US2358815A

US2358815A - Compressor apparatus

Info

Publication number: US2358815A
Application number: US71363A
Authority: US
Inventors: Lysholm Alf
Original assignee: JARVIS C MARBLE; LESLIE M MERRILL; PERCY H BATTEN
Current assignee: JARVIS C MARBLE; LESLIE M MERRILL; PERCY H BATTEN
Priority date: 1935-03-28
Filing date: 1936-03-28
Publication date: 1944-09-26
Anticipated expiration: 1961-09-26

Description

Sept. 26, 1944.`

Original Filed March 28, 1936 A. LYSHOLM COMPRESSOR APPARATUS 3 Sheets-Sheet 1 Sept 26 1944- A. LYsHoLM COMPRESSOR APPARATUS Qrignal Filed March 28, 1936 3 Sheets-Sheet 2 NVNI'R.

Sept. 26, 1944. AI LYSHOLM 2,358,815

COMPRES SOR APPARATUS Original Filed March 28, 1956 5 Sheets-Sheet 3 n arl;- BY

NEY

Patented Sept. 26, 1944YY COMPRESSOR APPARATUS Alf Lysholm, Stockhohn, Sweden, assigner, by

to Jarvis C. Marble, Leslie M. Merrill, and APercy H. Batten, as trustees Application March 28, 1936, Serial No. 71,363. Renewed February 8, 1940. In Sweden March 24 Claims. (Cl. 23d-143) The present invention relates to compressor apparatus and has particular reference to rotary compressor apparatus of the lcrewor worm type. Still more particularly the invention relates to compressor apparatus ior operation at constant or relatively constant speed and variable load, particularly as incorporated in gas turbine systems of the continuous combustion type.

Because of l the particularlyv advantageous utility in continuous combustion gas turbine systems of compressor apparatus embodying the principles of the present invention, the invention will be considered and .apparatus embOdying it will be described, in connection with gas turbine systems of the above mentioned type, but it is to be understood that the invention is not limited in its use to compressor apparatus embodied in this type of system.

In the case of a gas turbine plant where the compressor is driven by a turbine which is mechanically independent of the turbine producing power forexternal use, the compressor capacity may be controlled within wide limits by changing the speed of operation of the compressor independently of the speed of operation of the useful power turbine, the latter, particularly in cases where it is employed to drive an electric generator, being usually operated at constant speed. This kind of compressor control is however not possible if the compressor is driven by or mechanically connected to the useful power turbine and if the useful power turbine can not be operated at variable speed because of the character of the power output therefrom. In the latter instance, the quantity of air delivered by the compressor can be controlled by throttling to compensate for varying loads. 'I'his kind of control is however undesirable because it introduces into the system unavoidable throttling losses. It has also been proposed heretofore to admit suction air to diirerent stages of rotary compressors in a manner such that the suction air is admitted to a pressure stage higher than the normal low pressure stage when the load on the plant, and consequently the required output from the compressor, is reduced. With this method also, the emciency of the compressor drops materially from its normal efficiency when the compressor is operated under loads materially different from the normal load for which the compressor is designed. Control of the' compressor apparatus in order to take care of variable loads has also been suggested, in which the work of compression is divided up among a number ofindependently operable compressors, one or more of which may be disconnected, depending upon the amount of change in the load imposed on the system. This last-mentioned method of control is effective only to a certain extent, since by changing the number of compressors in operation it is possible to enect only a very coarse control of the quantity or pressure of the air delivered and in order to obtain the requisite nicety of control, resort must be had in addition to throttling, which involves the introduction of the undesirable and unavoidable throttling losses.

Amongst the major objects of the present invention are: to provide improved compressor apparatus capable of operating with acceptable efciency over a wide load rage while at the same time oper-)ating at constant speed or with variations in speed which Vare relatively minor as compared with the degree of variation of the load; to provide improved compressor apparatus of the screw type in which variable output may be obtained at constant speed of operation without involving undue losses; to provide improved screw compressor apparatus in which variations in capacity ol.' the apparatus are obtained at con-i stant speed by means of novel bleeding arrangements which permit a desired quantity of air to be bled from the compression spaces of the compressor before compression commences; and to provide improved gas turbine system apparatus of the continuous combustion type embodying compressor apparatus and controls therefore enabling the system to be Operated eiliciently at variable load and with constant or substantially constant speed of operation of the compressor apparatus constituting a part of the system.

For a better understanding of the nature of the present invention and the advantages to be derived from its use, reference may best be had to the ensuing portion of this specification in which is described several embodiments of apparatus for carrying the invention into effect and to the accompanying drawings forming a part hereof, in which such embodiments are illustrated.

