US2189210A - Fuel pump - Google Patents

Description

Feb. 6, 1940. J. P. JOHNSON FUEL PUMP Filed Marqh 12, 1938 INVENTOR.

Patented Feb. 6, 1940 UNITED STATES PATENT OFFICE FUEL PUMP poration of Ohio Application March 12, 1938, Serial No. 195,574

8 Claims.

This invention relates to fuel pumps of the rotary type, designed especially for use on aircraft, although its adaptability is not to be so restricted, and more particularly to an improved 5 means by which fuel may be, as a temporary expedient, delivered under pressure to the carburator, in the event that the fuel pump is inoperative for any reason whatsoever.

Reference should be had to my copending apl plication Serial No. 10,644, filed March 12, 1935, of which the present case is a continuation in part, for a more detailed explanation of the fuel pump herein referred to, the present invention presenting an improvement over the prior conlb struction found essential in order to increase the efficiency of the fuel pump as a whole.

The fuel by-pass means employed in the fuel pump disclosed in my copending application works satisfactorily, but without concern as to 20 the quantity of fuel'by-passed or the pressure drop in the fuel delivered to the carburator. Efficient operation requires the by-passing of a special quantity of fuel with a minimum pressure drop and it is, therefore, an object of the present 25 invention to provide an improved arrangement whereby the aforementioned conditions are obtained.

In aircraft design, light weight, compactness, and efficiency are of utmost importance and it is so therefore, a further object of the invention, to provide the improved by-pass means without in any manner sacrificing the foregoing factors. With the objects above indicated, and other objects hereinafter explained in view, my inven- 35 tion consists in the construction and combination of elements hereinafter described and claimed.

Referring to the drawing, Figure 1 is a top plan view, partly in section, m taken on line 2-2 ,in Figure 2, and showing a fuel pump embodying the present invention. Figure 2 is a side ,elevational view of the fuel pump illustrated in Figure 1, but with a portion in section to more clearly show the by-pass 45 structure.

Figure 3 is an end elevational view, partly in section, and'taken on line 33 in Figure 2.

In the drawing I have illustrated a rotary'fuel pump provided with a fuel by-pass,embodylng "'0 the present invention, and designed especially for use on aircraft where lightness, compactness, and emciency are of utmost importance.

The pump structure will be only briefly described herein, inasmuch as a detailed description is contained in my copending application hereto-.

fore referred to, and for a clearer understanding reference may be had thereto. I

The fuel pump is indicated generally by the numeral l0 and consists of a housing H, preferably of aluminum or some similar light-weight 5 material, having an axial opening l2 therein extending inwardly from one end of the housing and which is closed at the other end by an integral end wall l3. The housing II is provided with an'interiorly screw-threaded opening l4 on one side thereof, which communicates with the axial bore l2, while the opposite side of the housing is provided with a similar screw-threaded opening l5 which likewise communicates with the bore l2, as more clearly shown in Figure 3. These openings 14 and I5 are adapted to be connected, one withthe fuel supply and the other with the carburator which supplies the fuel to the motor, and the respective openings will be connected in the manner herein stated, depending on the direction of operation of the fuel pump.

A liner ILpreferably of hardened steel, is positioned within the axial bore l2 and is provided with an axial bore l8 which is eccentric with respect to the axial bore l2. This liner I l, as more clearly shown in Figure 3, has oppositely disposed, transversely extending openings l9 and I9 communicating respectively with the screwthreaded openings l4 and [5 so as to provide communication with the interior of the bore IS, the latter constituting a circular chamber.

A rotor 2|, preferably of hardened steel, is eccentrically positioned within the bore I8 and has a running engagement with the inner peripheral wall of the chamber at 22, which separates the opening l9 from the opening IS. The rotor 2| is provided with tubular extensions which extend axially thereof, and are suitably mounted for rotation in the housing. The body portion of the rotor 2| is provided with angularly disposed slots, positioned longitudinally, and within which are slidably mounted a plurality of blades 24, the blades being coextensive with the body portion of the rotor. The outer ends of the blades 24 are adapted for engagement with the inner 46 peripheral wall of the chamber, while the inner ends of the blades extend inwardly within an axial bore 25 provided in the rotor. A roller member 26 is freely positioned within the bore 25 and is adapted for engagement with the inner 50 ends of the blades 24 to maintain the latter in spaced relation. An axial extension 4| has one endprojecting through a cover plate attached to the open end of the housing H and its inner end resiliently or flexibly connected to the adjacent g end of the rotor 2|. By suitably connecting the extension 4| with the motor the rotor is positively driven as desired.

