GB2148414A - Labyrinth packing - Google Patents

Abstract

As a special feature the labyrinth packing has axially displaceable, co-rotating packing rings (4), which are sealed against the shaft or sleeve (1) by means of a cap-like gasket (5). Thus, the co-rotating packing rings can be automatically adjusted in the annular gap. However, this would mean that they would be forced against one side of the gap by the overpressure, which is to be avoided. This is achieved in that on the low pressure sealing surface chambers (43) are formed, which are connected via bores (44) with the overpressure side. The medium against which sealing is to take place consequently passes through these bores into the chambers and a centrifugal action builds up a pressure acting counter to the overpressure, so that rings (4) "float" in the annular gap. <IMAGE>

Description

SPECIFICATION Labyrinth packing The sealing of the shaft has presented a problem in connection with rotary pumps and compressors and various solutions are known for this. The particular solution is dependent on the media to be pumped or against which sealing is required, together with the desired degree of sealing. Known contact-free iabyrinth packings have an extremely low frictional resistance, but relatively high passage losses.

Much better sealing can be achieved with a slip ring seal, but this must be lubricated, because otherwise the parts undergo excessive wear or are even eroded. In certain cases it is also possible to use carbon glands, which do not require iubrication, but are subject to a certain wear.

In the case of machines for cryogenic uses, e.g. for pumping liquefied gases at low temperature, the shaft should be very well sealed.

However, difficulties occur due to the low temperatures, because on the one hand a contact-free labyrinth packing is not sufficiently tight, a slip ring seal requiring lubrication cannot be used, and a carbon gland is subject to excessive wear. In addition, the parts shrink due to the low temperatures.

The problem of the invention is to provide a contact-free labyrinth packing with narrow clearances, which is particularly suitable for use in cryogenic rotary machines, but which can also be used in other rotary machines.

According to the invention this problem is solved by a labyrinth packing having the features of claim 1.

The axial displaceability of the co-rotating rings combined with the bores and the chambers formed on the low pressure side of each ring ensures that the rings "float" with clearance between the stationary rings. In other words the medium to be pumped, i.e. the gas or liquid (liquefied gas) assumes the function of a hydrostatic lubricant, in that it ensures that there is no direct contact between the fixed and the co-rotating rings. The medium entering the chamber is hurled towards the outside in the case of an adequate rotational speed and brings about the lubricating action.

The invention is described hereinafter relative to an embodiment and the attached drawings, wherein show: Figure 1 the upper half of an axial section through a labyrinth packing.

Figure 2 a co-rotating packing ring in front view from the side and in which the chambers have been formed.

Figure 3 a section along line Ill-Ill of Fig. 2 and a half-side view of the ring according to Fig. 2.

The labyrinth packing shown in Fig 1 is constructed as a finally assembled unit with a sleeve 1, which is mounted and sealed on the not shown machine shaft and a casing 2, which is screwed on to the machine stator and is sealed with respect to the same.

The stationary part of the labyrinth packing comprises a stack of rings with the same external diameter and alternate small and larger internal diameter and which are housed in the casing. In the assembled state, the casing is closed by a cover 3. This construction of the stationary part makes it possible to very strictly adhere to the tolerances, because each of the rings is ground and lapped.

The above applies both with respect to the two end rings 21, 23, the four intermediate rings 22 and the five spacer rings 24. The cross-sectional profile of intermediate rings 22 is adapted to the shape of the co-rotating packing rings. The cross-sectionally rectangular end rings 21, 23 have a lateral recess on the outer circumference for a packing ring 25, which is used to provide the necessary sealing against casing 2 or cover 3. Cover 3 is sealed against casing 2 by packing ring 31. In the assembled state, all the rings 21 and 24 rest snugly on one another accompanied by metallic contact and rest on the inner bore of casing 2 and cover 3 under axial pressure.

Cover 3 and casing 2 are pressed together by a number of screws 32 which, for reasons of clarity in Fig. 1, are only indicated by a dot-dash line, Within cover 3 is formed an annular groove 33, whose function will be subsequently explained. The annular groove is connected by means of a bore 34 with a threaded blind hole 35.

