GB2078877A - Pump sealing arrangements - Google Patents

Abstract

A centrifugal pump has a drive shaft (2) rotating a pumping impeller (1) and an axially adjacent impeller (10) providing a dynamic seal for the pump chamber. A partition (22) separates the dynamic seal from a static seal comprising a carbon ring (42) on a carrier (44) on the shaft spring urged against a stationary ring 36 secured to the partition. The carrier is axially moved by centrifugally acting arms (58) to withdraw the sealing ring when a predetermined shaft speed is exceeded. <IMAGE>

Description

SPECIFICATION Pump sealing arrangements The invention relates to a sealing arrangement for a pump.

Specifically, the invention relates to a pump sealing arrangement ofthe type comprising a dyna -mic sealing device and a static sealing device, the ,static sealing device having a sealing ring rotatable with the pump shaft and spring-biassed to seal against a fixed annular surface, and centrifugal speed responsive means arranged to withdraw the sealing ring from the annular surface at a pump shaft speed above a predetermined speed.

A sealing arrangement of this type is known from GB 1 314 664, but the static sealing device is of complex construction and is structurally associated with the dynamic sealing device, which makes the static sealing device difficult to service.

The present invention accordingly provides a pump sealing arrangement of the type described in which the static sealing device is separated from the dynamic sealing device by a partition providing the fixed annular surface. By this construction, the entire static sealing device can be made readily accessible for servicing, in particular, for the replacement of the elements providing the sealing surfaces.

The present invention can thus provide a pump sealing arrangement of the type described in which the static sealing device comprises a member se cured to the pump shaft, a carrier for the rotatable sealing ring, a spring acting between the member and the carrier to bias the carrier in a direction to urge the ring against the annular surface, and weights carried by the member to pivot thereon in response to a predetermined shaft rotational speed to directly engage the carrier and move it in opposition to the spring bias.

The present invention also provides a pump sealing arrangement of the type described having in the static sealing device O-ring sealing means between the pump shaft and the rotatable sealing ring our a carrier for this ring, the O-ring sealing means being arranged to transmit shaft rotation to the sealing ring or carrier and to permit the move ment of the sealing ring towards and away from the annular surface by a rolling action.

Such O-ring sealing means provide a simple and highly effective means for permitting the necessary axial movement as well as for transmitting the rotational drive, whilst still maintaining an operative seal. To release the stress experienced by the rings in transmitting the rotational drive as long as the pump is running at a normal speed, the sealing ring or carrier can be arranged to become engaged by a member carried by the shaft when the axial withdrawal movement is complete. Such engage ment can provide a limit to this axial movement.

The dynamic sealing device of the sealing arrange ment can be of any suitable kind but is preferably constituted by an impeller additional to the pumping impeller and working in a chamber separate from the pumping chamber.

The invention is further described below, by way of example, with reference to the accompanying drawing, in which: Figure lisa partial sectional view taken along the axis of a centrifugal pump with dynamic and static sealing devices in accordance with the invention; Figure 2 is a partial rear view of the impeller of the dynamic sealing device; and Figure 3 is a fragmentary view of the impeller of Figure 2 on the line Ill-Ill of that Figure.

The illustrated pump, as shown at the left of Figure 1, has a centrifugal impeller 1 mounted on an end portion 2 of a shaft 3 to rotate therewith to effect pumping of a fluid through a chamber 4 within the impeller 1 is located. At the right hand side, not shown in Figure 1, is an electric motor which applies rotational movement when energised to a portion 6 of the shaft 3 extending through a bearing housing 5.

These parts are conventional, and will not be further described.

Between the chamber 4 and the electric motor, there are located dynamic and static sealing devices, designed to prevent leakage of fluid from the pumping chamber 4, and the ingress of air to the chamber.

Between the shaft portions 2 and 6 there is located an integral shaft portion 8 of intermediate diameter.

The dynamic sealing device comprises a turbinetype impeller 10 with a hub portion 12 splined to the shaft end portion 2 and sealed by O-rings 7 to the impeller 1 at one end, and to a radially-directed step between the shaft portions 2 and 8 at the other. The impeller 10 has a disc portion 14 extending from the hub portion 12 and provided on one side with radially straight vanes 16 extending from the hub portion to the periphery, and with shorter radially straight vanes 17 extending inwardly from the periphery between them. The impeller 10 works within a chamber 18 defined between an inwardly extending annular partition 20 of the pump housing, which separates the chambers 4 and 18, and the radial end wall of another housing portion 22.

The function of the impeller 10 is to produce a liquid annulus within the chamber 18 at a pressure higher than that generated by the impeller 1,so that neither fluid being moved by this impeller, nor air attempting to enter from the other side, cannot pass this annulus. This is achieved by a combination of centrifugal force and forced vortices generated within the chamber 18 by the impeller 10.

The static sealing device is received within a chamber defined by an outer sleeve 24, which extends away from the chamber 18 from a step in the housing partition 22, to which it is sealed by an O-ring 26. At its other end, the sleeve 24 is sealed by an O-ring 28 to an annular housing member 30. The pump housing is connected to the housing of the electric motor by bolts 32 extending through this annular member 30, which carries at its inner periphery bearings 34 for the shaft portion 6.

