US2438702A - Carburetor - Google Patents

Description

S. F. HUNT March30, 1948.

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Patented Mar. 30, 1948 CABBURETOR Scott F. Hunt, Meriden, Conn., assignor, by mesne assignments, to Niles-Bemcnt-Pond Company, West Hartford, Conn, a corporation of New Jersey Application October 26, 1944, Serial No. 560,435

9 Claims. (01. 261-41) The present invention relates to carburetors for internal combustion engines, and particularly to enrichment controls for such carburetors.

Most modern carburetors intended for use on aircraft engines are provided with a manual mixture or fuel-to-air ratio control by means of which the operator of the aircraft may select either a lean fuel-to-air ratio or a rich fuel-to-air ratio, depending upon the flight conditions en- 1 countered. Such carburetors are als'o'usually provided with a device for automatically increasin the fuel-to-air ratio when the load on the engine exceeds a predetermined value. Such devices are commonly termed enrichment controls.

Formerly, the enrichment control was usually set so that it operated to increase the fuel-to-air ratio when a definite engine load was exceeded, regardless of the setting or the manual mixture control. However, it has been found that a considerable fuel saving can be gained if the enrichment control is operated at a higher engine load when the mixture control is in its lean position than when the mixture control is in its rich position. Such operation of the enrichment valve permits the operation of the engine at higher engine loads with a lean fuel-to-air ratio. Therefore, the highest economical cruising speed is increased, and likewise the range of the aircraft on which such an arrangement is used.

In my copending application, Serial No. 498,151, filed August 11, 1943, I have illustrated an. arrangement wherein the automatic enrichment occurs at different values of engine load, depending upon whether the manual mixture control is in its lean or rich positions.

It is an object of the present invention to provide an improved and simplified mixture and enrichment control of the type illustrated in my copending application referred to above.

Another object of the present invention is to provide an arrangement wh'erein'the operating characteristics of a single enrichment valve are varied in accordance with the position of the manual mixture control.

Another object of the present invention is to provide an arrangement of the type described wherein the variation of the operating characteristics of the enrichment valve is accomplished by a device responsive to a fluid pressure which varies in accordance with the position of the manual mixture control.

Other objects and advantages of the present invention will become apparent from a considermounted in the chamber 40.

2 ation of the appended specification, claims and drawing, in which Figure 1 illustrates, somewhat diagrammatically, a carburetor for an internal combustion engine embodying the principles of my invention,

Figure 2 shows a cross-sectional view of a modified form of the enrichment control valve and operating mechanism therefor which may be used in the carburetor of Figure 1 to carry out the principles of my invention, and

Figure 3 illustrates a modified form of mixture control valve which may be used in place of the mixture control valve of Figure 1.

Referring to the drawings, there is shown in Figure l a body ill of a carburetor for an aircraft type internal combustion engine. Air enters the carburetor body ID at an inlet [2 and flows thru a Venturi restriction I4 and a passage I5, past a throttle l6 and a fuel discharge nozzle l8 to an outlet 20. A supercharger may be provided between the outlet 20 and the intake manifold of the engine. In certain cases the supercharger may be upstream from the inlet I2, r two superchargers may be used, one in each place.

The Venturi restriction l4 produces a pressure differential between the inlet l2 and the throat of the restriction which varies substantially in accordance with the square of the velocity of the air passing thru the restriction. Since the crosssectional area of the venturi is constant, this pressure differential may be taken as a measure The pressure differential between entrance l2 and the throat of venturi i 4 is utilized tocreate an air flow thru a secondary air passage extending from entrance H to the throat of venturi l4. A plurality of impact tubes 22 are provided, whose open ends project into the entrance I 2 to receive the impact of the entering air. The secondary air passage may be traced from entrance I2, thru tubes 22, a passage 24 interconnecting the impact tubes, a conduit 26, a chamber 28 in a pressure meter generally indicated at 30, a restriction 32, a chamber 34 in the pressure meter 30, a conduit 36, past a valve 38 into a chamber 40, and thence thru a conduit 42 to the throat of venturi l4.

