GB2115110A

GB2115110A - Improvements in or relating to arrangements for controlling starting of screw-type compressor

Info

Publication number: GB2115110A
Application number: GB08301609A
Authority: GB
Inventors: Josef Ott
Original assignee: Hoerbiger Ventilwerke GmbH and Co KG
Current assignee: Hoerbiger Ventilwerke GmbH and Co KG
Priority date: 1982-01-21
Filing date: 1983-01-21
Publication date: 1983-09-01
Also published as: FR2520060A1; FR2520060B1; GB2115110B; DE3301049A1; AT377336B; ATA22382A; IT8319184A0; IT1161602B; GB8301609D0

Abstract

An arrangement is provided for controlling starting of a screw-type compressor (1), whose delivery capacity may be regulated by a throttle valve (4) which is installed in the suction pipe (2). The throttle valve (4) is set by means of a regulating device (5) which is actuated by the pressure medium supplied by the compressor (1). A control valve (11), whose closure member is acted upon in the opening direction by a spring (12) and in the closing direction by the pressure medium supplied by the compressor (1), is disposed in a pipe (10) by passing the throttle valve (4). In this way, when the compressor plant is without pressure, the control valve (11) is open so that, when the compressor is started up, pressure is allowed to build up even if the throttle valve (4) is closed. As soon as the pressure has built up, the control valve (11) will close, whereupon the delivery capacity is further regulated by the throttle valve (4). <IMAGE>

Description

SPECIFICATION Improvements in or relating to arrangements for controlling starting of screw-type compressors The invention relates to an arrangement for control ing starting of a screw-type compressor, whose delivery capacity may be regulated by a throttle valve which is installed in the suction pipe and which may be adjusted by means of a regulating device which may be actuated by the pressure medium supplied by the compressor, a control valve being provided which bypasses the throttle valve.

In regulating the delivery capacity of screw-type compressors by a throttle valve installed in the suction pipe, it is necessary to keep the throttle valve closed while starting up the compressor in order to avoid suddenly overloading the compressor plant, in particular the drive motor. Immediately after starting up, however, the throttle valve must be opened so as to build up pressure which is required, in particular, for the oil injection. In order to actuate the throttle valve in this way, a certain minimum pressure is necessary which is not available from the pressure medium system during the initial operation of the compressor plant or after prolonged periods of stoppage.

It is known to start up a small air-control compressor, e.g. a piston compressor, which builds up the necessary minimum pressure for actuating the throttle valve, before starting up the screw-type compressor. This relatively complicated step is only possible, however, in the case of large compressor plants. It is further known to provide a solenoid valve which bypasses the throttle valve and which is opened when starting up the screw-type compressor and is closed after starting up. In this connection, electric devices must be provided for controlling the solenoid valve which not only makes the compressor plant more expensive but may also jeopardize operational reliability.

According to the invention, there is provided an arrangement for controlling starting of a screw-type compressor whose delivery capacity is regulatable by a throttle valve installed in a suction pipe of the compressor and adjustable by means of a regulating device which is actuable by the pressure medium supplied by the compressor, comprising a control valve arranged to bypass the throttle valve and having a closure member which is resiliently biased in a valve-opening direction and which is arranged to be acted upon in a valve-closing direction by the pressure medium supplied by the compressor.

It is thus possible to provide a simple arrangement for controlling starting of screw-type compressors which is actuated exclusively pneumatically and ensures the rapid build-up of pressure in the compressor plant without the use of an extraneous pressure medium. The control valve bypassing the throttle valve is open when the compressor plant is without pressure, so as to free a small suction cross-section which immediately allows the build-up of pressure when starting up the compressor. As soon as the pressure has reached a level which is sufficient for actuating the throttle valve, the control valve will close, whereupon the delivery capacity is further regulated by the throttle valve. Such an arrangement is particularly simple, with neither electrical devices nor an additional air-control compressor being used.

The control valve may be a pneumatically controlled two-valve which is actuated by way of a pressure regulator acted upon by the delivery pressure of the compressor. The object of the pressure regulator is merely to close the control valve and to keep it closed as soon as the pressure in the compressor plant becomes sufficiently high to actuate the throttle valve. A simple design of the regulator may therefore be used.

