GB2069360A - Membrane plate locking union - Google Patents

Abstract

A filter cloth locking union (10), for use with a filter press plate having an inflatable membrane (18) is of a resiliently deformable material and is in the form of a flanged bush (12) having a slurry feed aperture (19) therethrough and a feed recess (21) in an outer face (23) of the flange (13) communicating with the aperture (19). Within the flange (13) in the region of the recess (21) is a rigid metal bridge member (25) and a flexible reinforcing fabric (27) at the radially outward side of the bridge member (25). The thickness of the flange (13) is such that the outer surface (23) stands proud of membrane (18) and contacts an adjacent chamber plate when the press is closed, thus pressing the membrane (18) against the plate (15) to prevent leakage of pressure fluid from the space (22) between the membrane (18) and the plate (15) to the feed aperture (19). As shown, two unions (10) on opposite sides of plate (15) interlock. <IMAGE>

Description

SPECIFICATION Membrane plate locking union This invention relates to membrane plates for filter presses and in particular to filter cloth locking unions for such membrane plates.

It is essential to ensure a good seal between the slurry inlet and the space between the membrane and the body of the membrane plate, so as to preclude leakage of high pressure fluid within such space into the slurry feed or slurry into such space. For this purpose it is usual to provide a filter cloth locking union which secures the filter cloth and membrane to the membrane plate body in the region of the slurry inlet or feed aperture.

Such locking unions have the form of a flanged bush which passes through the feed aperture and is secured therein by an annular locking ring screwed into the locking union from the opposite side of the membrane plate. In the case of a double-sided membrane plate the locking ring is in fact another locking union and the screwing together of the two such locking unions simultaneously secures a filter cloth and membrane on each side of the membrane plate.

Such locking unions are of metal and are of robust construction so as to be able to tightly clamp the membranes onto the membrane plate. However, it has been found that no matter how tightly the locking unions are screwed together the membranes deform under the pressure of the high pressure fluid and leakage can occur with fluid pressures in the region of 40 psi (2.812 kg/sq cm).

To counteract this tendency it is known to provide extra screws which are arranged to pass through the two locking unions or locking union and locking ring so as to clamp the two together and increase the clamping effect of the locking union(s). With such screws in use pressures of up to 80 psi (5.624 kg/sq cm) may be used before leakage of high pressure fluid to the slurry feed aperture is experienced. Such measures are expensive and the operation of replacing a filter cloth or membrane is time consuming, adding further to the costs involved.

As an alternative to the above it is known to mould a membrane in situ on the membrane plate, the membrane passing through the slurry feed aperture. In the case of a double-sided membrane plate the two membranes are moulded integrally so as to be continuous within the slurry feed aperture. Leakage of high pressure fluid is thereby prevented within the limits of rupture of the membrane, but such membrane plates have the disadvantage that the membranes cannot readily be replaced if damaged.

It is an object of the present invention to provide a filter cloth locking union which is not subject to the aforementioned disadvantages and which readily allows for replacement of damaged filter cloths or membranes.

The invention provides a filter cloth locking union for use with a filter press membrane plate, the locking union having a slurry feed aperture therein, a feed recess in one face thereof in fluid flow communication with said aperture, and being of a rigid material at least in a region extending across said recess, the thickness of said locking union being such that in use the surface remote from said membrane plate is contacted by a surface of an adjacent plate prior to contact between the outer face of the membrane and such adjacent plate.

Preferably the locking union is of a deformable material and has a rigid bridge member extending across said recess.

Preferably the locking union is in the form of a flanged bush, in which case the recess may be in an outer face of the flange and may extend substantially radially from a substantially centrally disposed slurry feed aperture. With a locking union of such a configuration the rigid bridge member may be located within the flange and adjacent the slurry feed aperture. The recess and the bridge member may be in a radially extended portion of the flange.

The locking union may be provided with an engaging member or members adapted to engage a cooperating engaging member or members on a locking ring or second locking union.

