GB2116754A

GB2116754A - Suction control valve for rotary compressors

Info

Publication number: GB2116754A
Application number: GB08305842A
Authority: GB
Inventors: Josef Ott
Original assignee: Hoerbiger Ventilwerke GmbH and Co KG
Current assignee: Hoerbiger Ventilwerke GmbH and Co KG
Priority date: 1982-03-05
Filing date: 1983-03-03
Publication date: 1983-09-28
Also published as: IT8319922A0; DE3306025A1; AT377337B; IT1160505B; GB8305842D0; FR2522737A1; ATA88282A; FR2522737B1; DE3306025C2; GB2116754B

Abstract

Suction control valve (3) for rotary compressors (2), particularly for screw- type compressors with oil injection, comprising a closing member (11), which controls the suction line (12), and a control piston (18), which can be adjusted by a regulator (8) in dependence on output pressure against the force of a control spring (19) and acts on the closing member (11) of the suction control valve (3) in the closing direction. The closing member (11) is loaded by a special nonreturn spring valve (13) and formed separately from the control piston (8). A holding device (14), either an electrically operated magnet (15) or a fluid or mechanically actuated pump (Figure 2, not shown), is also provided to retain the closing member (11) closed. The opening of the closing member (11) can be delayed by means of the holding device (11), so that the compressor can start in an unloaded manner. <IMAGE>

Description

SPECIFICATION Suction control valve for rotary compressors The invention relates to a suction control valve for rotary compressors, particularly for screw-type com- pressores with oil injection, comprising a closing member which is spring-loaded in the closing direction, controls the suction line and can be adjusted in the closing direction by a control piston guided in a cylinder and acted upon by a control spring.

A suction control valve of this type is known from the German Offenlegungsschrift 2 944 053, the closing member of which, spring-loaded in the closing direction, is connected to the control piston, which is acted upon in the opening direction by the operating pressure produced by the compressor. In order to stop the delivery or regulate the rate of delivery, the pressure in the network supplied by the compressor can also act in the closing direction on another pressure surface of the piston which is greater than the pressure surface of the piston which is greater than the pressure surface acted upon by the operating pressure. When the compressor is put into operation the suction line is opened as soon as a certain pressure has built up.After the compressor has been turned offthe suction line is closed by the spring and the network pressure which is still in the container as soon as the operating pressure of the compressor has dropped. The opening and closing of the suction line is thus controlled as a function of the pressure of the pressure medium supplied by the compressor. There is no guarantee that the suction line will be closed immediately after the compressor has been turned off, so that it is possible for air mixed with oil to flow back into the suction line. For safety reasons it is therefore usually necessary to additionally provide a special non-return valve in the suction line. Furthermore, the relatively complicated structure of the known device is disadvantageous.

According to one aspect of the invention there is provided a suction control valve for a rotary compressor, said suction control valve comprising a closing member which is spring-biased in the closing direction and which is adapted for use in variable throttling of the input line of the compressor according to the extent that said closing member is opened, a control device adapted to be responsive to delivery pressure of the compressor to variably limit the extent to which said closing member can be opened, characterised by a selectively releasable holding device for holding the closing member in closed position until release of said holding device.

According to another aspect of the invention there is provided a suction control valve for a rotary compressor, particularly for a screw-type compressor with oil injection, comprising a closing member which is spring-loaded in the closing direction, controls the suction line and can be adjusted in the closing direction by a control piston guided in a cylinder and acted upon by a control spring, characterised in that the closing member, which is formed separately from the control piston, is loaded by a special non-return valve spring and provided with a holding device, preferably an electrically operated holding magnet, by means of which it can be retained in the closed position.

It is possible by means of the invention to provide that, when the compressor is put into operation, an unloaded start is ensured and, when the compressor is turned off, the suction line is immediately closed, without a special non-return valve being required for this purpose.

A preferred suction control valve embodying the invention acts as a special non-return valve both when the compressor is put into operation and when it is turned off, without any interference by the control piston; the non-return valve spring in this preferred embodiment is appropriately formed in a weak manner; so that the suction pressure produced by the compressor when it is put into operation is sufficient for the opening procedure; a required time lag, after which the suction line is opened in order to ensure an unloaded start, can be simply and accurately selected by means of the holding device; when the compressor is turned off the suction line is immediately closed, so that no medium mixed with oil can flow back; the rate of delivery can be regulated in a simple manner by means of the control piston in cooperation with the closing member.A further advantage lies in the simple construction of the preferred suction control valve embodying the invention and the simple form of the components of the latter.

In the preferred embodiment of the invention a stop, which limits the opening stroke of the closing member and can be adjusted by the control piston, is associated with the said closing member; the suction cross section released by the closing member can thereby be continuously adjusted in order to regulate the rate of delivery. In the same way, it is possible to close the suction control valve completely by means of the control piston.

The control piston is preferably acted upon by the control spring in the opening direction and control pressure in the closing direction of the closing member. In this respect a positive pressure regultor can be used to actuate the control piston, the control line of which regulator is only loaded with control pressure during the regulating operation. In order to be able to follow the occuring pressure fluctuations, pressure regulators of this kind, as is known, are provided with a discharge nozzle, through which air is constantly released in a negative regulator. A disadvantageous loss of pressure medium is thus prevented by using a positive pressure regulator.

