WO1997020144A1

WO1997020144A1 - Sealing element

Info

Publication number: WO1997020144A1
Application number: PCT/DK1996/000492
Authority: WO
Inventors: Jørn Holger KLAUSEN; Tage JØRGENSEN; Ingvard Mosby Madsen; Peter FRØSLEV
Original assignee: Danfoss A/S
Priority date: 1995-11-27
Filing date: 1996-11-26
Publication date: 1997-06-05
Also published as: AU7621696A; EP0864046A1; DK133895A

Abstract

The invention concerns a sealing element for the establishment of a sealing in a pump, in which a rotatable shaft (2) extends through a shaft hole (11) and through an internal tooth wheel (9) arranged in a pump chamber (7). The sealing element (19) comprises a first fixed sealing ring (20) having a breast (22) bearing against a side wall (5, 6) of the pump chamber, and a second flexible sealing ring (21) arranged between the rotatable shaft (2) and the first sealing ring (20). Preferably, the first sealing ring has a collar (24), the second sealing ring being arranged between the rotatable shaft and said collar. The invention is characterised in that the mounting height of the sealing element in the pump is very small. This is caused by the fact that the second sealing ring is arranged between the first sealing ring and the rotatable shaft, and that the breast of the first sealing ring is bearing direct against the first side wall.

Description

Sealing element

The present invention concerns a sealing element in a pump or a motor, comprising a pump housing with at least one side wall limiting an axial extension of a working chamber, and a rotatable shaft which extends at least through one shaft hole m the side wall, said sealing element comprising a first sealing ring, which is solid, and which extends around the rotatable shaft, and between said rotatable shaft and said first sealing ring is arranged a second sealing ring, which is flexible, and which produces sealing between the rotatable shaft and the solid sealing ring.

Sealing elements of this type are commonly known as standard machine elements for use m various machines, for instance pumps. The known sealing elements comprise two parts, each to be mounted in or at a machine element. A first part forms a stationary seat, which can be made of a ceramic material, and which is arranged in a packing. The sealing is meant for mounting in a side wall, for instance of a chamber m a pump, around a hole m the side wall for a shaft extending through the hole m the side wall. Another part forms a rotatable sealing ring, which can be made of a material containing graphite to reduce the friction, and which is also arranged in a packing. The packing for the rotatable sealing ring extends around and behind the rotatable sealing ring and is fixed to the shaft in a way that the sealing ring rotates together with the shaft by means of forces transferred by the packing. To keep the sealing ring bearing against the stationary seat, a helical spring is arranged behind the rotatable sealing ring for the purpose of pressing the sealing ring against the stationary seat. However, this sealing element has some disadvantages. The use of a stationary seat as one part implies that m the side wall it is necessary to provide bearing and fixing for the stationary seat. The extending of the packing around and behind the rotatable sealing ring implies that the axial extent of the sealing element becomes considerable. Further, the axial extent becomes even more pronounced by placing a helical spring behind the sealing ring. Besides, the number of components implies that in total the known sealing element becomes both a large axial and a large radial extent.

It is the purpose of the present invention to produce a sealing element for the tightening of holes m side walls for shafts, for instance rotatable shafts, which extend through the side wall into a chamber in a pump or a motor, said sealing element comprising only few parts and being of a limited axial extent.

This purpose is reached with a sealing element characterised m that the first sealing ring is bearing against an outside of the side wall and that the second sealing ring is arranged between the rotatable shaft and the first sealing ring, extending around the rotatable shaft and bearing against said rotatable shaft.

In a preferred embodiment the sealing element is characterised in that the solid sealing ring has an internal periphery with a diameter being larger than the largest diameter of an external periphery of the rotatable shaft, and that the flexible sealing ring has a smallest diameter equal to or smaller than the diameter of the external periphery of the rotatable shaft and a largest diameter equal to or larger than the diameter of an internal periphery of the solid sealing ring.

Thus the sealing element comprises two sealing organs, the first solid sealing ring and the second flexible sealing ring, respectively. The first sealing ring forms the sealing towards the side wall and the second sealing ring provides the sealing towards the shaft. A common bearing surface between the two sealing rings establishes the total sealing between the side wall and the shaft. The first sealing ring is preferably solid, and for the purpose of reducing the friction between the first sealing ring and the side wall of the pump house, it is coated with polytetraflourethen, such as distributed among others under the trade mark teflon®. Alternatively, the first sealing ring can be made completely of polytetraflourethen or of

PEEK. The first sealing ring can also be made of a material containing coal fibres or carbon. The second sealing ring is primarily an O-ring made of rubber to obtain a flexible and resilient sealing ring.

The present invention bears the advantage that the axial extent of the sealing element is very limited, partly because the first sealing ring bears direct against the outside of the side wall of the pump chamber, and partly because the second flexible sealing ring is arranged between the rotatable shaft and the first sealing ring, and not behind the first sealing ring. The very limited axial extent implies that it is possible to mount bearings supporting the rotatable shaft closer to the side wall.

