The conventional mechanical seal used to seal the rotating shaft of a product pump comprises a stationary seal ring connected to the pump housing and a rotatable seal ring connected to the impeller shaft, each seal ring having a lapped seal face opposing the seal face on the other ring. Resilient means such as coil springs and/or bellows urge one seal ring face toward the other in sealing relation.

Most mechanical seals of the type described above have a number of metal parts, such as bellows and springs, which bias the seal rings in sealing relation, and are exposed to the product fluid. In applications where the product fluid is non-abrading and non-corrosive, this does not present a problem; but in slurry pumps, the abrasive action of the pump fluid attacks the metal parts and greatly reduces service life.

While the typical mechanical seal is compact and is characterised by closely fitting, precision made parts, it is desirable to provide slurry pump seals with rather crude parts which can be manufactured with larger dimensioned tolerances and therefore at lower cost, because they wear out more quickly despite efforts to extend operating life. This also affects the manner in which they have to be mounted in the pump. Another important consideration is to have a spring which does not become inoperative due to "clogging" by solid particles within the slurry, or "frozen" due to crystallising of the slurry product that leaks to atmosphere between the seal

SUBSTITUTE SHEET

faces .

Prior art seals use a number of different types of springs and combination of spring and primary seal made from metal and/or elastomeric material. Shown in Figure 1 is a typical coil spring mechanical seal. This utilises a coil spring 1 to urge the stationary sealing ring face 2 toward the rotating sealing ring 3. An o-ring 4 provides the seal between the axially adjustable stationary seal ring holder 5. This mechanical seal is susceptible to failure because of clogging of the coil spring by slurry products which leak between the sealing rings.

A further type of conventional mechanical seal is shown in

/ Figure 2. In this seal, two annular elastomeric members 6 are used to both urge the respective rotating 7 and stationary 8 sealing faces together, and to hold the rotating seal 7 in the rotating seal face carrier 9.

This seal is not so susceptible to clogging, but cannot withstand normal slurry pump pressures which tend to extrude the elastomeric rings 6 out of contact with the sealing faces 7 and 8 and their respective seal face carrier.

The present invention seeks to ameliorate these disadvantages by providing a mechanical seal, for rotating shifts passing into a pressure vessel, comprising a first seal face mounted on a first seal ring holder and a second seal face mounted on a second seal ring holder, a first elastomeric annular member engaging said first seal ring holder to urge said first seal face into sealing engagement with said second seal face, and a second elastomeric annular member located on said

first seal ring holder to isolate the first annular from the internal pressure of said pressure vessel.

The elastomeric annular members are resistant to the abrasive and corrosive attack of the pump product. ,5 The invention will now be described by way of example with reference to the following drawings in which:

Figure 3 shows one embodiment of the present invention in which only one set of annular members are used; and

Figure 4 illustrates a second embodiment utilising a set 10 of annular members for each of the rotating and stationary sealing faces.

As shown in Figure 3, the rotating seal ring carrier 10 is attached by conventional means to the shaft 11. The rotating seal ring 12 is carried on the seal ring carrier 10 by means of 15 the seal ring boot 13.

The stationary seal housing 14 projects into the opening of the pump, and is sealed therein by means of the O-ring 15. The stationary seal ring 16 is held in the seal ring carrier 17 by means of the seal ring boot 18. A first elastomeric annular 20 member 19 is located in a recess 20 in the stationary seal assembly 14 in such a manner .such that, it seals between the stationary seal ring carrier 10 and the stationary seal housing 14. The outside diameter of the seal ring holder and the inside diameter of the stationary seal housing are such that 5 the first elastomeric annular member 19 is prevented from being extruded by the pump pressure between the stationary seal housing 14 and the stationary seal ring carrier 17.

A second elastomeric annular member 21 is located between

- A - the stationary seal housing 14 and the seal ring holder 17 to urge the stationary seal ring 16 into sealing engagement with the rotating seal ring 12. This is enhanced by the opposed surfaces of the recess 22 being inclined to each other to "squeeze" the elastomeric member 21 toward the rotating seal ring 12.

The embodiment illustrated in Figure 4 operates in the same manner as that described above, except that the rotating sealing ring 12 is held in a rotating seat holder 23 which is identical to the stationary seal ring holder 17, which utilises first and second elastomeric annular members 24 and 25 to perform in the same manner with the rotating seal ring carrier 26, as the annular members 21 and 19 perform with the seal ring holder 17. In this embodiment of the invention the elastomeric members 24 and 25 connects the rotating seal ring 12 with the drive shaft 11 of the slurry pump. Compression of the elastomeric member 25 is sufficient to maintain a friction drive without slip, whilst the first seal elastomeric member 24 locates and steadies the face in the radial direction and protects the elastomeric spring from blowout.

In the two assembly form of the invention, the stationary seal ring is connected to the housing by the second elastomeric assembly. The benefits of such a combination of sealing elements is that:

1. both elements are resistant to abrasive and corrosive attack;

2. the elastomeric spring provides a low spring constant which reduces the sensitivity to axial adjustment and allows easy fitment by unskilled personnel; and

3. the primary elastomeric sealing element protects the spring from blowout whilst allowing the sealing ring carrier to move axially and ensure that the sealing rings remain in contact.

The seal of this invention can be mounted as a cartridge or adapted directly to the pump shaft and casing.

The seal assembly of the present invention provides clearances between parts which are greater than those in conventional seal assemblies, permitting leakage deposits to be removed from the assembly more easily.