CA2161907A1 - Valve system for capacity control of a screw compressor and method of manufacturing such valves - Google Patents

Abstract

A lift valve communicating with a compression chamber of a variable capacity screw compressor is set forth including a valve housing, a piston reciprocally received within the valve housing, a shaft having a first end connected to the piston and a second end extending from the housing. The valve further includes a valve element connected to the second end of the shaft having a valve surface exposed to the compression chamber and a reciprocation mechanism for reciprocating the piston within the housing. The reciprocation mechanism includes a first pressure passage communicating with the housing adjacent a side of the piston, and a second pressure passage commllnicating with the housing adjacent and opposed side of the piston, wherein the valve surface is positively displaced toward and away from the compression chamber of the variable capacity screw compressor in response to the application of fluid pressure to at least one of the first and second pressure passages to vary the capacity of the screw compressor. Further, the lift valve is manufactured integral with the manufacturing of the compression chamber of the variable capacity screw compressor. This manufacturing process includes securing at least one lift valve to a housing of the variable capacity screw compressor in an operating position. Once secured to the housing, the shaft and consequently the valve element is fully extended from the valve housing and maintained in such position thus simultaneously machining an inner surface of the compression chamber and the valve surface such that the valve surface forms a continuation of the inner wall of the compression chamber when the variable capacity screw compressor is operating at full capacity.

Description

21~1907 VALVE SYSTEM FOR CAPACI~Y CONTROL OF A
SCREW COMPRESSQR AND METHOD OF
MANUFACTURING SUCH VALVES
TF.CH~ICAT FIF.T .n OF THF I~VFl~TION
The present invention relates to a valve system for controlling the capacity of a screw compressor. Particularly, the present invention is directed to double acting lift valves for controlling the capacity of a screw compressor as well as the m~n~lf~l-tllre of such double acting lift valves.

BA('T~GROUNn OF THF INVF~TION
Rotary screw co.l.~.essors of the type set forth herein comprise two rotors mounted in a working space which is limited by two end walls and a barrel wall ~ on~ing therebetween. The barrel wall nec~ss~rily takes the shape of two intersecting cylinders, each housing one of the rotors. Each rotor is provided with helically ~rtent~ing lobes and grooves which are interm~ch~.l to form chevron shaped compression chambers. In these chambers, a gaseous fluid is displaced and colllp.~ssed from an inlet ~h~nn~l to an outlet rh~nn~l by way of the screw compressor. Each compression chamber during a filling phase commllnic~tes with the inlet, during a compression phase undergoes a continllecl reduction in volume and during a discharge phase commlmic Ites with an outlet. A rotary screw compressor of this type is disclosed in U.S. Patent No. 4,435,139.
Rotary screw compressors of this kind are often provided with valves for regulating the built-in volume ratio for the capacity of the co..l~r~ssor. When continuous regulation is required, slide valves are often used, however, as with other regulation needs, it is sllfficif~nt to use lift valves.i Such lift valves are mounted in the barrel wall of the compressor C~WPWIN60\QUINCY\PAT APPL\126 _ 94 APP
9-26 95 (1:49pm 1 or may be mounted in one of the end walls and in this regard, normally in the high pressure end wall.
Several solutions for controlling the capacity of screw con~lessors operaf~ing at a constant number of rotations have been proposed. One such solution is disclosed in U.S. Patent No. 5,108,269 issued April 28, 1992.
This solution provides radially positioned valves in the side wall of the barrel with the valves being opened so as to commllni~te the particular co~ ssion chamber with either the inlet or outlet manifold. However, as will be rliccl~sse~l in greater detail hereinbelow, with such valves, colll~resslon losses due to leakage clearance valve and between the valves and the rotors are experienced to the extent that full capacity cannot be realized.
Of the above noted solutions, the use of conventional slide type valves which conctif~lte a portion of the barrel of the compressor has the advantage of providing a wide control range and the possibility that at a constant working ples~ule ratio in the compressor a relatively constant built in pres~ure ratio within the greater part of the control range can be brought about by means of a suitable tlim~nci~ning of the axial discharge port. The main disadvantage of slide valves is that they are expensive to m~nllf~lre in that close tolerances and accurate centering are required.
Further, the a~ting system which is normally a hydraulic system is also relatively expensive and complicated.
Another solution is to use a rotary type valve wherein the valves are in commllnic~fi~n with slots formed in the barrel through which gas is recirculated to suction to create at partial loads. This valve arrangement has the adv~ age of being less expensive to m~nllf~lre than collvelltional slide valve types, however, the capacity control is not as accurate as with C:~WPWIN60\QUINCY\PAT_APPL\126_9~ APP
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slide valve arrangem~nts. Further, built-in pressure ratio drops with decreasing loads are experienced. Moreover~leakage is obtained across the slots along the rotor bores, particularly at higher loads and at full loads.
This shortcoming will be described in greater detail hereinbelow with respect to Figure 7b. Accordingly, it has been determined that the use of lift valves achieves an economic balance between the need for accurate capacity control as well.as the need for minimi7ing m~nllf~lring costs and operating costs. Lift valves of this type have been known and permit succ.qccive co~llpression nodes within the barrel to commllnic~te with one another, thus, effectively re~ ing the capacity of the compressor. One such valve is disclosed in U.S. Patent No. 4,453,900 issued June 12, 1984.
Further, such valves may commllnic~te an o~/~,lying co~"plession node with a recirculation passage which returns pressurized fluid to the suction side of the compressor. However, it is noted that the opening of the lift valve is directly dependent upon the co",pl~sjion spring as well as the internal pres~lre of the co",pr~or. However, the a~l~tion of such valves is unreliable due to friction, corrosion and other environmPnt~l factors which often degradate the positioning of this type of lift valve. Further, while the face of the valve element takes on the approxim~te shape of the barrel, the valve element is separately formed by casting or other process within predetermined tolerances. In order to economically m~nllf~lre such valve ~lPm~ntc, the tolerances must be some what relaxed which may result in the leakage of pressurized fluid between compression chambers thereby degrading the Pffi~i~ncy of the compressor.
Clearly there is a need for an accurately controlled and inexpensively m~nllf~ red valve system for controlling the capacity of a oil flooded rotary screw type compressor. Such a valve system to include C\WPWlN60~eU~Y\PAT_~PPL\1~6 9~APP
9.~95 (1:~9p~

