US3349994A

US3349994A - Unloading system for rotary compressor

Info

Publication number: US3349994A
Application number: US512895A
Authority: US
Inventors: Bloom Carl
Original assignee: Worthington Corp
Current assignee: Studebaker Worthington Inc; Atlas Copco Holyoke Inc
Priority date: 1965-12-10
Filing date: 1965-12-10
Publication date: 1967-10-31
Anticipated expiration: 1984-10-31
Also published as: ES333740A1; GB1147238A; FR1504927A

Description

Oct. 31, C. BLOOM UNLOADING SYSTEM FOR ROTARY COMPRESSOR Filed Dec. 10. 1965 I 60 38 i z 7' Q 80 46 55 54 7i 50 56'. e 32-- s 4 02 G4-- 4a E: /j/66 68 w.\ K 20 fl. 4.3 g2 l2 \l6 0 2o 40 so I 80 '00 AIR DEMAND AS A OF FULL CAPACITY F! G. 2

- FIG. 3

CA R L B LO 0 M United States Patent C) 3,349,994 UNLOADING SYSTEM FOR ROTARY COMPRESSOR Carl Bloom, Springfield, Mass, assignor to Worthington Corporation, Harrison, N.J., a corporation of Delaware Filed Dec. 10, 1965, Ser. No. 512,895 11 Claims. (Cl. 23045) ABSTRACT OF THE DISCLOSURE An unloading system for rotary compressors including a pumping device operatively associated with the discharge of the compressor to rapidly evacuate the compressor discharge during the unloading of the compressor. This rapid evacuation of the compressor discharge materially and rapidly reduces the power consumption of the compressor.

This invention relates to a new and improved compressor unloading system for materially increasing the overall operational efficiencies of compressors by satisfactorily and materially reducing the power consumption thereof under all but fully loaded conditions.

On, for example, conventional rotary compressors of the prior art which are equipped with large gas receivers in the nature of large air-oil tank means, compressor unloading is generally accomplished by closing of the compressor intake manifold and the concurrent bleeding of the compressor discharge manifold and air-oil tank means to atmosphere, to result in a large reduction of compressor power consumption. A primary disadvantage of this procedure is the limited speed with which the said discharge manifold and air-oil tank means may be bled down without resulting in undesirable. oil foaming. Conversely, if lower rates of bleed down are utilized to prevent oil foaming, the reduction in compression power consumption, and attendant increase in the overall operational efiiciency of the compressor, are markedly reduced,especially in applications wherein rapid and frequent cycling ofthe compressor between fully loaded and fully unloaded conditions is required.

It is, accordingly, a primary object of this invention to provide new and improved apparatus which will enable automatic and very rapid bleed-down of a compressor discharge manifold, concurrently with compressor unloading, to result in very significant decreases in compressor power consumption at such times without giving rise to problems in the nature of oil foaming.

Another object of this invention is to provide a means for reducing the power consumption of a compressor by evacuating the discharge manifold to a pressure well below atmospheric.

Another object of this invention is the provision of apparatus as above which are particularly adaptable for use in materially increasing the overall operational efliciencies of compressors which are required to rapidly and frequently cycle between fully loaded and fully unloaded conditions.

Another object of this invention is the provision of apparatus as above which also function to rapidly and automatically reduce the flow of lubricating oil to the compressor, concurrently with compressor unloading, to even further increase the overall operational efliciency of the compressor.

A further object of this invention is the provision of apparatus as above which require the use of only inexpensive and readily available components of well established design and proven dependability whereby, the-costs of fabrication and installation of the apparatus are mini mized, and long periods of maintenance-free, satisfactory operation thereof assured.

3,349,994 Patented Oct. 31, 1967 The above and other objects and advantages of my invention are believed made clear by the following detailed description thereof taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a schematic diagram of a rotary compressor which incorporates the new and improved compressor unloading system of my invention therein;

FIGURE 2 is a schematic diagram of a modified form of the oil control valve assembly of the system of FIG- URE l; and

FIGURE 3 is a graph of power plotted against capacity for a plurality of rotary compressors, including one which utilizes the new and improved unloading system of my invention.

Referring now to FIGURE 1, a rotary compressor system is generally indicated at 10 and comprises a conventional rotary compressor 12 which includes a discharge manifold 14 and a compressor suction control as indicated generally at 16. An oil-air tank 18 is connected as shown to the compressor discharge manifold 14 by a conduit 20 extending therebetween, and a check valve 22 of conventional construction, for example of the swing check or disc type, is connected as shown in the conduit 20 to permit fluid How in the latter only in the direction from the compressor discharge manifold 14 to the oil-air tank 18.

