Rotary compressor systems conventionally comprise a compressor unit driven by a motor which receives a gas to be compressed through inlet valving and delivers a compressed gas and liquid lubricant mixture to some form of separator to separate the liquid from the compressed gas. Clean compressed gas is delivered from the separator normally through a final filter element to a clean compressed gas storage tank from which the compressed gas is drawn as required by an end user. The liquid lubricant is returned from the separator via a filter and liquid cooler to an inlet region of the compressor unit. The cost of such systems is to some extent related to the number of parts of the system and the piping and connecting joints that are required to connect the system parts together. Moreover the number of parts tend to produce a relatively large or bulky compressor system package which in itself is undesirable and leads to added costs. There have been numerous attempts to restrict rotary compressor package size and to restrict the amount of piping and connecting joints required in the system by various means.

U. S. Patent Specification No. 5,487,769 discloses one possible form of integrated apparatus for separating liquid lubricant from a hot compressed gas and for cooling the separated liquid lubricant which might be used in a rotary compressor system. In the apparatus disclosed in U. S. Patent No. 5,487,769, the mixture of liquid lubricant and hot compressed gas is delivered to a first inner chamber within an outer container wall whereby liquid lubricant collects in a lower region of the inner chamber. A first group of cooling tubes extend upwardly from a lower region of the inner chamber to a further or second chamber within the outer container wall with a second group of cooling tubes leading downwardly from the second chamber to a third chamber located below the first inner chamber. Liquid lubricant is caused to flow from the lower region of the first inner chamber through the first group of cooling tubes to the second chamber and therefrom through the second group of cooling tubes to the lower third chamber. A fan is provided to blow a cooling air flow over the two groups

of cooling tubes.

The objective of the present invention is to provide improved arrangements for use within a rotary compressor system which will enable a decrease in the cost of the system while also enabling the production of a rotary compressor system having a smaller overall package size. A preferred objective is to provide an improved arrangement for separating and cooling liquid lubricant from heated compressed gas flow in rotary compressor systems.

In the following description, reference will be made to"air"and "compressed air", however, it should be recognised that any"gas"or "compressed gas"could also be substituted for this terminology. Moreover,"oil" should be understood to include any liquid lubricant including synthetic oils or water.

Accordingly, the present invention provides a combined arrangement for cooling a liquid lubricant and for separating said liquid lubricant at least partially from a compressed gas stream for use in a rotary compressor system, said arrangement including upper header vessel, a second lower header vessel, a plurality of tube means extending downwardly from said first upper header vessel to said second lower header vessel connecting internal zones of said header vessels whereby the liquid lubricant collecte in a lower region of said first upper header vessel can flow down said tube means to be received in said second lower header vessel, said first upper header vessel including first inlet means for receiving a mixture of liquid lubricant and compressed gas and a compressed gas outlet means leading from an upper region of said first upper header vessel, and said second lower header vessel including a liquid lubricant outlet means.

Preferably each of the said tube means extends into said first upper header vessel to form a weir means spaced from an inner wall surface of said first upper header over which, in use, the liquid lubricant flows to pass downwardly along said tube means, said first inlet means being located above said weir means.

Conveniently the compressed air and oil inlet means may include an inlet tube means extending into said first upper header vessel and along at least a

portion of an upper wall zone of said first upper header vessel. Preferably, the inlet tube means includes a plurality of openings directed towards said upper wall zone of the first upper header vessel. Preferably the second lower header vessel includes an oil filter through which said oil passes to reach said oil outlet means. In an alternative preferred arrangement, said oil outlet means may be connected to an oil filter means. Preferably said compressed gas outlet means is connected to a separator filter element. Conveniently a pre-separator means is provided within the first upper header vessel between said compressed air and oil inlet means and said compressed gas outlet means.

The present invention also anticipates providing a rotary screw compressor system including an oil cooler and compressed air and oil separator arrangement as described above.

Several preferred embodiments of the present invention will hereinafter be described with reference to the accompanying drawings, in which:- Figure 1 is a schematic drawing of a rotary compressor system including an arrangement according to the present invention; Figure 2a is a detailed view of one preferred embodiment of an oil cooler and compressed air and oil separator arrangement according to the present invention; Figure 2b is a cross-sectional view taken along line B-B of Figure 2a; Figures 3a and 3b are detailed cross-sectional views of alternative tube configurations capable of use in the present invention; and Figures 4a, 4b, 4c and 4d are alternative possible weir arrangements capable of use in the present invention.

Referring first to Figure 1, a typical rotary compressor system 10 is illustrated embodying a combined oil cooler and oil separator in a single assembly 11, which is described hereinafter in greater detail with reference to Figures 2a and 2b. The rotary compressor system comprises a rotary compressor unit 12 (typically a screw compressor unit) driven by a motor 13.

The compressor unit 12 receives air to be compressed through an inlet air filter and valve arrangement 14. Compressed air and entrained oil mixture is discharged from the compressor unit 12 along line 15 to be received through an

inlet 16 of the assembly 11. Compressed air is separated from the entrained oil in the assembly 11 and is delivered via an outlet 17 to a final separator filter 18.

A minimum pressure valve 19 is provided to require the compressed air within the assembly 11 to be at a minimum pressure before it is discharged via line 20 to a storage vessel 21 from which it can be drawn, as required, by an end user.

Oil separated from the compressed air in the assembly 11 flows downwardly and is discharged via an outlet 22, an oil filter 23 and a line 24 to be returned to an inlet region of the compressor unit 12. Figure 1, apart from the assembly 11, illustrates a basic rotary compressor system and it will be recognised that any refinements and modifications to the operation and configuration of the system known from the prior art can also be employed in the practical performance of this invention.