~ ~161907 a plurality of serially positioned lift valves which may be readily m~nllf~lred within a _ero tolerance, with each when opened re~nrin~ the capacity of the compressor a predetermined amount.

SUMl\lA~Y OF THF. INVF.NTION
A primary object of the present invention is to overcome the aforementioned shortcomings associated with known valve systems.
Another object of the present invention is to provide a series of lift valves for effectively controlling the capacity of a screw compressor.
Yet another object of the present invention is to provide a series of double acting lift valves for accurately controlling the position of the lift valve and thus the capacity of a screw compressor.
A further object of the present invention is to ensure reliable operation of the double acting lift valves by providing a two way shaft seal about an exposed end of the valve for prc:vell~ing leakage from the valve and oil leakage into such valve.
An even further object of the present invention is to provide a series of lift valves wherein operating losses due to leakage about the valve are minimi7P~l while assembly costs are reduced.
A further object of the present invention is to provide a series of double acting lift valves for controlling the capacity of a screw compressor wherein a surface of each valve which is exposed to a compression ~h~mhPr of the screw co,llpressor forms an effective confin~l~tion of a surface of the compression chamber of the screw compressor.
Yet another object of the present invention is to m~rhine the 2~ surface of each valve .simlllt~nf~ously with the m~rhining of the surface of C:~WPWIN60\QI~ICY\PAT_APPL\1~6_9~PP
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~` 2161907 the compression chamber of the screw compressor in order to reduce m~mlf~llring cost as well as operating losses.
A further object of the present invention is to positively and accurately axially position the surface of each valve during the m~rhining of the surface of the operating chamber of the screw compressor.
An even further object of the present invention is to m~int~in the radial positioning of the surface of each valve during the m~rhining of the surface of the col~lpl~ssion chamber as well as during the operation of the screw colnplessor.
Yet another object of the present invention is to provide a series of lift valves wherein each lift valve housing is a single cast unit thereby minimi7ing leakages associated with related valves and reducing assembly costs.
These as well as additional objects of the present invention are achieved by providing a series of lift valves commlmicating with a compression chamber of a variable capacity screw compressor with each valve including a valve housing, a piston reciprocally received within the valve housing, a shaft having a first end conntqcted to the piston and a second end exten~ing from the housing. Each valve further includes a valve element: conn~cte~l to the second end of the shaft having a valve surface exposed to the compression chamber and a reciprocation mech~ni.cm for reciprocating the piston within the housing. The reciprocation m~h~ni~m including a first pl~s~ure passage commllnic~ting with the housing ~jacPn~ a first side of the piston, and a second pressure passage commllnic~ting with the housing ~ nt an opposed side of the piston, wherein the valve surface is positively displaced toward and away from the compression chamber of the variable capacity screw compressor C\WPWIN60\QU~CY\PAT_APPL\126_9~ PP
9-26-95 (1:~9pm) ` 2~ n7 in response to the application of fluid pressure to at least one of the first and second pressure passages to vary the capacity of the screw compressor.
Additionally, the lift valve is manufactured integral with the m~nllf~lring of the colllplession chamber of the variable capacity screw S coll~plessor. This m~mlf~lring process in~ cles securing at least one lift valve to a barrel portion of the variablè capacity screw compressor in an operating position. As mentioned above, the lift valve in~hlcles a valve housing, a shaft t ~tPn~ling from and reciprocally received within the valve housing and a valve surface of a valve element secured to a remote end of the shaft. Once secured to the housing, the shaft and consequently the valve element is fully ~ en~le~ from the valve housing. The process further indudes m~int~ining the shaft in the fully ~ n(~ecl position, and .simlllt~neously m~hining an inner surface of the colll~ression chamber and the valve surface such that the valve surface forms a co. .~ tion of the inner wall of the con~l~ssion chamber when the variable capacity screw coln~lcssor is operating at full capacity. In this m~nner, zero tolerance is evidenced between the valve structure and the surface of the conlL)lession chamber.
These as well as additional advantages of the present invention will become apparent from the following det~ cl description of the invention when read in light of the several figures.

