GB2041450A - Rotary positive-displacement fluid-machines - Google Patents

Abstract

A device for controlling the supply of liquid for cooling, sealing and lubricating a meshing-screw compressor, or a sliding-vane compressor, has a check valve 6 and a slide valve e.g. a piston valve 11, in a common housing 1. The check valve is in a discharge duct 5 and the piston valve is exposed to the discharge pressure upstream of the check valve and biassed by a spring 17 towards a stop 18. The piston valve controls flow between ducts 12 and 13 conveying liquid to a rotor 4. Rising discharge pressure causes the piston valve to open the upper duct 12. The slide valve may also control a venting duct (20) connected to the discharge duct downstream of the check valve. Fig. 2. <IMAGE>

Description

SPECIFICATION Control device The invention relates to a control device, especially for the cooling liquid in screw and sliding-vane compressors with liquid injection.

in screw and sliding-vane compressors it is necessary to control the liquid injected into the compressor for cooling and sealing the gap between the rotor and the compressor casing. An interlock device must be provided which interrupts the liquid injection when the compressor is shut off, in order to prevent flooding of the compressor with the still pressurized cooling liquid. Furthermore, it must be ensured that the interlock device operates the liquid admission immediately when the compressor is started up, in order to prevent friction between the rotor parts and the compressor casing. In addition, a shutoff valve is required between the compressor and the following pressure vessel which, after the shutdown of the compressor, automatically prevents a flowback of the compressed medium in the compressor and through the intake pipe into the environment.However, it may be necessary to reduce the medium pressure effecting the liquid injection or also the pressure prevailing in the pressure vessel when the compressor is shut off. This requires a further cutout device, which connects the pressure line or also the pressure vessel with the open air or the intake side of the compressor.

For the execution of these functions various embodiments are known, which consist of separate control and shutoff valves. The individual valves must be interconnected by pipes. Since the individual valves often have different types of connections, reducer and adaptor connections are required. This leads to a high expenditure. In addition, a substantial number of joints for the high-pressure cooling liquid is present, which considerably increases breakdown incidence, especially if the compressor is not stationary and the installation is subject to vibrations.

Furthermore, control devices are known, in which the required functions are performed by electrical pressure switches, timing switches and magnetic valves. These assemblies are also expensive, in particular because additionally electrical lines and a power contract are necessary. Moreover, the electrical devices are subject to breakdowns.

The object of the invention is to substantially reduce the constructional expenditure in such a control assembly as well as the number of joints subject to breakdowns, whilst improving the functioning of the control device.

This is achieved according to the invention in that a check valve in the pressure line of the compressor and a piston slide valve or the like operated by the compressed medium, which controls the injection pipe carrying the cooling liquid and leading to the compressor, are located in a common valve housing. This constitutes a simple mechanism, which can perform all the required functions. Connection lines between the individual valves and, especially, joints subject to breakdown are largely avoided in this arrangement, owing to which the operational safety of the control device and thus of the compressor plant as a whole is substantially improved.

In a preferred embodiment of the invention, the valve housing is attached directly to the compressor casing. This also eliminates connection lines between the compressor and the control device, which thus forms an integral unit with the compressor.

The slide valve can be acted upon in one direction by a return spring which pushes it into its end position where it shuts off the injection line, and in the other direction by the pressure of the compressed medium. With this arrangement, the injection line will be kept closed by the action of the return spring as long as the compressor is inoperative.

However, as soon as a pressure builds up, the injection line is immediately freed, so that cooling liquid is fed in.

A simple construction of the control device according to the invention results when the check valve and the slide valve are arranged along a common axis, preferably one behind the other in a common casing bore, where an end stop for the slide valve is fitted between them. However, the slide valve can also be located in a duct extending transversely to the axis of the check valve and may have an extension passing diametrally through the pressure line of the compressor, which extension defines the end position of the slide valve. In this case, the control device will have a shorter constructional length.