The operating parts of the pump are, of course, so arranged that the pump may be operated in either direction without the necessity of rearrangement thereof, which is quite advantageous in view of the fact that different types of motors operate in different directions. It is not necessary, therefore, to change the position of the pump, irrespective of the direction of rotation of the motor used.

When the pump is used on an airplane, the rotor is operated at various speeds, depending upon the R. P. M. of the motor, as the rotor is usually connected to the motor to operate at the same or slightly greater R. P. M. The volume of fuel pumped by the pump therefore varies with the changes in the R. P. M. and at 2000 R. P. M. approximately 350 gallons of fuel per hour are pumped by the pump. Such a volume of fuel is, of course, out of proportion to the volume of fuel adapted to be handled by the carburator, and means must therefore be provided to return the excess fuel to the inlet side of the pump. Furthermore, for efllcient operation of the motor, the fuel should be delivered at a constant pressure irrespective of the volume required and the pressure most effective has been found to be approximately 3 pounds, although this may vary a somewhat, depending upon different conditions.

Means is, therefore, provided in the pump to maintain the volume of fuel discharged at a constant pressure and irrespective of flying condition.

A second housing 43 has a circular wall 44 and is removably connected to the top of the first mentioned housing H by a plurality of bolts 45. The housing 43 has a transverse partition 46 adjacent its lower end, which partition is provided with a transverse axial opening forming a valve seat 41 and a second transverse opening 49 is provided in the housing I I adjacent the fuel inlet opening l4, when the rotor operates in the the direction of the arrow shown in Figure 3, to provide a fuel passageway communicating with the upper side of the valve seat 41. The lower end of the housing 43 is provided with a transverse opening 56 in alignment with an opening 5| provided in the housing |,adjacent the fuel outlet opening, and provides a passageway for the fuel communicating with the under side of the valve seat 41.

A valve member 52 is adapted to engage the valve seat 41 and has a depending extension 53 slidably mounted in an opening provided in the housing The housing may also have a flange 54 which extends into an opening in the housing 43 and centers one with respect to the other. The extension 53 of the valve member 52 is mounted so as to have a dash pot operation to minimize vibration imparted thereto. The valve member 52 therefore, controls the flow of excess fuel from the outlet opening l5 to the inlet opening l4, thus permitting a recirculation of the fuel in excess of that capable of being handled by the carburetor.

The valve member 52 is normally closed and yieldably resisted in its movement by a spring 55 of the desired size, which is disposed in a sleeve 56, closed at its lower end, and which sleeve is provided with an extension 51 projecting through an axial opening provided in the valve member 52. The extension 53 of the valve member is hollow as shown in Figure 2, and the end of the extension 51 is adapted to receive a washer 58 for maintaining the extension on the valve member and the end of the extension may be peened over at 59, or otherwise deformed, so as to secure the washer against displacement. The extension 53 -is then closed by means of a disc 66 which is soldered or otherwise secured so as to prevent the leakage of any fuel thereby. The sleeve 56 is slidably mounted in an opening provided in a cover plate 6|, removably connected to the upper end of the housing 43 by a plurality of bolts 62. The cover plate 6| has an axial hollow extension 63 exteriorly screw-threaded to receive a looking nut 64.

A member 65 which is exteriorly screw-threaded at its upper end has an enlarged portion 66 slidably mounted in the upper end of the sleeve 66 and engageable withthe upper end of the spring 55. The sleeve 56 is longitudinally slotted at its upper portion to receive a projection 61 formed on the lower end of the enlarged portion 66 to prevent relative angular movement therebetween. A manually operated member 68 has an axial interiorly screw-threaded opening which cooperates with the screw-threaded member 65 and by turning the member 68,- in one direction or the other, the pressure of the spring 55 may be varied. A circumferential flange 69 is formed on the member 68 and is adapted to be secured between the nut 64 and the end of the extension 63 so as to clamp the member in the desired adjusted position. Thus by adjusting the member 66 any desired compression may be obtained in the spring 55, thereby exerting the proper pressure on the valve member 52, say 3 pounds, or the desired pressure at which fuel is delivered to the carburetor.

