Diaphragm housing

Abstract

A diaphragm housing (10) comprises: a body (12) having a front end (14) and a laterally spaced rear end (16); an inner chamber (18) extending laterally from an entrance (20) in the front end (14) generally towards the rear end (16); an annular diaphragm seat (30) laterally spaced from the entrance (20) and extending radially inward into the inner chamber (18), the annular diaphragm seat (30) terminates at a radially inner wall (35) which is radially inwardly spaced from the interior of the annular sidewall (29); and an annular cavity (32) extending rearward from the diaphragm seat (30), and wherein an outer diameter of the annular cavity (32) is larger than the diameter of the radially inner wall (35).

Description

FIELD OF INVENTION The present invention generally relates to a diaphragm housing, to a diaphragm assembly and a diaphragm pump including the diaphragm housing. BACKGROUND OF THE INVENTION Known diaphragm pumps comprise a diaphragm which is mounted within a chamber so called diaphragm housing. The diaphragm of the pump separates the pumped medium, usually in the form of a slurry, from relatively clean fluid (propelling fluid) that is in contact with the moving and vulnerable parts of the pump. The pumping motion of the propelling fluid and flexible diaphragm is effected by means of the moving parts (such as a piston) displacing and pressurising the propelling fluid. The piston is connected to a driving unit by means of a piston rod and is reciprocated within the cylinder so that the diaphragm carries out successive suction and discharge strokes at a particular frequency under the influence of the propelling fluid. During the suction stroke the diaphragm is displaced out of the chamber with the pressure in the chamber less than the pressure in an inlet line, so that a certain amount of slurry flows into the pumping chamber via the inlet. During the discharge stroke, the piston forces propelling fluid into the chamber whereby the slurry introduced during the suction stroke is displaced into a discharge pipe via the outlet. In order to ensure the correct function of the suction stroke and the discharge stroke, one-way valves are mounted in the inlet pipe portion and in the outlet pipe portion respectively. In use, the diaphragm may be secured within the chamber by clamping the outer periphery of the diaphragm between a diaphragm seat of the chamber and a diaphragm clamping member whereby the diaphragm sits sealingly against the diaphragm seat. During the discharge stroke, the pressure in the chamber is sufficiently high to cause an interior annular sidewall of the chamber to splay radially outwards to some extent. The result is that stresses are introduced into the interior annular sidewall. These stresses are most severe in (concentrated at) the outer periphery of the chamber proximate to the diaphragm seal but still in contact with the slurry. Such stresses in the chamber results in corrosion fatigue of the housing, and ultimately failure of the diaphragm housing. An example of a known diaphragm housing which is used in high-pressure applications is shown in Figure 1, The housing 1 includes a stress release formation 2 having a large inner radius starting at a smaller diameter than the diaphragm seat 3. An inner bowl 4 is seated within the stress release formation 2 to support the diaphragm (not shown) and fills the stress release formation 2. To fill the stress release formation 2 and adequately support the diaphragm (not shown) the inner bowl 4 has a large footprint and subsequently increases the footprint of the housing 1 which increases manufacturing cost thereof. It is desirable to obviate or mitigate the high stress concentration that is generated in the housing to reduce corrosion fatigue in the diaphragm housing and eliminate the need for an inner bowl in current diaphragm housing design which increases the footprint of the housing substantially It is among the objects of an embodiment of this invention to provide means which may at least ameliorate this problem or provide a useful alternative. SUMMARY This summary is provided to introduce a selection of concepts that are further described in the detailed description below. This summary is not intended to identify indispensable features of the claimed subject matter, nor is it intended for use as an aid in limiting the scope of the claimed subject matter. According to a first aspect there is provided a diaphragm housing comprising: a body having a front end, a laterally (i.e. axially) spaced