Fuel metering means

April 9, 1946.

C. F. SCHORN

FUEL METERING MEANS

Filed June 19, 1944

2,397,984

Sheets-Sheet 1

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INVENTOR.

AT7OENEY

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April 9, 1946.

2,397,984

C. F. SCHORN

FUEL METERING MEANS

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April 9, 1946.

2,397,984

C. F. SCHORN

FUEL METERING MEANS

Filed June 19, 1944 3 Sheets-Sheet 3

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£7JFt ScJiorh

INVENTOR.

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ATTORNEY.

Patented Apr. 9,1946

2,397,984

UNITED STATES PATENT OFFICE

2,397,984

FUEL METERING MEANS

Carl F. Schorn, Detroit, Mich., assignor to George

M. Holley and Earl Holley

Application June 19,1944, Serial No. 541,009

Claims.

The object of this invention is to regulate the ratio of fuel to air in an internal combustion engine.

Figure 1 shows diagrammatically the elements of my invention in its simplest form. s

Figure 2 shows diagrammatically the elements of the preferred form of my invention.

Figure 3 is an enlarged view of the left-hand portion of Figure 2.

In Figure 1, 10 is the fuel entrance and II is the fuel outlet. 12 is a shaft which is driven at engine speed or a fraction thereof. 13 is the main fuel pump which supplies fuel to the engine. 14 is an auxiliary or recirculating positive displacement fuel pump which creates pressures in proportion to the square of the engine revolutions per minute and thus forms part of the control mechanism for regulating the fuel flow. 15 is a connection which admits the intake manifold pressure from the engine side of a supercharger 158 and communicates through pipe 159 to discharge into a chamber 49 which contains a flexible metal capsule assembly. This capsule assembly is divided into two sections sealed one from the other. The lower section 18 is partially evacuated while the upper section 17 is communicated to engine exhaust pressure by means of connection 16.

Valve 19 is the fuel measuring device connected to the capsule assembly and is located in a fuel passage 20 and controls the fuel flow from passage 20 to a fuel outlet passage 21. The valve 19 is supported by a spring 22. The passage through the center of valve 19 permits the pressure in chamber 49 to be applied to the lower end of the valve.

The positive displacement pump 14 creates a pressure differential across the restriction between the orifice 23 and the needle 25, which pressure drop varies directly with the square of the revolutions per minute of the engine by circulating fuel from fuel entrance 10 through pump 14 to chamber 24 past restriction 23—25 back into the fuel inlet 10. The movable needle 25 is responsive to a temperature device 26, which is located adjacent to the air intake 156 of the engine and is provided to control the area of the restriction 23. The temperature device is located within a chamber 170 and an opening 171 causes circulation of air through this chamber and out through the opening 172 adjacent to the throttle 157.

Λ diaphragm 27 responds to the pressure differential across the restriction 23—25 since the chamber 28 located to the right of diaphragm 27 (Cl. 123—119) is connected through the passage 29 to the fuel inlet pressure.

The chamber 31 to the right of diaphragm 30 is communicated through passage 47 to the fuel in passage 20, therefore, the drop in pressure across the diaphragm 30 is the same as the drop across the metering valve 19. Diaphragms 27 and 30 are connected to each other by means of the shaft 32. Connected to the diaphragm 30 is 10 the balanced pressure control valve 33. When the engine speed causes an increase in the pressure drop across diaphragm 27, the shaft 32 and diaphragm 30 moves to the right and valve 33 moves to the left to increase the fuel discharge opening 15 from chamber 21 to outlet passage 34. This causes an increase in the pressure drop across the valve 19 and thus across the diaphragm 30.

Fuel in passage 34 raises the diaphragm 35 and fuel discharges to the engine through outlet II. 20 Diaphragm 35 is loaded with the spring 36 and the inlet fuel pressure which is supplied through passage 37. There is then maintained an adequate pressure in the pipe II.

A fuel venturi 38 in the passage leading to the 25 valve 19 creates a pressure difference which responds to the flow of fuel. The pressure of the fuel entering the venturi 38 is applied to.the upper side of the diaphragm 39 and the decreased pressure in the throat of the venturi 38 is applied to 30 the lower side of a diaphragm 39 through the passage 40. Diaphragm 39 is supported by spring 41 and supports the tapered needle 42, which controls the supply of the extra fuel needed for high power, especially in an air-cooled engine where 35 extra fuel is required to prevent the engine from overheating.