A further development of the control device according to the invention consists in that the cylinder space at one end of the slide valve communicates with the pressure line of the compressor and the cylinder space at the other end of the slide valve communicates via a separate duct with the intake side of the compressor. With this arrangement it is ensured that, even in the case of compressor start with closed intake pipe, the admission of cooling liquid is effected at the right time. The underpressure occurring in this case at the intake side of the compressor promotes the opening movement of the slide valve, so that the latter opens the injection line before the full compressor pressure is established in the pressure line.

The slide valve can, in addition to the injection line, also control a venting line which, as viewed in the direction of flow, leads, from behind the check valve, from the pressure line into the open air or to the intake side of the compressor. In this embodiment, simultaneously with the opening of the injection line for the cooling liquid the vent line of the pressure side of the compressor is closed, so that the pressure required for the injection of the cooling liquid can build up rapidly.

Further details and advantages of the invention will be apparent from the following description of two exemplary embodiments which are schematically illustrated in the drawings, in which: Figure 1 shows a longitudinal section through a screw compressor with a control device according to the invention fitted thereon, and Figure 2 shows a longitudinal section through a variant of the control device.

In both embodiments the control device has a housing 1, which is directly built on to the compressor casing 2 of a screw compressor.

As shown in Fig. 1, the screw compressor has an intake pipe 3, a rotor 4 and a pressure pipe 5, which extends into the housing 1 of the control device. In Fig. 2, the compressor casing 2 is shown only in part. The medium to be compressed is drawn in through the intake pipe 3, compressed by the rotation of rotor 4 and conveyed into the pressure pipe 5 in housing 1 of the control device.

In the pressure pipe 5 a check valve 6 is fitted, which consists of a shutoff disc 7, a closing spring 8 and a retaining ring 9 supporting the latter. The compressed medium is conveyed through the check valve 6 in the direction of the arrow 10 into a pressure vessel not shown. The housing 1 furthermore accommodates a spool valve or piston slide valve 11, which controls an injection pipe 1 2 leading to the compressor for the admission of a cooling liquid to the rotor 4 when.the latter rotates. The cooling liquid is fed in from the outside through a feed pipe 1 3 to the valve 11. The working chamber of the valve, constructed as a bore, is referenced 14. One end of the valve 11, namely the right-hand end in the drawing, is in open communication with the pressure pipe 5.The cylinder space 1 5 at the other end of the valve 11 is, by contrast, closed and communicates only through a duct 1 6 with the intake side of the compressor.

The cylinder space 1 5 contains in addition a return spring 17, which pushes the sleeve valve 11 into an end position, in which the injection pipe 1 2 is closed. An end stop 18, constructed as a pin in Fig. 1 defines this end position. By contrast, according to Fig. 2, the valve 11 is provided with an extension 19, which diametrally traverses the pressure pipe 5 and thus defines the end position of the valve 11. In the embodiment according to Fig. 1 the check valve 6 and the valve 11 are arranged one behind the other in a common bore of the casing, whereas according to Fig.

2 the pressure pipe 5 traverses the housing 1 in a straight line and the valve 11 extends transversely thereto.

When the compressor is not driven, that is, when the rotor 4 is at rest, the same pressure prevails in the compressor casing 2. The valve 11 keeps the injection pipe 1 2 closed, so that the cooling liquid which is under pressure in the feed line 1 3 cannot enter the compressor.

This prevents the cooling liquid from flooding the compressor while the rotor is at standstill and from passing through the intake pipe 3 into the open. The intake pipe 3 can be provided with a closure device (not shown).

The compressor can be started up both with open or closed intake pipe 3.

When the compressor is started up with open intake pipe 3, there builds up rapidly, in consequence of full delivery, in the pressure pipe 5 in front of the check valve 6 a pressure, the magnitude of which depends on the flow resistance of the check valve 6. This pressure acts directly on the right-hand front face of valve 11. The control device is so designed, that this pressure is sufficient to move the valve 11 into the left-hand end position against the force of return spring 1 7.