The valve 38 is operated by a sealed bellows 44 The bellows 44 is fixed at one end, so that the position of the free end, to which valve 38 is attached, varies in accordance'with the air pressure in the chamber 40. The bellows 44 is preferably filled with nitrogen or some other suitable temperature responsive fluid, so that the position of valve 38 Varies not only with the pressure but with the temperature of the air in the chamber 40, and hence with the density of that air.

In the secondary air passage, the pressure diiferen'tial between the entrance l2 and the throat of venturi I4 is divided into two component pressure drops, one across the restriction 32 and the other across the valve 38. The valve 38, as previously mentioned, is positioned in accordance with the density of the air flowing thru the passage I5. Valve 38 is moved toward open position as theair density increases and toward closed position as the air density decreases. If the volume of air flowing per unit time thru passage l5 remains constant while its density decreases, then the mass of air flowing is decreased, but the pressure differential set up by the venturi I4 remains constant. However, the movement of valve 38 toward closed position causes the component pressure drop across valve 38 to increase, and the component pressure drop across restriction 32 to decrease, reflecting the decrease in the mass of air flowing. By proper design of valve 38, the pressure drop across restriction 32 may be made to vary substantially in accordance with the mass of air flowing thru passage I 5. This pressure differential across restriction 32 acts on a diaphragm 46 which separates the chambers 28 and 34. The force applied to diaphragm 46 is transmitted to a valve 48, on which it acts in a closing direction.

The fuel enters the carburetor from a fuel pump or other source of fuel under superatmospheric pressure. It flows thru a conduit 50, a valve 52 in a pressure regulator 54, a conduit 56, a mixture control valve mechanism generally indicated at 58, a jet system 60, an idle valve I25, a conduit 62, a valve 64 in a pressure regulator 66, and a conduit 68 to the fuel discharge nozzle l8.

The pressure regulator 54 includes a diaphragm I0 separating a pair of expansible chambers 12 and I4 and connected at its center to the valve 52. A spring I6 biases the valve 52 toward open position. A restriction 18 connects the chambers I2 and I4.

A portion of the fuel entering pressure regulator 54 flows thru chamber I4, restriction I8, chamber 12, a conduit 80, a chamber 82 in the pressure meter 30, past the-valve 48, and thru a conduit 84 to the main air passage I5. Alternatively, the conduit 84 may lead to the fuel tank, the fuel pump inlet, the fuel conduit 62, or elsewhere, as long as it leads to a point maintained at a pressure continuously lower than that in chamber 82.

The pressure meter 30 includes a diaphragm 86 separating the chambers 34 and 82 and a diaphragm 88 separating the chamber 28 from a fourth expansible chamber 90. The valve 48 is biased toward closed position by a spring 92.

The chamber 90 is connected thru a conduit 94 to the fuel conduit 62 downstream from the jet system 50. The pressure in chamber 90 is therefore the same as that in the fuel line downstream from the jet system. The pressure in chamber 82 is the 'same as that in chamber 12 of pressure regulator 54.

The position of diaphragm I0 and valve 52 is determined by the balance between the spring I6 plus the pressure in chamber I2 acting in a valve opening direction and the pressure in chamber I4 acting in a valve closing direction. If the balance between these forces is upset, the diaphragm I0 and valve 52 move, thereby varying the pressure in chamber I4 until the balance is restored. Since the pressures in chambers 12 and I4, under equilibrium conditions, differ by a substantially constant amount dependent on the strength of spring I6, the pressure in. chamber I2 may be used as a measure of the pressure in chamber I4, which is substantially the same as the pressure on the upstream side of the jet system 60.

