AU729486B2

AU729486B2 - Improvements to compressor systems

Info

Publication number: AU729486B2
Application number: AU53881/98A
Authority: AU
Inventors: Anthony John Kitchener; Gerard Daniel Kitchener
Original assignee: CASH RES SCREW COMPRESSORS Pty
Current assignee: Individual
Priority date: 1997-02-11
Filing date: 1998-02-11
Publication date: 2001-02-01
Anticipated expiration: 2018-02-11
Also published as: AU5388198A

Description

riutnu i i 2twb1U Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged:

C

Invention Title: IMPROVEMENT[S TO COMPRESSOR SYSTEMS The following statement is a full description of this invention, including the best method of performing it known to us 1 IMPROVEMENTS TO COMPRESSOR SYSTEMS The present invention relates to improvements in compressors, particularly rotary screw compressors.

The use of rotary screw compressors to compress gases such as air for industrial purposes is widespread. Such compressor units used are a major source of noise, and consequently it is common to enclose the compressor unit, including all operational components except the storage vessel, within a noise attenuating cabinet. The storage vessel may be located remotely from the enclosed cabinet.

In contrast, it is common for small piston compressors to be manufactured with the compressor and motor mounted directly onto the storage vessel. The :whole unit including the storage vessel is then enclosed in a noise attenuating cabinet to reduce noise. A cabinet to receive the compressor unit and storage vessel is expensive and restricts access to parts that require regular servicing.

15 This specification will refer to the compression of air, however it is to be :understood that the present invention is applicable to the compression of any 00 gas.

Compressor systems include inlet arrangements for admission of the air to be compressed, the arrangement normally regulating air flow in some way 20 into a compressor unit. Typically the inlet is required to regulate the amount of air flowing into the compressor in order to keep the compressed air receiver vessel at or below a certain preset maximum pressure. This has been accomplished in the past using a feedback system, whereby the pressure in the receiver vessel is monitored and the compressor inlet closed or restricted when the receiver vessel pressure achieves the preset maximum pressure level. This method of controlling the inlet flow is expensive.

Further, when the receiver vessel pressure achieves the preset maximum pressure level, the motor and compressor would often be turned off. Similarly, when demand for compressed air had ceased, the motor and compressor would be turned off.

2 This can create problems, especially in screw compressors, where the pressure downstream from the compressor can leak back through the compressor, out through the inlet and escape into the atmosphere. There are many problems associated with the leakage of compressed air, for example the air which has just been compressed in a screw compressor contains significant amounts of oil, which will escape out of the inlet with the leaking compressed air when the compressor is switched off. This leads to oil loss in the system and spilt oil around the air inlet which is hazardous in the workplace, environmentally unfriendly and unsightly.

Another problem with rotary compressor systems is that often, the motor will drive the compressor through a belt drive system and the tension in the belt must be kept within a preset range. In order to tension the belt, the compressor and motor have had to be securely mounted in a subframe. Conventional belt *:drive systems typically incorporate additional pulleys designed to be locked into 15 place to adjust the tension. As the belt wears and the tension changes and therefore a regular program of belt tension adjustment is required.

The present invention therefore seeks to solve at least one of the abovementioned problems. Further, the present invention preferably seeks to provide a compressor system package that has a lower centre of gravity than 20 existing compressor systems mounted to receiver vessels, reduced enclosure package costs, provide better access for servicing, and reduced noise transmission levels.

Accordingly, a first aspect of the present invention provides a rotary gas compressor system including a rotary compressor unit, a motor driving said compressor unit, a compressed gas liquid separator vessel, and a receiver vessel to receive the clean compressed gas, said rotary compressor unit and said motor being housed within a sound attenuating enclosure with said separator vessel and said receiver vessel being located externally of said sound attenuating enclosure.

3 This provides the advantage that the separator vessel is external to the enclosure, thus allowing the enclosure to be of reduced dimension, the system to have a lower centre of gravity as the separator vessel can be positioned on the ground, and allows greater access to the separator vessel.