Rl~TF.F nF..C,CRIpTION OF THF. nR~WINGS
Figure 1 is a diagr~mm~tic view of the screw type compressor and supporting controls to which the present invention may be readily adapted;
Figure 2 is a perspective view of a partially cut away screw colll~res~or incorporating valves in accordance with the present invention;

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~` 21619~

Figure 3 is a block schematic view of the overall operation of the screw compressor in accordance with the present invention;
Figure 4 is a perspective view of a screw compressor housing incorporating the present invention;
Figure 5 is an elevational view of the lift valve in accordance with the present invention;
Figure 6 is a cross-sectional view of a lift valve in accordance with the present invention;
Figure 7A is a cross-sectional view of the lift valve in accordance with the present invention in operation in the screw compressor housing;
Figure 7B is a cross-sectional view of a prior art spiral or turn valve in operation in the screw compressor housing, and Figure 7C is a cross-sectional view of a prior art lift valve in operation in the screw compressor housing.

nFTATT F~n nF.~C~TT~TION OF THF. p~F.F_~T~ED
F.l\/~ROm~F.l~TS
- - - The present invention relates to improved lift valves and improved methods for m~nl~f~t~lring such lift valves for rotary screw compressors.
Figure 1 is a diagr~mm~tic-, view showing the compressor system 100 to which the present invention may be readily adapted. Compressor system 100 preferably includes an improved oil-flooded rotary screw compressor 102 and an electronic control system 104. In the preferred embodiment of the invention, the colllp~ or 102 as well as the several capacity reduction lift valves 322 (only one illustrated) are controlled in accordance with the electronic control system described in co-pending U.S. Patent C\WP~160\QUINCY\PAT_APPL\126 9~ APP
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~ 2161907 Application Serial No. 08/346,251 çntitl~od "System And Methods For Controlling Rotary Screw Compressors," n~ming Steven D. Centers and Paul Burrell as inventors, filed November 23, 1994 and ~ccigne~l to the same ~C~1gn~e as thls appllcatlon.
S This related co-pending application is hereby incorporated in thepresent ~icclosllre by reference, and conct~ tes the primary source of det~ l disdosure of the electronic control system. However, those features of the control system that are most relevant to the operation of the present invention will be described briefly in enough detail to f~ te use of the ;llVt~ .iV~ capacity redllctic.n lift valves. Rrr~l . ;.-g again to Figure 1, compressor 102 is powered by an electric motor 214. Electronic control system 104 includes control housing 236 (cont~ining the main electronic control components of the system), and relay housing 106 cont~ining relays and ~wi~hgear for the system. Air end 314 of con~lessor 102 is conn~ctecl to a air/lubricant reselvoir 312, which provides air to service air output 346.
As referred to hereinabove, compressor 102 is provided with four capacity reduction lift valves. When a~l~te~, each of these valves acts to effectively bypass a part of the compressor screw, re.l~lcing the capacity colllpre~sor 102 by ~rox;m~tely 12.5%. Thus, by opening one valve, a 12.5% reduction in output capacity is obtained, and by opening all four valves, capacity of the compressor is reduced by 50%. Intermediate levels of capacity of reduction, such as 25% and 37.5%, are similarly obtained by opening from one to four of the capacity reduction valves. For clarity, only one capacity reduction valve, valve 322, is shown in Figure 1. Each of the capacity reduction valves is a positive double acting air operated valve, and each is controlled by a four way solenoid valve in response to C.\WPW~160\QUINCY~PAT_APPL\126_94 APP
926-95 (1:~9pr~