A bypass conduit 24 extends as shown from the compressor discharge manifold 14 to a portion of the conduit 20 downstream of the check valve 22 to enable fluid flow from the said compressor discharge manifold to the oil-air tank 18 around the said check valve. An auxiliary pump 26 is connected in the bypass conduit 24 to enable the rapid evacuation of the compressor discharge manifold 14 through the said bypass conduit. The auxiliary pump 26 is designed to operate whenever the compressor 12 is operating, whereby the former may conveniently be riven from the drive shaft of the latter as indicated schematically by the dashed line 27 in FIGURE 1.

A compressed air'supply conduit 28 extends as shown from the top of the oil-air tank 18, and includes a demister 30 connected therein as shown for removing water and oil from the compressed air prior to the utilization thereof.

A lubricating oil supply line 32 extends from the bottom of the oil-air tank 18 to the rotary compressor 12, and includes oil filter means 34 and oil cooler means 36 positioned therein as shown. A plunger operated, oil control valve 38, of generally conventional construction, is also included in the said oil supply line, and may be conveniently actuated as shown by an extension 40 of the compressor suction control actuating rod. The rotary compressor 12 and oil control valve 38 are designed so that movement of the compressor suction control actuating rod 44 in the direction indicated by arrow 42 will function to both unload the said compressor and partially close the oil control valve 38 to materially reduce the How of oil to the rotary compressor 12 through oil supply line 32 during those times when the said compressor is operating under unloaded conditions.

Referring now to FIGURE 2, a modified form of con trol means for use with rotary compressor assemblies which comprise suction unloader pressure regulations is indicated generally at 41. In this case, the operation of plunger operated, oil control valve 38 is controlled by the pressure signal fed to the compressor suction unloader actuator 43. To this efiect, the control means 41 comprise a housing 44 into which the valve operating plunger 46 extends as shown. A diaphragm 48 extends across the interior of the housing 44 to divide the latter into

chambers

50 and 52, respectively, with the chamber 50 being vented to atmosphere by the clearance between the oil control valve actuating rod 46 and the housing 44 as indicated at 54. A biasing spring 55 is positioned as shown 3 between the housing 44 and diaphragm 48 to bias the latter away from the oil control valve 38.

The oil control valve actuating rod 46 is connected to the central portion of the diaphragm 48, as indicated at 56, so as to be movable therewith, and a conduit 58 extends as shown from the chamber 52 in housing 44 to suction unloader pressure actuator 43, whereby pressure signals from the latter may be readily communicated to the said chamber through the said control pressure conduit.

In the operation of the compressor assembly of FIGURE 1, the rotary compressor 12 is unloaded by movement of the compressor suction control actuating rod 40 in the direction indicated by arrow 42 to both close the compressor suction control 16 to unload the compressor 12, and partially close oil control valve 38 to materially reduce the fiow of oil to the said compressor.

As this occurs, the pressure in compressor discharge manifold 14 falls below the pressure of the compressed air in the oil-air tank 18, whereby the check valve 22 closes to prevent reverse flow therebetween through conduit 20. Concurrently therewith, operation of the auxiliary pump 26 results in very rapid evacuation of the compressor discharge manifold 14 through conduit 24 connected therebetween to very rapidly reduce the pressure in the said compressor discharge manifold to a value well below atmospheric pressure.

This very rapid reduction in the pressure in the compressor discharge manifold 14 and the very low pressure achieved in the discharge manifold 14 reduces the power consumption of the rotary compressor 12, under unloaded conditions, to less than of the full load power consumption of the said rotary compressor. Thus it may be readily appreciated that the new and improved compressor unloading system of my invention enables very rapid reduction in the discharge pressure of a rotary compressor concurrently with the unloading thereof, with attendant significant increase in overall compressor operation efiiciency; while preventing undesirable oil foaming, as discussed hereinabove due to the fact that rapid bleed down of the oil-air tank 18 is rendered unnecessary in the unloading of the compressor.

Movement of the compressor suction control actuating rod 40 in the direction indicated by arrow 42 to unload the rotary compressor 12, also results in a partial closing of the oil control valve 38, as discussed above, whereby the fiow of oil to the compressor through oil supply conduit 32 is materially reduced to materially reduce the load on the auxiliary pump 26 and the power consumption of the compressor during such time as the rotary compressor 12 is operating under unloaded conditions.