Preferably, the enclosure may be mounted on the receiver vessel thus reducing the overall package costs. As rotary compressors do not have pulses of gas entering the receiver vessel, unlike piston compressors, the receiver vessel is not a substantial source of noise. Additional sound attenuation can be provided by mounting the motor and or compressor to the receiver vessel via vibration isolating mounts.

A second aspect of the present invention is a vibration isolating mount for a motor or compressor comprising a shaft spaced from a tube by an elastomeric material. This arrangement has been found to restrict the flow of vibration and noise from the motor and/ or compressor. This is especially important if the 15 motor is attached to a metal surface such as a receiver vessel.

*A third aspect of the present invention is an apparatus for tensioning a drive belt connecting a motor to a compressor wherein one of either the motor or compressor is securely located and the other of the motor or compressor is pivotally supported by a single support member arranged such that the weight of 20 the other of the motor or compressor provides a self adjusting tensioning means for the drive belt. In this way the motor and compressor can be mounted such that the drive belt is constantly kept at the correct tension without the need for S* additional tensioning devices.

A fourth aspect of the present invention is a gas inlet for a compressor system including a motor, compressor, gas liquid separator vessel, a receiver vessel and control means, wherein gas flow through the inlet in either direction is regulated by a control means controlling a valve in response to pressure in the receiver vessel. The inlet is closed when the pressure in the receiver reaches a predetermined level, and the closure of the valve also restricts the leakage of compressed gas and oil out of the inlet.

4 In a preferred embodiment, the gas inlet includes an inner body containing an aperture through which compressed gas may escape when the control means closes the inlet with the valve by diverting compressed gas from the separator vessel to the inner body, which houses the valve. The increased pressure behind the valve causes the valve to move to a closed position. The compressed gas in the inner body behind the valve is able to leak through the aperture, thus decreasing the pressure downstream of the compressor and in the separator vessel. This has the advantage that the air escaping is sourced from the separator vessel and is therefore substantially oil free. Further, the gas pressure downstream of the compressor will drop once the inlet valve is closed and the aperture open, which reduces the pressure difference across the compressor and therefore less air will leak past the compressor. This also reduces part or no load power consumption as the pressure across the compressor is reduced.

15 PREFERRED EMBODIMENT One of the embodiments of the present invention will now be described with reference to the accompanying diagrams in which: Figure 1 shows a schematic side view of the compressor system of a first aspect of the present invention with interconnecting piping omitted for the sake S. 20 of clarity; Figure 2 shows a schematic end view of the compressor system of the first aspect of the present invention again with interconnecting piping omitted for S•the sake of clarity; S"Figure 3 shows a schematic cross section of a separator vessel in accordance with a second aspect of the present invention Figure 4 shows a schematic cross section of an air inlet in accordance with a third aspect of the present invention.

Figure 5 shows a schematic side view of an apparatus for tensioning a belt in accordance with the present invention.

In figures 1 and 2, a rotary screw compressor system 20 is shown. The system 20 consists of a compressor package 21 joined to a vessel 6 by a number of side plates 14. The compressor package 21 consists of a cabinet 1 enclosing a motor 2, a rotary compressor unit such as airend 3, a cooler 5, an inlet filter 12 and an inlet regulator 13. A separator vessel 4 is mounted externally from the cabinet 1 which allows a smaller and therefore cheaper cabinet 1 to be used, as the separator vessel 4 is not a major source of noise.

Further, the separator vessel 4 requires frequent maintenance and enclosure in a cabinet would add to the compressor down time and maintenance time.

Also in figures 1 and 2, locating and mounting assemblies 60 for mounting the motor 2 and airend 3 onto the receiver vessel 6 is disclosed. The airend 3 is mounted to support tubes 9 of the locating assemblies 60, the support tubes 9 being mounted from shafts 11 via bushes 10. Each support tube 9, one at either end of the airend 3 as shown in figure 2, enclose one of the shafts 11, which is supported between endplates 14. Isolating and supporting the tubes 9 on the shaft are bushes 10, typically made from a flexible material such as poly-urethane, as shown in figure 5. As there is no metal to metal 15 contact, the transmission of vibration from the airend to the storage vessel is greatly reduced. This arrangement eliminates metal to metal contact which has been a major source of noise generation and transmission.