For any given constant cross-sectionalv area of the fuel passages thru the jet system 60. the pressure diiferential across it is a measure of the fuel flow thru it. This pressure differential, or rather a smaller pressure differential which is a measure of the pressure differential across the jet system, is applied thru the diaphragms 86 and 88 of pressure meter 30 to the valve 48, on which it acts in an opening direction.

From the foregoing, it may be seen that the valve 48 is positioned in accordance with the balance between two forces, one of which varies in accordance with the mass of air entering the carburetor, and the other in accordance with the mass of fuel entering the carburetor. Furthermore, the valve 48 controls the mass of fuel entering the carburetor, since it controls the pressure in chamber 82. The pressure in the chamber 82 is transmitted to chamber "I2 of pressure regulator 54 where it controls the position of valve 52 and hence the pressure on the upstream side of the jet system 60.

The pressure regulator 66 operates to maintain a substantially constant pressure on the downstream side of the jet system 60 and thereby to prevent variations in pressure at the fuel discharge nozzle I8, which may be due to operationof the throttle or to variations in engine speed, from reaching the downstream side of the jet system and eflecting the fuel flow.

The pressure regulator 66 includes a pair of expansible chambers 9Ii and 98 separated by a flexible diaphragm I00, which is attached at its center to the value 64. A spring I02 biases the valve 64 toward closed position. The chamber 96 is connected thru a conduit I04 to the conduit 26 and thence thru the passage 24 and impact tubes 22 to the air entrance I2. The chamber 98 is connected to the conduit 62.

The mixture control 58 includes a disc valve I06 fixed on a shaft I08. The disc valve I06 controls the flow of fuel thru ports opening into conduits I I0 and H2 which lead into the jet system 60. When the disc I08 is in the position illustrated in full lines in the drawing, fuel can flow to the jet system only thru the conduit IIO, This full line position of the disc valve I06 is known as the lean position of the mixture control 58. When the disc valve I06 is in the dotted line position shown in the drawing. the fuel can flow thru both the conduits I I0 and H2. The dotted line position of disc valve I06 is termed'the rich posi tion of the mixture control. The disc valve I06 can also be moved to a cut-off position wherein it cuts off the flow thru both conduits H0 and I I2.

The conduit IIO conducts fuel either thru a fixed restriction or jet II4, or thru a restriction I I6 controlled by an enrichment valve I I8 biased to closed position by a, spring I20 The conduit I I2 conducts fuel to a fixed restriction I22. Fuel -fiowing thru the restrictions II 6 and I22 also flows thru another restriction I24 which limits sure meter 30 acts on valve 48 in a closing directlon. When the differential pressure acting on diaphragm 48 is small, as under low air flow conditions, the spring 92 becomes the predominating force acting on valve 48. A closing movement of valve 48 causes an increase in the fuel flow thru the main fuel line. since the closure of valve 48 increases the pressure in chamber 82 of pressure meter 30 and hence in chamber 12 of pressure regulator 54. Furthermore, the spring 16 of pressure regulator 54 biases valve 52 in an opening or fuel flow increasing direction.

The idle valve I25 is pivotally attached to a lever l28, whose opposite end is connected by a link I30 to an arm I32 fixed on the shaft 4 of throttle I6. The idle valve is normally wide open when the throttle is beyond a range of positions near its closed position, usually termed the idling range. As the throttle moves into the idling range, thereby decreasing the air flow, the idle valve I25 moves toward closed position. At the same time, the springs 92 and I6 cause operation of valve 52 in an opening direction. The valve 52 is thereby opened sufficiently so that its restrictive eifect on the fuel flow is less than that of the idle valve I25. Therefore the fuel flow under idling conditions is controlled primarily by the valve I25 in accordance with the position of the throttle, and not by the pressure meter 30 in accordance with the mass of air en-' tering the engine.