rear end, an inner chamber extending axially from an entrance in the front end towards an internal rear wall opposite and axially spaced from the front end, and an annular sidewall surrounding the inner chamber between the front end and the internal rear wall; an annular diaphragm seat laterally (i.e. axially) spaced from the entrance and extending radially inward into the inner chamber, the annular diaphragm seat including a front face orientated towards the entrance against which a diaphragm sealingly sits, the diaphragm seat terminates at a radially inner wall which is radially inwardly spaced from the interior of the annular sidewall; and an annular cavity extending rearward from a rear face of the diaphragm seat, wherein the outer diameter of the radial limit of the annular cavity is larger than a diameter of the radially inner wall of the diaphragm seat. The radial limit of the annular cavity may be radially outwardly spaced from the radially inner wall Optionally, the diameter of the annular cavity may be larger than a diameter of a sealing area of the diaphragm seat. The sealing area of the diaphragm seat may be defined by the area where a diaphragm sits sealingly against the front face of the diaphragm seat. Optionally, an axial length of the annular cavity may be larger than an axial thickness of the annular diaphragm seat. Optionally, an inner profile of the annular sidewall defines a front side arc (in crosssection) at the front face side of the diaphragm seat and a rear side arc (in cross-section) at a rear face side of the diaphragm seat. The front side arc may extend from the interior of the annular sidewall towards the front face of the annular diaphragm seat. The rear side arc may extend from the rear face at least partially towards an internal rear wall. Optionally, a radial limit of the annular cavity is defined by a transition arc (in crosssection) which extend from the rear face side of the diaphragm seat at least partially towards an internal rear wall. Optionally, the radial limit of the annular cavity is further defined by a rear side arc (in cross-section) at the rear face side of the diaphragm seat and wherein the transition arc extends from the rear side arc at least partially towards the internal rear wall. Optionally, the rear side arc and the transition arc are separated by a cylindrical portion. Optionally, the transition arc may have a larger radius than the front side arc. Optionally, the transition arc has a similar radius to the front side arc. Optionally, the annular cavity includes a radial outer portion which is defined by a portion of the profiled annular sidewall at a rear face side of the diaphragm seat and a radial inner portion defined by the interior rear wall. More specifically, the radial outer portion of the annular cavity is defined as the portion of the annular cavity which extends from the rear face of the annular diaphragm seat towards the rear wall with the radial limit of the annular cavity defined by the rear side arc and the transition arc. Optionally, the annular cavity includes a radial outer portion which is defined by the portion of the annular cavity radially outward from the radially inner wall of the diaphragm seat and a radial inner portion defined by the interior rear wall. Optionally, the inner radial portion extends from the radial outer portion radially inward beyond an annular perimeter surface of the diaphragm seat. Optionally, the internal rear wall defines a substantially cylindrical protrusion extending axially towards the front end so that an end of the cylindrical protrusion is axially rearward of the diaphragm seat rear face The cylindrical protrusion may extend axially towards the front end so that an end of the cylindrical protrusion is axially rearward of the diaphragm seat rear face. Optionally, the diaphragm housing includes a frusto-conical diaphragm support extending rearward and radially inward form the cylindrical protrusion towards a narrow end at the rear end of the housing. Optionally, the diaphragm housing includes a bore extending from the narrow end of the support member through the rear end of the housing. Optionally, the annular sidewall has an inner profile defining a shoulder formation extending radially into the chamber and thereby separating a front portion of the chamber extending rearward from the entrance, from a rear portion of the chamber extending from the front portion rearward, so that the front portion has an increased diameter relative to the diameter of the rear