~ 2161907 signals from the electronic control system 104. The four way solenoid valves for controlling the four capacity reduction lift valves are ~ecign~te~l in the drawing as SVl, SV2,SV3, and SV4.
Compressor 102 has an inlet valve 336 controllable to vary the amount of inlet air supplied to compressor 102. When inlet valve 336is closed, no air is provided to co~nplessor 102,so co~plessor 102 is "unloaded" and runs freely with minim~l compression load. When inlet valve 336is fully open, the co,l,pressor is "loaded" or provided with input air. Inlet valve 336 can also be controlled to open partially in a "mo~ ted" operating mode, so that compressor 102 is only partially loaded. The operation of inlet valve 336is controlled by solenoid valves SV5 and SV7 which respond to signals from electronic control system 104.
Valve SV5, when activated, closes inlet valve 336 and unloads compressor 102. Valve SV7, when activated, partially closes inlet valve 336so that compressor 102 is only partially loaded. Valve SV7is conn~ç~erl to a proportional regulator. Thus, when activated, valve SV7 provides closing pressure through the proportional regulator to inlet valve 336 that varies with the pressure in reservoir 312. As system pressure is increased, the amount of closure of inlet valve 336 upon activation of valve SV7is also increased. Electronic control system 106is also connecte~l to blowdown valve SV6 which can be activated to release pressure from the system when unloaded and at shutdown.
Referring now to Figure 2, the compressor 102 will now be described in greater detail. Spe~ific~lly, the compressor 102 is a constant velocity oil flooded rotary screw type compressor which is driven by an electric drive motor 214 which drives the main shaft 6 which is supported by bearing assembles 8 and 10 which are housed in bearing housings 12 and C~WPWIN60\QVINCY\PAT_APPL\126 94APP
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14 respectively. Positioned at the end of the main shaft 6 is a positive displ~c~mt?nt lubricant pump 16 for providing ~ffi~iPnt lubricant injection under all operating conditions. Secured to the main shaft 6 is a first rotor 18 while secured to a second rotary shaft (not shown) mounted parallel to S shaft 6 inclllclec a second rotor 20. The second shaft is similarly mounted in bearing housing 22. As rli~ 55e~1 hereinabove, the screw type co~ r~ssor includes an inlet valve 336 which controllably moves between a dosed position as illustrated in Figure 2 and a fully opened position when the screw co~ r~sor is operating at full capacity. Further, when the screw co---~r~or is ope~ g at less than full capacity, the inlet valve 336 may be positioned somewhere between a fully opened and fully closed position or osrill~t~l between such positions as described in the above-noted co-pending application.
As ~icc~lsse~l hereinabove, lift valves 322, 324, 326 and 328 commtlni~te with the con~L,lession chamber 24 formed within the barrel 26 of the co...~l~sor 102. As illus~ ed in Figure 2, a bore 28 is provided in the barrel 26 which may selectively provide communication between compression nodes and consequently reduces the capacity of the compressor 102. Alternatively, bore 28 may commllnir~te with passage 29 in the barrel housing for returning pressurized fluid to the suction side of the compressor. As liccllssetl hereinabove, when in the open condition, each of these valves act to ~rfe~;tiv~ly by-pass a part of the compressor screw and thus reduce the capacity of the co~.pl-essor by a~pl.~x;m~tely 12.5%.
Accordingly, by opening all four valves, the capacity of the compressor is reduced by 50%. k is the structure and process of m~n~lf~lring the lift valves 322, 324, 326 and 328 which conctit~lte the essence of the present C:\WPWIN60~QU~CY\PAT_APPL\126 94~PP
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~ 2161907 invention. Accordingly, these valves will be liccllcce~l in greater detail hereinbelow. -- -Figure 3 is a block s~h. m~ti~ diagl~l. of air control line connections and air control eqnirn~nt in accordance a plcfe~led embodiment of the invention. Again, this control system is ~liccllcced in detail in the above-noted co-pending application and will be only briefly ~iccllcsecl herein.
The air control equipment includes a control panel 302 having a pressure switch 304, an air filter in-~i~tor switch 306, a line pl~SUl~ tr~nccll~cPr 308,and a l~ic.voir pressure tr~nc~lucPr 310. Separator sc~veilges 311 of reservoir 312 are conn~cte~l to air end low pr~ss.ll~ point 314 of compressor 102 through line filter orifices 316, sight gauges 318, and line f~ters 320.
The four way solenoid valves SV1 through SV4 are conn~c,ted to control lift valves 322, 324, 326, and 328 respe~iv~ly. Valves SV1 through SV4 are preferably four-way positive action solenoid valves. An air supply input for valves SV1 through SV4 is conn~cte-l to a pressurized air outlet of reservoir 312 by way of pressure regulator 330 and automatic inline filter 332. Pl~ur~ regulator 330 may be omitted if the col~lpressor system 100 will not be operated above 125 psi full load pressure. Valves SV1 through SV4 can also be connfcte-l by two lines to low pressure point 333 below air f~ter 334, on inlet valve 336 which is inct~llP~l on the air intake port of col~lessor 102. These two lines provide ~h~llst ports for valves SV1 through SV4, for each direction of stroke of the valves.
The provision of double action lift valves 322, 324, 326, and 328 rather than single action lift valves provides a significant advantage in the context of co~plessor system 100. This feature will be described in greater detail hereinbelow.

