GB2047808A

GB2047808A - Gas compressors

Info

Publication number: GB2047808A
Application number: GB8005028A
Authority: GB
Original assignee: Hoerbiger Ventilwerke GmbH and Co KG
Current assignee: Hoerbiger Ventilwerke GmbH and Co KG
Priority date: 1979-04-13
Filing date: 1980-02-14
Publication date: 1980-12-03
Also published as: DE3001488A1; IT1130917B; AT358705B; IT8019569A0; ATA279479A; BE881461A

Abstract

Control arrangement for the cooling liquid of a compressor 1 with liquid injection e.g. a screw compressor, comprises a stop valve 8 in an injection pipe 9, the valve being closed while the compressor is at stand-still and bridged by a by-pass duct, which possesses a smaller flow cross-section than the open valve and allows liquid to enter the compressor at a reduced rate while valve is closed. The by-pass duct may consist of a bore (27), Fig. 2 (not shown), which extends through a movable closure member (16) of the stop valve 8. Alternative by-pass ducts are described, Figs. 3 and 4 (not shown). <IMAGE>

Description

SPECIFICATION Control arrangement for the cooling liquid of a compressor with liquid injection The invention relates to a control arrangement for the cooling liquid of a compressor with liquid injection, in particular a screw compressor, with an oil stop valve which is built into the injection conduit and which is closed when the compressor is at stand-still.

In a screw compressor and a multiple cell compressor, it is necessaryto inject a liquid into the compressor housing in order to cool the compres soy, to preventthe rotor from rubbing against the housing, and to seal the gap between the rotor and the housing. In order to avoid on the one hand flodding of and on the other hand damage to the compressor due to insufficient lubrication, the liquid injection must be controlled accurately. After the compressor has been stopped, the liquid supply must be shut off immediately, during starting, however, an immediate release of the liquid supply is required.

A known control arrangement uses an oil stop valve which is built into an injection conduit and a closure member of which is provided with a closing spring which maintains the oil stop valve closed when the compressor is at stand-still. As soon as the compressor starts and produces a feed pressure, the latter causes the oil stop valve to open by means of a control diaphragm or a piston. This control has been found very satisfactory in practice. In many cases, however, it is demanded that the compressor should be supplied with cooling liquid when the rotor is still at stand-still, in order that sufficient lubrication is ensured even upon starting the rotor.

Control arrangements are already known in which the oil stop valve is open with the compressor at stand-still. Therein the oil stop valve is maintained open during the operation of the compressor by means of the feed pressure. Upon switching off of the compressor the oil stop valve is closed for a shorttime, butsubsequently opened again, so that cooling liquid can travel into the standing compressor because of the pressure still prevailing in the installation. In this case the risk of flooding the compressor exists, this being deleterious for a fresh start.

Also unnecessary oil consumption is connected therewith. Finally these control arrangements which require actuation of the closure member of the oil stop valve in both directions are relatively complicated.

The invention is based on the object to provide an improved control arrangement with an oil stop valve which ensures sufficient lubrication and cooling of the compressor during starting, but avoids flooding by the cooling liquid.

The invention solves this problem in the control arrangement referred to above in that the oil stop valve is bridged by a by-pass duct which possesses a smaller cross-section than the open oil stop valve and which is open even when the oil stop valve is closed. With this construction the oil stop valve can be closed upon switching the compressor off and can remain closed during the entire stand-still. In spite ofthis, during the stand-still of the compressor, an admittedly small quantity of liquid which, however, is sufficient for a risk-free start of the rotor, is supplied to the compressor. The quantity of liquid supplied during stand-still can be dimensioned by the selection of the cross-section of the by-pass duct.

Thus the control arrangement according to the invention combines the advantages of the two known constructions, that is to say the construction with the oil stop valve closed during stand-still of the compressor, and that with the oil stop valve open during stand-still, without possessing the weaknesses of them.

In a preferred constructional form of the invention, the by-pass duct consists of a bore which extends through the closure member of the oil stop valve and which may be angled under certain circumstances.

This construction is simple to produce and does not require alterations of the valve housing, so that it can be realised even afterwards in oil stop valves already in existence.

In a further embodiment of the invention, the by-pass duct may consist at least partly of at least one axial groove in the closure member which in a manner knownperse is guided by an extension in a cylinder bore and is provided with a pressure compensating duct extending through it. This construction, too, can be produced simply without alteration of the valve housing. Housing, it is also possible to provide one or more axial grooves or channels in the cylinder bore in which the extension of the closure member is guided, or however to provide a duct which extends through the cylinder wall.

Finally, a further variant of the invention provides that the by-pass duct is formed by a notch in the sealing region of the valve seat or the closure member of the oil stop valve. This notch also ensures that when the oil stop valve is closed during stand-still of the compressor, a dimensioned quantity of liquid is introduced into the compressor housing, in order to ensure a risk-less starting.