The oil control valve control means of FIGURE 2 operate to partially close the oil control valve 38 concurrently with the unloading of the rotary compressor 12 through the use of the same positive pressure signal which is fed from the suction unloader actuator 43 to the compressor suction control 16 to unload the said rotary compressor. To this effect, the said positive pressure signal is also fed from the suction unloader actuator 43 to the chamber 52 in housing 44 through conduit 58 connected therebetween. This results in an increase in pressure in the said chamber and attendant movement of the diaphragm 48 and oil control valve actuating rod 46 toward the said oil control valve to partially close the latter and reduce the load on the auxiliary pump 26 as discussed above.

The significant advantages, in addition to oil foaming prevention, provided by the new and improved compressor unloading system of my invention, as compared to the compressor unloading systems which have heretofore been utilized, are believed made clear by a comparison of the following ratios of compressor power consumption under unloaded conditions to compressor power consumption under full load conditions at 100 p.s.i. Thus, for standard compressor unloading systems utilizing modulating control means, the said ratio has been determined by the actual taking of test data and subsequent calculations to be approximately 0.63. The said ratio for compressor unloading systems which function through the bleeding of the compressor discharge manifold to atmosphere has been similarly determined to be aproximately 0.20; while the said ratio for the new and improved compressor unloading system of my invention has been similarly determined to range from a high of 0.15 to a low of 0.10, to thus make clear the significant advantages provided by use of the latter. It is to be noted that the above ratios are for steady state operation, and since the new and improved compressor unloading system of my invention acts more quickly than the system of bleeding the discharge manifold pressure of atmosphere, the significantly reduced compressor power consumption is in effect over a longer part of the unloaded portion of the load-unload cycle. Thus, total compressor power consumption savings for the new and improved compressor unloading system of my invention are therefore even greater when the compressor is partially loaded than would be indicated by the said ratios.

This is believed made clear by a comparison of the curves of FIGURE 3, wherein compressor power consumption as a percent of full load power is plotted against air demand as a percent of full load capacity. Curve 60 represents the factors, as again determine-d by the actual taking of test data and subsequent calculations, for a rotary compressor utilizing a standard unloading system of the modulating control type. Curve 62 represents these factors, similarly calculated, for a rotary compressor utilizing an unloading system wherein the suction is either fully open or fully closed. Curve 64 represents these factors, similarly calculated, for a rotary compressor utilizing an unloading system wherein the suction is either fully open or fully closed, but which bleeds the compressor discharge manifold pressure to atmosphere each time the suction is closed. Curve 66 represents these factors, similarly taken, for a reciprocating compressor utilizing an unloading system of the constant speed type. Curve 68 represents these factors, similarly taken, for a rotary compressor utilizing the new and improved compressor unloading system of my invention. With particular regard to curve 68, it is believed of interest to note that the rotary compressor requires approximately 12% of full load power while operating under unloaded or zero c.f.m. (cubic feet per minute) condltions, which is, of course, significantly lower than that provided by

curves

60, 62, 64 and 66. In addition, curve 68 is believed to make clear, as discussed hereinabove, that compressor power consumption under partrally loaded conditions, as for example in the 20% to capacity range, is significantly lowered through the use of the new and improved compressor unloading system of my invention.

While these have been shown and described herein, as the preferred embodiments of the invention, it will be understood that minor changes in the process and apparatus may be made without departing from the scope of the invention as disclosed and claimed. Thus, for example, although not at present preferred, the drive means for auxiliary pump 26 may be modified, in any convenient manner, to effect the drive of the said auxiliary pump only upon operation of the compressor unloading means to unload the compressor, rather than on the continuous basis described hereinabove. In one form, this modification could encompass the incorporation of non-illustrated clutch means through which the said auxiliary pump is driven, with the said clutch means being engageable only in response to the operation of the compressor unloading means to unload the compressor.

What is claimed is:

1. In a compressor system, a compressor having intake and discharge means, unloading means cooperatively associated with said compressor and operable to unload said compressor, discharge conduit means and bypass means associated with said compressor discharge means, and pump means having separate intake and discharge means, said pump intake means connected with said bypass conduit means, said pump means operable to rapidly evacuate the said compressor discharge means whereby, the power consumption of said compressor may be rapidly and materially reduced by operation of said pump means to rapidly evacuate said compressor discharge means concurrently with the operation of said compressor unloading means to unload said compressor.

2. In a compressor system as in claim 1 wherein, said pump means are operable continuously with the operation of said compressor.