The co-rotating packing rings 4 are clearly indicated by narrow haching and individually shown in Figs. 2 and 3. So as not to overburden Fig. 1 with reference numerals, the reference numerals given in the following detailed description of the co-rotating rings only appear in Figs. 2 and 3. The co-rotating rings 4 are placed on sleeve 1 and each is secured against twisting by two diametrically facing pins 11 inserted in sleeve 1.

The bore of rings 4 is selected in such a way that they are easily axially displaceable on sleeve 1. In the fitted state, the pins 11 engage in the diametrically facing axial grooves 41.

Rings 4 have a rectangular cross-sectional profile with a one-sided, thickened edge 40 in the vicinity of the bore and in which is formed an inner annular groove 42. On assembly, in said groove is placed a plastic gasket 5 (cf.

Fig. 1), which seals the ring against sleeve 1.

The sealing surfaces of the outer, rectangular part of the packing ring are ground and lapped, so that in the fitted state, they are located with a small, precisely defined clearance in the gaps between the fixed rings 21 and 23. In the flat sealing surface of packing ring 4 are formed shallow chambers 43, which are deepest at the inwardly directed side 43' and pass outwards into the sealing surface. This run-out edge is therefore indicated by a thin line 43" in Fig. 2. Each chamber 43 is connected by a through-bore 44 to the opposite sealing surface of the packing ring. The bores are advantageously made on the front side of the chambers in the rotation direction.

The labyrinth packing is fitted on the machine (pump or compressor) in such a way that it is exposed to more pressure p on the right-hand side in Fig. 1 than on the left-hand side. This is indicated in Fig. 1 by arrow p.

Only on pressurizing in this direction do the cap-like gaskets seal the co-rotating, axially displaceable rings 4 against sleeve 1 and only in this way is the desired quasi-hydrostatic lubricating action brought about by the liquid or gaseous medium sealing with overpressure p.

The operation can be explained as follows.

The overpressure p of the medium passes into the extreme right-hand, axial annular gap in Fig. 1 and therefore attempts to press the axially displaceable packing ring 4 on to the left-hand, adjacent, fixed ring 22. However, medium under and overpressure passes through bores 44 into chambers 43 in which, by a type of centrifugal action, a pressure is built up which establishes an equilibrium, so that the co-rotating packing ring "floats" in the annular gap.

As is conventional with labyrinth packings, the overpressure gradually decreases, there always being a larger or smaller leakage loss.

The leakage loss can be reduced if the overpressure is reduced, by producing a counterpressure on the low pressure side. In the embodiment of Fig. 1, this can be brought about by supplying a counterpressure through bore 34 into the annular gap 33 of cover 3.

Instead of being placed on a sleeeve, it is obvious that the co-rotating packing rings can be directly fitted to the machine shaft.

Claims (7)

1. Labyrinth packing for rotary machines assembled from rings, characterized in that each packing ring (4) co-rotating with shaft (1) is secured against twisting on the shaft, but is axially displaceable and is sealed against the shaft by a cap-like gasket (5), and that it has through-bores (44) leading from the high pressure side sealing surface to the chambers (43) formed on the low pressure side sealing surface, which are not interconnected, but are uniformly distributed over the packing ring circumference.

2. Labyrinth packing according to claim 1, characterized in that the chambers (43) are constructed in such a way that they are deepest at the radially inwardly directed side (43') and run out both laterally and outwardly into the low pressure side sealing surface.

3. Labyrinth packing according to claim 2, characterized in that the through-bores (44) are provided in such a way that they issue at the lower side (43') of chambers (43).

4. Labyrinth packing according to claim 3, characterized in that the through-bores (44) issue at the front side of chambers (43) in the rotation direction.

5. Labyrinth packing according to claim 1, in the form of a completely assembled unit, characterized in that the co-rotating packing rings (4) are fitted to a sleeve (1) which can be mounted on the rotary machine shaft, whilst stationary packing rings (21-23) are housed in a casing (2) with cover (3).

6. Labyrinth packing according to claim 5, characterized in that an annular groove (33) open towards sleeve (1) is provided on the low pressure side of casing (2), said annular groove being connected to a bore (34).

7. A labyrinth packing or seal constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.