ANNULAR ELASTOMERIC SLURRY SEAL

Abstract: A rotary mechanical seal for a rotating shaft passing into a pressure vessel, the seal having stationary and rotating seal rings (12) with at least one of the rings (12) supported in an axially biased holder (9), characterised by an elastomeric annular member (11) held in a groove, which groove is so designed as to obviate clogging or crystallising in the gap between the seal face holder (9) and the housing (10). Preferably, the groove has a protrusion located on its outer edge which has sloped inner and outer faces to co-operate with the annular elastomeric member (11) so that the member (11) protrudes past or is flush with the edge.

Description: ANNULAR ELASTOMERIC SLURRY SEAL The present invention relates tΩ a rotary mechanical seal for rotating shafts passing into a pressure vessel, and in particular, to such a seal for a slurry pump. To 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 towards the other in sealing relation. Most mechanical seals of the type described above use an elastomeric annular member to seal the stationary seal face carrier within the housing, whilst still allowing the carrier to move in an axial direction and transmit the spring force to urge one face against the other. This elastomeric annular member is held within a groove in the housing, with typically close clearances on both sides of the groove, between the seal face carrier and the housing. This close clearance is designed to provide backing to the elastomer to prevent extrusion under pressure and to hold the annular member in position during assembly and adjustment. In applications where the product fluid does not contain solids then the above arrangement does not normally present a problem. However in slurry pumps where particulate solids are present or the mixture has a tendency to crystallise, the close clearance on the product side is likely to get clogged and the seal will not function properly. Prior art seals rely on an elastomeric annular member in a fully surrounded close clearance groove to keep the pumped product from leaking, whilst providing the resilience in the axial direction to ensure the spring force is transmitted to the stationary face. * "'"''""" τ ' r Shown in Figure 1 is a typical mechanical seal. This utilises a coil spring 1 to urge the stationary sealing ring face 2 toward the rotating sealing ring 3. An elastomeric annular member (in this case an O-ring) provides the seal between the axially adjustable stationary holder 5 and the seal housing 6. This mechanical seal is susceptible to failure because of clogging of particles in the small gap 7. The present invention seeks to ameliorate this disadvantage by providing an elastomeric annular member of suitable size, and a groove of appropriate design so as to obviate clogging or crystalising in the gap between the seal face holder and the housing. The invention will now be described by way of example with reference to the following drawings in which: Figure 2 shows one embodiment of the present invention in which only one annular sealing element is utilised; and Figure 3 illustrates a second embodiment utilising a duality of annular sealing elements where both stationary and rotating elements are spring urged towards each other. Figure 4 describes the size and shape of the groove for the elastomeric annular member. As shown in Figure 2 the stationary housing 8 projects into the pump casing and contains seal face 12. The rotating seal face carrier 9 being spring urged by an elastomeric member in compression 13. The rotating seal holder 10 contains the groove of the present ivention and the elastomeric annular member 11. Figure 3 shows two seal face carriers 9, both resiliently mounted in the annular elastomeric member 11, and spring urged by elastomeric member 13. Figure 4 shows details of the groove of one embodiment of the present invention. Angle 14 is shallow, preferably less than 45 degrees to avoid hang-up of material or bridging across the gap between point 16 and the seal face holder or carrier 17. Angle 15 is shallow, preferably less than 45 degrees, and designed to provide retention of the elastomeric member during installation and adjustment. The cross-sectional area of the groove is such that the annular elastomeric member 11 should protrude or be equal in protrustion to the point 16 of the seal housing 17. The point 16 should be no less in height than half the overall groove height to ensure maximum resilience of the elastomer in transmiting the spring forces. Features: The features of annular elastomeric sealing elements of preferred embodiments of the present invention are: 1. The elastomeric face of the element is exposed to the slurry providing a resilient sealing surface, which will prevent the deposition or crystallisation of slurry particles. 2. With no extended lip on the sealing element's groove, and the elastomeric material protruding or flush with the edge of the housing, there is no possibility of material collecting between the housing and the seal face carrier (even if the housing is rotating), and thus no possibility for the gap to become clogged. 3. With the sealing element groove of the present invention, the cross-sectional shape of the elastomeric member is not 30 critical, and standard O-ring or rectangular sections may be adopted. The major benefit of the above features is to allow the seal carrier to remain axially free within the housing and to transmit the spring force to the faces. This is not possible in slurries with prior art designs. It should be obvious to people skilled in the art that alterations and modifications to the above described seal without departing from the spririt or scope of the present invention. SUBST8TUT SHEET

Claims: THE CLAIMS . 1. A rΩtary mechanical seal for a rotating shaft passing into a pressure vessel said seal comprising an elastomeric annular member held in a groove in a seal housing and bearing on a seal face holder in a sealing manner, wherein said groove is of appropriate design so as to obviate clogging or crystallising in the gaps between the seal face holder and the housing. 2. A rotary mechanical seal according to claim 1 wherein said groove has a protrusion located at one end and which is not less in height than half the overall groove height. 3. A rotary mechanical seal according to claim 2 wherein said groove has a floor and the protrusion has an inner surface which forms a shallow angle to the floor of the groove. 4. A rotary mechanical seal according to claim 3 wherein said angle is less than 45°. 5. A rotary mechanical seal according to claim 3 or 4 wherein said protrusion has an external face which is angled, to a plane normal to the floor of the groove, at a shallow angle. 6. A rotary mechanical seal according to claim 5 wherein said angle is less than 45°. 7. A rotary mechanical seal according to any one of the proceeding claims wherein the elastomeric annular member is of such cross-sectional dimension that it extends within the groove to or beyond the protrusion. SUB S TITUTE SHEET

Inventors: WALKER IAN CRAIG, WALKER, IAN, CRAIG
Applicants: WARMAN INT LTD, WARMAN INTERNATIONAL LIMITED
Application year: 1988
Main classification: F04D29
IPC codes: F04D29, F16J15