The locking union may also be provided with a flexible reinforcing member in said flange, the flexible reinforcing member being located so as to extend outwardly from the radially outward edge of said bridge member.

Preferably the thickness of said flange is sufficient to provide that in use the outer surface of said flange is contacted by a surface of an adjacent plate prior to contact between the outer face of the membrane and such adjacent plate.

The invention will now be further described with reference to the accompanying drawings in which: Fig. 1 is a sectional elevation on line I-I of Fig. 2 showing part of a double-sided, corner feed membrane plate and two locking unions; and Fig. 2 is a plan view of one embodiment of locking union in accordance with the invention.

Referring now to the Figures there is shown a locking union 10 and a second locking union 11 interengaged therewith. Each locking union 10, 1 1 is in the form of a flanged bush such that each is provided with a bush portion 12 and a flange portion 13. The bush portions 12 are adapted to be inserted in an aperture 14 in membrane plate 1 5 from opposite sides of the plate 1 5 and are prevented from falling out thereof by virtue of their interengagement. For this purpose each locking union 10, 1 1 is provided adjacent the free end of the bush portion 12 with an annular engaging recess 17 so as to form an annular engaging rib 16. Recess 17 of union 10 is provided internally of bush portion 12 and the recess 17 of union 11 is provided externally of bush portion 12 whereby each rib 1 6 is engaged in the recess 17 of the other union.The unions 10, 1 1 are of deformable material for a purpose to be described but such deformability serves also to facilitate the interengagement and removal of the unions 1 O, 1 1.

Attached to each side of membrane plate 15 is a membrane 18 and the unions 1 0, 11 have substantially centrally disposed bores 19 providing a slurry feed aperture. In the outer face of a radially extended portion 20 of each flange 13 is feed recess 21 which communicates with the bore 19 and allows slurry to be fed from bores 19 to the region between a membrane 18 and the recess of adjacent chamber plates (not shown). Air or other fluid under pressure is then supplied to the region 22 between each membrane 18 and the plate 15 to which it is attached so as to compress the slurry between membrane 18, and the recess of an adjacent chamber plate, express water from such slurry and to form a cake for subsequent removal after separation of adjacent plates.The fluid pressures used in such a process can cause fluid to leak from space 22 between membrane 18 and plate 15 to the slurry feed bores 19, or alternatively slurry can seep along the same route in the reverse direction during charging of the press, unless adequate sealing of the membrane 18 to the plate 1 5 in this region can be effected.

The locking unions 10, 11 effect this sealing in the following manner. The thickness of flanges 13 is such that the outer surfaces 23 of flanges 13 stand slightly proud of the outer surfaces 24 of the membranes 18. In consequence when the press is closed to bring the membrane plates 15 and adjacent chamber plates (not shown) together, contact between the outer surface 23 of the locking union of a membrane plate 15 and a surface of an adjacent chamber plate occurs before any contact between the membrane 18 and the chamber plate can occur. Since the locking unions 10. 1 1 are deformable, the pressure exerted in the press causes sufficient deformation of the locking unions 10, 11 for the outer surfaces 24 of the membranes 1 8 subsequently to come into contact with the respective adjacent chamber plate.However, the pressure applied to the locking unions 10, 11 is transmitted through the flanges 13 to the membranes 18 and effects sufficient sealing of membranes 18 to membrane plate 15 as to allow fluid pressures of 120 psi (8.436 kg/sq cm) and above to be sustained in spaces 22 without leakage of fluid to the slurry feed bores 1 9.

In order that the pressure between a locking union and an adjacent chamber plate be applied in the region of the slurry feed recess 21, in which region there is no contact between the locking union and the chamber plate, a rigid bridge member 25 in the form of a steel plate is disposed in the flange 13 of each locking union 10, 11. The bridge member 25 extends across the slurry feed recess 21 adjacent the bore 19. To ensure that pressure is applied to the end regions of the bridge member 25 and the outer surface 23 of the flange 13 has a locally raised surface in this region, for example by means of ridges or bosses 26.Since the bridge member 25 is rigid, pressure applied to its end regions on one side thereof will be transmitted to the opposite side along the whole length thereof and in consequence the pressure will be transmitted to the membrane 18 in the region of the feed recess 21 as well as in the region of the remainder of the locking union.

