GB2124311A

GB2124311A - Radial face seals

Info

Publication number: GB2124311A
Application number: GB08318172A
Authority: GB
Inventors: Klaus Bofinger; Jean Tornare; Paul Duron
Original assignee: Cryomec AG
Current assignee: Fives Cryomec AG
Priority date: 1982-07-09
Filing date: 1983-07-05
Publication date: 1984-02-15
Also published as: GB8318172D0; IT8348655A0; IT1172290B; SE8303856D0; DE3321598A1; FR2529987A1

Abstract

A double slide ring seal for hydraulic rotary machines such as pumps and turbines, in which the sealing pressure is generated by spring pressure is characterised by at least one sealing slide ring (10) and at least one resilient closed chamber (17) formed by bellows (15, 16) the pressure in the chamber (17) being controlled to open the seal (10, 11) in accordance with the rotary movement of the machine to be sealed and the pressure acting against the slide ring seal. The closed chamber (17) is located so as axially to displace annular element (12) relative to a shaft (1). The annular element 12 carries a further slide ring 14. The annular element (12) is connected to the slide ring (10) via a bellows (13). The annular element may carry the slide ring (10) (Fig. 2). A labyrinth seal (22) and a pressurized gas seal may be provided downstream of the double slide ring seal. <IMAGE>

Description

SPECIFICATION Double slide ring seal The invention relates to a double slide ring seal, in particular for hydraulic rotary machines such as pumps and turbines. Slide ring seals comprise slide surfaces which are perpendicular to the axis of rotation. The sealing pressure is generated by spring means. At high pressure differences, the internal pressure also contributes to the pressing of the sealing element, and thus the sealing. A distinction is made between those types which are disposed in a pressure compartment and those disposed outside it.

Slide ring seals offer particularly good sealing at low speeds of rotation and at high static pressures, and have relatively low wear under these conditions. When at rest, and if the spring pressure is sufficient, the seal pressure completely suffices to ensure satisfactory sealing.

At high rotational speed and high contact pressure, slide ring seals are exposed to considerable wear. Consequently in such cases a so-called contactless seal, such as a labyrinth seal, is preferred. In the case of labyrinth seals, pressure and velocity energy are lost in annular gaps which act as constrictions.

The present invention is intended to provide a double slide ring seal which can act both as a slide ring seal and also as a labyrinth seal, depending on the speed of rotation and the contact pressure.

A double slide ring seal according to the present invention is thus characterised by at least one sealing slide ring comprising at least one resilient, closed member which is controlled in accordance with the rotary movement of the machine to be sealed and the pressure acting against the slide ring seal, the member being located so as axially to displace the slide ring seal relative to the shaft. The accompanying drawing shows two embodiments of the device according to the invention, which is described hereinafter in terms of its construction and operation.

Figure 1 is a partial section through a hydraulic rotary machine in the region of a double slide ring seal, and Figure 2 is an analogous section through such a machine in the region of a single slide ring seal.

Referring now to the drawing there is shown the shaft 1 of the machine, on which the rotors (not shown) are disposed. The shaft 1 is supported in the stator 2.

An inlet nozzle 3 can be seen to the right in the stator 2. The arrows show the direction of flow of the flow medium in the system.

The pressure P1 existing in the inlet is transmitted between the shaft and stator in the direction indicated by the arrows. The medium which is being handled flows around a centrifugal impeller 4 disposed on the shaft 1. The centrifugal impeller 4 absorbs part of the applied pressure P 1, and effects a certain return flow of the medium into the inlet 3 through a feedback channel 5.

The remainder of the medium progresses between the centrifugal impeller flange 6 and a bush 7 to a chamber 8 in front of the slide ring seal. In the chamber 8 there is a pressure P2 which is less than the pressure P 1 in the inlet. The slide ring bearing consists of two slide rings 10 and 11. The slide ring 11 is firmly disposed in the flange 6 of the centrifugal impeller 4. The counter slide ring 10 is disposed in a part 9 of a displaceable annular element 1 2 and divided radially into two parts. The part 9 is connected to the displaceable annular element 12 by way of a closely pleated spring bellows 1 3.