portion. Optionally, the diaphragm housing includes an inlet and an outlet extending from opposed sides of the annular sidewall into the rear portion of the chamber. The inlet and outlet may be positioned at opposed operative upper and lower ends of the annular sidewall although other configurations are possible. Optionally, the outer surface of the body may be substantially planar adjacent the inlet and outlet. Optionally, the body includes an annular front face extending radially between an exterior surface of the annular sidewall and the entrance. The front face may include a plurality of radially spaced apertures arranged to correspond with apertures in a front cover. Optionally, the body includes rear face which extend radially between the outer surface of the body and the bore. The rear face may include a plurality of radially spaced apertures. The radially spaced apertures may allow the diaphragm housing to be secured to a driving assembly of a diaphragm pump. Optionally, the diaphragm seat extends into the chamber by less than 10% of the inner chamber at a point nearest the diaphragm seat. According to a second aspect there is provided a diaphragm housing assembly comprising: a diaphragm housing according to the first aspect; a housing cover arranged to be secured to the front end of the diaphragm housing and cover the entrance; a diaphragm clamping member receivable in the inner chamber; a diaphragm housed within the inner chamber with an outer periphery of the diaphragm clamped between the diaphragm clamping member and the front face of the diaphragm seat; and a support ring seated within a portion of the annular cavity, the support ring positioned radially inward from the diaphragm seat to support a portion of the diaphragm. It is to be appreciated that the diaphragm clamping member and the housing cover may either be two independent components which may be removably secured to one another or be a single component. Optionally, annular sidewall has a profile defining a shoulder formation extending radially into the chamber and thereby separating a front portion of the chamber extending rearward from the entrance, from a rear portion of the chamber extending from the front portion rearward, so that the front portion has an increased diameter relative to the diameter of the rear portion. Optionally, the diaphragm clamping member includes a cylindrical portion defining an internal sidewall and a peripheral wall surrounding the internal sidewall and extending therefrom and terminating at an outer rim portion spaced rearward from the cylindrical body portion. The peripheral wall and the internal sidewall may define a pumping chamber forward of the outer rim portion. The diaphragm clamping ring further includes a flange extending radially outward from a front portion of the cylindrical portion. The flange of the diaphragm clamping member may be arranged to be received in the front portion of the chamber with the peripheral wall and outer rim portion arranged to be received within the rear portion of the chamber. Optionally, the internal sidewall of the diaphragm clamping member defines a straight surface adjacent the peripheral wall and a frusto-conical surface which extends rearwards from the straight surface of the cylindrical body portion. Optionally, the diaphragm clamping member includes an inlet and outlet extending through the peripheral wall and which corresponds with the inlet and outlet of the diaphragm housing when received in the inner chamber. Optionally, the diaphragm is frusto-conical shape with an outer radial portion of the diaphragm clamped between a rear face of the rim of the diaphragm clamping member and a front face of the diaphragm seat. The diaphragm may include a connection arrangement whereby the diaphragm may be secured to a diaphragm shaft extending from the diaphragm through the bore in the rear portion of the housing. Optionally, an area between the rear face of the rim of the diaphragm clamping member and a front face of the diaphragm seat in which the outer radial portion of the diaphragm is clamped defines a clamping zone. The volume of the annular cavity may be larger than a volume of the clamping zone. Optionally, the volume of the radial outer portion of the annular cavity may be larger than the volume of the clamping zone. In other words, the volume of the portion of the annular cavity which is not occupied by the support ring may be larger than the volume of the clamping zone. Optionally, at least a portion of the diaphragm cover is arranged and