In the drawings:

Fig. 1 shows more or less diagrammatically in longitudinal cross section a gas turbine system of the continuous combustion type comprising apparatus embodying the invention;

Fig. 2 is a section similar to Fig. 1 showing another arrangement of apparatus embodying the invention;

lIl'ig. 3 is a wtransverse section through compresser apparatus having hand operated bleeding means embodying the invention;

Fig. 4-is a longitudinal section partly in elevation of another form of compressor apparatus embodying the invention;

Fig. 5 is a section taken on the line 5-6 Fig. 4;

Fig. 6 is a plan view of the compressor shown in Fig. 4;

Fig. 7 is a view similar to Fig. 6 but with a portion of the compressor casing broken away; and

Fig. 8 is a fragmentary section similar to Fig. 5 of a modification of the compressor apparatus shown in Figs. 4 to 7.

Referring now more particularly to Fig. 1, I0 designates generally a double rotation radial flow gas turbine of known kind having shafts I2 and I4 upon which are mounted the armatures of electric generators I6 and I8. The turbine and generators are mounted in a common frame or casing 28 having bearings 22, 24, 26 and 28. Shaft I2 is arranged to drive a compressor 30 and shaft I4 drives a compressor 32.

Compressor 30 is of the screw-type and, in the embodiment illustrated, comprises two rotors 34 and 38 mounted in suitable bearings in housing 38. As will be observed from Fig. 1 and more particularly from Figs. 3, 5,. and 8, a characteristic feature of the rotors is that they are dissimilar in cross-sectional contour, consisting of a male rotor having lobes projecting wholly or substantially wholly beyond the pitch circle of the rotor, and a female rotor having grooves lying wholly or substantially wholly within the pitch circle of the rotor. This construction produces Working spaces having materially different characteristics from those obtainable with intermeshing rotors of twin form such as are provided by intermeshing gears or rotors of the Roots type and as employed in the appended claims, it, will be understood that the terms male rotor and female rotor define rotors of this dissimilar cross-sectional nature.

The rotors are preferably space packed. That is, clearance is provided between the rotors and the walls of the casing andgbetween the intermeshing portions of the rotors. The rotor construction may advantageously be in accordance with the principles disclosed in my co-pending application, Serial No. 44,935, filed October 14, 1935. Because of the utilization of space packing, the rotors may be operated at the very high speed resulting from direct connection of the rotors to the turbine. This connection is made through the coupling 48 connecting shaft I2 with the shaft part 42 of rotor/ 34. The gear 44, fixed on the rotor shaft 42 meshes with gear 46 fixed to the shaft part 48 of the rotor 38 and provides drive for the latter rotor and maintains the peripherally spaced relation of the intermesh- A ing parts of the two rotors. y Rotor 36 is provided side of the compressor as distinguished from the suction side located behind the plane of the assaeis drawings. In order to prevent direct communication between the'inlet and the outlet of the compressor, the end surfaces at the right of the rotors are partly closed by an end wall member 48 which on its front side is provided with an opening 8| for the flow therethrough of the com- 'inder for a valve member such as the plunger 38 which when it is in the position indicated in the ligure closes the opening 58. An annular space 82 communicating with an outlet 84 provides communication between the interior of the compressor casing and the atmosphere when. the valve member 60 moves outwardly beyond the space 62. It will thus be evident that the opening afforded at 84, which may conveniently be termed a bleeder-opening, may be brought into full or partial communication with the interior of the compressor, depending upon the position of the valve member 30.

The compression spaces formed in the compressor will be in communication with the bleeder opening at the moment when normal compression in such spaces commences and if the bleeder valve is opened, compression in such spaces will commence only after the time when the thread or lobe limiting the posterior boundary of the compression space has passed the bleeder opening. 'I'his will be at a time subsequent to the normal commencement, of compression with the bleeder valve closed.

As indicated in the drawings, it is advantageous to have the bleeder valve extend, in its closed position, inwardly so that the inner end of the valve is flush with the inner surface of the casing and preferably the inner face of the valve is made to conform to the curvature of the casing. The reason for this is to avoid any large leakage space at this point, through which the air being compressed in one compression space may leak past the posterior limiting lobe, to the next succeeding space on the other side of such lobe.

The bleeder valve member 38 is provided with a stem 66 forming the armature of a solenoid 68 and is also encircled by a spring 'I0 located between the housing-and an abutment plate 12. Spring i8 tends to move the valve member to open position and this tendency is opposed by the action of the solenoid winding, which when finally energized has suflicient strength to overcome the action of the spring and maintain the valve member in the closed position shown in the drawings. Solenoid 68 is energized by current supplied through wires 'I4 and I6 from the generator mains indicated generally at I8.

