Multistage blowdown valve for a compressor system

Information

  • Patent Grant
  • 6371731
  • Patent Number
    6,371,731
  • Date Filed
    Wednesday, June 27, 2001
    23 years ago
  • Date Issued
    Tuesday, April 16, 2002
    22 years ago
Abstract
A multi-stage blowdown valve is provided that uses a single control signal to simultaneously decompress the interstage and the second stage in a compressor system. The valve uses a series of sliding spools located linearly within a single bore to either prevent or allow fluid communication between two isolated passageways each having an inlet port and a discharge port. The valve, when used as a two stage blowdown valve in a multi-stage compressor system, can prevent compressor failure from occurring by ensuring that both the interstage and the second stages are decompressed. not only the interstage.
Description




FIELD OF THE INVENTION




The present application relates gene rally to a control valve. More specifically i t re lates t o a control valve used with compressors. Most specifically it relates to a blowdown valve used with one or more oil free two stage screw compressors.




BACKGROUND OF THE INVENTION




Power consumption for a two stage dry (oil free) screw compressor is significantly reduced if the interstage and the second stage are both decompressed when the compressor i s running unloaded. The problem with decompressing both stages. however, is that if the second stage blowdown valve malfunctions. the interstage blowdown valve will decompress the interstage and leave a large differential pressure on the second stage. This large differential pressure will raise the temperature of the second stage, possibly leading to compressor failured.




Previous compressors avoided the above problem by only unloading pressure from the second stage and not from both stages. The disadvantage however, of unloading pressure only from the second stage when running the compressor unloaded is that the compressor's power consumption is greater than if both stages are unloaded.




Previous valve mechanisms for compressors have not adequately addressed the problem of simultaneously decompressing two isolated stages. U.S. Pat. No. 3,260,444 to Williams discloses valve mechanisms


104


and


110


which are controlled by the same control line


158


and operate in a similar manner. With valve


104


, for example, control line


158


can move piston


130


to control whether pipe


106


is in communication with pipe


113


or pipe


102


. The disadvantage with using these valves as blowdown valves for a two stage compressor is that if one valve should malfunction, the other valve may continue to function, possibly leading to compressor failure.




What is desired, therefore, is a reliable mechanism for a two stage dry screw compressor to decompress the interstage blowdown valve when the second stage blowdown valve is activated.




SUMMARY OF THE INVENTION




Accordingly, it is a primary object of the present invention to provide a blowdown valve for two stages of a multi-stage compressor such that the valve reliably decompresses the interstage when the second stage is decompressed.




The object of the invention is achieved by a blowdown valve that uses a single control signal to simultaneously decompress the interstage when the second stage is decompressed. The valve uses a series of sliding spools located linearly within a single bore to either prevent or allow fluid communication between two isolated passageways each having an inlet port and a discharge port. The valve can be reliably used as a two stage blowdown valve in a multi-stage compressor sv'stem.











BRIEF DESCRIPTION OF THE DRAWINGS





FIGS. 1A and 1B

each show an isometric cross-sectional view of the multistage blowdown valve of the present invention wherein the valve is in a closed position and an open position, respectively.





FIGS. 2A and 2B

each show an isometric cross-sectional view of a second embodiment of the multistage blowdown valve of the present invention wherein the valve is in a closed position and an open position. respectively.





FIGS. 3A and 3B

are front cross-sectional and side cross-sectional views, respectively, of the valve of FIG.


2


A.





FIG. 4

is a diagram showing the multistage blow down valve of

FIGS. 1A and 1B

used with a compressor system.





FIG. 5

is a partial exploded view of the improved operative connections of a compressor system of

FIG. 4

used with the multistage blowdown valve of FIGS.


1


A and


1


B.











DETAILED DESCRIPTION OF THE INVENTION





FIGS. 1A and 1B

show the preferred embodiment for the multistage blowdown valve


50


of the present invention. Referring to these figures., the multistage blowdown valve


50


has two inlet ports,


26


,


30


and two discharge ports


28


,


32


. When the valve


50


is in a closed position as shown in FIG.