Again, since the locking unions 10, 11 are deformable and the bosses 26 are relatively small, contact between the remainder of the surfaces 23 of the locking union and the surface of an adjacent chamber plate is not prevented.

It will be appreciated that the fluid pressure in space 22 creates a tendency for the radially extended portion 20 of flange 13 to bend outwardly away from membrane 18, This in turn creates a tendency for the flange 13 to be cut by, or to fracture adjacent the radially outer edge of bridge member 25. In order to prevent or at least minimise the risk of such cutting or fracture a flexible reinforcing member 27 is provided in the flange 13 to extend radially outwardly from the bridge member 25. The flexible reinforcing member 27 may be a fabric, a sheet of thermoplastics material or a relatively thin sheet of metal, although a fabric reinforcing member is preferred. The reinforcing member 27 also serves to distribute the pressure loading on the membrane 18 more evenly and thereby reduce local stresses therein, thus ensuring a longer working life of the membrane 18.

Preferably the locking unions 10. 1 1 are formed of a rubber material, which may be the same material as that from which the membranes 18 are formed. For example natural rubber may be used although an ethylene propylene rubber is preferred since advantageously it has low set properties.

Although the invention has been described in particular in relation to a corner feed membrane plate it is applicable to the case of a centre feed membrane plate. In such a case the locking union is formed having a plurality of angularly spaced radial feed recesses 21 and a rigid bridge member 25 is provided in respect of each recess 21.

Claims (17)

1. A filter cloth locking union for use with a filter press membrane plate, the locking union having a slurry feed aperture therein and a feed recess in one face thereof in fluid flow communication with said aperture, and being of a rigid material in at least a region extending across said recess, the thickness of said locking union being such that in use the surface remote from said membrane plate is contacted by a surface of an adjacent plate prior to contact between the outer face of the membrane and such adjacent plate.

2. A locking union according to claim 1 wherein said locking union is of a resiliently deformable material and has a rigid bridge member extending across said recess.

3. A locking union according to claim 1 or claim 2 wherein said locking union is in the form of a flanged bush.

4. A locking union according to claim 3 wherein said recess in in an outer face of said flange.

5. A locking union according to claim 4 wherein said recess extends substantially radially from said aperture.

6. A locking union according to claim 5 wherein said bridge member is located within said flange and adjacent said aperture.

7. A locking union according to claim 6 wherein said recess and said bridge are in a radially extended portion of said flange.

8. A locking union according to claim 6 or claim 7 comprising a flexible reinforcing member in said flange.

9. A locking union according to claim 8 wherein said flexible reinforcing member is located so as to extend radially outwardly from a radially outward edge of said bridge member.

10. A locking union according to claim 8 or claim 9 wherein said flexible reinforcing member comprises a sheet of fabric.

11. A locking union according to any one of claims 3 to 10 wherein said flange is of a sufficient thickness whereby in use an outer surface thereof lies outwardly of an outer surface of a membrane of said plate.

12. A locking union according to claim 11 wherein said outer surface of said flange is provided with protuberances thereon at least in a region adjacent said bridge member.

13. A locking union according to any one of claims 1 to 12 wherein said locking union is provided with an engaging member or members adapted to engage a cooperating engaging member or members of a locking member.

14. A locking union according to claim 13 wherein said locking member comprises a second locking union.

15. A locking union according to claim 2 or any claim dependent thereon wherein said bridge member comprises a metal plate.

16. A locking union substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A membrane plate having secured thereto at least one locking union according to any one of claims 1 to 16.

1 8. A filter press comprising a plurality of membrane plates according to claim 17.