GB2394025A

GB2394025A - Thermostatically controlled valve for lubricant-cooled gas compressor

Info

Publication number: GB2394025A
Application number: GB0129343A
Authority: GB
Inventors: Terrence Edward Coker
Original assignee: Compair
Current assignee: Compair
Priority date: 2001-12-07
Filing date: 2001-12-07
Publication date: 2004-04-14
Anticipated expiration: 2021-12-07
Also published as: GB2394025B; GB0129343D0

Abstract

A retro-fit device for lubricant cooled gas compressors adapted to discharge a gas and lubricant mixture, having a separator for separating the mixture and a means to return the lubricant to the compressor. The device, positioned between the separator and compressor, comprises a thermostatically controlled restrictor valve 22 between inlet 32 and outlet 33. The temperature sensitive element of the thermostat is exposed to lubricant flowing between the inlet and outlet such that the restrictor valve restricts lubricant flow when the temparature falls and increases flow when the temperature increases. The device may comprise a sleeve 35, axially slidable within a bore 31, which contains the thermostat and controls lubricant flow. The thermostat may comprise cylinder 37, containing a wax, moveable with the sleeve, and piston 38. As the wax melts, in response to temperature increase, it lifts the sleeve increasing lubricant flow. The valve may have a bypass to ensure a minimum lubricant return flow.

Description

1. DEVICE FOR LUBRICANT-COOLED COMPRESSOR

This invention relates to a retro-fit device for improving the performance of an existing lubricant-cooled gas compressor.

A number of gas compressors, whether of the piston, the slidng vane or the screw type, discharge a mixture of the compressed gas and a lubricant, which latter is then separated from the gas and recycled to cool and to lubricate the compressor. In a screw compressor gas is compressed between male and female helical rotors and the recycled lubricant provides a seal between the rotors.

A major problem encountered in the operation of lubricant-cooled air compressors is that of condensation of water from the indrawn air. It is not practicable to dry the incoming air, which will precipitate moisture when compressed unless temperatures are maintained high enough for the water to remain as vapour. During normal operation the temperature of the compressed air will be high enough to prevent substantial precipitation but at start up or when the compressor is idling (because of a temporary reduction in the demand for the compressed air) temperatures will drop below the dew point of the compressed air so that water will collect in the separator and form an emulsion with the lubricant. When this is returned to the compressor lubrication will be adversely affected, causing high maintenance and shortened life for the compressor.

A principal object of the present invention is to address the problem of condensation when operating an existing lubricant coiled gas compressor.

In accordance with the present invention there is provided a retro-fit device for incorporation in a lubricant-cooled compressor, the compressor being of the kind which discharges a mixture of lubricant and compressed gas and wherein means is provided for separating the lubricant from the compressed gas downstream of the compressor and for returning the separated lubricant to the compressor, the device comprising a housing having an inlet and an outlet whereby it may be incorporated in the line between the separating means and the compressor by which lubricant is returned to the compressor and a thermostatically controlled restrictor valve within the housing located in the passage between the inlet and outlet with the temperature sensitive element of the thermostat exposed to the temperature

l se9;est of lubricant flowing between the inlet and outlet such that the restrictor valve will restrict said flow when said temperature falls and increase said flow when said temperature increases.

Preferably the outlet communicates with a cyclindrical chamber within the housing which is coaxial with, intermediate the ends of and of greater diameter than a bore within the housing communicating with the inlet, a sleeve being movable axially of the bore whereby an opening in the wall of the sleeve may be brought into or out of register with the chamber, the thermostat being within the bore whereby it will respond to changes in the temperature of lubricant passing through the housing thereby to displace the sleeve to vary the area of said opening which is exposed to the chamber. The thermostat may comprise a cylinder moveable with the sleeve, a piston fixed at one end relative the housing and a wax within the cylinder at the free end of the piston, the wax being of a kind which increases in volume as it liquifies in response to an increase in temperature.

The cylinder is preferably spring loaded to move the sleeve to restrict the lubricant flow when permitted so to do as the wax solidifies in response to a drop in lubricant temperature.

By-pass means is preferably provided in the housing by pass mg the thermostatically controlled restrictor valve, the by-pass means being adapted to ensure a minimum return flow of lubricant to the air-end independently of the restrictor valve.

The by-pass means may comprise a by-pass duct within the housing which directly communicates the inlet with said chamber.

The by-pass duct may have a restriction, which may be adjustable.

A prefered embodiment of the present invention will now be described by way non-limitative example with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a known screw compressor of the kind to which the device of the invention is adapted to be

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À 3. fitted, and Figures 2 and 3 are similar sectional elevations of a thermostatically controlled restrictor valve in accordance with the present invention showing the restrictor valve respectively in a fully open and partially closed condition.