A relief valve 43 loaded with a spring 44 and connected through a passage 45 with the passage 34 is provided so that when the pressure gen40 erated by the main fuel pump 13 exceeds a set value aboVe the pressure in discharge passage, the fuel flows back and is recirculated into the fuel inlet 10. This puts a ceiling on the pressure drop through the metering system. By controlling the 45 maximum pressure drop that can occur through the metering system, the droop in the air flow curve at high engine speeds can be compensated for. A manual mixture control valve 46 introduces a restriction 48 across the recirculating pump 14 so 50 that when this valve is moved from the full rich position marked FR to the cruising lean position marked CL, valve 46 increases the area of the restricted passage leading from the high pressure side of the pump 14 back to the entrance 10. 55 This means that at a given speed there is less

2,397,884 pressure drop across the diaphragm 27 and therefore less pressure acting on the rod 32, and, therefore, less pressure drop across diaphragm 30 and valve 19, thus less fuel is discharged at It. When the valve 46 is moved into the position marked SO, which means shut off, there is a wide-open short circuit across the pump 14, and the pressure drop across the metering valve 19 drops to substantially zero and no fuel flows.

Operation of Figure 1

When the mixture control valve 46 is in the position shown, that is, in full rich position, fuel entering at 10 is raised in pressure by the pump 14 and acts on diaphragm 27, which pushes rod 32 to the right and opens valve 33, which lets fuel for the engine into passage 34 and past the diaphragm 35 to the fuel outlet 11. The pressure drop across the restriction 23—25 and, therefore, the drop across diaphragms 27 and 30 and the valve 19 varies (for a given temperature) as the square of the engine speed. The flow past the valve 19 at any given opening will vary as the square root of the drop across the valve. Therefore, the flow varies directly with engine speed. The size of the opening past valve 19 is controlled by the intake manifold pressure in chamber 49. Therefore, the flow into the engine varies with engine speed and manifold air pressure.

As the plane ascends, the pressure in capsule 17 falls and thereby causes a relative decrease in the capsule height at a given manifold air pressure. This causes the valve 19 to further move to increase the opening between passages 20 and 21 and, therefore, the fuel flow to the engine is increased. The Increase in flow compensates for the increase in air flow into the engine (at any given engine speed and manifold pressure) caused by the decrease in pressure on the exhaust side of the engined An increase in intake manifold temperature causes an increase in the size of the opening through restriction 23 and, thereby, the metering head across valve 19 is reduced for any given speed. This change in metering head compensates for the temperature variations in manifold temperature reducing the fuel flow as the temperature Increases.

With increased engine speed and manifold pressure, the increase in the fuel flow through the fuel venturi 39 causes the pressure drop across diaphragm 39 to increase until the weight of the spring 41 is overcome and additional fuel passes valve 42 and is admitted to the engine.

To operate at better economy, the valve 46 is manually rotated clockwise into the cruise lean CL position and the drop across the restriction 23 is lowered because of the added fuel capacity of the restriction 48. This causes a lower metering head across the metering valve 19 and therefore a decreased fuel flow at any given engine speed.

The device shown has been divorced from the air control means of the engine and its operation is quite independent of the air flow and of the density of the air entering the engine, being controlled simply by the revolutions per minute, the temperature of the air entering the engine cylinders and the intake manifold pressure, which are the controlling factors in determining its desired fuel supply.

However, to make the disclosure complete, an air entrance 156 is shown with a throttle 157, a supercharger housing 159, communicating with the inlet manifold. The temperature responsive element is shown located in a chamber 170 con30 nected by a passage 172 with the engine side of the throttle 157 and through opening 171 with the manifold air pressure. The element 26 is thus held at the temperature of the manifold. The fuel outlet I i is shown discharging into the center of the supercharger housing 158.

