US2958457A - Gradual bleed control - Google Patents

Description

Nov. 1, 1960 s. s. Fox ET AL GRADUAL BLEED CONTROL 2 Sheets-Sheet 1 Filed May 26, 1959 INVENTOR.

' Nov. l, 1960 s. s. FOX ETAL 2,958,457

GRADUAL BLEED CONTROL Filed May 26, 1959 2 Sheets-Sheet 2 2,958,457 Patented Nov.. l, 1960 ice GRADUAL BLEED CNTROL Navy Filed May 26, 1959, Ser. No. 816,029

1 Claim. (Cl. 2150-115) This invention relates to an axial flow compressor, and more particularly to control of a compressor bleed valve in such a manner as to reduce the load or drag of the compressor in stating the turbine.

Compressors of the axial flow type are made up of a plurality of bladed stages which act to increase the pressure of gases flowing through the compressor, each succeeding stage further compressing the gases. A detrimental characteristic of axial llow compressors is a tendency to surge or stall at low speeds, sometimes resulting in physical damage to the compressor or its associated structure. This characteristic is due to the fact that the various stages of the compressor are designed for maximum elhciency as a unit at one particular compressor speed.

The conditions of surging are found to occur under certain conditions of light load and are known to depend on the volume of gas which the compressor is handling and on the pressure at which it is being delivered. In other words, for every volume there is a critical pressure above which pulsations are liable to occur; and vice versa for every pressure there is a critical volume below which pulsations are liable to occur.

The speed at which an axial flow gas turbine power plant can be started is below the design speed of its compressor and, consequently, starting is very diflicult if surge or pulsation exists.

lt is well known that pulsations in a compressor may be prevented, at least to a great extent, by throttling the flow of gas through it, as by throttling the intake, or by wasting gas from the delivery side of the machine, or by by-passing it from the delivery side to the intake. More is gained in compressor performance than is lost by dumping or wasting the gases which have been compressed arid had work done on them.

Various methods have been used for bleeding axial ow compressors and for controlling the bleeding thereof. ln the present invention this control functions in accordance with a measurement of the percent of bleed flow. The applicants found this apparatus to be a decided improvement over those devices which controlled the bleeding as a function of airow or as a function of compressor pressure ratio. The operation of a bleed valve is desirable only when necessary as it means, of course, a loss of energy.

An object of the invention is to provide an axial flow compressor bleed control mechanism which is relatively simple and which is dependable in operation.

Another object of the invention is to provide an axial ow compressor bleed control mechanism which provides gradual closing of the bleeds over a given speed range so as to obtain maximum performance from the compressor.

Another object of this invention is to provide a bleed valve which is dependent upon the percent of bleed ilow rather than upon the air iiow through the compressor or the compressor pressure ratio.`

Yet another object is to provide an axial tlow compressor bleed control which causes the valves which bleed the compressor to close gradually as the powerplant increases in speed.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description which is considered in connection with the accompanying drawings wherein:

Figure l illustrates a diagrammatic view of an axial flow split spool gas turbine power plant having the improved compressor bleed control mechanism of the present invention connected thereto.

Figure 2 is a graph illustrating how the gradual closing of the valve is effected.

Referring to Figure 1 in detail, indicates an axial flow split spool gas turbine power plant having inlet 2, compressor section 3, combustion section 4, turbine section 5 and exhaust nozzle 6. The compressor section is surrounded by casing '7 and has mounted therein a plurality of rotor blades 9. interposed between each row of rotor blades 9 are rows of stator vanes 10 which serve to turn the gases flowing through the compressor so that they strike the succeeding rotor blades 9 at the most eiicient angle.

A bleed control line 8 which preferably extends from an intermediate stage of the compressor and which functions in accordance with a measurement of percent bleed How, is used to regulate gas ilow through the compressor. This control line 8 passes through the housing 11 in which the butterfly valve 12 is rotatably mounted on one end of the shaft 13. The other end of shaft 13 extends into the interior of the uid cylinder 15 where as will be more apparent hereinafter its pinioned extremity 16 meshes with the rack teeth 17a on the spool-type piston 17 within cylinder 15. Chamber 18 in cylinder 15 between sections 14 and 19 of piston 17 is preferably vented to the i atmosphere as shown through conduit 2li.