A directly acting control valve may advantageously be used which simultaneously takes on the function of the two-way valve. A simple embodiment of this type consists in the control valve having a diaphragm which controls a duct bypassing the throttle valve. In this connection the diaphragm is acted upon by the pressure prevailing in the compressor plant. In the closed state, it leaves the passage through the duct free, whereas when acted upon by pressure it closes the duct. A spring, which acts in the opening direction and whose spring force is selected in accordance with the desired closing pressure, may be provided.

In a further embodiment, the control valve is provided with a sliding piston which may be slid in a cylinder bore and controls a duct bypassing the throttle valve. This control valve too only comprises a small number of easily manufactured components.

In order to keep the bypass duct open when the compressor plant is without pressure, a spring which acts upon the sliding piston in the opening direction is advantageously provided in this case as well.

In a further embodiment of the invention, the control valve may be fitted in the housing or in the closure member of the throttle valve, e.g. in a throttle slide or a throttle flap. No single apparatus apart from the throttle valve is then required for the arrangement for starting control and additional connection pipes may also be dispensed with.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a compressor plant which is provided with the arrangement constituting a preferred embodiment of the invention for starting control; and Figures 2, 3 and 4 show three embodiments of the invention which are fitted in a throttle valve of a screw-type compressor, each shown in an axial median section through a closure member of the throttle valve.

The compressor plant illustrated in Figure 1 comprises a screw-type compressor 1 with a suction pipe 2 and a pressure pipe 3. Athrottle valve 4, which is adjusted by a regulating device 5, acted upon via a regulating pipe 6 by the pressure of the medium to be compressed in the pressure pipe 3, is fitted in the suction pipe 2. An oil tank 7, from which an oil-injection pipe 8 leads back to the screw-type compressor 1, is inserted in the pressure pipe 3 downstream of the compressor 1. In addition, a pressure-resisting valve 9 formed as a non-return valve is disposed in the pressure pipe 3.In order to control starting of the screw-type compressor 1, a control valve 11, whose closure member is acted upon in the opening direction by a spring 12 and in the closing direction, via a control pipe 13 leading from the pressure pipe 3, by the pressure medium supplied by the compressor, is arranged in a bypass pipe 10 bypassing the throttle valve 4.

Figure 2 shows part of the suction pipe 2 in which the throttle valve 4 is fitted. The throttle valve 4 comprises a throttle flap which is pivotable about an axis in the form of an operating rod 14 inserted into the suction pipe 2. The bypass pipe 10 comprises two bores provided in the wall of the suction pipe 2 on both sides of the throttle valve 4 and extending approximately radially. The control valve 11 is in the form of a diaphragm 15 which covers the bores of the bypass duct 10 and is secured to the suction pipe 2 by a cap 16 with a connection point 17 for the control pipe 13. The diaphragm 15 is loaded in the opening direction of the control valve 11 by a spring 12.

In the embodiment shown in Figure 3, the control valve 11 is fitted in the operating rod 14 of the throttle valve 4. An axial cylinder bore 18, in which a sliding piston 19 controlling the bypass line 10 formed by a trasverse bore may be displaced, is provided in the operating rod 14. The spring 12 holds the sliding piston 19 in the open position shown in Figure 3. A connection point 17 is provided at the outer end of the cylinder bore 18 for supplying the control pressure.

Another embodiment is shown in Figure 4, in which the throttle valve 4 comprises a closure member 21 fitted displaceably in a valve housing 20.

The closure member 21 regulates the cross-section of the suction pipe 2 which passes through the valve housing 20. In this case, the control valve 11 is fitted in the closure member 21 of the throttle valve 4 and, as in the embodiment shown in Figure 3, comprises a sliding piston 19 which is displaceable in a cylinder bore 18. Atransverse in a cylinder bore 18. A transverse bore in the closure member 21 is provided as a bypass pipe 10. The connection point 17 at the end of the cylinder bore 18 is used for joining the control pipe 13 and the spring 12 acting upon the sliding piston 19 keeps the control valve 11 open in the absence of control pressure.