The motor 2 is similarly fixed to a base plate 41 which is supported by a single locating assembly 60 consisting of tube 9, bush 10 and shaft 11 similar to 20 those described above for mounting the airend 3. As motors used with airends are typically electrically powered and the transmission of the power to the airend 3 is via a belt 40, the motor is relatively free of large out of balance forces.

However, there is a need to tension the belt between the motor 2 and airend 3.

Accordingly, in the present invention the motor 2 is only attached to a single locating assembly 60, as shown in figures 1 and 5. By placing the shaft 11 in a position close to the airend 3, torque is generated around shaft 25 due to the weight of the motor 2. This torque is counteracted by the belt 40, thus providing tension to the belt 40. The amount of tension desired can be adjusted depending on the weight of the motor 2, by the positioning of the locating assembly 60, either closer to the centreline of the motor 2 to decrease the torque, or further away from the centreline of the motor 2, to increase the torque.

Alternatively weight may be added to the platform on which the motor 2 sits.

6 It is envisaged that the position of the locating assembly will be fixed in a predetermined optimum position for a given type of motor.

It should be realised that the above system of tensioning the drive belt can be reversed and the motor 2 may be supported by two locating assemblies 60 and the airend 3 by a single locating assembly 60, whereby the belt 40 will still be tensioned by the weight of the airend 3.

Typically, the separator vessel employed is a substantially vertical or horizontal cylinder. A type of oil separator vessel 4 can be seen in Figure 3, wherein the vessel 4 includes upper end plate 23 and lower end plate 24.

Attached to upper end plate 23 is a plate 18, which forms a seal with the upper end plate 23. A mixture of oil and air from the outlet of the airend 3 enters the vessel 4 through an inlet 15 which is perpendicular to the centreline of the cylindrical vessel 4, where the oil sinks under gravity to the lower part of the vessel and collects. The oil collected in the bottom of the vessel 4 then passes 15 through a filter 16 and returns to the airend 3 through outlet 17. Compressed air S* passes through an air/oil separator filter 19 removing most of the oil left in the air. The air then passes out of the vessel 4 through a valve 21 which ensures the pressure of the air leaving is above the minimum pressure desired. A purge line 31 scavenges any oil remaining at the bottom of the air/oil separator 19, and returns this to the airend 3. The location of the oil filter 16 at the bottom of the vessel 4 situated in the collected oil 22 removes the need for a separate oil filter, thus reducing leakage and making the overall unit cheaper.

"In order to regulate the flow of atmospheric air into the inlet regulator 13, a valve assembly 32 is fitted, as shown in figure 4. The valve 32 is typically fitted between the air inlet filter 12 and the airend 3. Normally the most expensive part of an inlet valve is the valve body. A valve body 35 is shown comprising a t-piece, which may be constructed from readily available parts, thus substantially reducing the cost. A valve seat 26 and inner body 29 are attached to interior of the valve body 35, preferably by a threaded arrangement. An actuator 30 is slidably located within the inner body 29 and is driven by compressed air from the airend 3. A valve 28 is situated on the inlet side of the actuator 30 as shown in figure 4. In use, a control means including a solenoid 33 is connected to the receiver vessel 6, and when maximum pressure is reached, the solenoid 33 opens a connection from the separator vessel 4 to the inner body 29, which allows compressed air to flow into the inner body 29 of the inlet regulator 13.

The increased pressure in the inner body 29 pushes the actuator and valve 28 onto the valve seat 26 thus stopping the flow of air through the inlet regulator 13.

A biasing spring (not shown) may be used to keep the valve and actuator away from the valve seat when the pressure in the receiver vessel 6 is below the predetermined maximum.

While the air pressure in the receiver vessel is at or above the maximum pressure, compressed gas can escape to the atmosphere from an aperture 37 in the inner body 29 thus lowering the pressure inside the separator vessel 4, and reducing part load power consumption of the airend by reducing the pressure difference across the inlet and outlet of airend 3. When the air pressure in the 15 receiver vessel is below the maximum pressure, the solenoid 33 does not allow air to enter the inner body 29 and therefore there is no loss of compressed air.

