States Patent [191 Parrent AIR DOME CONSTRUCTION FOR PRESSURE VENTING FUEL PUMPS Russell Parrent, Fairfield, ll].

[73] Assignee: Airtex Products Div., United Industrial Syndicate, New York, NY.

22 Filed: Mar. 30, 1972 21 Appl. No.: 239,426

[75] Inventor:

Primary Examiner-William L. Freeh Assistant Examiner-Leonard Smith Attorney-Zalkind, Horne & Shuster [57] ABSTRACT In bleed back or vent type fuel pumps pressure in the Oct. 16, 1973 flow line from the pump to the carburetor is relieved when the engine is not operating. Such vents, however, cause loss of pump outlet pressure, so called shut off pressure, when the engine is operating but the pump, although under power, is delivering no fuel because the carburetor is full and the float valve is closed. An air dome construction is provided to prevent air in the air dome from leaking into the fuel in the pump during this time of pump shut off while the engine is running. Air in the fuel is avoided which otherwise would be circulated inside the pump resulting in delay in building up pressure when the carburetor requires more fuel. The air dome also maintains a suitable pressure at the pump outlet during such periods of shut off. These advantages are brought about by providing an air dome having a passageway which rises from the fuel chamber into the air dome beyond the open end and prevents air in the dome from leaking back into the fuel when the pump is not actually providing fuel flow but permits the air pressure built up in the air dome to maintain a high shut off pressure for a considerable length of time so as to be immediately available when the carburetor float valve opens.

8 Claims, 4 Drawing Figures AIR DOME CONSTRUCTION FOR PRESSURE VENTING FUEL PUMPS In general, air domes are provided in fuel pumps for cushioning effect on the fuel as the diaphragm effects pumping strokes to even out the flow of fuel. A smoother flow of fuel permits increased discharge rate since the pump diaphragm does not have to force each charge of new fuel against a solid head of fuel already trapped in the pump and lines. The air entrapment in air domes within the fuel section of a pump allows the incoming fuel to be pushed out against an air pocket which is compressible. This condition allows the pump to take longer strokes and displace a larger volume of fuel with each stroke.

The normal fuel pump using air dome construction is a demand type pump pumping whatever fuel the carburetor requires, discharge being shut off,when the carburetor bowl is full, by the float valve in the carburetor bowl. However, even with fuel flowing, the pump is partially shut off if fuel is pushed out against a solid head of fuel, thus, slowing down the discharge rate. The air domes allow the pump to flow more freely due to the air dome cushion efi'ect without partial shut off when there is a demand at the carburetor for more fuel.

The air within the air dome in the present invention is maintained and confined in the outlet dome where it is effective and of use while pumping, yet cannot escape from the desired entrapment due to an elongated collar which protrudes up into center area of the air dome to provide a passageway for fuel into the air dome for compressing air therein.

A problem with vehicle engines, particularly in hot weather, is the fact that when the engine is shut down heat picked up by the fuel pump and carburetor during a so-called"soak period, causes a very high pressure due to the fuel expansion in the pump and outlet line to the carburetor. This well-known condition results in forced opening of the carburetor float valve and causes flooding when the engine is restarted. Restart can be extremely difficult and sometimes impossible until a period of time has passed for the excess fuel in the engine intake system to evaporate so that a proper air-fuel mixture can be achieved.

In order to prevent such flooding, many fuel pumps provide for a bleed back or vent from the outlet valve chamber to the fuel chamber and thence from the fuel chamber to the inlet valve chamber. Hence expanding fuel thus vented through the pump from the carburetor line can ultimately return to the fuel tank. Vent arrangements may take various forms such as indentations in valve seats or by-pass ports drilled in the material of the pump body leading from the fuel chamber to the valve chambers.

While the method of using vents is expedient to minimize engine flooding, a problem arises in that generally much pressure is lost in the line from the fuel pump to the carburetor during engine operation when the pump is operating at so called shut off, the carburetor-float valve being closed and the pump diaphragm not actually moving. This necessitates delay in renewing proper outlet pressure to once more effect proper flow. A further problem is the fact that conventional air domes on the outlet side during the shut off period permit air trapped therein to leak back into the fuel. This air must be circulated for a period of time until exhausted to the carburetor, and during this period of time the outlet pressure of the pump is lower than required. More speciflcally, during operation of the engine when outlet pump pressure is say, 6 lbs. per sq. in., and carburetor demand ceases, the float valve being closed. and the pump operating but without outlet flow, the static pressure at the outlet of the pump could drop to be below 4 lbs. per sq. in. This is due to the vents in the valves. Further, air leaking from the outlet air dome into the fuel in the pump aggravates the condition. Since the static pressure of the spring which operates the diaphragm of the conventional fuel pump may provide 6 lbs. per sq. in. diaphragm pressure, it is apparent that the pump would have to be operated for the time needed to rebuild the pressure to six pounds, the proper outlet flow pressure.