The mode of operation of the arrangement described is as follows: When the screw-type compressor 1 illustrated in Figure 1 is started up, the throttle valve 4 is initially closed. When the compressor plant is without pressure, e.g. when starting up for the first time or after a prolonged stoppage, the throttle valve 4 cannot be opened since the operating pressure necessary for the regulating device 5 is absent. The control valve 11, on the other hand, is held open by the spring 12 since no pressure is supplied initially through the control pipe 13. The screw-type compressor 1 can thus draw medium through the bypass pipe 10, so that pressure builds up relatively rapidly in the oil container 7. The pressure-resisting valve 9 promotes this build-up of pressure.The oil injection is immediately fed through the pipe 8, so that damage to the screw-type compressor on account of inadequate lubrication is avoided. As soon as the pressure has reached a level sufficient for actuating the throttle valve 4, the control valve 11 is closed, whereupon the delivery capacity of the screw-type compressor 1 is further regulated by actuating the throttle valve 4 by way of the regulating device 5 which is acted upon by the pressure prevailing in the pressure pipe 3 via the regulating pipe 6. When the pressure pipe 3 loses pressure after the compressor plant has been shut down, the regulating device 5 closes the throttle valve 4. Since the control pipe 13 also loses pressure, the spring 12 opens the control valve 11 and thus the bypass line 10, so that the compressor plant is ready to be started up again.

In the embodiments illustrated in Figures 2,3 and 4, the control valve is actuated directly by the pressure medium supplied through the control pipe 3 by way of the connection point 17. In the case of the embodiment shown in Figure 2, this acts upon the diaphragm 15 so that, at an adequate level of the delivered pressure, the diaphragm 15 is pressed against the force of the spring 12 onto the openings of the bores forming the bypass duct 10. As soon as the pressure in the control pipe 13 is reduced, the spring 12 lifts the diaphragm 15 of the bores again.

In the case of the embodiments shown in Figures 3 and 4, the control pressure supplied through the connection point 17 acts upon the sliding piston 19 which in this case too closes the bypass duct 10 against the force of the spring 12 at a corresponding level of the pressure delivered. Instead of this direct actuation of the control valve 11, it is also possibie, however, to provide a simple two-way valve as a control valve and to actuate it with the aid of a pressure regulator which may iikewise be constructed in a simple manner. The control pipe 13 provided in Figure 1 would then lead to the pressure regulator. In the case of all the embodiments, when the screw-type compressor is started up, a pressure immediately builds up which is sufficient for actuating the throttle valve.

Claims

1. An arrangement for controlling starting of a screw-type compressor whose delivery capacity is regulatable by a throttle valve installed in a suction pipe of the compressor and adjustable by means of a regulating device which is actuable by the pressure medium supplied by the compressor, comprising a control valve arranged to bypass the throttle valve and having a closure member which is resiliently biased in a valve-opening direction and which is arranged to be acted upon in a valve-closing direction by the pressure medium supplied by the compressor.

2. An arrangement as claimed in claim 1, in which the control valve is a pneumatically controlled two-way valve which is arranged to be actuated by way of a pressure regulator acted upon by the delivery pressure of the compressor.

3. An arrangement as claimed in claim 1, in which the control valve has a diaphragm which controls a duct bypassing the throttle valve.

4. An arrangement as claimed in claim 1, in which the control valve is provided with a sliding piston which is slidable in a cylinder bore and controls a duct bypassing the throttle valve.

5. An arrangement as claimed in any one of claims 1 to 4 in which the control valve is fitted in a housing or in the closure member of the throttle valve.

6. An arrangement as claimed in claim 5, in which the throttle valve is a butterfly valve and the closure member is fitted in the butterfly thereof.

7. An arrangement as claimed in claim 5, in which the throttle valve is a poppet valve and the closure member is fitted in the slidable element thereof.

8. An arrangement for controlling starting of a screw-type compressor, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. A compressor including an arrangement as claimed in any one of the preceding claims.