On the annular element 12, opposite the part 9, there is fitted a further slide ring 14 which faces in the opposite direction to the slide ring 10. The displaceable element 1 2 is connected to the stator by means of two concentric spring bellows. The outer spring bellows 1 5 forms, together with the inner spring bellows 16, a closed annular chamber 17. A pressure line 18 opens into the chamber 17.

Compression springs 1 9 act on the opposite side of the displaceable annular element 12 to the spring bellows 1 5 and 16.

The axial slide path of the annular element 12 is limited by means of a stop 20 in the form of a setscrew screwed into the stator. The slide ring 1 4 is succeeded in the flow direction of the medium by a chamber 21 which acts as a constriction. The pressure, which is here still lower, is able to pass from the chamber 21 through a labyrinth seal 22 until it reaches the final cover 23 which rotates together with the shaft 1. Only a very small fraction of the gaseous medium finally flows between the stator 2 and the cover 23 to the outside. This smail fraction can be still further reduced by putting the labyrinth seal under pressure from the opposite side by means of a compressed air channel 24.

The method of operation of the displaceable slide ring seal according to the invention is hereinafter described. It is assumed that the machine is at rest either before the initial start-up or later, but that there is nevertheless a pressure acting from the system. This pressure penetrates as a static pressure as far as the slide rings 10 and 11. With the machine at rest, no pressure builds up in the annular closed chamber 17 through the pressure line 18, so that the spring bellows 1 5 and 1 6 are contracted, and thus pull the displaceable annular element 12 in the direction of the centrifugal impeller flange 6. The slide rings 10 and 11 are consequently tightly pressed against each other. Nevertheless, part of the pressure can penetrate from the chamber 8 through the narrow gap between the part 9 and the stator 2.

This pressure acts on the inside of the mobile annular element 12, and tends to move the latter in the direction of the cover 23 against the action of the spring bellows 15 and 16.

This action is opposed by the compression springs 1 9. The mostly gaseous medium present is unable to escape from the interspace between the densely pleated spring bellows 1 3 and the inner spring bellows 16. Consequently, the slide ring seal is in a properly sealed condition in the described inoperative system.

When the hydraulic machine operates, a pressure P1 is present in the inlet and penetrates as initially described as far as the slide rings 10 and 11. However, the pressure P1 is reduced to the pressure P2 by the action of the centrifugal impeller 4. A pressure which is controlled as a function of the speed of rotation is now applied to the annular closed chamber 17 through the pressure line 1 8.

The spring bellows 1 5 and 16 are consequently pushed outwards from each other. This means that the displaceable annular element 1 2 is displaced in the direction of the cover 23 against the action of the spring bellows 1 5 and 1 6 and of the compression springs 1 9. However, the part 9 of the radially divided displaceabie annular element 12 is displaced therewith in the same direction, as this part is connected to the annular element 12 by way of the closely pleated spring bellows 1 3. The displacement on the one hand causes a narrow gap to arise between the slide rings 10 and 11, so that the gap between the slide ring 14 and the shaft 1 becomes smaller.As a chamber is present both after the slide rings 10, 11 and, in the flow direction, after the slide ring 14, the now non-contacting slide ring seal acts as a labyrinth seal. The pressure in the chamber 21 which has already been strongly reduced now penetrates through the subsequent labyrinth seal.

As a special feature, the slide ring 14 comprises an excess portion on initial start-up. Consequently, if an excess pressure is applied to the annular closed chamber 1 7 through the pressure line 1 8, the slide ring 14 abuts the shoulder of the shaft 1 before the displaceable annular element 12 abuts the stop 20 of the stator 1. Only during continuous operation, when a constant pressure has built up n the system, does the slide ring 14 become so ground down that the aforesaid gap between the shaft 1 and slide ring 14 is attained. Only now does the displaceable annular element 1 2 abut the setscrew 20 which serves as the stop.