1


A. all ports


26


,


28


.


30


and


32


are fluidly isolated from one another. When the valve


50


′ is in an open position as shown in

FIG. 1B

, inlet port


26


is in fluid communication only with discharge port


28


and inlet port


30


is in fluid communication only with discharge port


32


. It should be apparent that the valve


50


could operate in a reverse direction with the inlet ports


26


,


30


acting as discharge ports and discharge ports


28


,


32


acting as inlet ports.




The multistage blowdown valve


50


has a main bore


68


that can have a single diameter, but preferably has three diameters


68


′,


68


″ and


68


′″. Larger diameter


68


″ facilitates a larger volume of fluid passage through the valve and also prolongs the life of the rings


36


. Thus, for example, the life of ring


36


on spool


17


will be prolonged by avoiding repeated contact with the edges of inlet


26


as the spool reciprocates through the bore


14


. The smaller diameter


68


′″ helps to center the spring


24


within the bore


68


.




Within the bore


68


are a plurality of spools


60


.


62


. and


64


that linearlv abut each other within the bore. Spools


60


and


64


each have a leg portion


42


bounded by two head portions


40


. Spool


62


has one head portion


40


bounded by two leg portions


42


. Adjacent spools are preferably coupled through the use of a mortise and a tenon. For example, each leg portion


42


of spool


62


can have a tenon


44


for fitting into a mortise


46


in a head portion of adjacent spools


60


and


64


.




Each head portion


40


further preferably has one or more rubber rings


36


inserted into a corresponding annular groove in the head portion such that each spool has airtight contact within the bore


14


as the spools move within the bore. The preferred type of ring used for ring


36


on the spools


16


-


20


or


60


.


62


and


64


are sometimes referred to as V-rings or U-rings which refer to the ability of the ring to fold when placed in a bore. The beneficial properties of the folding ring design include reduced sticking when the spools move in bore


14


, reduced sliding forces which allow lower and reapeatable control forces, improved sealing by the ring unfolding under pressure, and durability in that all of the desirable properties of the folding ring continue even after partial ring wear. The folding ring design also provides reliable operation when the spools move within the various diameters of the bore, for example, from diameter


14


′ to


14


″ or


68


′ to


68


″ and then back again.




The movement of spools


60


,


62


and


64


is controlled through pneumatic pressure applied against the head


40


of spool


64


through control port


34


. A spring


24


is located within the bore preferably at an opposite end of the control port


34


and extends laterally through the bore. The spring


24


abuts the head


40


from spool


60


to bias the valve to a closed position (see FIG.


1


A). Furthermore, spring means. such as compression spring


24


, counteracts the force of the control signal when the valve is in an open position (see

FIG. 1B

) and returns the blowdown valve to a closed position when the control signal is inactive. Alternatively, a tension spring and the control port could operate together at the same end of the bore, although those skilled in the art will realize that the control signal will operate in an inverse manner.





FIGS. 2A

,


2


B,


3


A and


3


B show another embodiment of the multistage blowdown valve


10


and


10


′ of the present invention.

FIG. 2B

shows the blowdown valve


10


′ in an open position and

FIGS. 2A. 3A

and


3


B show the blowdown valve


10


in a closed position. The multistage blowdown valve


10


generally differs from multistage blowdown valve


50


in that it has a different configuration of spools


16


-


20


and does not have a smaller bore near the compression spring


24


. Instead. the multistage blowdown valve


10


has a main bore


14


with two diameters


14


′ and


14


″.




Referring to

FIGS. 2A

,


2


B.