The screw compressor 10 illustrated in Figure 1 comprises a screw compressor 11 (known as the air-end) for compressing a gas such as air.

A motor 12 drives the rotors of the air end 11.

Air is taken to the air-end 11 via a gas intake filter 14. The quantity of air intake is controlled via a suction regulator 15 which is connected by a control line 15a to a reclaimer 13.

The discharge of the pressurized compressed air from the air-end 11 contains a large quantity of lubricant. This lubricant has to be separated from the compressed air before the latter passes into use. The compressed air and lubricant mixture is therefore discharged from the air- end 11 to the reclaimer 13 via an appropriate duct 24.

The separation of the gas and lubricant is achieved in two stages; primary separation of the lubricant and gas is carried out within the reclaimer 13 and final separation is completed through a special filter 18 which in the example shown is integral with the reclaimer 13 although it may be fitted downstream of the reclaimer 13. As is known per se the line 16 between the reclaimer 13 and the air-end 11 passes through a lubricant cooler 28.

A by-pass 16A controlled by a thermostatic valve is provided which diverts the lubricant through the by-pass when the temperature of the lubricant from the reclaimer is below a predetermined operating temperature.

The fully cleaned yes is subsequently passed through an after cooler 19 before passing to the plant discharge 20 and into use. A pressure transducer 26 responds to the pressure in the customer's gas main to energise the control system as and when required.

A small amount of reclaimed lubricant is injected directly to the air end 11 through a scavenge pipe 27 but the bulk of the reclaimed lubricant returns from the reclaimer 13 and filter 18 to the air end 11 through the line 16.

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À 8 8 ' À 4. In accordance with the present invention a thermostatically controlled restrictor valve 22 may be incorporated in the lubricant return line 16 simply by cutting the pipe 16 and connecting one cut end to the inlet 32 of the valve and the other cut end to the outlet 33 of the valve. The valve 22 comprises a housing 30 having a blind bore 31 communicating at its open end with the inlet 32 of the housing. The outlet 33 of the housing communicates with a cylindrical chamber 34 of greater diameter than the bore 31 and surrounding the same intermediate its ends. Axially slidable within the bore 31 is a sleeve 35 which has circumferential slit-like openings 36 and 36A in the same plane intermediate its ends. As shown in Figure 2, when the sleeve 35 is in a fully raised position within the bore 31 the openings 36 and 36A are fully in register with the chamber 34 and the flow of the lubricantbetween the inlet 32andtheoutlet 33 of the housing is substantially unrestricted by the sleeve 35. When the sleeve 35 is fully lowered in the bore 31 (Figure 3) on the other hand it restricts the flow of lubricant into the chamber 34 from the inlet 32.

Movement of the sleeve 35 is under the control of a thermostatic device which comprises a cylinder 37 integral with one end region of the sleeve and a piston 38 fixed relative to the blind end of the bore 31. Between the free end of the piston 38 and the blind end of the cylinder 37 is a capsule (not shown) of a wax which increases in volume as its temperature rises and it liquifies and decreases in volume as it solidifies as its temperature decreases. Because the wax is located where it will be exposed to the temperature of the lubricant flowing between the inlet 32 and outlet 33 of the housing as the temperature of the lubricant increases the sleeve 35 will be lifted from the position of Figure 3 to the position of Figure 2, thus increasing the flow of lubricant through the housing 30.

Conversely as the temperature of the lubricant falls and the wax solidifies and reduces in volume a compresion spring 39 will urge the sleeve 35 from the position of Figure 2 to the position of Figure 3, thus restricting lubricant flow through the housing 30. The provision of the spring 39 of course means that the valve operates independently of gravity so that the attitude of the device 22 when included in the line 21 is immaterial.

To ensure that there is always a minimum flow of lubricant through the housing 30 irrespective of the position of the sleeve 35 a by-pass line 40 is provided in the housing directly connecting the inlet 32 with the chamber 34. This safeguards against any malfunctioning or blockage of the

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sleeve 35 such as to cut off the flow of lubricant altogether or reduce it below a minimum level which will not adequately lubricate the bearings of the air-end. If necessary the by-pass line 40 has a restriction 41, which may be adjustable.

The invention has been described by way of example as applied to a screw compressor but it is also applicable to piston or sliding vane compressors of the kind which are similarly cooled by recycled lubricant.