Description of Figure 2

Figure 2 shows a more elaborate arrangement in which provision is made for the admission of water, etc. In Figure 2, 50 is the fuel entrance and 51 is the fuel outlet, 52 is an engine-driven shaft, driven at same speed of engine or some fraction thereof, 53 is a fuel pump supplying fuel to the engine, 54 is an auxiliary pump having a constant delivery per revolution; both pumps are driven by the shaft 52.

is a chamber connected through a passage 55 to the supercharger 158 of the engine through the pipe 159. (See Figure 1.) 56 is a connection for admitting atmospheric pressure to act on the left-hand side of a piston 57, the right-hand side of the piston 57. communicates with the chamber 89 through a restriction 98. The right-hand side of the piston 57 also communicates with the air entrance through a restriction 100. The difference of the pressures acting on the two opposite sides of the piston 57 is therefore somewhat less than the difference between atmospheric pressure and the pressure in the chamber 89, which is the pressure of the supercharger, and by changing the restriction 100, this difference is regulated.

is a group of three evacuated capsules located in the chamber 89 and secured to the left-hand wall thereof, and this group thus responds to the pressure difference between the manifold air pressure and whatever pressure remains in the exhausted capsules 58. 99 is a servo valve connected to and moved by the capsules 58 and by the piston 57. The valve 99 controls the admission of high pressure fuel from a passage 90 connected to the high pressure side of the pump 53 to a passage 91, which applies this high pressure to a chamber 97. This chamber 97 has a moving wall consisting of a diaphragm 93. Hence, the high pressure acting through the passage 90 pushes the diaphragm 93 to the right. The chamber 94 located on the right-hand side of the diaphragm 93 communicates through the pipe 95 connected to the fuel entrance 50, that is to the low pressure.

A passage 95', which is also connected to the low pressure pipe 95 and is also controlled by the valve 99 permits high pressure fuel to escape from the chamber 97 located on the left-hand side of diaphragm 93 when the valve 99 moves to the right. Hence, the pressure difference between that in the chamber 97 on the left-hand side of diaphragm 93 and the pressure in chamber 94 balances the differential between the capsule sealing pressure and the manifold air pressure acting on the effective area of capsules 58, plus or minus the effect of the atmospheric and manifold air pressure differential acting on the piston 57. Pressure in the chamber 97 is thus caused to vary with the manifold air pressure and is modified slightly by the atmospheric pressure. The pressure in 97 is transmitted through a passage 103 in the valve 59 to a chamber 105 located above a horizontal diaphragm 101.

This diaphragm 101 thus responds to the high pressure transmitted through passage 103 and compresses the compression spring 62 and moves the valve 59. A balance spring 102 is provided to keep the diaphragm 101 in equilibrium when

2,397,984 the pressure differential across diaphragm 10 i equals zero. The low pressure pipe 95 communicates with the chamber 106 below the diaphragm 101; therefore, the pressure differential across diaphragm 101 is the same as the pressure differential across diaphragm 99. The valve 59 thus responds to variations in the absolute value of the air pressure in the engine manifold and in the difference between the pressure of the atmosphere and the manifold air pressure.

The flow of fuel past the valve 59 is made to respond to the revolutions per minute of the engine by the following means: the positive displacement pump 54 creates a pressure difference between the inlet and the outlet, which will vary with the engine speed by circulating fluid first through the small restriction til and then (when sufficient pressure exists to unseat valve 115 against the load of spring 116) also through a restriction 63. The fuel flows in a circuit from the fuel entrance 50 through pump 54 through restrictions 110 and through a restriction 63 to the fuel inlet 50. The purpose of spring loaded valve 175 and restriction ill is to alter the relationship between the pressure drop across restriction 63 and engine speed to satisfy the empirical formula:

Basie engine fuel flow=

An internal combustion engine might be considered as a suction pump. During the intake stroke, the piston draws a mixture of air and fuel into the cylinders. The total volume of air and fuel drawn into the engine in any given time interval depends upon the number and size of the cylinders an engine has (displacement) and the crankshaft speed. In a four-cycle engine, since there is one suction stroke for each two crankshaft revolutions, the revolutions per minute of the engine is divided by two. Since we are concerned with the weight of air and fuel entering the engine and not volume, the density of the mixture must be considered.

Assume for the moment that air alone is being drawn into the engine, from the law of gases we have:

PV=MBT or where

M=weight of air in lbs.

P=pressure of the air in lbs. per sq. foot. B=air constant—53.34 approximately T=absolute temperature—degrees Fahrenheit V=volume in cu. feet displaced

For an engine, the formula may be written

PLAN BT2

L=length of stroke in feet A=area of piston in sq. feet N=revolutions per minute where weight of air entering the engine per unit of time —=the displacement of the engine per unit of time

For a given engine LAN/2 is a constant and since B is also a constant, the formula becomes

K'PN T

Because of the introduction of vaporizing fuel into the air and also because for practical reasons it is not possible to sample the air pressure and temperature in the engine cylinders, in actual 5 practice the above formula must be modified to read _v, _:Κ“(ΛΓ-Ο(Μ. A. P,—C¹) where M. A. P. equals manifold air pressure in pounds per square inch absolute.