dimensioned to fit within the entrance with a flange extending radially outward from a front portion the cover having a diameter greater than the entrance. The flange may include a annular rear face which is arranged to sit against a front face of the diaphragm housing while the at least a portion of the cover is received in the inner chamber through the entrance. Optionally, the support ring is substantially annular with an inner surface of the support ring frusto-conically shaped. The inner surface of the support ring and the diaphragm support is generally of a similar angle with an radial outer part of the support ring extending forward beyond the diaphragm seat so that the diaphragm is supported during a suction stroke. The opening between the support ring and the outer rim portion may be less than the thickness of the outer periphery of the diaphragm so that the support ring provide radial support to the diaphragm. Optionally, the support ring is housed within an radial inner portion of the annular cavity. Optionally, the support ring includes a plurality of holes that assist in deaeration. Optionally, the support ring and the internal rear face of the diaphragm housing include corresponding opening arranged to receive fastening elements to releasably secure the support ring to the internal rear wall. Optionally, an radial outer portion of the support ring is arranged to extend laterally beyond the diaphragm seat with an inner face of the support ring and the frusto-conical diaphragm support sloping at a similar angle. Optionally, the diaphragm housing and clamping member includes corresponding inlet and outlet openings which extends from an outer surface of the diaphragm housing into the pumping chamber. According to a third aspect there is provided a diaphragm pump which comprises: a diaphragm assembly according to the second aspect; a driving unit which is arranged in communication with the diaphragm via a propelling fluid to displace the propelling fluid and diaphragm towards a first position wherein the propelling fluid and diaphragm is withdrawn from the pumping chamber to suck slurry into the pumping chamber via an inlet and a second position wherein the propelling fluid and diaphragm is displaced into the pumping chamber to displace the slurry out of the pumping chamber via the outlet. Optionally, the driving unit consists of a piston which is in contact with the diaphragm via the propelling fluid (clean fluid) to displace the diaphragm between the first and second positions. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects will be apparent from the following specific description, given by way of example only, with reference to the accompanying drawing in which: Fig. 1 is a sectional view of a prior art diaphragm housing; Fig. 2 is a rear perspective view of a diaphragm housing according to a first aspect of the invention; Fig. 3 is a cross sectional view of the diaphragm housing taken along the line A-A as shown in Fig. 2; Fig. 4 is a front perspective view of the diaphragm housing of Fig. 3; Fig. 5 is a front perspective view of a diaphragm housing assembly according to a second aspect of the invention, including the diaphragm housing of the first aspect; Fig. 6 is a cross sectional view of the diaphragm housing assembly taken along the line B-B as shown in Fig. 5; Fig. 7 is a front perspective view of the diaphragm housing assembly of Fig.6 ; Fig. 8A is an enlarged, detailed view of the diaphragm housing as shown in Fig. 6; Fig. 8B is a further enlarged, detailed view of part of the diaphragm housing as shown in Fig. 8A; Fig. 9 is a rear view of the diaphragm housing assembly of Fig. 5; Fig. 10 is a detailed cross sectional view of the diaphragm housing assembly taken along the E-E as shown in Fig. 9;Fig. 11 is a front perspective view of the support ring of diaphragm housing assembly shown in Fig. 4; Fig. 12 is a rear perspective view of the support ring of Fig. 11; Fig. 13 is a cross sectional view of the support ring taken along the line G-G as shown in Fig. 11; Fig. 14A is a simplified drawing showing a diaphragm sealing area of the diaphragm housing of Fig. 2; Fig. 14B is a simplified drawing showing an alternative example of a diaphragm sealing area of a diaphragm housing; Fig. 14C is a simplified drawing showing a further alternative example of a diaphragm sealing area of a diaphragm housing; Fig. 14D is a simplified drawing showing a diaphragm sealing area of a prior art diaphragm housing; Fig. 14E is a simplified drawing showing a diaphragm sealing area of