The preceding discussion is based upon the engine in operation. Where, however, the engine is actually shut off, then the flooding condition described above can occur except for the vent arrangement. The air dome of the invention then functions like a conventional air dome.

Accordingly, the invention maintains the static shut off pressure at the outlet of the fuel pump when the engine is operating to maintain proper pressure despite the use of vented pump valves which would otherwise cause loss of shut off pressure at the pump outlet.

In effect, the invention does not change the characteristics of the pump during constant flow but stabilizes the shut off pressure while the engine is running to achieve the advantage of valves which are not vented while also achieving the advantage of permitting venting when the engine is shut down.

A detailed description of the invention now follows in conjunction with the appended drawing in which FIG. 1 is a longitudinal view largely in cross section illustrating the essential components of the invention; FIG. 2 is a view looking in the direction 2--2 of FIG.

FIG. 3 is an elevation of the fuel pump body member; and

FIG. 4 is a view looking upward in the direction of 4-4 of FIG. 1.

Referring to the drawing, the invention comprises a fuel pump having a body member 10 closed at its top side by a bonnet 15 which will be understood to carry a pivotal pump lever 18 which-actuates the diaphragm 20 via rod 23 and spring 26, all in the usual manner.

The diaphragm is clamped between members 10 and bers and secured in their positions by abutment of ribs such as 50 which extend longitudinally of the cylindrical walls of the chambers and extend at their bases a short distance radially to provide shoulders 53 which position

air domes

56 and 60 within the inlet and outlet valve chambers, respectively. A screen 62 is clamped between dome 56 and respective shoulders 53. The ribs provide large intermediate spaces 63 between the air domes and valve chamber walls so that fuel can flow longitudinally past the air domes, all as will be clearly understood by comparison of FIGS. 1 and 2. The air domes are force fitted against the ribs to maintain their proper position in abutment with respective shoulders 53.

The lower end of the fuel body is closed by a bottom wall 66 which, however, has an elongated collar 69 as part of the casting to effect a passageway 71 extending upwardly into the outlet valve chamber above the downwardly disposal open end of the outlet air dome 60. The fuel around the collar forms a liquid seal to prevent air from leaking from the dome back to the fuel pumping chamber through the outlet valve vents.

Thus, the collar 69 will be seen to be at the bottom of the valve chamber 40 which is otherwise closed. Since fuel must traverse the space between the walls of the valve chamber and the air dome, the bottom of the valve chamber is filled with fuel which rises at least to the top of the collar and forms a well around the lower end of the collar so that air in the dome is sealed against rising as bubbles in reverse, i.e., upward direction outside the dome back into the valve chamber and pumping chamber 33.

The central portion of the casting has a tubular passageway 73 open at its lower end to communicate with a disposable filter 76 and having a lateral outlet port 79 in the casting which extends externally of the pump body wall for connection to an outline line fitting by way of the tubular external nipple 82 as seen in FIG. 3, which also discloses the inlet connection nipple 85 connecting to inlet port 90. Nipple 85 leads directly to the inlet valve chamber 36 via port 90. (FIG. 1).

A filter holder can 93 connects threadedly to the threaded extension 96 of body member 10 and disposed within the filter holder is the conventional pleated filter 76 having a rubber bushing 100 which frictionally engages the lower end of the wall extension 102 of passageway 73 to secure the filter in position within the filter holder.

Any form of providing venting of the valves maybe used. For example, one expedient is to provide indentations, such as the indentations 103, in the valve seats. Thus, the valve discs 105 when closed cannot seal the indentations and pressure can vent from the carburetor 'line through the outlet valve, to the fuel chamber 33,

and thence through the inlet valve 43 back to the fuel tank (not shown).

The operation of the fuel pump will be readily understood from FIG. 1. Fuel is brought in through inlet 90 and up around the sides of the air dome 56, through inlet valve 43 to fuel chamber 33, thence through outlet valve 46 and down around the outlet chamber air dome 60, thence to the exterior of the filter 76. Fuel passes through the filter and flows upwardly through the passage 73 to the outlet port'79.

The particular feature of the invention resides in the collar 69, which, being above the fuel level in the outlet chamber air dome 60, prevents air from leaking back into the valve chamber and the pumping chamber. Thus, when the diaphragm is virtually motionless at shut off, no air is entrained in the fuel which would require being exhausted to the carburetor before necessary fuel outlet pressure can be achieved. While there is some leakage of fuel through the vent passages at this time in a system of this kind the air compressed in the dome 60 maintains substantially the outlet pressure of the pump for the shut off period, until the diaphragm commences pumping upon opening of the carburetor needle valve.