Claims

f2,','.t2 '" " is, CLAIMS:

1. A retro-fit device for incorporation in a lubricant-cooled compressor, the compressor being of the kind which discharges a mixture of lubricant and compressed gas and wherein means is provided for separating the lubricant from the compressed gas downstream of the compressor and for returning the separated lubricant to the compressor, the device comprising a housing having an inlet and an outlet whereby it may be incorporated in the line between the separating means and the compressor by which lubricant is returned to the compressor and a thermostatically controlled restrictor valve within the housing located in the passage between the inlet and outlet with the temperature sensitive element of the thermostat exposed to the temperature of lubricant flowing between the inlet and outlet such that the restrictor valve will restrict said flow when said temperature falls and increase said flow when said temperature increases.

2. A device as claimed in claim 1, wherein the outlet communicates with a cyclindrical chamber within the housing which is coaxial with, intermediate the ends of and of greater diameter than a bore within the housing communicating with the inlet, a sleeve being movable axially of the bore whereby an opening in the wall of the sleeve may be brought into or out of register with the chamber, the thermostat being within the bore whereby it will respond to changes in the temperature of lubricant passing through the housing thereby to displace the sleeve to vary the area of said opening which is exposed to the chamber.

3. A device as claimed in claim 2, wherein the thermostat may comprise a cylinder moveable with the sleeve, a piston fixed at one end relative to the housing and a wax within the cylinder at the free end of the piston, the wax being of a kind which increases in volume as it liqulfies in response to an increase in temperature.

4. A device as claimed in claim 3, wherein the cylinder is spring loaded to move the sleeve to restrict the lubricant flow when permitted so to do as the wax solidifies in response to a drop in lubricant temperature.

5. A device as claimed in any of the preceding claims, wherein by-pass means is preferably provided in the housing by passing the thermostatically controlled restrictor valve, the by-pass means being adapted to ensure a

: *; À r. À À À a,, À minimum return flow of lubricant to the air-end independently of the restrictor valve.

6. A device as claimed in claim 5, wherein the by-pass duct has a restriction.

7. A device as claimed in claim 6, wherein the restriction is adjustable.

*. . . . À À. 8 À

8. 8

À À I À 8. À À À Àe

6. A device as claimed in claim 5 as appendant to any one of claims 2-4, wherein the by-pass means comprises a by-pass duct within the housing which directly communicates the inlet with said chamber.

7. A device as claimed in claim 6, wherein the by-pass duct has a restriction. 8. A device as claimed in claim 7, wherein the restriction is adjustable.

9. A retro-fit device for incorporation in a lubricant-cooled gas compressor, the compressor being of the kind which discharges a mixture of lubricant and compressed gas and is provided with means for separating the lubricant from the compressed gas downstream of the compressor and for returning the separated lubricant to the compressor, the device being substantially as hereinbefore described with reference to and as shown in Figure 2 and Figure 3 of the accompanying drawings.

Amendments to the claims have been filed as hilows CLAIMS:

1. A retro-fit device for incorporation in a lubricant-cooled compressor, the compressor be mg of the kind which discharges a mixture of lubricant and compressed gas and wherein means is provided for separating the lubricant from the compressed gas downstream of the compressor and for returning the separated lubricant to the compressor, the device comprising a housing having an inlet and an outlet whereby it may be incorporated in the line between the separat mg means and the compressor by which lubricant is returned to the compressor, a bore between the inlet and outlet, a thermostatically controlled restrictor valve within the bore located so that a temperature sensitive element of the thermostat is exposed, in use, to the temperature of lubricant flowing between the inlet and outlet, and a sleeve moveable in the bore by the valve whereby an opening in the sleeve will control the outlet and restrict said flow when said temperature falls and increase said flow when said temperature increases.

A. . 2. A device as claimed in claim 1, wherein the the outlet communicates: '.

with a cylindrical chamber within the housing which is Coaxial with,....

intermediate the ends of and of greater diameter than said bore, and ÀÀ.

. wherein the sleeve is moveable axially of the bore whereby said opening in the wall of the sleeve may be brought into or out of register with the chamber, the thermostat being responsive to changes in the temperature of lubricant passing through the bore thereby to displace the sleeve to vary the area of said opening which is exposed to the chamber.

3. A device as claimed in claim 2, wherein the thermostat Comprises a cylinder moveable with the sleeve, a piston fixed at one end relative to the housing and a wax within the cylinder at the free end of the piston, the wax being of the kind which increases in volume as it liquifies in response to an increase in temperature.

4. A device as claimed in claim 3, wherein the cylinder is spring loaded to move the sleeve to restrict the lubricant flow when permitted so to do as the wax solidifies in response to a drop in lubricant temperature 5. A device as claimed in any one of claims 2-4, wherein a by-pass duct is provided in the housing by passing the thermostatically controlled restrictor valve, the duct directly communicating the inlet with said

chamber to ensure a minimum return flow of lubricant to the Compressor independently of the restrictor valve.