the prior art diaphragm housing of Fig. 1; and Fig. 14F is a graph illustrating the maximum stress in a front side arc of the diaphragm sealing area for the three design shown in Figs. 14A, Fig.14D and Fig. 14E. DETAILED DESCRIPTION OF EMBODIMENTS Reference is now made to the drawings, and particularly to Figs. 2-4, which show a diaphragm housing 10 according to an embodiment of the present invention. The diaphragm housing 10 includes a body 12 having a front end 14 and a laterally (i.e. axially) spaced rear end 16. The body further includes (i) a profiled internal rear wall 27 opposite, and axially spaced from, the front end and, (ii) an inner chamber 18 which extends laterally (i.e. axially) from an entrance 20 in the front end 14 of the body 12 towards the internal rear wall 27, and (iii) a profiled annular sidewall 29 surrounding the cavity and extending axially from the front end 14 of the body 12 to the profiled internal rear wall 27. The respective profiles of the rear wall 27 and the annular sidewall 29 will be described in more detail below. In the illustrated example, the body 12 is substantially cylindrical having an outer cylindrical surface 22 although other configurations are possible. The body 12 further includes (i) an annular front face 24 extending radially between the outer cylindrical surface 22 and the entrance 20, and (ii) an opposed rear face 26. The annular sidewall 29 has an inner profile defining a shoulder formation 28 extending radially into the chamber 18 and thereby separating a front portion 18.1 of the chamber extending rearward from the entrance 20, from a rear portion 18.2 of the chamber 18 extending from the front portion 18.1 rearward, so that the front portion 18.1 has an increased diameter relative to the diameter of the rear portion 18.2. The diaphragm housing 10, in this embodiment the profiled annular sidewall 29, further includes an annular diaphragm seat 30 which is laterally (i.e. axially) spaced from, and generally parallel to, the entrance 20 and which extends radially inward at least partially into the rear portion 18.2 of chamber 18. The diaphragm seat 30 is effectively an annular stub in this embodiment, although in other embodiments different configurations are possible. In this embodiment, the diaphragm seat 30 extends into the chamber 18 by less than 10% of the rear portion 18.2 at a point nearest the diaphragm seat 30. The diaphragm seat 30 includes a front face (a diaphragm sealing face 30.2) which is orientated towards the entrance 20. The front face 30.2 of the diaphragm seat 30 defines a sealing area 30.1 (shown more clearly in Figs. 8Aand 8B against which an outer radial portion of a diaphragm (as shown in Figs. 8A and 8B) sealingly sits, thereby providing axial support to the diaphragm mounted thereon. The diaphragm seat 30 also includes a rear face 30.3 (best seen in Fig. 8B). The diaphragm seat 30 (annular stub) 30 terminates at an radially inner wall 35 which is radially inwardly spaced from the interior of the annular sidewall and which is transverse (in this embodiment generally perpendicular) to the diaphragm sealing face 30.2. The radially inner wall 35 is the radially innermost point of the diaphragm seat 30. As best seen in Fig. 8A and particularly Fig. 8B, the annular sidewall 29 inner profile defines a front side arc (in cross-section) 31 having a relatively small radius R1 at the front face side of the diaphragm seat (annular stub) 30 and a rear side arc (in cross-section) 33 at the rear face side of the diaphragm seat (annular stub) 30. These front side 31 and rear side 33 arcs may be formed by machining, or, where the diaphragm housing 12 is made by a casting process, as a result of the casting process. The housing 10 includes an annular cavity 32 which extends rearward from the diaphragm seat 30 (at a rear side thereof). In this embodiment, the annular cavity 32 is defined partly by the annular sidewall’s 29 internal profile (which defines the radial limit of the annular cavity 32) and partly by the profiled internal rear wall 27 (which defines the axial limit of the annular cavity 32). The profiled annular sidewall 29 transitions into the profiled internal rear wall 27 at a curved transition surface 40 defining a transition arc (in cross-section) having a radius R2 which is larger than radius R1 of the front side arc. The transition arc 40 extends from the rear side arc 33 to the profiled rear wall 27. The radial limit of the annular cavity 32 is therefore defined by the rear side arc 33 and the transition arc 