The outlet 56 of the compressor 36 is connected by means of conduit to a combustion chamber 82 having a combustion space 64 surrounded by a jacket 86. Fuel such for example as oil is supplied by a pump, such as that indicated at 88, to the burner nozzles indicated at and 32. A governor 94 operated from the shaft I4 actuates a fuel control member 96 to control the amount of fuel fed to the combustion chamber under dierent conditions of load. A pressure relief valve Si connected to the discharge pipe of the pump 88 permits return of fuel oil to the supply pipe of the pump through the return pipe 33 when the control member 96 throttles or closes the passage of flow. The fuel control apparatus per se forms no part of the present invention and is diagrammatically illustrated. Any suitable apparatus for controlling the amount of fuel in y ""ase'is response` yto variationsy loadgon the system may be employed. l

The .compressor` 32, whichV is yshown with its f suctionsidein front ofthe plane of the drawings, isr connectedby means of coupling 88 to shaft |4 and -ls similar in` construction to the compressor 30 previouslyy described and need not be described in detail.` Compressor 32 has air inlet openings vat and |02 and is provided with-a bleeder'valve |04 urged toward openrposition by spring |08 and closed kby the solenoid |08, the latter being energized by currentderived` throughwires ||0 and i| 2 connected'into the electrical system'18. Theoutlet ||4 of compressor 32, which isplaced in communication with the compression ,spaces of the compressor, by means ofthe port I |3'which lies behind the plane of the paper, is connected by means of conduit ||8 to the combustion Acharnberil2.v

Insofar as air iiow is concerned, it will be seen that compressors 30-and 32 are arranged in parallel, both delivering to the outer chamber of the combustion apparatus, part of the air entering the inner chamber A84 to supply the oxygen necessary for. ,combustiony yof the fuel and through thejacket space around the ber. Motive fluid consisting of the gases from the inner chamber and inner chamcombustion the jacketing air isconducted through the 'twin pipes Hfandy the turbine I0 forexpansion in the turbine. Y s i As indicated, the generators `I8 and i8 feed into a common electrical systemV and, as is usual in cases of this kind,.operate synchronously.

With normal load on the system, the requisite yquantity of fuel is pumped to the combustion lchamber rand with the motive fluid generated therein by combustion of the fuel with the rair compressed in the compressors, the turbine gencrates the power required to operate the generators and also the power required to in addition drive the compressors.v Under such normal load conditionsgthe bleeder valves 'of the two compressors are closed Vand the compressors loperate under what maybe termedfull load compression.

When the load on, theplantchanges. the fuel supply is governed so that an increased quantity of fuel is supplied Vupon increased'load and a reduced quantity of` fuelis supplied with `decreasing load.,f',jAssuming constant normal full load, the quantity of air delivered bythe compressor remains constant. Upon rdecrease in load, the closl ing eiect exerted by the,solenoids Iwhich hold the bleeder valves closed is decreasedandthese valves,

will open to an extent governed by the degree o1' the reduction ,in the load,vso asjto openmore or lessthejbieeder openings.` Consequently, the

greater the decrease `infioad .on the plant, the greater will 'beg/th? quantity of air lwhich isgciisv chargedjthroughjtherbleederjiopenings and the smaller will,"bejthelvjquantityjoffa'ir which" is com- ".pr'essedintheicmpressrsjto ,the final pressure for delivery'gto. -the.-covrnbl'is'tion'ichamber; When the bleeder valves` are opened', the -nal pressure, vof the compressed airasjweuas the` y'qrnntity of' air `cornpressedfp'er unitofjtimew'ill be reduced,

because the ratio of vthe' volumeA oftherv compression spaces at the commencement ofl ythe com V"pression perio'df to the volume thereof at the end- [of the' compressionperiod constant. Il, aconstalnt final pressure is desired regardless of varia.- "tions" in: "load'for, if the 'final pressure'. is desired to beA variediwithj'.variations in load in la. manner other thanjthat ,e'il'ected` withthisapparatus;

this may beaccomplished by means to be herepart y owing inafter described and adapted to vary the ratio of compression space volume at the commencement and end of the compression periods.

The bleeder valve control need not necessarily be made dependent upon the electrical load on the plant but may be controlled by any other suitable factor which changes with and is indicative of changes in the value of the load.

An example oi such other control is illustrated in the plant shown in Fig. 2. In this embodiment, ythe gas turbine |0a is indicated as being of the axial ilow type connected for direct drive of a generator |22 which delivers the power output of the system. Turbine 10a also drives directly a compressor |24 similar in type to the compressors previously described except for the omission of the bleeder valve arrangement shown onl the compressor illustrated in Fig. 1. Compressor |24 is a high pressure compressor and is connected by means of a hydraulic coupling |28 of known construction to a low pressure compressor |28 which is alsooi the same screw type as that previously described. Both compressors are viewed from the presure side. Compressor |28 draws in low pressure air through inlet openings |30 and |32 and has an outlet |34 connected by means of conduit |38 to the inlet |38 of compressor |24. The latter has an outlet |40 connected by conduit |42 to a combustion chamber 82 similar in construction to that described in connection with Fig. 1. A governed fuel supply from pump 88 is supplied to the burner nozzles 90 and 82 as previously described. Motive fluid formed in the combustion chamber from the fuel which is burned with the air supplied from the compressors is expanded in the turbine to produce the power required for driving the generator and the compressors. y