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~ 21619Q7 A l~se~ v~ir air output 337 is connPcted to reservoir 312 to carry the compressed air output of the compressor-to the customer's service air piping system, and thus to the equipment operating on the compressed air generated by compressor system 100. Air output 337 is connPcted through an after cooler 339 to a mi~ n~ pressure check valve 341, the output of which is conn~ed to the ctlstomPr's service air piping system at service air output 346. Reservoir air output 337 is also connPcted to a solenoid operated blowdown valve SV6 which is connected to a muffler 343. When blowdown valve SV6 is ~ ted, air plessule in resel voir 312 is released to the environment through muffler 343.
The pressurized air outlet of reservoir 312 is connected by an air line to r~e. v~ir ples~ule tr~ncdtlcPr 310, and a mP~h~ni~l pressure gauge 338 is connecte~ to the same line next to reservoir 312. Similarly, a ples~ul;~ed air output of ræse,voir 312 is collnPcted to an input of automatic line filter 340. The output of automatic line filter 340 is connected to one air input side of shuttle valve 342 and to the input of pressure regulator 344. The output of pressure regulator 344 is connecte-l to a non-common connPc~iorl of three-way solenoid valve SV7. The other air input side of shuttle valve 342 is connected to the customer's service air at service air output 346 of colllples~or system 100.
The output of shuttle valve 342 is connPcted to pressure switch 304 and to a non-cornmon connection of three-way solenoid valve SV5. The common connection of three-way solenoid valve SV5 is connPcted to one air input side of shuttle valve 350. The other air input side of shuttle valve 350 is connected to the common connection of three-way solenoid valve SV7. The rPm~ining non~ommon cormection of each of three-way solenoid valves SV5 and SV7 is open for P~hallct The output of shuttle C\WPWlN60\QUlNCY'\PAT APPL\126 _ 9~. APP
9-26 95 (1:~9pm) valve 350 is connPcte~ by an air pipe to the input of gauge/pressure regulator 354. The output of gauge/~res~ule regulator 354 is connPctefl to the inlet valve 336 control side.
These particular air collnPction configurations and the use of three-S way valves SV5 and SV7 are signific~nt because they allow inlet valve 336 to receive operating air pl~s.lr~ more quickly during startup, so that inlet valve 336 can be imme~ tPly closed to provide an unloaded startup of compressor 102. At startup, there is no pressure in reservoir 312. There may, however, be pl~ule in the customer's service air line, due to stored pres~ure in an external reservoir and/or because other compressors are lu~ling to pres~ul;ze the service air line. k has been determined that when service air pressure is available, it is advantageous to make use of this pressure for startup control during the period before reservoir 312 is ples~url~ed.
At startup, the existence of pressure in the service air line and the lack of pless~lle in resel voir 312 will bias shuttle valve 342 to connect the service air line to three-way solenoid valve SV5. Three-way solenoid valve SV5 is then a~l~tP I to transmit the service air pressure to shuttle valve 350, while three-way solenoid valve SV7 is controlled to connect its common connection to the P~rh~llst end. The service air pressure biases shuttle valve 350 to connect the service air pressure to control inlet valve 336. Valve SV5 is then ~ tPd, which will unload colllpressor 102 prior to starting motor 214. In this way, compl-essor system 100 can be started without any loading, minimi7ing startup power usage and transient currents. When sufficient pressure is available in reservoir 312, air from reservoir 312 is provided to bias shuttle valve 342 toward three-way C\~1VPW~60\QVINCY\P~T APPL\126 9~APP
9-26-95 (1:~9pn~ -- --2161~07 solenoid valve SV5, allowing tran~mi~ion of the reservoir air to the inlet valve 336 control side. ~-Referring now to Figure 4, the barrel portion 26 of the screw col,lpr~sor housing is illu~ ed in detail. The barrel portion 26 is formed by casting and subsequently m~hinP~l to receive the respective rotors. The barrel wall nPcec~rily takes the shape of two intersecting cylinders, each housing one of the rotors 18 and 20. As licc~cs~l hereinabove with respect to Figure 2, lift valves 322, 324, 326 and 328 of which only lift valve 322 is illustrated commlmic~te with the coll.pression chamber 24 within the barrel 26 by way of bores 28. The double acting lift valve 322 includes a mounting flange 323 which permits the double acting lift valve 322 to be secured to the barrel 26 by way of bolts 325 (one of which is shown). In order to assure proper ~lignment of the lift valve with the barrel 26, opposed bolt holes 321 in flange 323 as well as the barrel 26 are staggered.
By doing so, the lift valve can only be mounted in one orient~tiQn. Also provided is a gasket 327 for providing a seal between the barrel 26 and mounting flange 323. The rPmaining lift valves 324, 326 and 328 are similarly mounted tc~ the barrel 26 in this manner.
In accordanoe with the present invention and in order to form a more effiçient screw compressor, each of the double action lift valves are secured to the barrel 26 in a manner ~ secl with respect to Figure 4 and ma~hinerl along with the m~hinin~ of the surface 25 of colllplession chamber 24 within the barrel 26. Referring to each of Figures 5, 6 and 7a, it can be noted that the surface 402 which is exposed within the colll~lession chamber 24 of the barrel 26 takes on a concave shape due to its m~hining along with the ma~hining of the colllpl~sion chamber 24 of the barrel 26.