Figure 2 shows a simplified example of the slide ring bearing according to the invention. Those parts which also appear in the embodiment of Figure 1, and which again have the same reference numerals in this case, will not be further described. The substantial difference between the modified embodiment of Figure 2 and that of Figure 1 is that the displaceable annular element 12 is no longer divided radially. The part 9 is thus eliminated. In this embodiment, there is a single slide ring in the form of a slide ring 30 between the centrifugal impeller flange 6 and the displaceable annular element 12, which is in one piece in this instance.

In this instance a radially outwardly directed annular shoulder 31 corresponds to the part 9 of the radially divided displaceable annular element 9. A stator part 32, fixed by screws, projects into the displaceable annular element 12.

The restoring action of the spring bellows 15 and 1 6 is in this instance supplemented by compression springs 33 between the screw-fixed stator part 32 and the annular shoulder 31 of the displaceable annular element 1 2. As the method of operation of this modified embodiment is completely analogous to the method of operation of the embodiment previously described, there need be no description of it.

The closed resilient member necessary for displacing the annular element 12 can be formed not only from spring bellows as shown on the drawing, but also by cylindrical telescopic tube portions which fit tightly into each other, to form a variable annular chamber.

The necessary restoring force can be attained by means of a tension spring disposed in the annular chamber. According to a further solution, the axially displaceable annular element 12 can be moved by means of several resilient members.

Such resilient members can be in the form of several mutually communicating cylinder-piston units.

Finally, it should be noted that the slide rings are advantageously in the form of carbon rings.

Claims

1. A double slide ring seal for hydraulic rotary machines such as pumps and turbines, in which the sealing pressure is generated by spring pressure, characterised by at least one sealing slide ring comprising at least one resilient closed member which is controlled in accordance with the rotary movement of the machine to be sealed and the pressure acting against the slide ring seal, the said closed member being located so as axially to displace the slide ring seal relative to the shaft.

2. A double slide ring seal as claimed in claim 1, wherein the resilient closed member is formed by two concentric spring bellows, the space enclosed between the two bellows being connected to a pressure line.

3. A double slide ring seal as claimed in claim 1, wherein the resilient closed member is formed from two cylindrical, telescopic tube portions which fit tightly into each other to form a variable annular chamber, there being disposed in the annular chamber a tension spring for contracting the member, and the annular chamber being operationally connected to a pressure line.

4. A double slide ring seal as claimed in claim 1, wherein the slide ring seal is fixed onto an axially displaceable annular element which is movable by means of the resilient member.

5. A double slide ring seal as claimed in claim 4, wherein the annular element is movable by means of several resilient members.

6. A double slide ring seal as claimed in claim 5, wherein the resilient members are several communicating cylinder-piston units, which are operationally connected to a pressure line.

7. A double slide ring seal as claimed in claim 4, wherein the annular element is divided in the radial direction, and the two parts of it are connected together by means of a spring bellows.

8. A double slide ring seal as claimed in claim 7, wherein both the said parts divided in the radial direction comprise a slide ring seal.

9. A double slide ring seal as claimed in claim 4, wherein the annular element is limited in its displaceability in the axial direction by means of an adjustable stop.

10. A double slide ring seal as claimed in claims 8 and 9, wherein the slide ring seal lying in the direction of the stop comprises an excess portion on initial start-up, so that this slide ring seal already makes sealing contact before the axially displaceable annular element which is divided into two parts makes contact with the stop.

1 A double slide ring seal as claimed in claim 1 , wherein one sealing slide ring succeeds in the flow direction, an annular gap which acts as a constriction.

12. A double slide ring seal as claimed in claim 8, wherein each sealing slide ring comprises, in the flow direction, a respective annular gap which acts as a constriction.

1 3. A double slide ring seal as claimed in claim 1, wherein the sealing slide rings are carbon rings.

14. A double slide ring seal as claimed in claim 4, wherein there acts on the annular element at least one compression spring which supplements the restoring force of the resilient member.

1 5. A double slide ring seal constructed and adapted to operate substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.