The 10W pressure compressor |28 is provided with an opening 84 and a bleeder valve 60 controlling this opening, the construction being similar to that previously described with reference to Fig. 1.` In this instance however, the control of the bleeder valve is different from that previously described. In this embodiment the stem 88 of the bleeder valve is provided with a piston |35 working with a. tight t in cylinder |31 and acted on by a spring 10 tending to move the piston and bleeder valve to a position in which the bleeder passage is opened. The upperside of piston |35 is placed in communication with the compressed air conduit |42 by means of the pipe |44.

Operation oi the system is as follows. Under full load operating conditions, the bleeder valve 60 is closed, as shown in the drawings, the strength of spring '|0 being such that the spring is compressed by application of normal full load air pressure to the upper side oi piston |36. Governor |46, under the assumed full load condition, is as shown in the drawings, with the pipes |64 and |48 connected and with` the inlet end of pipe |66 closed. The working chamber of the hydraulic coupling is filled with working iiuid and the two compressors are connected so that both are operated by the turbine. If it is now assumed that the load on the generator is reduced, the fuel supply is correspondingly reduced through the action of the governor and associated control mechanism. This results in a. reduction of the temperature of the motive uid as supplied to the turbine because of the 'proportionately lower amount of fuel as compared with air supplied to the combustion chamber. The reduced temperature of the motive iluid results in a reduction in the pressure prevailing in the combustion chamber and in the pipe |42 communicating therewith. This will be easily understood from the following calculation. The quantity of motive iluid flowing through a turbine can be expressed by the equation:

F: KN/i P K- F VBT At the rst moments after reduction of the fuel supply, the amount of motive fluid flowing` through the turbine is approximately the same as before, the reduction in quantity dueto the decreased fuel supply being of negligible order as compared with the quantity of air delivered by the compressor. Thus, if P and T represent initial pressure and initial temperature respectively at normal load, and P1 and T1 represent initial pressure and initial temperature respectively shortly upon reduction of the fuel supply,

For instance, if at normal full loa'd P=80 pounds per square inch, T=l800 degrees F. absolute,

"and if the temperature due to the reduced fuel supply is decreased to T1=1600, the pressure in the combustion chamber and in the pipe |42 will immediately be reduced to P1=8 %3=75.4 pounds per square inch Due to this reduction in the pressure the bleeder valve 60 commences to openlunder the inuence f spring 10. 'Ihis openlng'or partial opening of leialeeder valve 60 permits air to flow to a greater or lesser extent through the bleeder opening 64 to atmosphere. Thus, a reduced quantity ot air, corresponding to the reduced load and the reduced fuel supply, will be compressed and supplied to the combustion chamber. Reduction of the quantity of air compressed will tend to bring the temperature of the motive fluid back to about normal value, the quantity of motive iluid producedper unit of time now being reduced as compared with full load conditions and the pressure of the motive iiuid being reduced also because of the reduced pressure at which the air is ilnally delivered from the compressor system because of the bleeding of some of the air. It will be seen that for every value of part load, there is a deilnite position of the bleeder valve 60 and consequently for each suchvalue of part load, there is a deiinite quantity of air discharged from the bleeder opening. e

As the load on the system falls below the normal load value and as a consequence the pressure in conduit |42 is reduced, the pressure acting on piston |56 of the governor will also .be reduced. This piston then commences to move toward the right, as viewed in the figure, under the influence of spring |60 and this movement is transmitted to the plungers |50 and |62. Initial movement to the right from the position shown in the gure will have no eilect on the hydraulic coupling but after the load and the pressure of the motive iluid have fallen below a predetermined value of part load, for example, idling 10aa, the plunger |50 wu close the outlet of pipe |64, and simultaneously the plunger |62 will open the inlet of pipe |66. Movement of the governor to this .position closes the connection between pump |10 and the coupling, which is instead connected through pipes |48 and |66 to the supply vessel |68 to which the working uid in the coupling will ow by gravity, in the direction indicated by the arrow |18. Draining of the working fluid from`v the hydraulic coupling renders this coupling inoperative and thev compressor |28 ceases to operate. At this time a spring loaded check valve in the air conduit |36 connecting the two compressors is opened by the suction created by the compressor |24 and air is now compressed only in this compressor.