A piston H9 is aligned with the stem of valve H8. The piston H9 is biased into engagement with the stem of valve H8 by a spring I2I. One side of the piston H9 is exposed to the pressure in a cylinder which is connected thru a passage I23 to the conduit H2. The opposite side of piston H9 is exposed to the pressure of the fuel leaving the conduit i ii].

When the mixture control 5b is in its lean position, as illustrated in full lines in the drawin the valve I06 closes the conduit H2 so that the pressure in conduit H2 is substantially the same as the pressure on the downstream side of the jet system. This pressure is communicated thru conduit I23 to the left face of piston H9. The pressure acting on the right face of piston H9 is the pressure on the upstream side of the jet system. The piston H9 is therefore subject to a pressure differential which compresses spring I2I and holds the piston IE9 separated from the stem of valve H8. When the mixture control is moved to the rich position, however, the conduit I I2 is opened so that the pressures on both faces of piston H9 are equal. The spring i2i then moves piston H9 into engagement with the stem of valve H8, and applies an opening force to valve H8, opposite to the closing force. of spring I20, Therefore, a smaller fuel pressure differential across the jet H6 is effective to overcome spring I20 and open valve H8 when the mixture control is in its rich position than when the mixture control is in its lean position. The valve I I8 is therefore openat smaller engine load when the mixture control is in its rich position than when the mixture control is in its lean position.

While I have illustrated a particular type of in the are that my invention may be applied with equal facility to other types of carburetors. The carburetor illustrated may. for example, be modified by omitting the pressure regulator 54 and placing the valve 48 of the pressure meter 30 directly in the fuel line betwen the pump and the mixture control 58. This would require that the valve 48be reversed so' that it would open in a downward direction and close in an upward direction, the same as the present valve 52.

Figure 2 There is shown in Figure 2 a modified form of enrichment valve and control mechanism therefor which may be substituted for they valv II8 in Figure 1. Figure 2 also shows diagrammaticarburetor, it will be appreciated by those skilled cally, a mixture control 58 and a jet system 50, which correspond to the same elements in Figure 1, and the connections between the new enrichment valve mechanism and the mixture control and jet system.

A casting 250 forms a part of the body of a carburetor. The casting 250 is hollow, having the chamber 252 formed therein. The upper and lower ends of chamber 252 are open, and a sleeve member 25% is inserted thru the upper end and extends therethru to the lower end. The lower end of sleeve 254 is internally threaded to receive an orifice plate or jet 256. The jet 256 is generally cylindrical. One end of jet 256 is open and forms a valve seat 258. The other end of jet 256 is provided with a central bushing 260, which is apertured to receive the stem 262 of a valve 264 which cooperates with the seat 258. The end of jet 256 which carries the hub 260 is also provided with a number of circumferentially spaced orifices 26%. A spring retainer 268 is attaohed to the valve stem 252, and a spring 220 is retained between the retainer 268 and an external flange m on the bushing 2611.

A diaphragm 2 i 9 has its edges clamped between the upper surface of sleeve 25 5 and the under surface of another sleeve 2Y2. A cover plate 21d extends over the sleeve 212. The cover plate 214 is attached to the casting 25s by means not shown, and holds the sleeves 212 and 254 together. The interior of sleeve 212 forms a chamber 216, An elongated stem 2'38 is attached to the center of diaphragm 2W. The upper end of stem 218 extends into a guide nut 288 at the upper end of sleeve 2'82. A spring 22H surrounds the stem 218 and is retained between the nut 280 and the diaphragm 2 I 9.

Below the diaphragm 2M, the stem2i8 is enlarged to form a button 282 having a central aperture 28% which receives the upper end of valve stem 262.

The chamber 2'56 is connected thru a passage 286 to the conduit H2 of Figure l. The chamber 252 is connected by a passage 253 to the conduit iii] of Figure 1.