Owing to this, the injection pipe 1 2 is opened, so that the cooling liquid can flow from the feed pipe 1 3 through the working chamber 14 and the injection pipe 1 2 to the rotor 4 in the compressor. The cooling liquid prevents an overheating of the rotor 4 in the compressor casing 2 and serves at the same time for sealing it therein and also for lubrication purposes. If, on the other hand, the compressor is started up with closed intake pipe 3, no pressure great enough to operate the sleeve valve 11 builds up in the pressure pipe 5. However, there is formed on the intake side of the compressor an underpressure, which is transmitted through the duct 1 6 into the cylinder space 1 5 located at the left-hand end of valve 11.This underpressure has the effect that even in this case the valve 11 is pushed into its left-hand end position immediately after the start of the rotor 4, thus opening the injection pipe 1 2. Thus, the control device ensures in this case as well a timely cooling and lubrication of the compressor. When the compressor is shut off, the pressure in the pressure pipe 5 decays through the intake pipe 3, whereupon the return spring 1 7 brings the valve 11 back into its right-hand end position, in which it closes the injection pipe 12, so that a further admis sion of cooling liquid is prevented.

In the variant of the control device shown in Fig. 2, the valve 11 controls, in addition to the injection pipe 12, a venting pipe 20, which, as viewed in the direction of flow, branches downstream of the check valve 6 from the pressure pipe 5. To this end, the valve 11 has a further working chamber 21.

The venting pipe 20 passes through this working chamber and terminates through a duct 22 in the open. The duct 22 could also be led back into the intake pipe 3 of the compressor, possibly also through the cylinder space 15 of of valve 11. In the position shown in Fig. 2, the pressure vessel connected to the pressure pipe 5 of the compressor is vented through the venting pipe 20 and the duct 22. As soon as a pressure builds up in the pressure pipe 5 in front of the check valve 6, the valve 11 breaks the connection between the venting pipe 20 and the duct 22, so that pressure can build up in the pressure vessel. Immediately after shutdown of the compressor the valve 11 returns under the action of return spring 1 7 into the righthand end position, in which it connects through the working chamber 21 the venting pipe 20 with the duct 22. Thus, the control device effects in this case also a pressure relief of the pressure vessel.

Claims (10)

1. A control device particularly suitable for controlling the flow of cooling liquid to a compressor selected from screw compressors and sliding-vane compressors, which elevice comprises: a common valve housing, in which is provided a pressure duct for connection to the discharge side of said compressor, the housing further being provided with an injection pipe for conveying cooling liquid to said compressor; a check valve mounted in the pressure duct; and a valve member slidably disposed in the housing, arranged to close and open the said injection pipe, and operable by the pressure in the pressure duct to open the injection pipe as said pressure rises.

2. A control device according to claim 1 in which the valve member is a piston slide valve.

3. A control device according to claim 1 or 2 including a return spring acting on the said valve member in the direction which pushes said valve member into that end position where it closes the injection pipe, the valve member being acted on in the other direction by pressure of the compressed medium in the pressure duct.

4. A control device according to claim 1, 2 or 3 characterised in that the check valve and slidable valve member are arranged along a common axis.

5. A control device according to claim 4 in which the check valve and slidable valve member are one behind the other in a common casing bore, and an end stop is disposed in the bore between them for defining one end position of the slidable valve member.

6. A control device according to any of claims 1 to 3 characterised in that the slidable valve member is located in a duct provided in the valve housing and extending transversely to the axis of the check valve, and an extension is provided on the valve member diametrally traversing the pressure pipe duct, for defining the end position of the valve member.

7. A control device according to any one of claims 1 to 6, in which the valve housing contains a first cylinder space at one end of the slide valve member which space communicates with the pressure duct, and a second cylinder space at the other end of the slidable valve member which space communicates with a separate duct for communication with the intake side of the compressor.

8. A control device according to any one of claims 1 to 7 including a venting duct leading from the pressure duct downstream of the check valve, the slidable valve member being arranged to close said venting duct as said pressure in said pressure duct rises.

9. In combination, a liquid-cooled screw compressor having a compressor casing, and a control device as claimed in any preceding claim having its valve housing directly attached to the compressor casing.

10. In combination, a liquid-cooled sliding vane compressor having a compressor casing, and a control device as claimed in any preceding claim having its valve housing directly attached to the compressor casing.