The value of the constants in the above empirical formula may be determined from engine test data.

_lg Since the basic fuel air mixture entering an engine is held at substantially a fixed ratio, therefore, the same factor that governs the air flow into the engine may be used to govern the basic fuel flow. We may therefore write a formula for 2q the basic fuel flow into the engine as follows:

Fuel _{fi0W =} g(^P)(M; A- P.-C-) z

The constant K includes the mixture ratio fac25 tor. In actual practice, K will determine the design and shape of the metering orifice of the metering system disclosed in my application.

Since the back, pressures on the exhaust system of an engine used on aircraft varies for each alti30 tude and thereby affects the power output of the engine, it is necessary to modify the value of C¹for each altitude. Tiffs is accomplished in my disclosure by the use of the piston 51, Figure 2.

A movable restricting needle 65 is provided re35 sponsive to a temperature device 66, which corrects for the temperature variation of the air entering the engine cylinders. (See Figure 1.) The temperature device 66 may be located in the inlet manifold adjacent to the inlet valves.

The adjustment of the location of the restriction 63 is obtained by the action of diaphragm 140, which is pushed to the left by the spring 141 and the pressure in chamber 142 and is pushed to the right by the pressure in chamber 143. The 45 travel is limited by the adjustable screw and nut 141 and 148. With the manual valve 145 in the position shown, low pressure fuel is admitted to chamber 142 to the right of diaphragm 140 through the passages 144 and 164 controlled by the valve 145. Under this condition, the relatively low pressure in chamber 142 causes the high pressure in chamber 143 to move the diaphragm to the right, against the pressure of spring 41. When valve 145 is rotated 120° anti55 clockwise, it places the passage 70 in communication with the chamber 142 through the passages 160, 164 and 165. The compression spring 141 and the increased pressure in chamber 142 then overcomes the pressure in chamber 143 and the nut 148 engages with the stop 149 and the diaphragm 140 moves to the left carrying with it the restriction 63. When the flow through the venturi 78 exceeds a predetermined maximum, the spring 141 is again compressed and the lean mixture is restored.

The restriction 63 is carried by a perforated tube which is carried by two diaphragms 161 and 162. The fuel under pressure from the pump 54 acts against both diaphragms 161 and 162 so that 70 this pressure is balanced and has negligible effect on the location of the restriction 63.

A rod carried by the diaphragm 140 acts as a stop when the diaphragm 140 moves to the right and the rod engages with the adjustable stop 147. 75 In the upper right hand portion of Figure 2

8,397,984 is shown the device which increases the fuel flow with increasing revolutions per minute. A diaphragm 67 forms the left-hand side of a chamber 124; this chamber is connected through pipe 64 to the pressure side of the recirculating pump 54. The chamber 61 to the left of diaphragm 61 communicates with the low pressure side of the system through' pipe 96. Therefore, the pressure differential across diaphragm 61 varies as a func' tion of engine speed as modified by the poppet valve 116, spring 116 and restriction 111.

The diaphragm 150, which is connected through the rod 12 with the diaphragm 61, is subjected on its right-hand side to the pressure of the fuel as it leaves the fuel valve 69, the pipe 61 connecting the chamber 111 with the downstream side of valve 59. The chamber 11 to the left of diaphragm 150 communicates through the pipe 81 with the left-hand side of the valve 59; that is to say, to the high pressure side of this valve. Rod 12 connects the two diaphragms together.

- Hence, the pressure differential acting on the diaphragm 61 is balanced against the fuel pressure drop across the valve 59 acting on the diaphragm 150. Diaphragm 150 is lever connected to the valve 13, which, when the revolutions per minute Z increase, opens and increases the fuel flow from chamber III and hence the pressure drop across the valve 59 acting on the'diaphragm 150 increases; hence, the valve 13 opens so as to deliver fuel to the outlet passage 14 at such a rate as to create a pressure difference on the diaphragm 150, so as to balance the pressure difference acting on the diaphragm II.

