GB2075597A

GB2075597A - Rotary air compressors

Info

Publication number: GB2075597A
Application number: GB8014662A
Authority: GB
Original assignee: Hydrovane Compressor Co Ltd
Current assignee: Hydrovane Compressor Co Ltd
Priority date: 1980-05-02
Filing date: 1980-05-02
Publication date: 1981-11-18
Also published as: IT8148385A0; GB2075597B; ES501757A0; ES8300954A1; DE3162344D1; EP0050638B1; WO1981003207A1; EP0050638A1; HK97384A

Abstract

A rotary oil mist compressor has a rotor stator unit (10, 12) in which, in use, air is compressed and oil is injected into the air. A primary separation means comprising an impingement shield (24) around the stator separates the majority of the entrained oil droplets from the compressed air. Secondary separation means comprising one or more tubular filters (40) separate substantially the remainder of the entrained oil. The pathway between the primary and secondary separation means includes four substantially right angle bends, two of which are at the entry and exit of a secondary separation manifold (38) in which oil is coalesced by the acceleration and turbulence which occurs at each bend and then returned by the compressor pressure for re-use. The oil separation load on the tubular filters is thus reduced and the oil separation efficiency increased.

Description

SPECIFICATION Rotary compressors The invention relates to rotary oil mist com pressors, and is particularly concerned with the separation of the oil from the compressed air.

The term oil mist compressor is used herein to refer to those compressors, e.g. of eccentric rotor sliding vane type or of screw type in 'which oil is injected into the air to be com pressed and is subsequently separated from the compressed air, the separated oil being returned to the air inlet or sump of the compressor. In such compressors it is desir able that the separation of the oil from the compressed air be as efficient as possible firstly because it is frequently inconvenient for the compressed air to have a significant amount of entrained oil in it, and secondly because oil that is not separated is lost and must subsequently be replaced.

According to the present invention there is provided a rotary oil mist compressor having a rotor stator unit in which, in use, air is com pressed and oil is injected into the air and including a primary oil separation means for removing a proportion of the entrained oil from the air and a secondary oil separation means for removing substantially the remain der of the oil, the primary and secondary oil separation means being connected by a path way so constructed that, in use, the air is constrained to flow through three and prefera bly four successive bends pf substantially 90 .

At each of these bends the acceleration and turbulence of the gas that is caused results in the coalescing and deposition of a proportion of the entrained oil thus reducing the separa tion load to which the secondary separation means is subjected, and thus increasing the service life of the secondary separation means.

The secondary separation means preferably comprises one or more tubular coalescing elements, of e.g. ceramic material and these are preferably arranged with their axes verti cal. This latter feature is found to be prefera ble to arranging the tubular coalescing ele ments with their axes horizontal as is conven tonal since the oil trickles rapidly downwards and results in a greater proportion of the elements being unclogged with oil and thus available for separation.

Preferably the or each coalescing element communicates at its upper end with a com mon secondary separation manifold extending transverse to the axis of the coalescing ele ments. In the preferred embodiment the or each coalescing element has within it a tube into which the compressed air is constrained to flow, the or each tube having a plurality of spaced apertures in its wall. Thus the com pressed air is constrained to turn through 90 to enter the tube within the coalescing elements and to turn through a further bend of 90 when leaving the tube prior to actually passing through the wall of the coalescing element.

In the preferred embodiment the rotor stator unit and the primary separation means are situated in a compressor housing and the secondary separation means is situated in a separate housing detachably secured to the compressor housing. The removability of the secondary separation housing facilitates exchange and servicing of the coalescing elements.

Preferably the secondary separation housing has a compressed air outlet at its upper end.

The compressed air will therefore pass through the coalescing elements and then up to the outlet, while the coalesced oil will trickle downwards. This will mean that the oil will accumulate in a comparatively calm area of the secondary separation housing thus reducing the risk that it be re-entrained by the compressed air.

Further features and details of the invention will be apparent from the following description of one specific embodiment which will be given by way of example with reference to the accompanying drawings in which: Figure 1 is a longitudinal section through the compression section of a compressor; Figure 2 is a non-planar axial section through the compressor which passes through the lines 2-2 in Fig. 1 and ll-ll in Fig. 3; Figure 3 is a longitudinal section through the secondary separation section of the compressor along the line 3-3 in Fig. 2; Figure 4 is a scrap sectional view through the oil return bolt in the secondary separation manifold.