I f the load increases from the value at which compressor |28 is rendered inoperative, the accompanying increase in the amount of fuel supsure of the motive iiuid. 'I'he increased pressure of the motive nuid acting on piston |56 of the governor moves the plunger valves of the latter to the left and when a predetermined value of load is reached, the original connections are established, that is, the pump is again connected with the hydraulic coupling and the drain pipe |68 is closed. The pump rells the coupling with working liquid and the low pressure compressor |28 is brought back into operation. Reestablished operation of the low pressure compressor produces pressure in the connecting conduit |38 and as a consequence valve |80 closes. With this valve closed, the compressors again operate in series. Further increase in load causes the bleeder valve 60 to be brought more and more nearly t'o closed position, progressively cutting down theamount of air bled from the low presmeand,whennonnalfuliloadha| liconreaelied,thepartslieasainintimpositicm f in yWhile automatic control of the bleeder valve or Valves is advantageously employed, manual control face of which is curved to form a continuation of thecylindrical inner surface of the casing. A

'space vi|| surrounding the valvecommunicates with the bleeder outlet passage 2||. A stem 2|2 is attachedto the valve and is provided with a key 2|2a working in a suitable slot in the yoke 2|| to prevent rotation oi' the bleeder valve. The vupper portion of the stem is threaded at 2|4 through the hub of a hand wheel 2||, the rotation of which on the threaded stem acts to lift the valve.

In the position of the apparatus shown. the bleeder valve is closed and compression of trapped air takes place inthe compression space 2I| between the threads or lobes 2I2 and 2 i4 of the rotor |22. Space 2 i| extends helically toward the suction side of the compressor to a point where a cooperating thread or lobe of the rotor i|4 projects into the space so as to progressively reduce its volume upon rotation of the rotors in the directions indicated. The succeeding compression space 2I4, looking in the direction of rotation of the rotor. is still in communication with the suction side and remains so until the edge 2I| of the lobe 2li reaches the left hand unitingedge nl of the bleeder opening. At this moment. compression commences in space 2I|. If the bleeder valve l|| is then opened, air may escape through the bleeder opening without its having been appreciably compressed. From the foregoing it follows that. for instancespace 2| is in communication with the bleeder valve i|| during the period from the instant the edge 2i| of the lobe 2I4 reaches the left hand limiting edge 22| of the bleeder opening to the instant the edge 2 of the lobe 2I2 reaches the. right hand limiting edge 222 of the bleeder opening.

Advantageously the bleeder opening ||2 is shaped so that communication of the compression space with the atmosphere takes place with minimum throttling losses. To this end, it is preferable to make the limiting edges 22| and 222 of the bleeder opening parallel, or approximately parallel. to the helical edge 2i| of lobe 2|2 and consequently in the same relation with respect to the corresponding edges of the remaining lobes of the rotor. With the limiting edges of the bleeder opening parallel to the outer edges of the rotor lobes, maximum speed of opening and closing of the bleeder opening with respect to the compression spaces, will be obtained.

By making the lower surface of the bleeder valve curved to conform to the curvature of the inner surface of the casing, leakage back from the compression space 2in to the space 2i| is prevented when the edge 2I| passes the bleeder 5 opening I|2 under full load operating conditions closed.

vwhen the bleeder valve is As previously mentioned, the relation ofthe variation in final compression pressure to the variation in the quantity of air compressed at part loads can be varied as desired by changing the compression ratio which is eected under different conditions of 10nd.

Apparatus for accomplishing this is shown in Figs. 4 to '1. Referring now to these comprises a casing 224 in which rotors 22| and 22| are mounted, these rotors being geared together as in the compressors previously described and being adapted to be driven by means of a power input shaft 220. In this embodiment, six lobes are shown on one rotor and seven on the other in contrast to the three lobes shown for example in Fig. 3. It will be understood that the number of lobes per rotor may be varied as desired within the scope of the present invention.

The casing 224 is provided with inlet openings 22| and 221 and an outlet 229. In this instance, it will be observed that the inlet ports in the casing provide for both radial and axial admission of air to the compression spaces and both radial and axial discharge from the compression spaces.

Casing 224 has a portion 232 which does not follow the contour of the rotors but is spaced therefrom and in the space provided between the rotors and this portion of the casing, a slide 234 is provided, the inner surface of which is formed to the same radius as the radii of the rotors. This slide is axially movable as indicated in Fig. 4, through the medium of a control rod 23| which may be either manually operated or operated gures, the compressor 'automatically in response to load variations on curved edges 24| and 248, these latter edges determining the area for radial exhaust from the compression spaces and consequently affecting the total Vexhaust area from these spaces and the discharge pressure of the compressed air.

If we now assume the slide to be moved to the extreme right hand position with edges 238 and 24| abutting respectively against

edges

242 and 244, compression will commence at the moment intended for normal full load compression. This will be at the time when the edges of the rotor lobes, which cooperate to form a given compression space, pass the limiting edges of the inlet ports.

If it is desired to decrease the quantity of air delivered by the compressor. the control member or slide 224 is moved to the left from its extreme right hand position, to a position such for example as that shown in Fig. 'I and this movement opens up

passages

254 and 256 between the end edges 22| and 240 of the slide and the respectively cooperating casing edges 242 and 244. It will be evident that with the slide moved to this position, commencement of compression in any given compression space will be delayed until the edges of the lobes deilning the posterior boundary of suchspace pass beneath the slide edges 238 and 240.