To secure sufficient bearing for the first sealing ring towards the side wall, it is possible to use a spring, such as a helical spring, which is mounted behind the first sealing ring, and which establishes a force on the first sealing ring directed towards the side wall. An alternative way of establishing this force on the first sealing ring towards the side wall is especially useful m for instance pumps or motors, m which the shaft is a rotatable shaft extending into the pump chamber through the hole m the side wall. In this case leakages of the medium to be pumped are possible through the hole between the shaft and the periphery of the hole. The leakage of pump medium is exposed to a pressure established by pumping the medium into the pump chamber, and this pressure can be used to secure sufficient bearing for the first sealing ring towards the side wall. The pressure of the sealing ring will be increased automatically in step with an increase of the pressure m the medium.

In another preferred embodiment the sealing element according to the invention is thus characterised m that the first sealing ring comprises largely seen axial surfaces arranged between the bearing of the sealing ring against the outside of the side wall and the rotatable shaft, and that the axial surfaces comprise at least a first surface which is turned away from the outside of the side wall, and that a projected area of the surface, parallel to the outside of the side wall, is larger than a projected area parallel to the outside of the side wall of any other axial surfaces.

The medium leaking between the hole m the side wall and the shaft, which is exposed to pressure, will provide a pressure in the axial direction against the largely seen axial surfaces. If the projected area of the first axial surface, which is turned away from the side wall, is larger than the corresponding projected area of any axial surfaces turned towards the side wall, the resulting force on the first sealing ring will be directed towards the side wall. In certain cases it will then be possible to avoid a helical spring to establish a sufficient bearing of the first sealing ring against the side wall.

In the following the invention will be described with reference to the enclosed drawing:

By way of a section, the drawing shows a possible embodiment of a pump with a sealing element according to the invention. The pump comprises a pump housing 1. A rotatable shaft 2 is supported in bearings 3, 4 and extends into the pump housing 1 through a first side wall 5. Together with a second side wall 6 the side wall 5 forms an axial limitation of a pump chamber 7. The pump housing 1 comprises a chamber wall 8, which also forms a limitation of the pump chamber 7. Between the chamber wall 8 and the pump chamber 7 is arranged an external tooth wheel 32. An internal tooth wheel 9 is arranged in the pump chamber 7. The internal tooth wheel 9 is mounted on the rotatable shaft 2 and is meant for being driven by the rotatable shaft 2. A connecting element 10 is therefore arranged between the rotatable shaft 2 and the internal tooth wheel 9.

The first side wall is provided with a shaft hole 11 for the rotatable shaft. The second side wall is provided with an inlet 12 to the pump chamber 7 and an outlet 13 from the pump chamber 7 for a medium to be pumped. An end cover 14 bears against an outside 15 of the second side wall 6 and is provided with threaded holes 16 for the connection of hoses or pipes (not shown) to lead the medium to and from the pump. Between the first side wall 5 and the chamber wall 8, between the chamber wall 8 and the second side wall 6 and between the second side wall 6 and the end cover 14 sealing elements 17 are arranged in grooves 18. In the pump shown, the sealing elements 17 are packing rings, preferably O-rings.

Between the bearing 4 and the first side wall is arranged a sealing element 19. The sealing element 19 is the sealing element according to the invention. In the embodiment shown the sealing element comprises a first sealing ring 20 and a second sealing ring 21. In the embodiment shown, the first sealing ring 20 is solid and fixed, and the second sealing ring 21 is flexible.

The first sealing ring 20 comprises a breast 22 with a bearing surface 23 bearing against the first side wall 5. Further, the first sealing ring 20 comprises a collar 24 extending outward from the breast 22 in relation to the first side wall 5. The collar 24 has a smallest diameter d₂₄ which is larger than a diameter D₂ of the rotatable shaft 2, and the collar 24 extends around the rotatable shaft 2.

The second sealing ring 21 is arranged between the rotatable shaft 2 and the collar 24. The second sealing ring 21 has a smallest diameter d_2] which is equal to or smaller than the diameter D of the rotatable shaft 2. The second sealing ring 21 has a largest diameter D₂ι which is equal to or larger than the smallest diameter d₂ of the collar 24. Thus the second sealing ring 21 is bearing against the rotatable shaft 2 with its smallest diameter d_2] and against the collar 24 with its largest diameter D₂ι . Both the first sealing ring 20 and the second sealing ring 21 are made for rotating together with the rotatable shaft 2.

At its bearing with the side wall 5, the bearing surface 23 on the breast 22 of the first sealing ring 20 provides sealing against any leakages of pump medium under pressure, which might force its way out of the pump chamber 7 between the internal tooth wheel 9 and the first side wall 5 and on through the shaft hole 11. The bearing 23 of the breast 22 prevents pump medium from being led out between the breast

22 and the side wall 5. The bearing of the second sealing ring 21 against the rotatable shaft 2 or the collar 24 of the first sealing ring 20, respectively, prevents the leakage mentioned above from being led out between the rotatable shaft 2 and the first sealing ring 20.