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, ~ 2l~l9~7 Referring to Figure 5, the double action lift valve 322 includes a housing 410 which accommodates a piston (not shown~ and piston stem 412. Formed integral with the piston stem 412 is a valve PkPm-pnt 414 which includes the concave surface 402. Additionally, a flange 416 is S provided for positioning the valve against the barrel 26 when the valve is in the fully P'xtPn~PCl position as illu~ ed in Figure 7a. Again, the double action lift valve includes a mounting flange 323 which is cast with the housing 410 for securing the valve in place. In order to seal both pressuriæd air within the housing 410 as well as sealing out any oil which may leak past the flange 416, a two-way shaft seal 418 is secured to an end of the housing 410. Thè inner details of the lift valve 322 will now be ~liccllc5e~ in greater detail with respect to Figures 6.
As can be seen from Figure 6, the piston stem 412 is integrally formed with a piston member 411 which is reciprocally received within the housing 410. The piston stem 412 and piston member 411 may also be separate units secured to one another in any known m~nnPr. Further, it should be noted that the housing 410 is in the form of a one-piece cylinder c~cting With previous lift valves, the valve casing or housing 410 is formed from multiple sections which are secured to one another using sealing gaskets and the bolts. However, it has been determined by casting a single piece housing, not only are previous leakage points Plimin~te-~ the assembly time for assembling the lift valve is also reclllcP-I Further, with the one-piece construction, the flange 323 as well as bolt holes 321 can be so oriented that the lift valve 322 can only be mounted on the barrel in a single orientation thereby Plimin~ting incorrect inct~ tion of the lift valves if such valves are removed for shipping or service as referred to hereinabove. Again, it is critical that the lift valves be inct~llPcl in the C:\WPW~60\QUlNCY\Pl~T_APPL\126_9~ APP
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orientation in which they are initially m~m1f~ red such that the concave surface for 402 is properly oriented within the co~ ss;on chamber 324.
Additionally, in order to assure that the piston 411 and piston stem 412 do not change orientations with respect to the housing 410 after m~mlfa~1ring, a square pin 414 is received within a square hole 416 formed in the piston 411. In doing so, the square pin 414 will prohibit any rotation of the piston 411 with respect to the housing 410. While the particular embodiment illustrated in Figure 6 includes the square pin 414 and square hole 416, any m~h~ni~m for m~int~ining the oriPnt~tio~ of the piston 411 with respect to the housing 410 may be lltili7P~l The primary concern is to assure the proper orientation of the concave surface 402 within the compression chamber 324. Such an orient~tion may be m~int~inP(l by any acceptable means.
When the lift valve 322 is assembled, two pressure chambers are formed, one being pr~ule chamber 418 between the end of the housing 410 and the piston 411 the other being a second pressure chamber 426 formed between the piston member 411 and the two-way shaft seal 418.
Again, as described hereinabove, the two-way shaft seal 418 is provided in order to seal in both directions, that is the two-way shaft seal 418 seals in pressurized air within the pressure chamber 426 and seals out any oil external to the valve.
As rlicct~sce~3 hereinabove, each of the lift valves 322,324,326 and 328 are ~ tecl and de-ac~l~te~l by way of four-way solenoid valves SV1, SV2, SV3 and SV4 respe~iv~ly. That is, in order to manipulate the piston 411 within the housing 410, ples~uliæd air may be provided to either one of pressure chambers 424 or 426 while the other of the pressure chambers are P~rh~llcte~l That is, in order to force the valve elPmPnt 414 into the G\WPWIN60~QUINCY~PAT_APPL\126_9~, APP
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fully e~rtPn~led dosed position, pressurized air is provided to the pressure chamber 424 through passage 425 while- the pressure chamber 426 is Pxh~llste-l through passage 427. It should be noted that both passages 425 and 427 are positioned in a lower portion of the valve housing 410. This assures that conclenc~tion will be properly drained from the chamber 424 and 426 respectively. Likewise, should it be desired to operate the screw colllpressor at less than full capacity, pressurized air is supplied to the pl~ule chamber 426 through passage 427 of one or more of the lift valves while the pressure chamber 424 is P~rhallstec3 through passage 425 in order to reciprocate the piston 411 and consequently the valve PlPmpnt 414 to an open position. As ~iicMlssecl hereinabove, four way solenoid valves SVl, SV2, SV3 and SV4 are controlled to selectively ~resiul;ze and P~hal~st pressure chambers 424 and 426 in response to a ~Pm~n~ plaoed on the colllplessor system. In order to isolate the pl~S~iule chambers 424 and 426 from one another, piston 411 is provided with seals 428 and 430. Also, seal 432 is provided in the two-way shaft seal which is secured to an open end of the housing 410.
As ~iicM~sse(l hereinabove, the surfaoe of the valve PlPment 414 is ma~hinPd integral with the n~hining of the surfaoe 25 of the colll~ ;on chamber 24 of the barrel 26. That is, during the final mat hining of the ~. . .pr~or chamber side walls 25, in order to form the requisite tolerance between the rotors and such side wall, each of the lift valves 322,324,326 and 328 are positioned in their operating position secured to the barrel 26.
In this regard, the piston 411 and consequently the valve PlPmpnt 414 must be fully PYtPn~ed and maint~inP-l in the fully .o~tPn~P~ position throughout the m~hining process and particularly when the surface 402 itself is being ma~ hine~l In order to do so, the pressure chamber 424 is filled with C\WPW~N60\QUINC~\PAT APPL\L~6 9~,~PP
9~6-95 (1:~.9pG~