Further advantages and details of the invention are clear from the following description of constructional examples with reference to the drawings. In these Figure 1 illustrates a diagrammatic representation of a compressor installation with the control arrangement according to the invention, Figure 2 an axial section through the oil stop valve, and each of Figures and 4 a detail of modified constructional forms of the oil stop valve, in section.

The compressor installation according to Figure 1 consists of a screw compressor 1 with a suction pipe 2 and a feed pipe 3. A non-return valve 4 and a liquid separator 5 are built into the feed pipe 3; a consumer pipe 6 leads away from the liquid separator 5. A liquid pipe 7 leads to an oil stop valve 8 from which an injection pipe 9 leads to the screw compressor 1.

Finally a control pipe 10 branches off the feed pipe 3 upstream of the non-return valve 4 and terminates in a control chamber of the oil stop valve 8.

According to Figure 2, the oil stop valve 8 consists of a housing 11 with an inlet 12 and an outlet 13 which are separated from each other by an intermediate wall 14 which extends in an angled off manner and in which a valve seat 15 is located. The latter is associated with a closure member 16 which is actuated by a diaphragm 18 by way of a rod 17, the diaphragm 18 being clamped between the housing 11 and a cover 19. The cover 19 defines a control chamber 20 into which the control pipe 10 illustrated in Figure 1 terminates by means of a connector 21.

The closure member 16 is additionally loaded by a closure spring 22 and is guided in a cylinder bore 24 by means of a cylindrical extension 23; the cylinder bore 24 is provided in a gap 25 which is secured to the underside of the housing 11.

The closure member 16 is provided with a pressure compensating duct 26 which extends therethrough in an axial direction and which extends also through the cylindrical extension 23; it connects the cylinder bore 24 to the outlet 13. According to Figure 2, a radial bore 27 leads from the pressure compensating duct 26 to the outside, whereby a by-pass duct is formed which is open even when the valve is closed. This by-pass duct 26, 27 possesses a considerably smaller passage cross-section than the cross-section of the open valve.

In the constructional example according to Figure 3, the by-pass duct is formed partly by an axial groove 28 which is provided in the surface of the cylindrical extension 23 of the closure member 16.

The same effect can be attained by one or more axial grooves or channels in the sidewall of the cylinder bore 24. According to Figure 4, the by-pass duct consists of a notch 29 in a seat ring 30 which is inserted in the intermediate wall 14 of the housing 11.

The oil stop valve 8 has the object to control the supply of cooling liquid from the liquid separator 5 through the liquid pipe 7 and the injection pipe 9 to the compressor 1. When the compressor 1 runs, the feed pipe 3 is under pressure. This pressure affects the diaphragm 18 of the oil stop valve 8 through the control pipe 10, whereby the closure member 16 is lifted off the valve seat 15, and is kept open, by means of the rod 17. Because of the feed pressure prevailing in the liquid separator 5, the cooling liquid is fed to the compressor 1 through the open oil stop valve 8. When the compressor 1 is switched off, the pressure in the feed pipe 3 drops. The closure member 16 is then pressed onto the valve seat 15 by its closure spring 22. The oil stop valve 8 is closed thereby.However cooling liquid continues to flow into the injection pipe 9 through the by-pass duct which, according to Figure 2 consists of the radial bore 27 and the pressure relief duct 26, but in the constructional examples according to Figures 3 and 4 leads through the axial groove 28, orthe notch 29, respectively; it flows out of the injection pipe 9 into the compressor 1, namely as long as the pressure in the liquid separator 5 has not been completely removed. The quantity of liquid supplied can be dimensioned by the selection of the passage crosssection of the by-pass duct. Thereby the supply of a certain store of cooling liquid to the compressor 1 at stand-still is ensured, but flooding of the latter is prevented which would be possible with the oil stop valve 8 completely open.

Differing from the constructional examples illustrated, the by-pass duct may alternatively be formed by a bore in the intermediate wall 14 or by a duct which penetrates radially or obliquely through the wall of the cylinder bore 24.

Claims

1. Control arrangement for cooling liquid of a compressor with liquid injection, comprising an oil stop valve which is built into an injection pipe and which (in use) is closed when the compressor is at stand-still, characterised in that the oil stop valve is bridged by a by-pass duct which possesses a smaller cross-section than the open oil stop valve and which is open even when the oil stop valve is closed.

2. Control arrangement according to claim 1, characterised in that the by-pass duct consists of a bore which extends through a closure member of the oil stop valve.

3. Control arrangement according to claim 1, characterised in that the by-pass duct consists at least partly of at least one axial groove in a closure member of the oil stop valve, the closure member being guided by an extension thereof in a cylinder bore and being provided with a pressurecompensating duct extending therethrough.

4. Control arrangement according to claim 1, characterised in that the by-pass duct is formed by a notch in a sealing region of a valve seat or a closure member of the oil stop valve.