The fuel flowing through 14 passes the valve 211, the purpose of which is to maintain a definite pressure in the outlet passage 128. The valve 211 is moved by the diaphragm 109, which is loaded by the spring 109. The chamber to the left of diaphragm 109 communicates with the low-pressure side of the system through restriction 123. The pressure to the right of diaphragm will be maintained at the pressure necessary to balance the fuel pressure to the left of diaphragm 103 plus the pressure required to balance the load of spring 109.

The shut-off valve 115 and the by-pass 116 short circuit the diaphragm 108 when the valve 115 is rotated 90°. When this happens, the pressure is substantially equal on both sides of the diaphragm 108 and the valve 211 closes under the pressure of spring 109 and the flow of fuel is shut off.

Fuel flowing through venturi 13 creates a pressure drop at the throat of the venturi, which is responsive to the rate of flow. This throat pressure is communicated by the line 10 to the chamber to the left of diaphragm 135. The pipe 114 communicates with the right-hand side of the diaphragm 135. The pressure difference acting on the diaphragm 135 opens a valve 82, which admits fuel to the passage 125. This fuel flows past the shut-off valve 126 on its way to the passage 127, which communicates with the fuel outlet passage 128.

.Alternatively, when valve 151 is rotated 90°, water is admitted at the entrance passage 129 through the valve 151. This water enters under a pressure substantially equal to the fuel pressure from discharge side of pump 53, the water pressure is applied to the right-hand side of diaphragm 152 and thus moves the shut-off valve 126 to the left, which shuts off the fuel flowing through 125, (the valve 126 is mounted on the diaphragm 152). Water then flows through a passage 130 past the valve 131, which regulates ' the amount of water as the pressure difference between the pipe 10 and the pipe 114 varies with the fuel flow through the venturi 18. This water 5 then flows through the pipe 121 to the passage

128.

At low speed the pressure in passage on the discharge side of pump 64 acts on another diaphragm 119. This pressure is communicated 10 through the pipe 114. The spring 120 is located on the left-hand side of the diaphragm 119 and tends to open the valve 119. Chamber 122 to the left of the diaphragm 119 communicates with the low pressure fuel pipe 95 through the restriction 15 123 and through chamber 110. The valve 118 thus controls the flow of fuel for idle speed supplied from a passage 132 which communicates with the chamber 133 which in its turn communicates with the high-pressure fuel pipe 114. 20 By this means, during the lower revolutions per minute, when the pressure differential across diaphragm 119 is small, the valve 119 is opened to supply the fuel for idle. As the engine speed picks up and the pressure drop across pump 54 25 and, therefore, across diaphragm 119 increases the fuel flow past valve 118 is decreased and is Anally stopped.

The pressure relief valve 83 is shown in lower left hand portion of Fig. 2 and is operated by ₃₀ means of a diaphragm 85 and a compression spring 84. The right-hand side of the diaphragm 85 is subjected to the high pressure in the fuel line 114 through a passage (55. When the pressure in the discharge side of pump 58 exceeds 35 the designed limit above the inlet fuel pressure, then valve 83 is unseated against a spring 84, which spring normally holds the valve 83 seated.

Operation of Figures 2 and 3

The revolutions per minute of the engine create a pressure differential across pump 54. At low or idling engine speeds, the drop across pump 54 is determined in part by restriction 111 and is insufficient to overcome the force of spring 45 120 acting to hold open the idle valve 118, therefore, high pressure fuel from the main fuel delivery pump 53 flows through passage 114, through the chamber 133 to the right of diaphragm 135, through passage 132, past valve 118 50 into the discharge fuel passage 128. Sufficient pressure builds up in passage 128 to overcome the fuel pressure to the left of diaphragm 108 and the weight of spring 109 so that the idle fuel flows past the valve, 211.

As the engine speed is increased, the increase in pressure differential across fuel pump 54 causes the idle valve 118 to close. Meanwhile, the pressure differential causes the poppet valve 115 to leave its seat and thereby fuel is caused 60 to flow past restriction 63. The pressure differential across restriction 63 acts on diaphragm 67. The force acting on diaphragm 67 is balanced by the force acting on diaphragm 150, which diaphragm adjusts the fuel outlet valve 73 65 to regulate this differential. The drop across main fuel metering valve 59 is identical to the drop across diaphragm 150, and this drop constitutes the basic fuel metering head for the metering system. Manifold air pressure is trans70 mitted from the supercharger housing into chamber 89, which contains a partially-evacuated element 58 and the right side of piston 57, the expansion and contraction of element 58 plus the pressure drop across piston 57 moves the valve 75 99 to the left or right of the port entering the