40 which extends between the rear face side 30.3 of the diaphragm seat 30 and the rear wall 27. It is to be appreciated that the radial limit of the annular cavity 32 may comprise different forms. For example the curved transition surface 40 may extend from the rear face side 30.3 of the diaphragm seat 30 with the rear side arc 33 omitted. Alternatively, the curved transition surface 40 and the rear side arc 33 may be separated by a substantially cylindrical portion. The profiled annular sidewall 29 includes a generally cylindrical surface 37 extending from the shoulder formation 28 to the front side arc 31. An outer diameter 34 of the annular cavity 32 is larger than the diameter 36 of the radially inner wall of the diaphragm seat 30. In other words, the radial limit of the annular cavity 32 may be radially outwardly spaced from the radially inner wall 35 of the diaphragm seat 30. Alternatively, the outer diameter 34 of the annular cavity is larger than the diameter 36.1 of the sealing area 30.1 of the diaphragm seat 30. An axial length 32.3 of the annular cavity 32 may be larger than an axial thickness 30.4 of the annular diaphragm seat 30. The annular cavity 32 includes a radial outer portion 32.1 (defined by the profiled annular sidewall 29 and more specifically the rear side arc 33 and the transition arc 40) and a radial inner portion 32.2 (defined by the profiled internal rear wall 27). In other words, the radial outer portion 32.1 of the annular cavity 32 is defined by the portion of the annular cavity which is radially inwardly spaced from the radially inner wall 35 of the diaphragm seat. In the example shown the radial outer portion 32.1 of the annular cavity 32 extends from an area near (but on the opposite side of) the sealing area 30.1 of the diaphragm seat 30 radially outward beyond the generally cylindrical surface 37 of the rear portion 18.2 of the inner chamber 18. In an alternative embodiment, the radial outer portion of the annular cavity 32 extends from the radially inner surface 35 of the diaphragm seat 30 radially outwards but not beyond the generally cylindrical surface 37 of the rear portion 18.2 of the inner chamber 18. The radial inner portion 32.2 of the annular cavity 32 extends from the radial outer portion 32.1 radially inward beyond the radially inner wall 35 (which is the innermost part of the diaphragm seat 30). In the embodiment shown, the profiled internal rear wall 27 defines a substantially cylindrical protrusion 38 extending axially towards the front end. In this embodiment, the cylindrical protrusion 38 extends axially by a relatively small distance, such that an end 41 of the cylindrical protrusion 38 is axially rearward of the diaphragm seat rear face 30.3. The housing 10, in the embodiment the profiled internal rear wall 27, includes a frusto-conical diaphragm support 42 extending rearward and radially inward from the end 41 of the cylindrical protrusion 38 towards a narrow end 44 at the rear end 16 of the housing 10. The diaphragm housing 10 includes a bore 46 extending from the narrow end 44 of the diaphragm support 42 through the rear surface 26. The bore 46 in the illustrated example is substantially cylindrical to receive a diaphragm shaft, although other configurations are possible. The diaphragm housing 10 includes an inlet 48 and an outlet 50 extending from opposed sides of the outer surface 22 into the rear portion 18.2 of the chamber 18 through the annular sidewall 29. The inlet 48 and outlet 50 are positioned at opposed operative upper and lower ends of the diaphragm housing 10 although other configurations (e.g. the opposite configuration) are possible. As shown in the illustrated example, the outer surface of the body 12 is machined so that the area of the outer surface 22 adjacent the inlet 48 and outlet 50 is substantially planar to allow a flange of an inlet and outlet pipe (not shown) to be secured to the housing 10. The front face 24 includes a plurality of radially spaced apertures 52 (best seen in Fig. 4) arranged to correspond with apertures 80 in a housing cover 74 (best seen in Fig. 5) to secure the housing cover 74 to the front end 14 of the housing 10. The rear face 26 includes a first set of radially spaced apertures 54.1 and a second set of radially spaced apertures (best seen in Fig. 2 and 9). The first set of radially spaced apertures 54.1 extend from the rear face partially forward and allows the diaphragm housing 10 to be secured to a drive assembly of a diaphragm pump (not shown). The second set of radially