The compressor is of eccentric rotor sliding vane type having a compression section, seen in Fig. 1, within a housing 2 removably connected to the side of which by bolts 3 is a separate secondary oil separation section within a housing 4.

The compression section of the compressor does not differ significantly from known constructions and will therefore only be described briefly. The housing 2 is closed by two removable end plates 6 and 8 between which a stator 10 is secured. Eccentrically mounted within the stator is rotor 1 2 which may be rotated by a drive shaft 1 4 and which leaves a crescent shaped working space within the stator. A series of longitudinal slots are formed in the rotor each of which accommodates a sliding vane 1 6. The lower portion of the casing 2 defines an oil sump. During operation of the compressor the oil is circulated by virtue of the compressor pressure through one or more oil coolers 7 in which the oil is cooled by virtue of an air flow caused by fan blades 9 on the drive shaft 1 4.

In use the rotor is rotated and the vanes are kept in contact with the interior of the stator by centrifugal force. Air is drawn into the stator through an inlet 1 8 which is controlled by an unloader valve 20 of known type. Oil is withdrawn from the sump and injected into the crescent shaped working space within the stator which ensures an adequate gas seai between the vanes and the stator and the end plates. The air within the crescent shaped working space is compressed as the rotor rotates, and the compressed air exits through a series of outlet ports 22 in the upper part of the stator.

Surrounding the stator and coaxial with it is an impingement shield 24 which constitutes the primary separation section connected to the right hand end plate 8 which extends down below the oil level in the sump as seen in Fig. 2. A large proportion of the entrained oil droplets in the compressed air coalesce on the impingement shield and drip down to the sump and the air with the remaining entrained oil droplets flows to the left, as seen in Fig. 1 and thence around the end of the impingement shield and back to the right. This deceleration and change of direction causes further entrained oil droplets to coalesce and drip down to the sump. The air then passes towards and out through an outlet 26 into the secondary separation section.

The outlet 26 is a thermally actuated shutoff valve of the type described in British patent specification No. 1,218,769 and comprises a fixed tube 28 at the inlet end of which is a cap 30 having a closed end and apertures 32 formed in its side wall which fits inside the wall of the tube 28. A spring 34 urges the cap into the closed position in which no gas can pass in through the apertures 32. In use, the cap 30 is secured in the open position by solder so that air can flow into it. If however the temperature of the compressed air should rise above a predetermined value the solder melts and the tube is closed by the cap 30 under the action of the spring 34. The compressor pressure will then rise rapidly and the compressor will be throttled down by the unloader valve and then optionally turned off altogether by control means (not shown).

At the downstream end of the tube 28 there are eight outlet apertures 36 which communicate with a secondary separation manifold 38. Below the manifold 38 within the housing 4 there are two vertically arranged tubular ceramic secondary separation oil filters or coalescing elements 40 whose lower ends are closed and which are connected at their upper ends with opposite ends of the manifold 38. Within each coalescing element there is a coaxially disposed metallic tube 42 whose lower end is closed, whose upper end communicates with the interior of the manifold 38 and is provided with a plurality of outlet apertures 44 spaced around its periphery and along its length. Compressed air in the manifold 38 therefore passes down into the tubes 42, through the outlet apertures 44 and thence through the walls of the ceramic tubes 30 along substantially their entire length.The gas then passes upwardly in the housing 4 and out through an outlet 46.

Situated in the manifold 38 is an oil return bolt comprising a hollow tubular bolt 48, seen in Fig. 4, in the wall of which a number of apertures 50 are formed. Entrained oil that is coalesced and separated from the gas in the manifold flows through the apertures 50 an'd is then returned to the sump by the compressor pressure through a bore 52.

The two ceramic elements 40 are separated by a baffle 54 upstanding from the floor of the housing 4. Oil separated by the ceramic elements drips down on to the floor and then into a respective oil return aperture 56 whence it is returned to the sump by the compressor pressure through a common oil return bore 58.

In use, the air is compressed as described above and a considerable proportion of the entrained oil is coalesced against the primary separation means constituted by the primary impingement shield 28 and drips down to the sump. The air then passes round the end of the impingement shield 28 turning through 180 , as shown by the arrows in Fig. 1, the acceleration and turbulence caused thereby resulting in further coalescing and deposition of oil. The air then passes through one of the apertures 32 into the tube 28, thereby turning through a further 90 . Any oil that is coalesced during this turn will also drip down to the sump or will sink to the bottom of the tube 28. The flow path of the air then turns through a further 90 when passing through one of the apertures 36 into the manifold 38.