Valve ZiB corresponds to valve H8 of Figure i. It is opened by the fuel pressure differential across it in the same manner as valve H8. The diaphragm 2i!) performs the function of the piston I IQ of Figure 1, and the spring 22I corresponds to the spring I2I'. It may be seen that the pressure in chamber 216, above the diaphragm, is the same as the pressure in conduit H2 and therefore the same as the pressure at the left side of the piston Il9'in Figure 1. The pressure under the diaphragm 2I9 is the same as the pressure in the conduit Ho, and therefore, the same as the pressure acting on the right face of the piston I I9 in Figure 1.

The operation of valve 2|. by springs 220 and 22i and diaphragm 2l3 corresponds fully to the Figure 3 Figure 3 shows a modified form of enrichment valve and control mechanism therefor, which may be substituted for the enrichment valve N3 of Figure 1. Figure 3 also shows diagrammatically a mixture control 33 and a jet system 60, which correspond to the same elements of Figure 1.

A carburetor body casting 330 is bored out to form a chamber 302. The lower end of chamber 302 opens into bore extending upwardly from the bottom of casting 300, which forms a chamber 304 in the casting 300. The upper end ofchamher 302 is closed by an orifice plate or Jet 308 provided with a downwardly extending rim forming a valve seat 308. The orifice plate 308 is provided with a central aperture thru which a valve stem 3) passes, and a plurality of circumferentially spaced orifices 3|2. A spring 3 is retained between the upper surface of the orifice plate 306-and a retainer 3|3 fixed on a stem 3m.

A bushing 3|8 is inserted thru the chamber 304 and closes the communicating passage between chambers 302 and 304. The bushing H3 is provided with a central bore to receive a rod 320. A sleeve 322 slides on the outside of bushing 3|8 and extends upwardly therefrom. The sleeve 322 is provided near its center with a transverse wall 324'which is apertured to permit the passage of rod 320. A spring 326 is retained between the upper surface of bushing 3|! and the wall 324, and biases the sleeve 322 upwardly into engagement with a flange 323 formed on the rod 320. The lower end of rod 323 is attached to the free end of a bellows 330, whose opposite end is fixed to the bushing 3|3. A passage'332 is bored thru the bushing 3|3 and the casting 300, and connects the interior of bellows 330 to the conduit 2 of Figure 1.

A cap 334 is threaded into the bore in casting 300 to close the lower end of chamber 303 and is provided with an upwardly extending sleeve portion 336 which maintains the bushing 3|3 in place. The V. sleeve 336 is aperturedas at 333 so that the exterior of bellows 330 is exposed to the pressure in chamber 304, which is connected thru a passage 340 to the fuel line on the downstream side of the jet system. The bellows 330 may be provided with an internal spring 342, if desired.

come both the springs 3H and 326 to open the valve 3| When the mixture control is moved to its rich position, the pressure inside bellows 330 is greater than the pressure outside, so that the bellows 330 is expanded to the position shown in the drawing, thereby carrying the rod 320 and spring 322 downward, separating the upper end of sleeve 322 from valve 3| Under those conditions, the fuel pressure difl'erential then has onlyto overcoine the spring 3 in order to open the valve 3| It may, therefore, be seen that the particular value of fuel pressure differential which causes an opening of the enrichment valve 3| is smaller when the mixture control is in its lean position than when it is in its rich position.

While I have shown and described certain pre ferred embodiments of my invention, other modifications thereof will readily occur to those skilled in the art, and I therefore intend my invention to be limited only by the appended claims.