To assure that the fuel will be delivered at the pressure at which the valve 52 is set, irrespective of flying conditions which tend to produce varying pressure at the inlet opening I4, a balancing means is provided which consists, in the present instance, of an expansible and contractible bellows 10 encircling the sleeve 56 and having its lower end sealed to the lower end of the sleeve. The upper end of the bellows 10 is secured to the'cover plate 6| and the effective outside area of the bellows is equivalent to the area of the valve seat 41, it being subject to the suction of the pump created at the inlet opening M. The inside of the bellows 10 is in communication with the atmosphere by means of an opening in the member 66 and a small hole 1| provided in the member 68, this hole 1| being so small as to prevent any great loss of vacuum in the event the bellows should break, but which would not prevent proper operation of the pump. The dash pot mounting of the valve member 52 also tends to prevent impulses which are normally transmitted from the valve member to the bellows so as to prevent crystallization which frequently results in breakage.

In the event the pumping means should become inoperative for any reason, a fuel by-pass is provided by which fuel may be supplied to the carburetor. In the present instance, the transverse partition 46 is provided with a plurality of transverse openings 12, six of which are shown although not restricted thereto, and spaced in angular relation on diametrically opposite sides of the valve seat 41, as more clearly shown in Figure 1. A plurality of ball valve members 13 engage the under sides of the openings 12 and normally close the latter to prevent the passage of fuel therethrough. Springs 14 are housed in sleeves 15 secured to the housing 43 and have one of their ends engaging the respective valve ball members to yieldingly urge them into closed position. The fuel inlet opening l4 may be connected with a hand or wabble pump of any well known type, which is usually mounted on the instrument board or at some other location convenient to the pilot, and by operating the hand pump, fuel will be drawn from the fuel tank and forced into the inlet opening [4 under pressure. The fuel so introduced will pass upwardly through the passageway provided by the openings 49 and 48, to the upper side of the partition 46, and the pressure created by the hand pump will force the ball valve members downwardly against the tension of the springs, thereby unseating the same and permitting the fuel to pass through the openings l2 and into the pressure side of the pump, where it will flow through the passageway provided by the openings 50 and 5| and ultimately through the outlet opening 15 to the carburetor. By continuously operating the hand pump the fuel passageway will be filled with fuel under pressure and further operation of the hand pump will cause the fuel to exert a pressure on the under side of the valve member 52, thereby unseating the same so that, thereafter, the fuel will flow through the large opening forming the valve seat 46 with the result that there will be a minimum pressure drop in the fuel supply to the carburetor. Upon the unseating of the valve member 52, the ball valve members I3 will again be seated against their respective valve seats and will cease to function as by-pass valves so long as the pressure of the fuel exceeds the spring pressure on the valve member. The ball valve members 13 function in a manner that may be described as priming valves that is, they function in the first instance to supply the necessary amount of fuel in the fuel line.

It will be noted that the bellows and valve member 52 are connected together in such a manner as to permit some degree of independent movement relatively so as to prevent, as much as possible, the transmissionof vibrations from the movable valve member 52 to the bellows for the reasons heretofore explained.

While I have described the preferred embodiment of the invention, it should be understood that I am not to be limited thereto, inasmuch as changes and modifications may be resorted to without departing from the'spirit of the invention as defined in the appended claims.