The static sealing device comprises a static seal member in the form of a ring 36 trapped between the housing portion 22 and a radially-inwardly projecting lip on a retaining ring 38 secured to the partition 22 by bolts 40. The other member of the seal comprises a ring 42, of carbon, held in an annular carrier 44. The carrier 44 has annular recesses 46 on its inner face, each containing an O-ring 48 sealing to the shaft portion 8. An annular member 50 is secured to the shaft portion 8 by screws 52 to rotate therewith and has at its end towards the carrier 44 an annular recess in which is received a coil spring 54.

The spring 54 acts between the member 50 and the carrier 44 to urge the carbon ring 42 into face-sealing contact with the static ring 36, and maintains the sealing relationship when the pump is stationary or only slowly rotating.

To effect withdrawal of the ring 42 from contact with the face 36 when a predetermined minimum rotational speed of the pump has been achieved, the member 50 has arms 56 extending axially to overlie the carrier 44, on which arms are pivoted levers 58.

The levers are generally L-shaped and their weight is concentrated in portions forming the longer limb which extend axially in the stationary condition of the pump illustrated. The shorter limb extends inwardly and ends with a nose 60 received in an annular groove at the exterior of the carrier 44.

Preferably a plurality of the levers 58 are provided; conveniently three may be equally angularly spaced around the member 50.

It will be evident that as the rotational speed of the shaft portion 8 increases, the levers 58 will tend to pivot outwardly under centrifugal force. The nose portions 6 will engage the sides of the groove 62 and thus move the carrier 40 to withdraw the ring 42 from the ring 36, against the pressure applied by the spring 54.

Initially, the carrier 44 is rotated by the shaft portion 8 through the O-rings 48, the grooves 46 in the carrier 44 being designed to provide maximum interference in the radial direction with the O-rings, to ensure drive transmission from the shaft portion to the carrier. During the axial movement of the carrier 44, the O-rings 48 do not slide on the shaft portion 8 but roll within the grooves 46. In both these actions, the sealing function of the O-rings 48 is still performed.

A degree of rotational drive is transmitted by the spring 54, and rotational drive is transmitted subsequently by engagement between radial faces 64 and 66 on the carrier 44 and member 50 respectively which come into abutment after a certain axial movement ofthe carrier. This relieves the distorting load on the O-rings 48 during operation of the pump at normal speed. The abutment between the faces 64, 66 limits the axial movement of the carrier 44 in the direction of withdrawal and limits also the maximum throw of the levers 58.

An appropriately dimensioned pump of the kind illustrated can be arranged to effect separation of the rings 36 and 42 at a rotational speed which is greater by a small predetermined amount than the speed at which the dynamic sealing impeller 10 becomes fully effective. For example, the rings 36,32 can be arranged to separate at 800 r.p.m. when the dynamic sealing impeller becomes operative at 550 r.p.m., giving an overlap of 250 r.p.m. Contact between the rings during start up can be of the order of milliseconds, and of a few seconds only on stopping.

Claims (15)

1. A pump comprising a rotatable drive shaft and a sealing arrangement for the shaft, the arrangement comprising a dynamic sealing device, a static sealing device, and a partition between the dynamic and static sealing devices, the static sealing device having a sealing ring rotatable with the shaft, a bias urging the sealing ring against a stationary surface provided by the partition, and speed responsive means arranged to withdraw the sealing ring from > engagement with the stationary surface at a shaft speed exceeding a predetermined speed.

2. A pump as claimed in claim 1 wherein the sealing ring is mounted by an annular carrier movable on the shaft, the bias being provided by a coil spring acting between the carrier and a ring member secured to the shaft to rotate therewith.

3. A pump as claimed in claim 2 wherein the carrier is sealed to the shaft by O-rings received in internal grooves in the carrier.

4. A pump as claimed in claim 3 wherein the O-rings are arranged to roll in the internal grooves during the movement of the carrier.

5. A pump as claimed in claim 3 or 4 wherein the O-rings are arranged to transfer rotational movement from the shaft to the carrier.

6. A pump as claimed in claim 2,3, 4 or 5 wherein the spring acts to transfer rotational movement from the shaft to the carrier.

7. A pump as claimed in any one of claims 2 to 6 wherein the carrier and the ring member have faces positioned to engage after a predetermined withdrawal movement of the carrier to thereby limit the withdrawal movement and to transfer rotation of the shaft to the carrier through the ring member.

8. A pump as claimed in any one of claims 2 to 7 wherein the speed responsive means comprises centrifugally acting lever means pivoted on the ring member and engaging in an external groove in the carrier.

9. A pump as claimed in any one of claims 2 to 8 wherein the ring member is removably secured to the shaft.

10. A pump as claimed in any preceding claim wherein the stationary surface is provided by a ring surrounding the shaft and secured to the partition.

11. A pump as claimed in claim 10 wherein the ring is gripped between the partition and a retaining ring removably secured to the partition.

12. A pump as claimed in any preceding claim wherein the partition comprises part of a pump housing including a pumping chamber containing an impeller driven by the shaft, the partition mounting a casing removable to provide access to the static sealing device.

13. A pump as claimed in claim 12 wherein tt3e casing extends from the partition to a housing containing a motor and bearings for the drive shaft.

14. A pump as claimed in any preceding claim wherein the dynamic seal comprises a turbine type impeller rotated by the shaft and provided with straight radial vanes.

15. A pump sealing as herein described with reference to the accompanying drawings.