21619~7 pressuri_ed hydraulic fluid or oil which assures that the valve elemPnt 414 will remain in its fully P~tPn~lecl position ~sllming such fluid to be inco,l,~ ible. Accordingly, once the lift valves 322, 324, 326 and 328 are secured to the barrel 426, pressure chamber 424 is filled with an inco,ll~ressible fluid at which time the final m~rhining of the wall 25 of the com~lession rh~mhPr 24 is carried out. In doing so, the surface 402 of the valve PlPmPnt 414 exactly n~ ~trhPs and forms a co.~ ;o~ of the wall 25 of the colllpression chamber 24 which minimi7es any leakage around the rotor as the rotor passes over the surface 402.
10 . Rer~ lg now to Figures 7A ~LIou~ 7C, the distinct advantage of the ~resell~ invention over prior art valving systems will become clearly apparent. The present invention is illustrated in Figure 7a wherein the valve elPment 414 is positioned in its fully ~tPnclecl position. As can be seen from Figure 7A, the surface 402 of the valve elemPnt 414 forms a continll~tion of the surface 25 of the co,ll~ression chamber 24 of barrel 26.
Accordingly, as rotor 18 rotates past the valve elemPnt 114, there is no leakage between the surface 402 of the valve Pl~mPnt 414 and the rotor 18.
This is achieved because the surface 402 is m~chin~l integral with the surface 25 of the barrel 26. Further, the positioning of the valve PlemPnt 414 is assured due to the positive displ~cPment of the piston within the double acting lift valve. While the aforementioned prior art devices illustrate lift valves having concave surfaces, such lift valves are formed by way of a separate m~nllf~lring process and subsequently positioned within the compressor housing. Aordingly, these lift valve surfaces are manufactured to within predetermined tolerance, however, such manufacturing process cannot practically duplicate the curvature of the C`\WPWIN60\QUINCY~PAT_APPL\126_9~ APP
926-95 (1:~9pm~

compression chamber surface 25 and thus leakage by the rotor may still exist in such systems.
Referring to Figure 7B, clearly when using a turn and spiral valve variable capa. ;~y design, numerous ports 50 are provided near the bottom center line of the barrel 26'. As ~ ssed hereinabove, these ports are as deep as the housing material is thick and consequently air in the higher pressure co~ ression pocket blows around the tips of the rotors 18 and 20 as they pass these ports. Clearly, the rffirjency of the device is ~ignifi~ntly reduced and full capacity cannot be achieved.
The poppet type valve illustrated in Figure 7C includes a planar surface 52 on the valve el.oment 54 which also allows blow by around the rotor 18 rrslllting in a reduction in the efficiency of the system. Further, such a poppet type valve relies on a single acting piston to close the valves, thereby relying on the internal air pressure and/or a spring force to move the valve to the open position. Often times, the opening pressure may be low and consequently these valve designs may stick or operate erratically, again failing to provide the user with the m~imllm savings under part load conditions.
Clearly, it can be seen that by lltili7ing double acting lift valves having a single valve cylinder casting with a valve element which is m -~hinecl in conjunction with the m~rhining of the compression chamber wall provides an advantageous capacity control system wherein the compressor can reali_e 100% efficiency when the double acting lift valves are in the closed position and which may accurately control the capacity reduction as desired.
While the present invention has been described with reference to referred embo~liml ntc, it will be appreciated by those skilled in the art that C:\WPWIN60\QUI~ICY\PI~T_APPL\126_9~, APP
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~161~7 the invention may be practiced otherwise than as sperifi~lly described herein without departing from the spirit-and scope of the invention.
Therefore, it will be understood that the spirit and scope of the invention be limited only by the appended daims.

C~WPWIN60\QUINCY\PAT_APPL\126_9~ APP
9 26-95 ~:~9pm)

Claims (21)

1. A method of manufacturing a lift valve for use in a variable capacity screw compressor comprising the steps of:
securing at least one lift valve to a housing of the variable capacity screw compressor in an operating position, said lift valve including a valve housing, a shaft extending from and reciprocally received within said valve housing and a valve face secured to a remote end of said shaft;
fully extending said shaft from said valve housing;
maintaining said shaft in said fully extended position, and simultaneously machining an inner surface of said compressor housing and said valve face;
wherein said valve face forms a continuation of said compressor housing when said variable capacity screw compressor is operating at full capacity.