3. In a compressor system as in claim 1 further comprising, compressor drive means, and wherein said pump means are driven from said compressor drive means.

4. In a compressor system as in claim 1 further comprising, means cooperatively associated with said compressor and said pump means for supplying lubricating oil to said compressor, means for controlling the operation of said lubricating oil supply means by controlling the quantity of lubricating oil supplied thereby to said compressor, means cooperatively associated with said compressor unloading means and said lubricating oil supply control means and operable to cause the latter to reduce the amount of lubricating oil supplied to said compressor in response to operation of said compressor unloading means to unload said compressor whereby, the load on said pump means is reduced concurrently with the unloading of said compressor.

5. In a compressor system as in claim 4 wherein, said pump means are operable continuously with the operation of said compressor.

'6. In a compressor system as in claim 4 wherein, said means cooperatively associated with said compressor un loading means :and said lubricating oil supply control means comprise, a compressor unloading means actuating rod extending therebetween.

7. In a compressor system as in claim 4 wherein, said means cooperatively associated with said compressor unloading means and said lubricating -oil supply control means comprise, pneumatically operable means connected to the latter and means for communicating pressure signals from said compressor unloading means to said pneumatically operable means.

8. In a compressor system, a rotary compressor having an intake manifold and a discharge manifold, unloading means cooperatively associated with said intake manifold and operable to unload said compressor, discharge conduit means extending from said discharge manifold, check valve means in said discharge conduit means for preventing fluid flow therein in the direction toward said discharge manifold, bypass conduit means connecting said discharge manifold with a portion of said discharge conduit means downstream of said check valve means, pump means in said bypass conduit means for pumping fluid from said discharge manifold to said portion of said discharge conduit means, said pump means being operable to rapidly evacuate said discharge manifold whereby, the power consumption of said compressor may be rapidly and materially reduced by operation of said pump means to rapidly evacuate said discharge manifold concurrently with the operation of said compressor unloading means to unload said compressor, and flow of fluid into said discharge manifold through said discharge conduit means prevented by operation of said check valve means.

9. In a compressor system as in claim 8 wherein, said pump means are operable continuously with the operation of said compressor.

10. In a compressor system as in claim 8 further comprising, air-oil tank means connected to said discharge conduit means downstream of said portion of the latter, cond-uit means connecting said air-oil tank means and said compressor for supplying lubricating oil from said airoil tank means to said compressor, valve means in said conduit means for controlling the quantity of lubricating oil supplied therethrough to said compressor, and means cooperatively associated with said valve means and said compressor unloading means and operable to cause said valve means to reduce the amount of lubricating oil supplied to said compressor in response to operation of said compressor unloading means to unload said compressor whereby, the load of said pump means is reduced concurrently with the unloading of said compressor.

11. In a compressor system as in claim 10 wherein, said pump means :are operable continuously with the operation of said compressor.

References Cited UNITED STATES PATENTS 1,616,992 2/ 1927 Ruckstuhl 230-27 1,716,160 6/ 1929 Zworyskin et a1. 230-45 2,492,075 12/1949 VanAtca 230-45 2,826,353 3/1958 Auwarter et a1 230-45 2,914,242 11/1959 Meien-berg 230-45 2,958,455 1/1960 Steinherz et a1. 230-45 2,971,691 2/1961 Lorenz 230-45 3,101,187 8/1963 Campbell 230-27 3,110,473 11/1963 Frank et al. 253-3915 3,147,712 9/1964 Gaubatz 103-5 3,191,854 6/1965 Lowler et a1. 230-24 DONL'EY J. STOCKING, Primary Examiner. W. I. KRAUSS, Assistant Examiner.

Claims

1. IN A COMPRESSOR SYSTEM, A COMPRESSOR HAVING INTAKE AND DISCAHRGE MEANS, UNLOADING MEANS COOPERATIVELY ASSOCIATED WITH SAID COMPRESSOR AND OPERABLE TO UNLOAD SAID COMPRESSOR, DISCHARGE CONDUIT MEANS AND BYPASS MEANS ASSOCATIED WITH SAID COMPRESSOR DISCHARGE MEANS, AND PUMP MEANS HAVING SEPARATE INTAKE AND DISCHARGE MEANS, SAID PUMP INTAKE MEANS CONNECTED WITH SAID BYPASS CONDUIT MEANS, SAID PUMP MEANS OPERABLE TO RAPIDLY EVACUATE THE SAID COMPRESSOR DISCHARGE MEANS