The hollow piston 21 is secured to one end of piston 17 in any suitable manner and extends through the aperture 22 in the end of cylinder 15 into the reduced diameter portion 23 of cylinder 15. The walls of the aperture 22 engage the outer peripheral surface of hollow piston 21 to provide a fluid seal between chamber 24 in cylinder 15 and chamber 25 in the reduced diameter portion 23 of cylinder 15. Chamber 25 is vented through xed orifice 26 and fluid conduit 27 to the air intake section P2 of the compressor 3.

The elongated fluid conduit and variable bleed shaft assembly 23 is xedly secured to one end of cylinder 15 and extends through chamber 31 in cylinder 15, tln'ough the interior of piston 17 and the interior of hollow piston 21, through the preferably rectangular-shaped aperture 3i) in the end of hollow piston 21 and through the chamber 25 in the reduced diameter portion 23 of cylinder 15, and is journaled in cylindrical bore 32 in the end of cylinder 15. The inner surface 33 of hollow piston 21 engages the outer peripheral surface of the shaft assembly 28 to provide a iiuid seal between chamber 18 in cylinder 15 and chamber 2.9 in the hollow piston 21. The tubular portion 23a of the shaft assembly 28 is connected at one end to an intermediate stage P-3 of the compressor 3 through the iuid line 34, and extends beyond the surface portion 33 of the hollow piston 21 through ports 35 intoA iluid communication with chamber 29. The rectangularA tapered portion 36 of the shaft assembly 28 provides a variable bleed orice between chambers 29 and 25 in a manner which will be more apparent hereinafter.

The helical spring 37, which encircles the tubular porin the fluid housing 39. The interior of housing 39 is subdivided by the diaphragm elements 40 and 41 into the iluid chambers 42. 43 and 44. Spring element 45, disposed between one end of housing 39 and diaphragm 40, normally biases the diaphragm 40 inwardly' toward Chamber 43. Fluid line 46 connects chamber 42 with lluid line 34 and the tubular portion of shaft assembly 2S, Fluid line 47 connects chamber 43 with lluid line 27 and the air intake section of compressor 3, and fluid line 49 connects chamber 44 with chamber 25 in the reduced diameter portion of fluid cylinder 15.

The vertically disposed shaft is Xedly mounted within chamber 43 in any suitable manner. The link member 51 which is pivotably secured to shaft 51B at 52 pivotably supportsthe lever 53 at 54. The link element 55 is pivotably secured at one end to lever 53 at 56 and is secured at its opposite end to diaphragm 41B.

The horizontally disposed shaft 57 is rotatably mounted within chamber t3 as shown at 58 and S9. The yoke lever di) which is integrali with shaft S7 is pivotably secured to lever 53 at 61. Valve element 62 is xedly secured to and extends upwardly from one end of shaft 57 and as will be more apparent hereinafter engages the valve seats o3 and 64 respectively disposed at one end of fluid lines 55 and 66 which are respectively connected to chambers 31 and 24 of cylinder 15. The bellows element 67 shown cut away in part in the drawing is mounted on valve element 62 and encloses valve element 62 and its associated valve seats and is connected to the ambient atmosphere through iluid line 68.

Similarly valve element 69 is fixedly secured to and extends downwardly from the other end of shaft 57 to engage valve seats 7l) and 71 disposed at one end of fluid lines 72 and 73 which are respectively connected to chambers 31 and 24 of cylinder 15. The bellows element 74 mounted on valve element 69 encloses valve element 69 and its associated valve seats and is connected to the output section P-4 of compressor 3 through fluid line 75.