What is claimed is 1. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head enga-geable with the valve seat on saidpartition and a depending stem piloted in an opening in the adjacent portion of said housing proper to provide a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible and contractable bellows positioned axially within said hollowhousing, said bellows having its inner end closed and connected to the adjacent side of said valve head for movement therewith but in a manner such as to permit slight independent relative movement, while its outer end is connected to the adjacent portion of said hollow housing, the interior of said bellows being open to atmosphere, a coiled spring disposed axially within said bellows and having one end in engageinent with the inner end of said bellows for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with an opening extending transversely therethrough providing a valve seat on its under side, initially operable valve means mounted on said hollow housing and having a portion yieldably engageable with the last mentioned valve seat'and adapted to initially by-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed fuel thereby with a minimum pressure drop in the discharged fuel, the opening of said relief valve causing the pressure. acting on said initially operable valve means to drop to a point Where the same closes.

2. A fuel pump comprising a housing proper having afuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the .inlet opening to the outet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its lower side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head engageable with the valve seat on said partition and. a depending hollow stem piloted in an opening in the adjacent portion of said housing proper to provide a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible and contractible bellows positioned axially within said hollow housing, said bellowshaving its inner end closed and provided with anextension which projects f-reely through an opening in said valve head into said hollow'stem, means on the end of said extension for securing the latter to said valve member in a manner such as to permit slight independent relative movement, the outer end of said bellows being connected to the adjacent portion of said hollow housing, the interior of said bellows being open to atmosphere, a coiled spring disposed axially within said bellows and having one end in engagement with the inner end of said bellows for normaly maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby. the tension in the latter may be varied, said partition being further provided with an opening extending transversely therethrough providing a valve seat on its under side, initially operable valve means mounted on said hollow housing and having a portion yieldably engageable with the last mentioned valve seat and adapted to initially by-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, the continual introduction of additional by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed fuel thereby independently of said initially operable valve means with a minimum pressure drop in the discharged fuel.

3. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head engageable with the valve seat on said partition and a depending stem piloted in an opening in the adjacent portion of said housing proper to provide a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible and contractible bellows positioned axially within said hollow housing, said bellows having its inner end closed and connected to the adjacent side of said valve head for movement therewith but in a manner such as to permit slight independent relative movement, while its outer end is connected to the adjacent portion of said hollow housing, the interior of said bellows being open to atmosphere, a coiled spring disposed axially within said bellows and having one end in engagement with the inner end of said bellows for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with a plurality of transversely extending openings positioned on diametrically opposite sides of said axial opening providing initially operable valve seats on their under sides, valve members yieldably engageable with said last mentioned valve seats and adapted to initially by-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, springs mounted on said hollow housing and having portions engageable with said valve members for maintaining the latter normally in engagement with their respective valve seats, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed fuel thereby independently of said initially operable valve members with a minimum pressure drop in the discharged fuel.

4. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachablyconnected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head engageable with the valve seat on said partition and a depending stem piloted in an opening in the adjacent portion of said housing proper to provide a dash pot, said valve member beingnormally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible-and contractible bellows positioned axially within said hollow housing, said bellows having its inner end closed and connected to the adjacent side of said valve head for movement therewith but in a manner such as to permit slight independent relative movement, while its outer end is connected to the adjacent portion of said hollow housing, the interior of said bellows being open to atmosphere, a coiled spring disposed axially within said bellows and having one end in engagement with the inner end of said bellows for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with an opening extending transversely therethrough providing a valve seat on its under side,

- initially operable valve means mounted on saidhollow housing and having a portion yieldably engageable with the last mentioned valve seat and adapted to normally by-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the bypassed fuel thereby independently of said initially operable valve means with a minimum pressure drop in the discharged fu'el, said valve means closing upon the opening of said relief valve and remaining closed so long as the pressure of the fuel exceeds the spring load on said relief valve.

5. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head engageable with the valve seat on said partition and a depending hollow stem piloted in an opening in the adjacent portion of said housing proper to provide a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible and contractible bellowspositioned axially within said hollow housing, said bellows having its inner end closed and provided with an extension which projects freely through an opening in said valve head into said hollow stem for securing the bellows to said valve member in a manner such as to permit slight. independent relative movement, the outer end of said bellows being connected to the adjacent portion of said hollow housing, theinterior-of saidbellowsbeing open to atmosphere, a coiled spring disposed axially within said bellowsand having one end in engagement with the inner end of said bellows for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with an opening extending transversely therethrough providing a valve seat on its under side, initially operable valve means mounted on said hollow housing and having a portion yieldably .engageable with the last mentioned valve seat and adapted to initially by-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed fuel thereby independently of said initially operable valve means with a, minimum pressure drop in the discharged fuel, said valve means closing upon the opening of said relief valve and remaining closed so long as the pressure of the fuel exceeds the spring load on said reief valve.

6. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition, a movable relief valve member having a valve head engageable with the valve seat on said partition and a depending stem piloted in an opening in the adjacent portion of said housing proper to provid a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, an expansible and contractable bellows positioned axially within said hollow housing,

- said bellows for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with, a plurality of transversely extending openings positioned on diametrically opposite sides of said axial opening providing initially operable valve seats on their un der sides, valve members yieldably engageable with said last mentioned valve seats and adapted to initiallyby-pass fuel under pressure from the inlet opening to the outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, springs mounted on said hollow housing and having portions engageable with said valve members for maintaining the latternormally in engagement with their respective valve seats, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed' fuel thereby independently of said initially operable valve members with a minimum pressure drop in the discharged fuel, said last mentioned valve members closing upon the opening of said relief valve and remaining'closed so long as the pressure of the fuel exceeds the spring load on said relief valve.

'7. A fuel pump comprising a housing proper having a fuel inlet opening and a fuel outlet opening, pumping means in said housing adapted to transfer fuel from the inlet opening to the outlet opening, a second hollow housing detachably connected to said housing proper, said hollow housing being provided with a transversely extending partition having an axial opening therethrough to provide a valve seat on its outer side, said housings having aligned openings providing respective passageways between the outlet opening and the under side of said partition and the inlet opening and the outer side of said partition,

a movable relief valve member having a valve head engageable with the valve seat on said partition and a depending stem piloted in an opening in theadjacent portion of said housing proper to provide a dash pot, said valve member being normally adapted to control the flow of excess fuel thereby during the operation of said pumping means, a flexible impervious member disposed within said hollow housing and outwardly of said valve head, said flexible member being connected to the adjacent side of said valve head for movement therewith but in a manner such as to permit slight independent relative movement while its marginal portion is connected to the adjacent portion of said hollow housing, the outer side of said flexible member being in communication with the atmosphere, a coiled spring having one end in engagement with the adjacent face of said flexible member for normally maintaining said valve head in engagement with its valve seat, a manually operable means adjustably mounted on said hollow housing and having a portion engageable with the outer end of said spring whereby the tension in the latter may be varied, said partition being further provided with an open-' ing extending transversely therethrough providing a valve seat on its under side, initially operable valve means mounted on said hollow hous- 5 drop in the discharged fuel, the opening of said relief valve efiecting the closing of said initially operable valve means.

8. A fuel pump comprising a housing having fuel inlet and outlet openings, pumping means in said housing adapted to transfer fuel from said inlet opening to said outlet opening, said housing having a fuel return passageway between said outlet opening and said inlet opening, a relief valve movably mounted in said housing and ope eratively associated with said return passageway for normally controlling the flow of excess fuel therethrough during the operation of said pumping means, the under side of said relief valve being in communication with said outlet opening and the upper side in communication with said inlet opening, a flexible impervious member disposed within said hollow housing and outwardly of said valve head, means attaching said flexible member to the adjacent side of said valve head while the marginal portion of said flexible member is connected to the adjacent portion of the housing, the outer side of said flexible member being in communication with the atmosphere and the opposite side thereof being in communication with said fuel inlet opening, resilient pre-loading means operatively associated with said relief valve for normally maintaining the latter in closed position, said housing being further provided with a fuel by-pass passageway affording communication between said inlet opening and that portion of said'relief passageway between said relief valve and said outlet opening, an initially operable valve means operatively associated with said by-pass passageway for initially bypassing fuel under pressure from said inlet opening to said outlet opening independently of said pumping means so as to fill the passageway on the pressure side of the pump, the continual introduction of by-passed fuel creating a pressure upon the under side of said relief valve unseating the same to permit flow of the by-passed fuel thereby independently of said initially operable valve means with a minimum pressure drop in the discharged fuel.

JAMES P. JOHNSON.

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