I claim as my invention:

1. A fuel supply system for an internal combustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, a metering restriction in each of said branch passages, means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, valve means movable in an opening direction in response to said fuel pressurev differential for controlling the area of the restriction in one of said passages, spring means associated with said valve means for applying thereto a force acting in a valve closing direction, manually operable valve means for opening and closing another of said passages, means for applying an additional force to said pressure responsive valve means, means for controlling said force applying means including an expansible chamber having a movable wall, means connecting the interior of said chamber to said other passage between said valve means and the restriction therein, said wall being moved to control the application and removal of said additional force from said pressure responsive valve means in response to changes in pressure in said chamber due to operation of said manual valve Valve 3 corresponds generally to the valve H8 of Figure 1. The chamber 3l3 above the valve 3 is connected to conduit 3 thru a conduit 3|5. The chamber 302 on the downstream side of valve 3 is connected thru a conduit 3|! to a chamber 3|3 in the jet system corresponding to the chamber I03 of Figure 1. The valve 3 is therefore subject to the same fuel pressure differential as the valve 3 of Figure 1. When the mixture control is in its lean position, the pressure inside bellows 333 is'substantially the same as the pressure outside the bellows 330. The spring 326 then causes bellows 333 to collapse, moving sleeve 322 upwardly into engagement with valve 3. Under such conditions, the fuel pressure differential must overmeans and thereby to vary the resultant of the forces applied to said pressure responsive valve means so that it opens at different values of said fuel pressure differential, depending upon whether said manual valve means is open or closed.

2. A fuel supply system for an internal combustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, a metering restriction in each of said branch passages, means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, a valve movable in an opening direction in response to said fuel pressure differential for controlling the area of the restriction in one of said passages, first spring means biasing said valve to closed position, second spring means coacting with said first spring means, manually operable valve means for opening and closing another of said passages, and means responsive to the pressure in said other passage between said manual valve means and the restriction therein for restraining said second spring .means to vary the force acting on'said pressure responsive valve so that it opens at different values of said fuel pressure differential, depending upon whether said manual valve means is open or closed. v 3. A fuel supply system'for an internal com bustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, 9, metering restriction in each of said branch passages,

means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, a valve movable in an opening direction in response to said fuel pressure differential for controlling the area of the restriction in one of said passages, spring means biasing said valve to closed position, manually operable valve means for opening and closing another of said passages, and means responsive to the pressure in said other passage between said valve means and said restriction therein to vary the biasing force acting on said pressure responsive valve so that it opens at different value of said fuel pressure differential, depending upon whether said manual valve means is open or closed.

4. A fuel supply system for an internal combustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, a metering restriction in each of said branch passages, means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, a valve movable in an opening direction in response to said fuel pressure differential for controlling the area of the restriction in one of said passages, a stem for said valve, first spring means biasing said valve to closed position, manually operable valve means for opening and closing another of said passages, an expansible chamber having a movable wall aligned with said valve stem, second sp g means in Said chamber biasing said wall into engagement with said stem and effective to oppose said first spring means when said wall engages said stem, means connecting the interior of said chamber to said other passage between said valve means and the restriction therein, the exterior of said wall being subject to the pressure on the upstream side of the restriction in said one passage, said wall moving in response to a decrease in pressure in said chamber due to closure of said manua1 valve means to disengage said valve stem and thereby to increase the net force biasing said valve closed so that it opens at a higher value of said fuel pressure differential when said manual valve means is closed than when it is open.

5. A fuel supply system for an internal combustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, a metering restriction in each of said branch passages, means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, a valve movable in an opening direction in response to said fuel pressure differential for controlling the area of the restriction in one of said passages, a stem for said valve, first spring means biasing said valve to closed position, manually operable valve means for opening and closing another of said passages, an

oxpansible chamber, a flexible diaphragm forming one wall of said chamber and aligned with said valve stem, abutton carried by said diaphragm and recessed to receive the end of said stem, second spring means in said chamber biasing said diaphragm and button into engagement with said stem and effective to oppose said first spring means when said button engages said stem, means connecting the interior of said chamber to said other passage between said valve means and the restriction therein, the exterior of saiddiaphragm being subject to the pressure on the upstream side of the restriction in said one passage. said diaphragm moving in response to a decrease in pressure in said chamber due to closure of said manual valve means to disengage said valve stem and thereby to increase the net force biasing said valve closed so that it opens at a higher value of said fuel pressure differential when said manual valve means is closed than when it is open.