An added benefit is that when the airend 3 is running but not pumping air (ie when the receiver is full), the compressed air leaks past the rotors of the airend and tries to return back along the inlet. This is controlled by this aspect of 20 the present invention by the valve 28, which does not allow air and any accompanying oil, to escape from the inlet. This is important as the air leaking out of the upstream side of the airend 3 contains significant amounts of oil, which would leak out of the inlet, and may foul the inlet filter. Further, the aperture 37 allows compressed air to flow from the inner body 29, and as the compressed air has come out of the separator vessel it is substantially oil free.

Accordingly, the pressure in the separator vessel and downstream of the compressor reduces and therefore pressure across the rotors decreases which results in less air leaking past the rotors and towards the inlet regulator 13.

Further, part load power consumption is reduced as the pressure differential across the airend 3 is reduced.

Claims

1. A rotary gas compressor system including a rotary compressor unit, a motor driving said compressor unit, a compressed gas/liquid separator vessel, and a receiver vessel to receive the clean compressed gas, said rotary compressor unit and said motor being housed within a sound attenuating enclosure with said separator vessel and said receiver vessel being located externally of said sound attenuating enclosure.

2. A rotary gas compressor system according to claim 1 wherein the compressor unit and the motor are located above and are mounted from said receiver vessel.

3. A rotary gas compressor system according to claim 1 or claim 2 wherein the receiver vessel forms part of the enclosure.

4. A rotary gas compressor system according to any one of claims 1 to 3 wherein the motor or the compressor or both are mounted to the receiver vessel by vibration isolating mounts comprising a tube spaced from a shaft by an Selastomeric material.

5. A rotary gas compressor system according to claim 4 wherein in the or each said vibration isolating mount the tube is able to rotate with respect to the shaft. S6. A rotary gas compressor system according to claim 5 wherein one of either the motor or the compressor unit is securely located with a drive belt actively connected between the motor and the compressor unit, the other of the motor or compressor being pivotally supported by a single vibration isolation mount arranged such that the weight of either the motor or compressor unit tensions the drive belt so that the drive belt connecting the securely located motor or the compressor unit to the other of the motor or the compressor unit is tensioned by pivotal movement of the other of the motor or the compressor unit.

7. A rotary gas compressor system according to any of claims 4 to 6, wherein the vibration isolating mount or mounts connect the motor and/or the compressor unit to the receiver vessel. ooooo

8. A rotary gas compressor system according to any one of claims 1 to 3 further including apparatus for tensioning a drive belt connecting the motor to the compressor unit wherein one of either the motor or the compressor unit is securely located and the other of the motor or the compressor unit is pivotally supported by a single support member arranged such that the weight of the other of the motor or the compressor unit provides a self adjusting tensioning means for the drive belt. S9. A rotary gas compressor system according to claim 8 wherein the motor and the compressor unit are attached to the receiver vessel of the compressor system. A rotary gas compressor system according to any one of claims 1 to 9 wherein the compressor unit includes a gas inlet for introducing gas to be compressed into the compressor unit, gas flow through said gas inlet to the compressor unit in either direction being regulated by a control means controlling a valve in response to pressure in the receiver vessel.

11. A rotary gas compressor system according to claim 10 wherein gas and or oil is restrained from leaking out of the gas inlet by the valve actuated by pressure from compressed gas in the separator vessel, such that the control means actuates the valve to close the inlet when the pressure in the receiver vessel reaches a predetermined limit.

12. A rotary gas compressor system according to claim 10 or claim 11 wherein the gas inlet includes an inner body containing an aperture through which compressed gas may escape when the control means closes the inlet with the valve by diverting compressed gas from the separator vessel to the inner body, which houses the valve thus decreasing the pressure downstream of the compressor unit and in the separator vessel.

13. A rotary gas compressor system as claimed in any one of claims 10 to 12 wherein an actuator for the valve is biased towards a position open. o.

14. A rotary gas compressor system as claimed in any one of claims 10 to 13 wherein the gas inlet includes a hollow T-shaped inlet body. oo.. DATED this 27th day of November, 2000 CASH RESEARCH SCREW COMPRESSOR PTY. LTD. WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA SKP/SJM:BA:jc P9590AUOO