Link member 76 which is pivotably mounted on shaft Si) at 77l pivotably mounts the lever 7S in its slot 79. The link element Sil is pivotably mounted at one end to lever "I8Y at 81 and is Xedly secured to diaphragm 41 at its other end. Yoke link 82 is pivotably connected to lever 73 at 83 and to yoke lever et) at 61. The U- shaped member 84, which encircles and supports pin 85 on link 76, threadedlyengages bolt 86 which is rotatably mounted on the projected portion 87 of lever 78 between integral ilanges 89 and 9) thereon.

An understanding of the manner in which the irnproved compressor air bleed control mechanism of the present invention provides a gradual rather than an abrupt bleed as the aircraft builds up its speed may be obtained by first referring to Figure 2 of the drawing. As shown therein, it is a characteristic of two bleeds in series that the pressure ratio when plotted against the ratio Ps3/Ps2 where Ps3 is the pressure on the upstream side of the first bleed;

Ps2 is the pressure on the downstream side of the second bleed; and

Px is the pressure between the two bleeds will follow a line comparable to line AAl when one bleed is variable and fully open, and will follow an operating line BB1 when the variable bleed is diminished.

Pressure Ps3, intermediate compressor pressure at P3, and Ps2, inlet compressor pressure at P2, are available in our compressor and therefore, it is only necessary that we obtain some intermediate pressure, Px, to permit us to use this type of graph actuation to perform our gradual bleeding function. Referring to Figure l, we note that our control provides a variable bleed at 30 and a fixed bleed 26 with chamber 2S therebetween. The pressure in chamber 25 is Px.

When the compressor bleed valve 12 is full open and the variable bleed shaft assembly 28 is far right, the variable bleed at 3G is large and we are operating on line AAI (Fig. 2), as engine acceleration causes the pressure ratio Ps3/Ps2 to increase and the pressure ratio Ps3-Ps2/Ps-Ps2 to decrease. Bleed 12 is full open when the engine is started and as the engine accelerates we move from point a to point a on operating line AA1. At point A1, the pressure ratio Ps3-Ps2/Px*Ps2 is such that sufficient force is exerted on diaphragms 40 and 41 that they begin to move leftwardly. Line XX in Fig. 2 represents the ratio value at which linkage 92 of unit 39 is designed to operate at, to cause bleed valve 12 to gradually close and to be fully closed at point b. This slight leftward movement of the diaphragm 40 and 41 and linkage unit 92 as will be described more fully hereinafter, causes valve elements 62 and 69 to unseat, gradually increasing the pressure in chamber 24 while decreasing the pressure in chamber 31. This change in force on piston 17 causes it to move to the left to begin to close bleed valve 12. The leftward movement of piston 17, in carrying the variable bleed shaft assembly 28 with it, reduces the bleed opening at 30, due to the contouring of the bleed shaft assembly 28', to reduce pressure Px in chamber 25. The shaft assembly 28 will move leftwardly to a point where pressure Px is reduced to such a value that the diaphragms and linkage unit will be brought back into equilibrium which in turn brings piston 17 to equilibrium. Referring to Fig. 2, we see that our operating line ran from point a to point a', at which point the bleeds begin to close. With the diminishing of Px, we began operating between point a and point c until our system came into equilibrium at point c. With the system in equilibriurn we operate along `operating line CCl to point c', at which point, due to engine acceleration and the consequent increase of pressure Ps3, pressure difference .Px-Ps2 becomes suciently strong to again be able to move the diaphragm units 40 and 41 to the left with the consequent leftward movement of piston 17. As the bleed opening 30 is diminished in size again, due to the leftward movement of piston 17, pressure Px is again reduced to bring the system to equilibrium. During this leftward movement of piston 17, we have been operating between points c and d as shown in Fig. 2 and with the system again in equilibrium we operate on operating line DD1 to D1 from d to d.

This series of leftward movements of diaphragms 40 and 41, piston 17 and piston 21 together with the series of equilibrium operating points attained at different Ps3/Ps2 ratio, cause the gradual closing of bleed valve 12. This gradual closing would not be possible if port 30 did not become increasingly small with the leftward movement of piston 17 to diminish Px and bring the system to equilibrium for any given ratio of P3/P2. Once in equilibrium, engine acceleration is required to increase pressure Ps3 and start the leftward movement of piston 17 once more.