If for the moment we disregard the eiiect on the outlet opening or the movement of the slide to the left from its full load position.- it will be evident thatthe compression ratio will be altered by such movement to the left since the volume of the compression space at the moment com-l pression commences is decreased as compared with full load adjustment. while the volume of the compression space at the moment when the exhaust port opens remains constant. This terior boundary of the compression space has would result in decreased pressure at the moment of discharge from the compressor space.

Obviously however, movement of the control slide toward the left to a part load position will cause the area of the outlet opening to be decreased and, consequently, as the volume of the compression space at the instant compression commences is decreased by movement of the slide, the volume when exhaust occurs is de-' creased and the final compression volume is also decreased. It will be evident that the change in the relation of the volume of the compression space at the moment when compression commences to the volume of the compression space at the moment when exhaust or discharge commences can be varied as desired by suitably relating the contours of the edges of the slide which control the commencement of compression and the termination of compression in the various positions of the slide.

From the foregoing description of this embodiment, it will be evident that the control slide constitutes a bleeder valve for delaying the normal time of commencement of compression as compared with full load compression. By use of the slide form of bleeder valve, it is however possible, if desired, to accomplish the additional function with this single valve member of obtaining such constancy or variation in the compression ratio with change in compressor capacity as may be desired.

Fig. 8 shows a modiiication of the apparatus illustrated in Figs. 4 to 7. The construction is similar to that described above except the form of the control member or slide which in this instance is in the form'of a cylinder 250 the lower f portion of which is cut oi and connected with a member 262 the inner surface of which is formed to the same radius as the radii of the rotors. As in the example previously described, the control member is axially movable by means of a control rod 284. As will be easily understood from the drawings, the shape of the control member 260 facilitates manufacturing of the apparatus as compared with the shape of the control member according to Figs. 4 to 7.

From the foregoing description, it will be evident that many specific different forms of structure may be employed .within the scope of the invention and it is to be understood that the invention embraces all that falls within the scope of the appended claims when they are construed as broadly as is consistent with the state of the prior art.

Certain subject matter disclosed but not claimed in this application forms the claimed subject matter of my copending application Serial Number 500,010, filed August 25, 1943.

I claim:

1. A compressor of the rotary screw type including a casing having an inlet and an outlet for fluid and an end wall, a plurality of rotors mounted in said casing, each of said rotors havpassed, said opening and means for controlling iiow through said opening.

2. A compressor' of the rotary screw type including a casing having an inlet and an outlet for fluid and an end wall, a plurality of rotors, mounted in said casing, each of said rotors having spiral lobes and intervening spiral grooves of uniform height and depth respectively along their lengths, the lobes and groovesfintermeshing and cooperating with each other and with the casing to form spaces registering at different times with said inlet and said outlet and which are displaced axially of the compressor by rotation ot the rotors to come into communication with said end wall, a bleeder opening in said casing located so that compression can commence in any one of said spaces only after the rotor lobe defining a pos-. terior boundary of the compression space hasl passed said opening, said opening having opening and closing edges disposed substantially parallel to the edges of the rotor lobes passing the opening and means for controlling iiow through said opening.

3. A compressor of the rotary screw type including a casing having an inlet and an outlet for uid and an end wall, a plurality of rotors mounted in said casing, each of said rotors having spiral lobes and intervening spiral grooves of uniform height and depth respectively along their lengths, the lobes and grooves intermeshing and cooperating with each other and with the casing to form spaces registering at different times with said inlet and said outlet and which are displaced axially of the compresor by rotation of the rotors to come into communication with said end Wall, a bleeder opening in said casing for permitting escape from the compressor of fluid in said spaces, a valve for controlling'said opening, said valve having a smooth inner surface winch in closed position of the valve provides substantially a continuation of the inner surface of the casing and means for actuating said valve to open or close said opening.

4. A compressor of the rotary screw type including a easing having an inlet and an outlet for fluid and an end wall, a plurality of rotors mounted in said casing, each of said rotors having spiral lobes and intervening spiral grooves of uniform height and depth respectively along their lengths, the lobes and grooves intermeshing and cooperating with each other and with the casing to form spaces registering at diierent times with said inlet and said outletl and which are displaced axially of the compressor by rotation of the rotors to come into communication with said end wall, and means movable relative to said casing to alter the volume of the spaces at the beginning of compression therein.

