This invention relates to a method for sealing a shaft of a rotor in a compressor element, between a rotor chamber formed in a housing, in which at least one rotor for the compression of gas is situated, and a bearing chamber, formed in the housing, in which at least one bearing, lubricated with lubricating liquid, for the shaft is situated, which sealing element comprises a floating gas sealing and a floating liquid sealing.

Volumetric compressors comprise one or more rotors which are arranged in a rotor chamber where gas under pressure is produced. These rotors are fixed upon a shaft beared it opposite sides outside of the rotor chamber in bearing chambers adjoining thereto, whereby these bearings are lubricated by means of lubricating liquid, mostly oil.

Mostly, the bearing chambers are connecting to the interior of a gearwheel case which also is lubricated with oil.

It is obvious that the rotor chamber and each bearing chamber must be separated from each other, such that no compressed air flows towards a second chamber and that, in the first place in oil-free compressors, no oil will leak into the rotor chamber.

As a consequence, the passage of the shaft between the rotor chamber of a bearing chamber is sealed with a double sealing, consisting of a gas sealing combined with a liquid sealing.

Mostly, floating sealings are used which are movable in respect to the housing, in consideration of the fact that

sealings mounted fixedly in the housing do not offer the possibility of absorbing the production and mounting tolerances.

The floating liquid sealing may be a thread sealing, whereas the gas sealing may be of the labyrinth type.

The application of the gas sealing and the liquid sealing in the housing is relatively time-consuming and expensive.

The invention aims at a method for sealing the shaft of a rotor of a compressor element which avoids these disadvantages and is relatively fast and inexpensive.

According to the invention, this aim is achieved in that the gas sealing and the liquid sealing together are pre- mounted in a sleeve which subsequently is provided in the housing.

Preferably, the gas sealing and/or the liquid sealing are secured in the sleeve by the radial spring effect of a divided spring in a groove in the sleeve, whereby this divided spring also provides for the axial pressure force of this gas and/or liquid sealing against the shoulder of the sleeve.

In order to provide the axial pressure force of these sealing elements, use is made of springs and rings, whereas the securing of the sealings is obtained by means of clamping rings, so-called"circlips", which is more complicated.

The invention also relates to any sealing which is suit- able for applying the method according to the invention.

Thus, the invention relates to a sealing element for sealing a shaft of a rotor in a compressor element, between a rotor chamber, formed in a housing, in which at least one rotor for the compression of gas is situated, and a bearing chamber, formed in the housing, where at least one bearing, lubricated with lubricating liquid, for the shaft is situated, which sealing element compri- ses a floating gas sealing and a floating liquid sealing and which is characterized in that the gas sealing and the liquid sealing are mounted together in a sleeve.

In a particular form of embodiment of the invention, the sleeve, between the gas sealing and the liquid sealing, is provided with at least one degassing channel.

Preferably, the sleeve, at least around the liquid sealing and/or the gas sealing, is provided at its interior side with a groove in which a divided spring is provided which pushes this liquid sealing and/or the gas sealing axially against a shoulder of the sleeve.

Between a part of the liquid sealing and the shoulder against which it is pushed by the spring, a resilient sealing ring may be provided.

With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, a preferred form of embodiment of a method for sealing the shaft of a rotor of a compressor element and of a sealing element used therewith according to the invention are described, with reference to the accompanying drawings, wherein: Figure 1 schematically represents a cross-section of a part of a compressor element according to the invention;

Figure 2, more detailed, shows a cross-section of the sealing element from the compressor element according to figure 1.

In figure 1, a screw-type compressor element is represen- ted, comprising two cooperating rotors 1 which are arranged in a rotor chamber 2.

The rotor chamber 2 is limited by a housing 3. At both extremities,. each rotor 1 is provided with a shaft 4 which is beared by means of a bearing 5 which is arranged within a bearing chamber 6 formed inside housing 3.

For simplicity's sake, in figure 1 only one extremity of one rotor 1 and its bearing 5 are represented.

The bearing chambers 6 connect to the interior of a gearwheel case 7 in which the non-represented drive of the synchronization gearwheels 8, which provide for the synchronization of the rotors 1, is arranged.

Into this gearwheel case 7 and onto the bearings 5, oil is supplied for lubrication.

In order to prevent that compressed gas from the rotor chamber 2 flows to the bearings 5 and the gearwheel case 7 or oil from these bearings 5 and gearwheel cases 8 ends up in the rotor chamber 2 and, therefore, in the compressed gas, the shaft 4 between the rotor chamber 2 and the bearing chamber 6 is surrounded by a sealing element 9.

As represented in detail in figure 2, this sealing element 9 substantially consists of a sleeve 10 in which, at the side of the rotor chamber 2, a floating gas sealing 11 and, at the side of the bearing 5, a floating

oil sealing 12 are mounted.

The gas sealing 11 is a labyrinth sealing which, thus, consists of a ring 13 which is provided with a series of adjacent ring-shaped grooves 14 in its interior.

With its extremity situated most distant from the rotor chamber 2, the ring 13, by the intermediary of a divided spring 15, is pushed against a shoulder 16 which is formed by a narrowing of the sleeve 10.

The divided spring 15 consists of a cylinder spring with one convolution which is interrupted over 5 to 10 and which, therefore, is not only springy in axial direction, but also provides for a radial spring effect.

Due to the radial spring effect, this spring 15 becomes situated in a groove 17 which is provided around the ring 13 in the interior side of the sleeve 10. The spring 15 is taken up between a side wall of this groove 17 and a collar 18 at the exterior side of the ring 13, such that the gas sealing 11 is secured in axial direction.

The liquid sealing 12 is a floating thread sealing and consists of a ring 19, in the interior side of which a groove 20 in screw-thread shape is provided.

The liquid sealing 12 is secured in a manner analogous to the gas sealing 11 and is pushed by means of a second divided spring 21, which is identical to the spring 15, against a shoulder 22 of the sleeve 10.

By radial spring effect, the spring 21 is situated in a groove 23 which is provided in the sleeve 10 around the ring 19.

At its exterior side, the ring 12 has a collar 24, and it is with this collar 24 that the ring 12, under the influence of the spring 21 and by the intermediary of a resilient sealing ring 25, is pushed against the shoulder 22.

The aforementioned shoulders 16 and 22 form the side walls of a part 10A, with a smaller diameter, of the sleeve 10. In this part 10A, a groove 26 is provided, onto which a number of degassing channels 27 give out.

The sealing 9 is pre-composed of the sleeve 10, the gas sealing 11 and the liquid sealing 12 and then, as a whole, is slid over the shaft 4. The sealing 9 is fixedly clamped in a recess 28 of the housing 3.

The housing 3 is provided with an outlet which connects to the degassing channels 27, such that gas under pressure, which possibly still might leak through the gas sealing 11, can escape into the ambient atmosphere, and that the space between this gas sealing 11 and the liquid sealing remains at atmospheric pressure.

The sealing 9 can seal the shaft 4 in an efficient manner and can be provided in the housing 3 in a fast and simple manner.

The invention is in no way limited to the sealing method and a sealing used therewith described heretofore and represented in the accompanying drawings, on the contrary may such method and sealing be realized in various variants without leaving the scope of the invention, as defined in the accompanying claims.