The apparatus can be simply constructed if the control piston is arranged coaxially behind the closing member and acts on the latter with a piston rod. The piston rod forms the stop for limiting the opening stroke of the closing member.

Preferably the holding device comprises an armature or anchor plate which is secured to the closing member and which is associated with an electromagnetic arranged in the valve chamber. It is, however, alternatively possible to use a holding device which consists of a mechanical catch, which acts on the closing member and which can preferably be actuated by pneumatic or electrical means. It also lies within the scope of the invention to actuate the catch manually.

Further details and advantages of the invention will become apparent from the following description of the preferred embodiment which is illustrated in the drawings, in which: Figure 1 shows the connection diagram of a compressor system with the preferred suction control valve embodying the invention, which is schematically illustrated in axial cross section; and Figure 2 shows a variant of the suction control valve, also in axial cross section.

Figure 1 shows a rotary compressor 1 with a drive motor 2, which sucks in the medium which is to be compressed by way of a suction control valve 3. A pressure line 4 leads from the compressor 1 to a container 5, which is filled in its lower part with oil, while a service line 6 leads away from its upper part.

An oil injection line 7 is also provided, which extends from the lower region of the container 5, which is filled with oil, and leads into the compressor 1. The compressor system is regulated by means of a proportional regulator 8, which is connected into a signal line 9 extending from the service line 6 and leading to the suction control valve 3.

The suction control valve 3 comprises a valve chamber 10 in which a closing member 1 1,which controls the suction line 12 of the compressor 1, is displaceably mounted. The closing member 10 is loaded in the closing direction by a non-return valve spring 13. A holding device 14 is arranged in the central part of the valve chamber 10 and, in the embodiment according to Figure 1, consists of an electromagnet 15, incorporated in the valve chamber 10, and an associated anchor plate or armature 16, which is secured to the end ofthe guide rod 17 of the closing member 11, the guide rod 17 passing through the electromagnet 15. Finally, a control piston 18 is displaceably mounted in the valve chamber 10 and is acted upon by a control spring 19.

The piston rod 20 of the control piston 18 projects towards the anchor plate 16 of the closing member 11. The end of the piston rod 20 forms a stop 21, which limits the lifting movement of the closing member 11.

The proportional regulator 8 comprises a diaphragm 22, which is loaded on one side by a spring 23 and on the other side by the pressure medium supplied through the inlet 24. A valve body 25 is secured to the diaphragm 22, cooperates with a valve seat 26 and controls a duct 28 leading to the outlet 27. A discharge nozzle 29 leads from the duct 28 into the open. The initial tension in the spring 23 can be adjusted by means of a screw cap 30.

!n the variant of the suction control valve 3 shown in Figure 2 the holding device consists of a mechanical catch with a pivotably mounted pawl 31, which is loaded by a spring 32 and engages behind the closing member 11. The abutting surfaces of the pawl 31 and the closing member 11 are bevelled, so that, under the effect of the spring 32, the pawl 31 presses the closing member 11 into the closed position at its seat. A diaphragm 33 is provided to actuate the pawl 31 and acts on an extension 35 of the pawl 31 by way of a finger 34. The diaphragm 33 is actuated by a pneumatic pressure medium; which is supplied by way of a control line 36 to a control pressure chamber 37, which is provided in a housing cover 38 gripping the diaphragm 33.As in the case of the embodiment according to Figure 1, the closing member 11 is also mounted in the valve chamber 10 by means of a guide rod 17 and loaded by a nonreturn valve spring 13. The lifting movements of the closing member 11 are also limited in this case by a control piston 18 which, together with the end of its piston rod 20, forms a stop 21. The pawl 31 could be actuated manually instead of by the diaphragm 33.

When the compressor system illustrated in Figure 1 is turned off the closing member 11 closes the suction line 12 under the action of the non-return valve spring 13. When the compressor 1 is put into operation an underpressure, which tends to immediately open the suction control valve, is produced behind the closing member 11. However, the holding device 14 keeps the suction control valve 3 closed during the start-up period, so that an unloaded start of the compressor 1 is possible. In the embodiment according to Figure 1 the electromagnet 15 is excited by a circuit line, which is not shown, for this purpose, so that it attracts the anchor plate or armature 16 and thus holds the closing member 11 in the closed position.As soon as the compressor 1 has been put into operation, the electromagnet 15 is de-energised, whereupon the closing member 11 opens the suction line 12 immediately and the complete delivery ofthe compressor 1 commences.

When the compressor turned off the closing member 11 acts, under the action of the non-return valve spring 13, as an automatic non-return valve and causes the suction line 12 to immediately close. This ensures that pressure medium. This ensures that pressure medium and the oil injected through the injection line 7 into the compressor 1 does not flow back under the action of the pressure in the container 5 into the suction line 12 and into a filter which may be arranged upstream of the latter.