Reference will now be made to Figures 2a and 2b of the annexed drawings. The assembly 11 includes a first upper header vessel 25 in the form of a tube, a second lower header vessel 26 also in the form of a tube, and a plurality of tubes 27 interconnecting the interior zone 28 of the upper header vessel 25 to an interior zone 29 of the lower header vessel 26. The upper header vessel 25 may be made from steel circular pipe or pipe made from any other material including plastics with end caps 30,31 secured thereto, conveniently by welding. The vessel 25 may not necessarily be made from circular pipe but could also be made from any other readily available pipe cross- section. For example, oval, square or rectangular pipe might also be used. In some applications, oval or rectangular pipe where the major axis of the cross- section is arranged vertically, might be preferred. Figure 2a illustrates the lower header vessel 26 to also be made from pipe closed at both ends by end caps 32,33 welded to the pipe section. The pipe section of the lower header vessel 26 may be the same size and cross-section as the upper header vessel 25 or alternatively the size and/or cross-section may be different. Furthermore, while Figure 2a illustrates the lengths of the vessels 25,26 to be generally the same, this would not necessarily always be the case.

The inlet 16 to the assembly 11 for the mixture of compressed air and entrained oil droplets delivered via line 15 includes a tube 34 closed at an inner

end 35 and arranged to run adjacent to an upper inner wall zone 36 of the upper header vessel 25. The tube 34 includes a plurality of upwardly and outwardly directed apertures 37,38 to direct a flow of compressed air and entrained oil against the inner wall zone 36. This will provide a first primary separation of oil from the compressed air such that the oil will flow down along the walls of the vessel to be collected in a pool 39 in the bottom of the upper header vessel 25. The compressed air released by this primary separation flows along an upper zone 40 of the vessel 25 to the outlet 17. As shown in Figures 2a and 2b, the pipes or tubes 27 extend an equal distance into the interior of the vessel 25 with the open end of the tubes 27 acting as a weir 41 over which oil flows when the level in the pool 39 has increased to a sufficient level. While passing over such a weir arrangement, oil generally flows down the inside surface of the tubes 27 in good thermal contact therewith. This allows space for further compressed gas released from the oil to flow upwardly through the central region of the tubes 27 ultimately to the outlet 17. The downwardly flowing oil collects in the second lower header vessel 26 to be ultimately returned via the filter 23 to the compressor unit 12. While the oil filter 23 is shown external to the lower header vessel 26, it may be mounted either horizontally outwardly or inwardly of the vessel 26 or upside down relative to the configuration shown in Figure 2a.

As further illustrated in Figures 2a, 3a and 3b, various means may be provided to improve the dissipation of heat from the oil flowing downwardly in the tubes 27. This may include the provision of outer fins 42 either separate to or integrally formed with tubes 27, and internal tubes 43 to increase the area of oil flowing downwardly in heat conductive contact with the metal of the tube or tubes 27,43. The material of the tubes 43,27 may be selected to improve heat conduction capabilities and may include steel, copper and aluminium and their alloys.

As shown in Figure 2a, the end of the upper header vessel 25 adjacent the outlet 17 may have a wire mesh pre-separator device 44 through which the compressed air must flow to reach the outlet 17. If desired a baffle or weir member may be provided to retain the oil pool 39 to the right thereof with the

wire mesh pre-separator device 44, at least in normal operation, remaining substantially out of bulk oil contact. The final separator filter element 18 may be configured as shown in Figure 2a, inverted from this configuration, horizontal disposed, or even mounted to a vertical extension of the interior of the upper header vessel 25. The minimum pressure valve 19 may be of any conventional design.

Figures 4a to 4d illustrate various possible cooling tube weir means 41 as alternatives to the use of an open ended tube as shown in Figures 2a, 2b. It is generally desirable to have the tube ends in the configuration of Figures 2a, 2b fairly accurately in the same horizontal plane to ensure an even distribution of oil flow down all the tubes 27. If, however, the assembly 11 is mounted, in use, at several degrees off the horizontal, oil flow will predominate down one or perhaps a few tubes 27 thereby limiting the potential cooling effect of the arrangement. To minimise the effect of this, arrangements as shown in Figures 4a to 4c might be used. In these arrangements one or more apertures 50 are provided around the circumference of the tube 27 with each such aperture 50 having a lower, preferably horizontal, weir edge 51 and upstanding and converging side edges 52,53. The edges 52,53 may be straight or curved as illustrated. The effect of these arrangements is that if the assembly 11 is titled, the relatively lower tube ends will receive less flow through the apertures 50 because of the converging side walls than the relatively higher apertures 50 which counteracts the effect of the tilt. As shown in Figure 4c, the end of the tube 27 might be open or might include a passage 54 to enable compressed air from the tube to flow ultimately to the outlet 17. Figure 4d illustrates another possible weir arrangement where the flow passage is defined essentially by a circumferential gap 56 above the tube end edge 55. Thus if the oil level 57 builds up to above the top edge of the gap 56, no further flow is permitted into the tube 27 thereby maintaining oil flow along the inner walls of the tube.

The arrangements described in the foregoing enable a screw compressor system to be built with an oil separator and oil cooler combined in a package or volume size not substantially bigger than a normal oil cooler for such a system.

This overall package size is reduced, piping and piping connections are reduced and overall manufacturing costs are reduced.