In the embodiment shown, the first sealing ring 20 has a breast 22 comprising an axial surface 25, which is turned away from the side wall 5. Leakages of pump medium as described above, where pump medium under pressure is led out through the shaft hole 11 in the first side wall 5 and on to a space 26 between the rotatable shaft 2 and the collar 24, will exert a pressure on the axial surface 25. As the axial surface 25 is turned away from the first side wall 5, the pressure exerted on the axial surface 25 by the pump medium m the space will increase the force with which the first sealing ring 20 is bearing against the first side wall 5. This increase will be proportional to the pressure of the pump medium, and therefore the sealing between the first side wall 5 and the breast 22 of the first sealing ring 20 will be proportional to the pressure and thus reduce the risk of leakages.

A bowl 27 is arranged behind and around the first sealing ring. The bowl 27 is provided with a flange 28 extending outward in relation to the bowl 27. A helical spring 29 extends between a rear plate 30 and the flange 28. The rear plate 30 is provided to prevent the second sealing ring 21 from being displaced in relation to the pump chamber 7. The helical spring 29 is meant for establishing a certain minimum power for the bearing 23 of the breast 22 against the first side wall 5. Further to this minimum power, an additional power will be established by a possible leakage of pump medium into the space 26 between the rotatable shaft 2 and the collar 24 as described above.

In a preferred embodiment as the one shown, the bearing between the breast 22 of the first sealing ring 20 and the first side wall 5 is established direct on an outside 31 of the first side wall 5. This implies that it is not necessary to provide a separate bearing ring m the first side wall 5 for the bearing of the breast 22 against the side wall 5. If, for instance, the side wall 5 is made of a ceramic material, and if, for instance, the first sealing ring 20 is made of a material containing graphite or a material covered with teflon®, it will be possible to establish a sufficient sealing between the first sealing ring 20 and the first side wall 5, and at the same time the friction between the sealing ring 20 and the side wall 5 will be so low that no thermal or mechanical damages will occur on the sealing ring 20 or the side wall 5.

In the above, the sealing element according to the invention is described with reference to a specific embodiment of a pump and with reference to a specific embodiment of a sealing element comprising a solid ring with a collar and a breast, and an elastic ring. However, it will be possible to use the sealing element m other types of pumps than the one shown. If the pump is, for instance, provided with a rotatable through-going shaft, thus extending through both the first side wall and the second side wall, it will be possible to use several sealing elements according to the invention. Besides, it will be possible to produce a different geometric shape of the first sealing ring as well as of the second sealing ring. Springs of other types than helical springs can also be used.

Claims

Patent Claims

1. Sealing element (19) for a pump or a motor, comprising a pump housing (1) with at least one side wall (5, 6) limiting an axial extension of a working chamber (7), and a rotatable shaft (2), extending through at least one shaft hole (11) m the side wall (5, 6), said sealing element (19) comprising a first sealing ring (20) , which is solid, and which extends around the rotatable shaft (2), and between said rotatable shaft (2) and said first sealing ring (20) is arranged a second sealing ring (21), which is flexible, and which produces sealing between the rotatable shaft (2) and the first sealing ring (20), characterised in that the first sealing ring (20) is bearing against an outside (31) of the side wall (5, 6) and that the second sealing ring (21) is arranged between the rotatable shaft (2) and the first sealing ring (20), extending around the rotatable shaft (2) and bearing against said rotatable shaft (2) .

2. Sealing element according to claim 1, characterised in that the first sealing ring (20) has an internal periphery with a diameter (d₂J being larger than the largest diameter (DJ of an external periphery of the rotatable shaft (2) , and that the second sealing ring (21) has a smallest diameter (d J equal to or smaller than the diameter (D₂) of the external periphery of the rotatable shaft and a largest diameter (D_?J equal to or larger than the diameter (d₂J of an internal periphery of the first sealing ring (20) .

3. Sealing element according to any of the preceding claims, characterised in that the first sealing ring

(20) is made of a carboniferous material.

4. Sealing element according to any of the preceding claims, characterised in that the first sealing ring

(20) is a solid ring with a surface made of a first friction reducing material, preferably polytetraflourethen, and that the second sealing ring

(21) is an adjacent elastic ring made of a different material, preferably rubber, and that the first sealing ring (20) and the second sealing ring (21) have a common diameter.

5. Sealing element according to any of the preceding claims, characterised in that the first sealing ring

(20) comprises at least one largely seen axial surface (25) arranged between the bearing (23) of the sealing ring (20) against the outside (31) of the side wall (5, 6) and the rotatable shaft (29, and that at least one of the axial surfaces (25) s turned away from the side wall (5, 6) , and that a projected area of the surface, parallel to the outside (31) of the side wall (5, 6) is larger than a projected area parallel to the outside of the side wall of any other axial surfaces.

6. Sealing element according to any of the preceding claims, characterised in that a spring element (29) is arranged behind the first sealing ring (20) and provides a forward force against the side wall (5, 6) on the sealing r ng 20.