5. A compressor of the rotary screw type including a casing having an inlet and an outlet for fluid and an end wall, a plurality of rotors mounted in said casing, each of said rotors having spiral lobes and intervening spiral grooves oi uniform height and depth respectively along their lengths, the lobes and grooves intermeshing and cooperating with each other and with rotary screw type in-f cluding a casing having an inlet and an outletf:l

for iluid and an end wall, a' plurality oi rotors mounted in said casing, each of said rotors having spiral lobes and intervening spiral grooves` oi uniform height and depth respectively along;

their lengths, the lobes and grooves intermeshing and cooperating with each other and with the casing to form spaces registering at different times with said inlet and said outlet and which are displaced axially oi the compressor'by rotation of the rotors with said end wall and a mounted between said casing and said rotors and cooperating with the rotors and with portions of the casing to vary, upon movement of the member. the volumesof the spaces at the commencement of compression and the volumes of the spaces at the termination of compression, the variation in said volumes due to such movement oi the member eil'ectng a change in the compression ratio of the compressor. t

7. A compressor of the rotary screw type into come into communication member movably Amencement therein at fullload. i; l 9. yIn. the operation ot l a rotary compressorof the: type-v havinga lcasing providingv an; inlet and.

ankoutlet:forr ilu id,,a 4 plurality of rotors mounted ,Y

speed.v oit- .koperation thereof; comprising5a bleeder valve member movable tovent said spaces until their kplume is less'than thevolumeatthefmoment oi commencement of vfull load compression, l

whereby to-delay thegcommencement of compressiony injsuchspaces ,as compared with for rotation in said casinssmehrof said krotors Ahaving Ispiral lobes and intervening-spiral grooves,yv r of uniformi heighty and. Adepth respectively along l thelfylenths, the lobes and grooves intermeshl ing and cooperatingwitheach other and with the casing tol formspacesregisteringgatE ditlerent timeswith saidixiletandvsaid outlet and'which arex displaced axially ,of the compressor upon rotation of the-rotors so asttocoxne into communication with an en d wall of .theA casingl to eiIect compression, that improvement which consists in vvarying thecapacityoi the compressor while maintaining substantiallyconstant speed of operation thereof by altering y,the `eilective initialvolume for compression of said spaces.

10. `In the operation of, a rotary *compressor of the typehaving a Casing providing kan inlet and e an outlet for iluid, apluralityof rotors mounted cluding a casing having an inlet and an outlet for l spiral grooves of for rotation insaidl casing, each of said rotors having spiral lobes and intervening spiral grooves of kuniform height and depth respectively along their lengtha'the lobes and grooves intermeshing and 'cooperating lwith* eachother and with the casing toiorm lspaces registering at Adifferent times with said' inlet and said` outlet and which are displaced axiallyfof the compressor upon yro- 40 tation of the rotors so as tc come into communiand cooperating with each other and with the casing to form spaces registering at diilerent times with said inlet and said outlet and which are displaced axially of the compressor` by rotation of the rotors to come into :communication with said end wall to compress and discharge uid adjacent said end wall, an axially slidable member interposed betweeny said rotors and a portion of said casing, said member having an end arranged to move awayirom cooperating portions of the casing to provide passage for n escape oi' fluid from the spaces upon movement of said member toward thedischarge end ofthe compressor, whereby to delay commencement o1'l the compression period, and said member having an opposite end portion vfor reducing the area kof the outlet opening of the compressor upon movement of the member toward the discharge end of the compressor, and means operable from the exterior of the compressor yfor adjusting lthe position of said member. v Y v v 8. A compressor of the rotary screw type including a casing having ,anl inlet and an outletv for fluid and an end wall, a plurality oi' rotorsv mounted in said casing, each of said rotors having spiral lobes land intervening spiral groovesv of uniform heightanddepth respectively along,

their lengths, the lobes and grooves intermeshing and cooperating .with each othervand with the casing to iormyspacesfrregistering at dlilerent times with said inlet and said outlet and which are displacedariallyoi thecompressorxby rotacation kwith an end wall of fthe casing to effect ume by'decreasing the eiectviveiinal compression ,volume loi.' said spaces.,

1l. A compresor of. the rotary screw `type including 4a casinghavingan'A inlet and an 4outlet i'or iluld'and anv end Wall,l a plurality of, rotors mounted insaidcasing, each of said rotors having vspiral: lobes and intervening spiral lgrooves y of uniformheightand depthrespectively along their lengths, the' lobes` `and grooves intermeshingand cooperating with each other and with the,

casingto'forml spaces registering at different times with saidinlet andv said outlet andwhich are vdisplaced axially, of the compressor by rotation'of lthe rotors` to come into communication with said'end wall,,and meansincluding a bleeder valve 'member 'adjustable to cause initiation of partl loadycompression in any given compression 'space .'with said rotors v in any. different angular positions of rotation.