3


A and


3


B. within bore


14


are a plurality of spools


16


-


20


that linearly abut each other within the bore. Each spool


16


-


20


has a leg portion


42


and a head portion


40


. Adjacent spools are preferably coupled through the use of a mortise and a tenon. For example, each head portion


40


of each spool


16


-


20


can have a mortise


46


for fitedly receiving a tenon


44


on the leg portion


42


of the adjacent spool.




Although the present invention uses a plurality of spools within the bore, a single spool could also be used for the same function. However, a plurality of individual spools


16


-


20


or


60


,


62


and


64


are preferably used because they create a better seal by reacting to both the control pressure and internal pressures produced from the inlet ports. However, it is more preferable to use the spools


60


,


62


and


64


shown in

FIGS. 1A and 1B

because less linear deviations will occur during spool movement than with the configuration of spools


16


-


20


shown in

FIGS. 2A and 2B

.




It should be apparent to those skilled in the art that although the valve described herein is for a two-stage compressor the valve can be adapted for compressors having three or more stages. To create a multi-stage blowdown valve, the valve described herein merely needs a longer bore, additional spools and extra inlet and discharge ports.





FIGS. 4 and 5

show the multistage blowdown valve used with a dual stage compressor system


1002


. The dual stage compressor system


1002


described herein is best described in U.S. patent application Ser. No. 09/179,523. The multistage blowdown valve


10


can have many applications and be used with many compressor systems. Thus, it should be understood that the compressor system


1002


described herein is merely given as an example and not meant to be limiting.




The operation of compressor system


1002


will now be briefly described. Referring to

FIG. 4

, the first-stage compressor


102


compresses the air to approximately thirty (30) psi. The compressed air is transmitted from the first stage compressor


102


into the innerstage piping


104


. The compressed air flows through the piping


104


to an innerstage cooler


106


. The cooler


106


drops the air temperature by approximately three hundred degrees Fahrenheit (300° F). The cooler


106


is connected to the discharge of the first stage compressor


102


via a coupling plate


108


.




The compressed air is transmitted through the innerstage cooler


106


into another innerstage pipe


112


. The pipe


112


is connected to a moisture trap


110


via coupling plates


108


A. The moisture trap


110


is connected to the innerstage piping that leads to the second stage compressor


114


via innerstage pipe


116


which is also connected to the moisture trap


110


via coupling plates


108


B.




This compressed air is transmitted into the inlet of the second stage compressor


114


. The second stage compressor


114


compresses the air approximately another seventy (70) psi, which brings the air up to approximately one hundred (100) psi. The compressed air is transmitted from the second stage compressor


114


into the second stage compressor discharge pipe


118


. The pipe


118


is connected to another discharge pipe


118


A leading to a compressor package discharge cooler


120


. The cooler


120


again drops the temperature of the compressed air transmitted therethrough by approximately three hundred degrees Fahrenheit (300° F).




Innerstage pipe


116


has a bung


150


welded thereto, which connects the innerstage pipe


116


to the inlet port


26


of the multistage blowdown valve


10


. The connection to inlet port


26


is through a pipe elbow


151


, pipe nipple


152


, pipe coupling


153


, and pipe nipple


154


. A muffler


450


is attached to the discharge port


28


of the blowdown valve


10


. The purpose of the muffler


450


is to reduce the amount of noise that would be created when any trapped air pressure is vented to atmosphere.




Discharge pipe


130


B is attached to the moisture trap


126


, has a T shaped bung


170


A welded thereto, and has a package temperature probe


2010


is located within it. One end of the T-shaped bung


170


A has one end of a pipe elbow


128


A coupled thereto. The other end of the pipe elbow


128


A is coupled to the discharge pipe


130


A. A pipe nipple


171


is connected to the other end of the bung


170


A, which is threaded onto a coupling


172


, which is connected to pipe nipple


173


. The inlet port


30


of the multistage blowdown valve


10


is connected to the pipe nipple


173


. The discharge port


32


of valve


10


has an exhaust muffler


440


operatively connected thereto. The muffler


440


reduces the amount of noise created when any trapped air pressure is vented to atmosphere.