VWhen point b is reached in Fig. 2 bleed valve 12 is completely closed and we operate on operating line BB1 with the valve 12 in this closed position.

The linkage system between the diaphragms 40 and 41 and the valve elements 62 and 69 ampliftes and balances the forces generated upon the diaphragm pressure loads to provide movement of valve elements 62 and 69' as a function of the pressure ratio Ps3/Px. Rotation of shaft 57, with valve. elements 62 and 69 affixed thereto, is controlled by movement of lever 53` about its pivot point 54. Pivotal motion of lever 53v is controlled in part by movement of diaphragm 40 and its attached link 55'. Pivotal motion of lever 53 is also controlled through link 32 by the rotation of lever 73, which pivots about 85 as a result of diaphram 41 and its attached link 80. The position of pivot point 54 on llever 53 relative to its end pivots and the position of pivot point 85 on lever 78 relative to its end pivots and the relative areas of diaphragms 40 Iand 411 determine the lpressure ratio Ps3/Px at which lthe valve elements 62 and 69 are actuated. Lever 78 is slotted so that the pivot point 8S thereof can be adjusted to obtain a desired critical Ps3/Px pressure ratio setting. This adjustment is obtained by rotation of set screw or bolt 86.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as speciiically described.

What is claimed is:

In a multi-stage axial llow compressor having at least one bleed port for bleeding an intermediate stage of the compressor and at least one valve for regulating the area of said port; the combination therewith of the improvement for providing a gradual closing of the bleed port overa given speed range in order to obtain maximum performance from` the compressor, said improvement comprising a lluid cylinder having a reduced diameter portion at one end; a spool-shaped piston capable of reciprocal motion located within the large end of the cylinder and dividing said end into a rst, second and third chamber; coupling means for mechanically coupling the piston to the said bleed valve for permitting the valve to be closed upon movement of the piston; a hollow piston integral with one end of the spool piston extending into the reduced portion of the cylinder and having a rectangular aperture in the end thereof which leads into a fourth chamber formed by the one side of the hollow piston and the side and end walls of the reduced part of the cylinder; a iluid conduit having a tapered extremity said conduit being axially disposed in the center of the cylinder so that it passes through the interior of the spool piston,

through the interior of the hollow piston, and is affixed in the end of the reduced portion of the cylinder so that its tapered extremity engages the rectangular aperture of the hollow piston whereby a variation in the size of the aperture is accomplished by movement of the piston along the conduit; means for venting the fourth chamber with a iluid intake section of the compressor; a biasing means for normally biasing the spool piston towards the reduced portion of the cylinder; an adjustable mechanical linkage means operatively connected to both the fluid cylinder and the compressor for Iadmitting huid from the fluid intake section of the compressor to the iirst chamber of the cylinder and for admitting fluid from an intermediate stage of the compressor into the fluid conduit of the cylinder whereupon said iluid passes through the aperture in the hollow piston into the fourth chamber whereby the pressure of the said uid in the fourth chamber causes the spool piston and the hollow piston to move against the spring biasing means until an equilibrium is reached because of the cl'osing of the aperture in the end of the hollow piston by movement of the tapered extremity of the fluid conduit therethrough and because of the substantially constant ow of iluid pressure from the fourth chamber through the venting means into the intake section of the compressor whereupon an increase in compressor speed causes a corresponding movement. of the linkage means resulting in movement of the spool piston against the spring biasing means to a new equilibrium point, this series of movements of the spool piston causes a gradual closing of the bleed valve over a given speed range.

References Cited inthe tile of this patent UNITED STATES PATENTS 2,732,125 Ruby Jan. 24, 1956 2,837,269 Torell June 3, 1958 2,863,601 Torell Dec. 9, 1958 2,886,968 Johnson May 19, 1959

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