I claim:

1. A fuel pump comprising a pump body having an inlet and an outlet and having a fuel chamber comprising an actuatable pumping diaphragm; said pump body further comprising inlet and outlet valve chambers communicating the respective inlet and outlet with said fuel chamber, and valves in said valve chambers having respective fuel bleeds to vent fuel pressure through said fuel chamber from outlet to inlet upon engine shut down; one said valve chamber having an air dome therein below the respective valve thereof and spaced from the wall thereof to permit fuel flow between the air dome and said wall; said air dome being open at its lower end; means to prevent air leakage through the respective fuel bleed of said one valve chamber from said air dome to said fuel chamber during pump shut off while said diaphragm is being actuated, to prevent circulation of air within said pump, said means comprising a tubular collar extending upwardly into said air dome effecting a fuel passage into said air dome through said open end to entrap air therein and effecting a liquid seal below said open end within said valve chamber to preclude air escape.

2. A fuel pump as set forth in claim 1, wherein said body comprises a casting having a wall closing one end of the other valve chamber and facing the open end of the air dome therein; said air dome having a closed end opposite the open end thereof and the valve in said valve chamber being disposed beyond the closed end of said air dome.

3. A fuel pump as set forth in claim 1, said one valve chamber being the outlet valve chamber of said fuel pump wherein fuel flow passes through the valve thereof to the air dome there and thence through said tubular collar, entrapping air in said air dome and effecting said liquid seal, including filter means secured to said body through which fuel flow passes from said tubular collar, and passage means for conducting fuel flow from said filter to said outlet.

4. A fuel pump comprising a pump body having an inlet and an outlet and having a fuel chamber comprising an actuatable pumping diaphragm, said pump body further comprising inlet and outlet valve chambers communicating the respective inlet and outlet with said fuel chamber, and valves in said valve chambers having respective fuel bleeds to vent fuel pressure through said fuel chamber from outlet to inlet upon engine shut down; one of said valve chambers having an air dome therein open at its lower end and said pump body having a tubular collar extending upwardly into said air dome effecting a fuel passage into said air dome through said open end and effecting a liquid seal therearound to prevent air leakage through the respective fuel bleed of said one valve chamber from said air dome to said fuel chamber during pump shut off while said diaphragm is being actuated, to thereby prevent the end of said tubular collar protruding into said one valve chamber so as to effect said liquid seal.

6. A fuel pump as set forth in claim 4, wherein said pump body comprises a casting having a pair of elongated chambers effecting said valve chambers; an air dome in the other of said valve chambers and open at the bottom; said tubular collar extending from an end of said one valve chamber as an integral portion of the casting; means for locating the air dome in said one valve chamber so that said open end extends predeterminedly beyond the end of said tubular collar protruding thereinto so as to effect said liquid seal.

7. A fuel pump as set forth in claim 6, wherein said casting has a wall closing one end of said other valve chamber and facing the open end of the air dome therein; each of said air domes having a closed end opposite the open ends thereof and the valves in said valve chambers being disposed beyond the respective closed ends of said air domes.

8. A fuel pump as set forth in claim 7, said one valve chamber being the outlet valve chamber of said fuel pump wherein fuel flow passes through the valve thereof; a spacing between the air dome in said valve chamber and the valve chamber wall for fuel flow from the valve of said valve chamber into the open end of the air dome therein and thence through said tubular collar thereby entrapping air in said air dome and effecting said liquid seal; including filter means secured to said body through which fuel flow passes from said tubular collar; and passage means for conducting fuel flow from said filter to said outlet.

Claims

4. A fuel pump comprising a pump body having an inlet and an outlet and having a fuel chamber comprising an actuatable pumping diaphragm; said pump body further comprising inlet and outlet valve chambers communicating the respective inlet and outlet with said fuel chamber, and valves in said valve chambers having respective fuel bleeds to vent fuel pressure through said fuel chamber from outlet to inlet upon engine shut down; one of said valve chambers having an air dome therein open at its lower end and said pump body having a tubular collar extending upwardly into said air dome effecting a fuel passage into said air dome through said open end and effecting a liquid seal therearound to prevent air leakage through the respective fuel bleed of said one valve chamber from said air dome to said fuel chamber during pump shut off while said diaphragm is being actuated, to thereby prevent circulation of air within said pump.

5. A fuel pump as set forth in claim 4, wherein said pump body comprises a casting having an elongated chamber effecting said one valve chamber; said tubular collar extending from an end of said one valve chamber as an integral portion of the casting and means for locating the air dome in said one valve chamber so that the open end thereof extends predeterminedly beyond the end of said tubular collar protruding into said one valve chamber so as to effect said liquid seal.