2. In a variable capacity screw compressor, a lift valve communicating with a compression chamber of the compressor comprising:
a valve housing;
a piston reciprocally received within said valve housing;
a shaft having a first end connected to said piston and a second end extending from said housing;
a valve surface connected to said second end of said shaft and exposed to said compression chamber, and displacement means for displacing said piston within said housing, said displacement means comprising a first pressure passage communicating with said housing adjacent a side of said piston, said first pressure passage being in selective fluidic communication with one of an inlet pressure and an outlet pressure of the variable capacity screw compressor, and a second pressure passage communicating with said housing adjacent an opposed side of said piston, said second pressure passage being in selective fluidic communication with one of the inlet pressure and the outlet pressure of the variable capacity screw compressor;
wherein said valve surface is positively displaced toward a compression chamber of the variable capacity screw compressor in response to the selective application of inlet fluid pressure to said first pressure passage and outlet fluid pressure to said second pressure passage and positively displaced away from the compression chamber of the variable capacity screw compressor in response to the selective application of outlet fluidic pressure to said first pressure passage and inlet fluid pressure to said second pressure passage to vary the capacity of the screw compressor.

3. The method as defined in claim 1, further comprising the step of maintaining an angular orientation of said valve face with respect to said valve housing during said machining step.

4. The method as defined in claim 1, wherein said step of maintaining said shaft in said fully extended position includes pressurizing at least one chamber within said valve housing.

5. The method as defined in claim 4, wherein said chamber is pressurized with a substantially incompressible fluid.

6. The method as defined in claim 4, wherein said incompressible fluid is oil.

7. The method as defined in claim 1, wherein a plurality of lift valves are secured to said housing prior to said step of machining, said inner surface of said compressor housing.

8. The lift valve as defined in claim 2, wherein said valve surface forms substantially a continuation of an inner surface of said compression chamber when said piston is in a fully extended position.

9. The lift valve as defined in claim 2, further comprising an alignment means for maintaining a rotational position of said valve surface with respect to said valve housing.

10. The lift valve as defined in claim 9, wherein said alignment means includes a male stud extending from a base of said valve housing, and a cooperating female receptacle formed in said piston for receiving said stud.

11. The lift valve as defined in claim 2, wherein said first and second pressure passages are formed in a lower surface of said housing.

12. The lift valve as defined in claim 2, further comprising a double shaft seal means formed between said housing and said shaft for preventing fluid in the compressor from entering said housing and preventing fluid from escaping from said housing.

13. The lift valve as defined in claim 2, further comprising mounting means for mounting said valve housing on the compressor in a predetermined position.

14. The lift valve as defined in claim 8, wherein said valve surface is a concave surface.

15. The lift valve as defined in claim 14, wherein said valve surface is simultaneously machined during the machining of the compression chamber.

16. The lift valve as defined in claim 2, wherein said valve housing is formed of a single unitary cast.

17. A system for varying an output capacity of a rotary screw compressor comprising a plurality of double acting lift valves mounted adjacent to and in communication with a compression chamber of the compressor; said double acting lifting valves including a valve housing, a piston reciprocally received within said valve housing thereby dividing said valve housing into first and second chambers, a shaft extending from and reciprocally received within said valve housing having a first end secured to said piston, and a valve surface secured to a second end of said shaft and exposed to the compression chamber;
a first pressure passage communicating with said first chamber in said housing, said second pressure passage being in selective fluidic communication with one of the inlet pressure and the outlet pressure of the variable capacity screw compressor;
a second pressure passage communicating with said second chamber in said housing, said second pressure passage being in selective fluidic communication with one of the inlet pressure and the outlet pressure of the variable capacity screw compressor; and control means for controlling the position of said piston in said housing by selectively communicating one of said first and said chambers in said housing to one of said inlet and outlet pressure and the other of said first and second chambers in said housing to the other of said inlet and outlet pressure for positively retracting and positively extending said shaft and said valve surface toward and away from said compression chamber.

18. The system as defined in claim 17, wherein said valve surface forms substantially a continuation of an inner surface of said compression chamber when said piston is in a fully extended position.

19. The system as defined in claim 17, further comprising an alignment means for maintaining a rotational position of said valve surface with respect to said valve housing.

20. The system as defined in claim 17, further comprising a double shaft seal means formed between said housing and said shaft for preventing fluid in the compressor from entering said housing and preventing fluid from escaping from said housing.

21. The system as defined in claim 17, wherein said control means comprises a plurality of electronic control valves for selectively controlling the pressurizing and exhausting of said first and second chambers in response to control signals received from a central processor unit for maintaining a predetermined pressure at an output of the compressor.