The proportional regulator 8 serves to regulate the rate of delivery of the compressor 1 as a function of the pressure in the service line 6. When this pressure in the service line 6 has reached a certain value, which can be adjusted by pretensioning the spring 23 of the regulator 8, the valve body 25 is raised from the valve seat 26, whereupon a regulating signal reaches the suction control valve 3 by way of the signal line 9. This signal acts upon the control piston 18 and moves the latter against the force of the control spring 19. The piston rod 20 acts in the closing direction upon the closing member 11, which rests via the anchor plate 16 against the stop 21. The suction control valve is thus closed with increasing pressure in the service line 6, as a result of which the delivery is throttled. The rate of delivery is thus continuously adapted to the respective use. When the pressure in the service line 6 has reached a certain maximum value, the suction control valve 3 is completely closed. The valve 25,26 of the proportional regulator 8 remains open, so that medium still delivered by the compressor 1 when the suction control valve 3 is closed can be discharged by way of the discharge nozzle 29 of the proportional regulator 8. As soon as the pressure in the service line 6 drops, the proportional regulator 8 closes completely or partially, whereupon the pressure in the signal line 9 is reduced by the discharge nozzle 29. The control piston 18 then releases the closing member 11 under the action of the control spring 19, so that the suction control valve3 can re-open. When the valve 25,26 of the proportional regulator 8 is closed, no pressure medium is discharged by way of the discharge nozzle 29, so there is no pressure loss.The discharge nozzle 29 can therefore have a relatively large section of passage, without any disadvantageous pressure loss, as a result of which fouling and freezing are prevented.

The suction control valve according to Figure 2 basically operates in the same way as the embodiment descriped with reference to Figure 1. The only different element is the holding device, by means of which the closing member 11 is retained in the closed position in order to guarantee an unloaded start. Figure 2 shows that the pawl 31 engages behind the closing member 11 under the action of the spring 32 when the closing member 11 moves from the open position into the closed position. The pawl 31 retains the closing member 11 in the closed position until the control pressure chamber 37 is loaded via the control line 36 with a pressure medium, which pivots the pawl 31 upwards by way of the diaphragm 33 against the force of the spring 32 and thus releases the closing member 11. The latter can then release the suction line 12, so that the delivery of the compressor commences. The rate of delivery is regulated in the manner described with reference to Figure 1, namely via the control piston 18, which acts by way of the piston rod 20 on the guide rod 17 of the closing member 11, as a result of which the suction control valve 3 is opened to a greater or lesser extent as a function of the pressure.

By means of the described suction control valve 3, it is thus possible to keep the suction line 12 of the compressor 1 closed during starting,thus permitting an unleaded start. Furthermore, by means of this suction control valve 3, the rate of delivery of the compressor 1 an be continuously regulated in an advantageous manner. When the compressor is turned off the suction control valve acts as a nonreturn valve, so that the suction line is immediately closed and a reflux of medium mixed with oil is impossible.

Claims

1. A suction control valve for a rotary compressor, said suction control valve comprising a closing member which is spring-biased in the closing direction and which is adapted for use in variable throttling of the input line of the compressor accord ing to the extent that said closing member is opened, a control device adapted to be responsive to delivery pressure of the compressor to variably limit the extent to which said closing member can be opened, characterised by a selectively releasable holding device for holding the closing member in closed position until release of said holding device.

2. A suction control valve according to claim 1 characterised in that said holding device comprises an electromagnet.

3. A suction control valve according to claim 2 characterised in that a guide rod of the closing member passes through the electromagnet, which acts upon an armature connected to the guide rod.

4. A suction control valve according to claim 1 characterised in that said holding device comprises a mechanical catch with a spring-loaded, pivotally mounted pawl which engages the closing member.

5. A suction control valve according to claim 4 characterised in that fluid pressure-operated means is adapted for releasing the mechanical catch.

6. A suction control valve according to any preceding claim wherein the control device comprises a control piston guided in a cylinder and movable towards the closing member in the closing direction by control pressure against a control spring.

7. A suction control valve for a rotary compressor, particularly for a screw-type compressor with oil injection, comprising a closing member which is spring-loaded in the closing direction, controls the suction line and can be adjusted in the closing direction by a control piston guided in a cylinder and acted upon by a control spring, characterised in that the closing member, which is formed separately from the control piston, is loaded by a special non-return valve spring and provided with a holding device, preferably an electrically operated holding magnet, by means of which it can be retained in the closed position.

8. A suction control valve according to claim 7, characterised in that a stop, which limits the opening stroke of the closing member and can be adjusted by the control piston, is associated with the closing member.

9. A suction control valve according to claim 7 or 8, characterised in that the control piston is acted upon by the control spring in the opening direction and by control pressure in the closing direction of the closing member.

10. Asuction control valve according to claim 7, 8 or 9, characterised in that the control piston is arranged coaxially behind the closing member and acts on the latter with a piston rod.

11. A suction control valve according to any one of claims 7 to 10, characterised in that the holding device consists of an armature or anchor plate which is secured to the closing member and which is associated with an electromagnet arranged in the valve chamber.

12. A suction control valve according to any one of claims 7 to 10, characterised in that the holding device consists of a mechanical catch which acts on the closing member and can preferably be actuated by pneumatic or electrical means.