6. A fuel supply system for an internal combustion engine, comprising a fuel conduit, three parallel branch passages in said conduit, a metering restriction in each of said branch passages, means for controlling the fuel pressure differential across said branch passages to control the fuel flow therethru, a. valve movable in an opening direction in response to said fuel pressure differential for controlling the area of the restriction in one of said passages, a stem for said valve, first spring means biasing said valve to closed position, manually operable valve means for opening and closing another of said passages, a cylinder, a piston movable in said cylinder and aligned with said valve stem, second spring means in said cylinder biasing said piston into engagement with said stem and effective to oppose said first spring means when said piston engages said stem, means connecting the interior of said cylinder to said other passages between said valve means and the restriction therein, the exterior of said piston being subject to the pressure on the upstream side of the restriction in said one passage, said piston moving in response to a decrease in pressure in said cylinder due to closure of said manual valve means to disengage said valve stem and thereby to increase the net force biasing said valve closed so that it opens at a higher value of said fuel pressure differential when said manua1 valve thru three parallel passages leading from a common inlet to a common outlet, each passage having a restriction therein, said valve mechanism comprising a first valve located in a second of said passages and movable in an opening direction in response to a predetermined fluid pressure differential across said restrictions for augmenting the now thru one of said passages, spring means associated with said first valve for applying thereto a force acting in a valve closing direction, a manually operable valve for opening and closing a third of said passages, means for applying an additional force to said first valve, means for controlling said force app ying means including an expansible chamber having a movable wall, means connecting the interior of said chamber to said third passage between the manually operable valve and the restriction therein, said wall being moved to control the application and removal of said additional force from said first valve in response to changes in pressure in said chamber due to operation of said manual valve and thereby to vary the resultant of the forces applied to said first valve so that it opens at different values of said fluid pressure differential, depending upon whether said manually operable valve is open or closed.

8. Valve mechanism for controlling the flow thru three parallel passages leading from a common inlet to a common outlet, each passage having a restriction therein, said valve mechanism comprising a first valve located in a second of said passages and movable in an opening direc- 11 tion in response to a predetermined fluid pressure difierential across said restrictions for all!- 'menting the flow thru one of said passages, spring means associated with said first valve for applying thereto a force acting in a valve closing direction, a manually operable valve for opening and closing a third of said passages, and means responsive to the pressure in said third passage between said manually operable valve and the restriction therein to vary the biasing force acting on said first valve so that it'opens at diflerent values of said fluid pressure differential, depending upon whether said manually operable valve is open or closed.

9. Valve mechanism for controlling the flow thru three parallel passages leading from a common inlet to a common outlet, each passage having a restriction therein, said valve mechanism comprising a first valve located in a second of said passages and movable in an opening direction in response to a predetermined fluid pressure difierential across said restrictions for augmenting the flow thru one of said passages, a

stem for said valve, first spring means biasing said valve to closed position, manually operable valve means for opening and closing a third of said passages, an expansible chamber, a flexible diaphragm forming one wall of said chamber and aligned with said valve stem, a button carried by said diaphragm and recessed to receive the end of said stem, second spring means in said chamclosure of said manual valve means to disengage said valve stem and thereby to increase the net force biasing said valve closed so that it opens at a higher value of said fluid pressure diil'erential when said manual valve means is closed than when it is open.

SCOTT-F. HUNT.

REFERENCES CITED file of this patent:

UNITED STATES PATENTS Number Name Date 1,606,491 Abernethy et a1. Nov.- 9, 1926' 1,967,619 Justheim July'24, 1934 2,193,533 Kishline et al. Mar. 12, 1940 2,295,656 Hersey et al. 1------ Sept. 15, 1942 2,348,008 Hunt May .2,- 1944 2,361,227 Mock Oct. 24, 1944 The following references are of record in the i

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