The multistage blowdown valve


10


of the present invention will exhaust any trapped pressure at shutdown or unload of the two stage compressor


1002


that might be trapped in innerstage pipe


116


and in the discharge piping


130


B from the second stage compressor


114


. Due to the integration of the interstage and second stage blowdown valves, the interstage and the second stage will be decompressed simultaneously. Therefore, if the second stage blowdown valve malfunctions and fails to open, the innerstage blowdown valve will remain open thus averting possible compressor failure.




Additional modifications need to be made to the compressor system


1002


to use it with the multistage blowdown valve


10


of the present invention. Tubing elbow


180


, which was attached to the moisture trap


126


, is now attached to a shuttle check valve


492


. One side of the shuttle check valve


492


is connected to the moisture trap


126


through a pipe fitting


494


. The other side of the shuttle check valve


492


is connected to a tubing elbow


490


which is connected to tubing


488


. Tubing


488


has an elbow


480


connected to its other end which is connected to a first end of tubing T


460


. Previously, tube fitting


190


was operatively connected to check valve


128


A, but is now connected to a second end of tubing T


460


. The third end of tubing T


460


is connected through a pipe fitting


470


to check valve


128


A.




The dual blowdown valve


10


,


50


of the present invention lowers the pressure ratio across the second stage, i.e., the value of the pressure across the second stage minus the pressure across the interstage, divided by the value of the pressure across the interstage. Through testing, it has been determined that using the dual blowdown valve of the present invention can lower the second stage pressure ratio under normal operating conditions from a value above six to a value below three.




One of the benefits of maintaining a low-pressure ratio across the second stage compressor during normal operations is that it lowers operating temperatures in the second stage compressor. Tests of the dual blowdown concept have shown that a standard blowdown system had a second stage compressor discharge as high as 360 degrees F during normal cycling operation. Under the same cycling operation the dual blowdown system had a maximum second stage compressor discharge temperature of 295 degrees F. In this test, the dual blowdown system ran 22 percent cooler than the standard system. These cooler operating temperatures obtained from using the dual blowdown valve


10


,


50


can lead to a longer compressor lifespan.




It should be understood that the foregoing is illustrative and not limiting and that obvious modifications may be made by those skilled in the art without departing from the spirit of the invention. Accordingly. reference should be made primarily to the accompanying claims. rather than the foregoing specification. to determine the scope of the invention.