2,397,884 passage 9i. When the pressure in chamber 89 increases, the valve 99 tends to move to the left to admit high pressure fuel into passage 91 to the left of diaphragm 93. Sufficient fuel is admitted to create a pressure differential across dia- 5 iPhragmx93 to return the valye 99 to its neutral position.’The right side of the diaphragm 93 is communicated withthe low-pressure side of the system. 'The -pressuredrop across diaphragm 93 thus varies with the manifold air pressure in 10 ' chamber 89 and to the right of piston 87. The pressure in 97 is transmitted through the passage 103 in the center of the valve 59. The pressure in the chamber 105 is thus equal to the pressure in the chamber 97. The chamber 106 is also IS communicated to the low-pressure side of the system; therefore, the pressure drop across diaphragm 101 is equal to the pressure drop across diaphragm 93 and thus also varies with manifold air pressure. The load on diaphragm 101,20 acting against the force of the balancing springs 102 and 62, position the metering valve 59. An increase in jnanifold air pressure caused an increase in the metering passage past valve 59. .

The basic flow through the metering -system 2S varies with the size of the metering passage controlled by downward movement of the valve 59 and with the square root of the metering head across the valve 59, which metering head is created by the speed of the engine. The high pres- 30 sure fuel from pump 53, therefore, flows through the fuel venturi 78, past the metering valve 59 past the fuel outlet valve 73 into discharge passage 128, past the pressure valve 217 into the engine. 35

At high basic fuel flows, corresponding to high engine output, the valve 82 in response to the pressure drop in venturi 78 opens to admit additional fuel through the passage 128 past valve 217 into the engine. At these high basic fuel ⁴⁰flows, water may be substituted for the additional fuel flow past valve 82 by opening the water supply valve 151. This causes the valve 126 to move to the left to close passage 125. Meanwhile, water is admitted past valve 131 into the discharge 45 passage 128, past the valve 217 into the engine.

To compensate for changing temperature of the mixture entering the engine cylinders, the temperature-responsive device 66, which is located in the engine intake manifold, moves the gq needle 65 to the right with increasing mixture temperatures. This causes an increase in the size of the restricted fuel passage and thereby reduces the drop across the fuel metering valve 59. 55

When it is desired to operate at best economy mixtures in the cruising range of the engine, the manually controlled valve 145 is rotated 120° anticlockwise; this places the right side of the diaphragm 140 in communication with the throat qq of the fuel venturi 78. Therefore, the pressure drop across the diaphragm 140 is equal to the pressure drop in the throat of the fuel venturi 78. At low fuel flows corresponding to the cruising range of the engine, the pressure drop is insufficient to overcome the load of the spring 141 and, therefore, the restriction 63 is moved to the left to increase the size of the restricted opening in the recirculating pump system and, therefore, the metering head across the fuel me- 70 tering valve 59 is reduced and the fuel flow is decreased.

As the fuel flow through the fuel venturi 78 increases beyond the flow corresponding to engine power at which best economy mixtures are 75 safe, the pressure drop across the diaphragm 140 becomes sufficient to overcome the weight of the spring 141 and thereby the restriction 83 is moved to the right to enrichen the carburetor mixture.

Relief valve 83 acts to maintain the discharge pressure of pump 53 at a constant value above the pressure of the fuel entering the device. Should the pressure rise through pump 53 and exceed that determined by the force of spring 84, the valve unseats and permits fuel to be by-passed to the inlet side of the system.

As the plane ascends, the decrease in atmospheric pressure causes a relative increase in the pressure drop across the piston 57. This has a direct effect on the servo valve 99 and, therefore, upon the diaphragm 93 and upon diaphragm 10 ί which opens fuelmetering valve 59 as an increase in manifold mixture pressure occurs.

The carburetor, therefore, enrichens the mixture with an increase in altitude to compensate ’Tor the increase in engine power due to a decrease in the back pressure- on the engine.

To shut the fuel system off, mineral valve 115 Is rotated 90°. This places the right «side “of diaphragm 108 in communication with the left side, and since the chamber ITO communicates with the low pressure side of the system through restriction 123, the pressure differential across the diaphragm 100 is reduced to substantially zero and the spring 100 pushes the valve 217 into the closed position.