Oil coalesced at this point will be deposited in the manifold 38, or in the tube 28 whence it will drip into the manifold. The air in the manifold then passes into one or other of the tubes 42, thus turning through a further bend of about 90 . The air then further passes through one of the apertures 44 in the tubes 42, turning through a further 90 bend and then through the material of the ceramic ele ments 40, where substantially all the remain ing entrained oil is coalesced. Finally the air passes upwards and then out through the outlet 46. Oil that is deposited within the manifold 38 is returned to the sump by the oil bolt 48 as described above, whilst oil coalesced by the ceramic elements 40 flows downwardly, drips onto the floor of the hous ing 4 and is returned to the sump via the bore 58.

The compressor in accordance with the invention provides compressed air that is sub stantially free of entrained oil. If one or more of the ceramic elements should become clogged it may simply be replaced by remov ing the lower portion of the housing 4. The entire housing 4 is detachable from the remainder of the compressor which facilitates access and servicing. It will be appreciated that any desired number of ceramic elements may be used according to requirements and in addition these may be arranged in series rather than in parallel. Although the invention has been described with reference to an eccentric rotor sliding vane compressor it will be appreciated that the invention is also applicable to, e.g. screw compressors.

Claims

CLAIMS 1. A rotary oil mist compressor having a rotor stator unit in which, in use, air is compressed and oil is injected into the air and including a primary oil separation means for removing a proportion of the entrained oil from the air and a secondary oil separation means for removing substantially the remainder of the oil, the primary and secondary oil separation means being connected by a pathway so constructed that, in use, the air is constrained to flow through three successive bends of substantially 90 . 2. A compressor as claimed in Claim 1 in which the pathway is so constructed that, in use, the air is constrained to flow through four successive bends of substantially 90 . 3. A compressor as claimed in Claim 1 or Claim 2 in which the secondary separation means comprises one or more tubular coalescing elements. 4. A compressor as claimed in Claim 3 in which the or each coalescing element is arranged with its axis substantially vertical. 5. A compressor as claimed in Claim 3 or Claim 4 in which the or each coalescing element communicates at its upper end with a common secondary separation manifold extending transverse to the axis of the coalescing elements. 6. A compressor as claimed in any one of Claims 3, 4 or 5 in which the or each coalescing element has within it a tube into which the compressed air is constrained to flow, the or each tube having a plurality of spaced apertures in its wall. 7. A compressor as claimed in any one of the preceding claims in which the rotor stator unit and the primary separation means are situated in a compressor housing and the secondary separation means is situated in a separate housing detachably secured to the compressor housing. 8. A compressor as claimed in Claim 7 in which the secondary separation housing has a compressed air outlet at its upper end. 9. A compressor as claimed in Claim 7 or Claim 8 when dependent on Claim 5 in which the compressor housing and the secondary separation housing communicate by means of a tube which has apertures in its side wall at its inlet end communicating with the interior of the compressor housing and apertures in its side wall at its outlet end which communicate with the secondary separation manifold. 10. A compressor as claimed in Claim 9 in which the tube between the compressor housing and the secondary separation housing forms part of a thermally responsive valve. 11. A compressor as claimed in any one of the preceding claims in which the stator has a plurality of outlets along its length and is surrounded by an impingement shield constituting the primary separation means so arranged so that the compressed air passes along inside it, the said pathway being so constructed that the air then turns through substantially 180 and flows in the opposite direction towards the secondary separation means.

1. A rotary oil mist compressor having a compressor casing within which there is a rotor stator unit in which, in use, air is compressed and oil is injected into the air and including a primary oil separation means for removing a proportion of the entrained oil from the compressed air and a secondary oil separation means for removing substantially the remainder of the entrained oil, the primary and secondary oil separation means being connected by a pathway so constructed that, in use, the compressed air is constrained to flow through three successive bends of substantially 90 , the pathway including a secondary separation manifold, in which, in use, oil droplets coalesce and collect, there being an oil return passageway communicating with the manifold adapted to return the oil collected in the manifold back to the compressor casing for re-use.

1

2. A rotary oil mist compressor substantially as specifically herein described with reference to the accompanying drawings.

CLAIMS (3rd Sep 1980)