Claims
  • 1. A method for controlling a single or a network of oil less, two stage screw compressor packages, operatively connected to a pressure system in which pressure is to be maintained within a desired pressure range, for controlling the operation of the single or the network of screw compressor packages, the method comprising the steps of:providing at least one or a network of oil less, two stage screw compressor packages; operatively connecting the at least one or a network of oil less, two stage screw compressor packages to a pressure system in which pressure is to be maintained within a predetermined range of possible pressures; operatively connecting an electronic control system to at least one two stage screw compressor package; controlling the operation of the at least one or a network of oil less, two stage screw compressor packages by; determining the pressure exiting the first and the second screw compressor stages; comparing the determined pressure exiting the first screw compressor and the second screw compressor stages with a predetermined range of possible pressures; and if the determined pressure exiting either the first or the second screw compressor stages equals or exceeds the predetermined range of possible pressures, shutting down the screw compressor package before the screw compressor package is damaged; and following the shutting down of the screw compressor package, simultaneously releasing pressure within a first and a second compressor stage by a single valve means controlled by a single control signal.
  • 2. The method of claim 1 further comprising the steps of:determining the temperature of the gas exiting the first and the second screw compressor stages; comparing the determined temperature exiting the first screw compressor and the screw second compressor stages with a predetermined temperature limit; shutting the screw compressor package down before the package is damaged, if the exiting temperatures exceed such predetermined temperature; and following the shutting down of the screw compressor package, simultaneously releasing pressure within a first and a second compressor stage by a single valve means controlled by a single control signal.
  • 3. The method of claim 1 further comprising the steps of:cooling the air prior to the air entering the second stage screw compressor by operatively positioning at least one cooling means between the stage one screw compressor and the stage two screw compressor; cooling the air prior to the air entering the end user air system by operatively positioning at least a second cooling means between the stage two screw compressor exit and the compressor package exit; establishing a high predetermined temperature limit for the temperature of the air exiting each cooling means; measuring the temperature of the air exiting each cooling means by operatively connecting measuring means to each cooling means; if the exiting temperatures exceed a predetermined temperature limit, shutting the screw compressor package down before the package is damaged; and following the shutting down of the screw compressor package, simultaneously releasing pressure within a first and a second compressor stage by a single valve means controlled by a single control signal.
  • 4. The method of claim 1 further comprising the steps of:operatively positioning lubricating oil containing means in the stage one screw compressor and the stage two screw compressor for lubricating parts isolated from each screw compressor compression chamber; measuring the oil pressure of both the stage one screw compressor and the stage two screw compressors by operatively connecting measuring means to the each lubricating oil containing means; establishing a range of predetermined operating oil pressures; if the oil pressure deviates from the predetermined oil pressure range, shutting the screw compressor package down before the package is damaged; and following the shutting down of the screw compressor package, simultaneously releasing pressure within a first and a second compressor stage by a single valve means controlled by a single control signal.
  • 5. The method of claim 1 further comprising the steps of:measuring the pressure of the air exiting the screw compressor package after the second stage cooling means; measuring the temperature of the air exiting the screw compressor package after the second stage cooling means; establishing a range of screw compressor package discharge temperatures and pressures; if either the temperature or the pressure exceeds a predetermined limit, shutting down the screw compressor package; and following the shutting down of the screw compressor package, simultaneously releasing pressure within a first and a second compressor stage by a single valve means controlled by a single control signal.
RELATED APPLICATION

This application is a continuation of commonly owned U.S. patent application 09/422,284, filed Oct. 21, 1999, of Centers which is a continuation-in-part of commonly owned U.S. patent application Ser. No. 09/179,523, filed Oct. 27, 1998, of Centers et al. now U.S. Pat. No. 6,102,665, issued Aug. 15, 2000, which is a continuation-in-part of commonly owned U.S. Provisional Patent Application Serial No. 60/066,008, filed Oct. 28, 1997, of Centers et al., the disclosures of which are herein incorporated by reference.

US Referenced Citations (23)
Number Name Date Kind
3260444 Williams et al. Jul 1966 A
3756753 Persson et al. Sep 1973 A
3927708 Hulme Dec 1975 A
3936239 Shaw Feb 1976 A
4076468 Persson et al. Feb 1978 A
4084618 Gurries Apr 1978 A
4105064 Toro et al. Aug 1978 A
4155535 Seamone May 1979 A
4339233 Krueger Jul 1982 A
4646785 Ruedle et al. Mar 1987 A
4678406 Pillis et al. Jul 1987 A
5044894 Field et al. Sep 1991 A
5163478 Fries Nov 1992 A
5332696 McKenzie Aug 1994 A
5335696 McKenzie Aug 1994 A
5655379 Jaster et al. Aug 1997 A
5713724 Centers et al. Feb 1998 A
5738497 Hensley Apr 1998 A
5833925 Shu et al. Nov 1998 A
5860801 Timuska Jan 1999 A
6053421 Chockley Apr 2000 A
6102665 Centers et al. Aug 2000 A
6283716 Centers Sep 2001 B1
Provisional Applications (1)
Number Date Country
60/066008 Oct 1997 US
Continuations (1)
Number Date Country
Parent 09/422284 Oct 1999 US
Child 09/892587 US
Continuation in Parts (1)
Number Date Country
Parent 09/179523 Oct 1998 US
Child 09/422284 US