12. Acompressor of the rotary screwA type including a casinghavingnninletand an outlet for ijluid endwall,\a `plurality-of rotors mounted in said casing-,.each of ,said -rotors have ingfspirallobes and intervening spiralgrooves f of uniformheight and-depth respectively alongk theirlengths, the lobeaand; grooves intermeshing: Y v

and `cooperating;witheach otherandwith the withV said endywall,` andfmeans ,fori varyingthe capacity ofthe compressor.A without 'changinggthe ,thek com- 4.

oneof a seriesoi y.

casing to form spaces registering at different times with said inlet and said outlet and which tion of the rotors with respect to both the initiation and the termination of compression in any given one of said spaces.

` 13. A compressor of the rotary screw having a casing providing an inlet and an outlet for iiuid, a plurality of rotors moimted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at dinerent times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with vsaid outlet, a bleeder opening in said casing located so that compression can commence in any v .one of said spaces only after the rotor lobe dellning a posterior boundary of the compression space has passed said opening and means for cona about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the interstantially a continuation of the inner surface4 of Ythe casing and means forb actuating said valve to open or close said opening.

16. A compressor of the rotary screw type having a casing providing an inlet and an outlet for fluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, and means movable relative to said casing to alter the volume of the spaces at the beginning of compression therein.

17. A compressor of the rotary screw type having a casing providing an inlet and an outlet for iluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces meshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, a bleeder opening in said casing located so that compression can commence in any one of said spaces only after the rotor lobe defining a posterior boundary of the compression space has passed said opening, said opening having opening and closing edges disposed substantially parallel to the edges of the rotor lobes passing the opening and means for controlling ow through said opentering at different times with said inlet and said outlet and being decreased ln volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, a bleeder opening in said casing for permitting escape from the compressor of Vduid in said spaces, a valve for controlling said opening, said valve having a smooth inner surface which in closed position of the valve provides subregistering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, and means movable relative to said casing for altering the volume of the spaces at the commencement of compression therein and simultaneously altering the volume of the compression spaces at the termination of compression therein.

18. A compressor of the rotary screw type having a casing providing an inlet and an outlet for uid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors.

after passing out of communication with said inlet and before coming into communication with said outlet, and a member movably mounted between said casing and said rotors and cooperating with the rotors and with portions of the casing to vary, upon movement of the member, the volumes of the spaces at the commencement of compression and the' volumes of the spaces at the termination of compression, the variation in said volumes due to such movement of the member efv fecting a change in the compression ratio of the compressor.

lengths and cooperating with each other and with the casing to form compression spaces registering at different timeswith said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, an axially slidable member interposed between said rotors and a portion of said casing, said member having an end arranged to move away from cooperating portions of the casing to provide passage' for escape of fluid from the spaces upon movement of said member toward said outlet whereby to delay commencement of the compression period and said member having an opposite end portion for reducing the area of the outlet opening of the compressor upon movement of the member toward the outlet, and means operable from the exterior of the compressor for adjusting the position of said member.

20. A compressor of the rotary screw type having a casing providing an inlet and an outlet for fluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively,`the interrneshing lobes and grooves being of substantially unifonn height and depth respectively along their length and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, and means for varying the capacity of the compressor without changing the speed of operation thereof comprising a bleeder valve member movable to vent said spaces until their volume is less than the volume at the moment of commencement of full load compression, whereby to delay the commencement of compression in such spaces as compared with the commencement therein at full load.

21. In the operation of a rotary compressor of the type having a casing providing an inlet and an outlet for fluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at diiTerent times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes oi'A said rotor after passing out of communication with said inlet and before coming into communication with said outlet to effect compression, that improvement which consists in varying the capacity of the compressor while maintaining substantially constant speed of operation thereof by altering the eiIective initial volume for compression of said spaces.

22. In the operation of a rotary compressor of the type having a casing providing an inlet and an outlet for fluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at diierent times With said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet to effect compression, that improvement which consists in reducing the capacity of the compressor while maintaining substantially constant speed of operation by decreasing the effective initial volume for compression of said spaces, and modifying the decrease in delivery pressure which would result from such decrease in effective initial volume by decreasing the effective final compression volume of said spaces.

23. A compressor of the rotary screw type having a casing providing an inlet and an outlet for i'luid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, and means including a bleeder valve member adjustable to cause initiation of part load compression in any given compression space with said rotors in any one of a series of different angular positions of rotation.

24. A compressor of the rotary screw type having a casing providing an inlet and an outlet for fluid, a plurality of rotors mounted for rotation about parallel axes in said casing including a male rotor and a female rotor having intermeshing spiral lobes and grooves respectively, the intermeshing lobes and grooves being of substantially uniform height and depth respectively along their lengths and cooperating with each other and with the casing to form compression spaces registering at different times with said inlet and said outlet and being decreased in volume by contraction in a direction parallel to the axes of said rotors after passing out of communication with said inlet and before coming into communication with said outlet, and control means having adjustable portions cooperating with said rotors to vary the relation of the angular position of rotation of the rotors with respect to both the initiation and the termination of compression in any given one of said spaces.

ALF LYSHOLM.