spaced apertures 54.2 extend from the rear face into the radial inner portion 32 of the annular cavity 32. Referring to Figs. 5-10, a diaphragm housing assembly 55 which includes the diaphragm housing 10 is shown. The diaphragm housing assembly 55 (details of which are best seen in Fig. 5) includes a diaphragm housing cover 74 arranged to be secured to the front end 14 of the diaphragm housing 10, and a diaphragm clamping member (or ring) 56 which is housed within the inner chamber 18 and held in place by the diaphragm housing cover 74. It is to be appreciated that that the diaphragm clamping member 56 and the housing cover 74 may either be two independent components which may be removably secured to one another or be a single component. The diaphragm clamping member 56 includes a cylindrical body portion 58 defining an internal sidewall 59 and a peripheral wall 61 surrounding the internal sidewall 59 and extending therefrom and terminating at an outer rim portion 60 spaced rearward from cylindrical body portion 58. The peripheral wall 61 and the internal sidewall 58 define a pumping chamber 62 forward of the outer rim portion 60. The diaphragm clamping member 56 further includes a flange 64 extending radially outward from a front portion of the cylindrical body 58, which is arranged to be received in the front portion 18.1 of the inner chamber 18, with the peripheral wall 61 and outer rim portion 60 arranged to be received within the rear portion 18.2 of the inner chamber 18. The internal sidewall 59 defines a straight surface 68 adjacent the peripheral wall 61 and a frusto-conical surface 66 which extends rearwards from the straight surface 68 of the cylindrical body portion 58. An inlet 70 and outlet 72 each extend through the peripheral wall 61 and are in registration with the inlet 48 and outlet 50 of the diaphragm housing 10 when the clamping member 56 is housed in the inner chamber 18. The diaphragm housing cover 74 comprises a cylindrical body 75 arranged and dimensioned to fit within the entrance 20 and a flange 76 extending radially outward from a front portion of the cylindrical body 75. The flange 76 of the diaphragm housing cover 74 may in certain embodiments extend radially beyond the outer surface 22 . Alternatively, the flange 76 of the diaphragm housing cover 74 may have a similar or smaller diameter than the outer surface 22. The flange 76 includes an annular rear face 78 which is arranged to sit against the annular front face 24 of the diaphragm housing 10 while at least a portion of the cylindrical body 75 is received within the entrance 20. The diaphragm housing cover 74 includes a plurality of radially spaced openings 80 (Fig. 5) which correspond and are in registration with the apertures 52 in the front face 24 of the diaphragm housing 10 to allow the cover 74 to be secured to the diaphragm housing 10 using suitable fasteners. The diaphragm housing assembly 55 also includes a diaphragm 82 housed within the inner chamber 18 to divide the inner chamber 18 between the pumping chamber 62 (located operative in front of the diaphragm 82) and a clean fluid chamber 83 (located operatively behind the diaphragm 82). The diaphragm 82 comprises a substantially frusto-conical shape with a radial outer portion 82.1 of the diaphragm 82 clamped between the outer rim 60 of the clamping member 56 and the diaphragm seat 30 so that the diaphragm 82 creates a fluid tight seal at the contact area 30.1 between the pumping chamber 62 and the clean fluid chamber 83. The diaphragm 82 includes a connection arrangement 84 whereby the diaphragm 82 may be secured to a diaphragm shaft (not shown) which extends from the diaphragm 82 through the bore 46 in the rear end 16 of the housing 10. An area between the rear face of the outer rim 60 of the clamping member 56 and the front face 30.1 of the diaphragm seat in which the radial outer portion 82.1 of the diaphragm 82 is clamped defines a clamping zone 85. The volume of the annular cavity 32 may be larger than a volume of the clamping zone 85. More specifically, the volume of the radial outer portion 32.1 of the annular cavity 32 may be larger than the volume of the clamping zone 85. In other words, the volume of the portion of the annular cavity 32 which is not occupied by a support ring 86 may be larger than the volume of the clamping zone 85. The diaphragm housing assembly 55 further includes a support ring 86 which is housed within the radial inner portion 32.2 of the annular cavity 32. The support ring 86 is substantially annular with an inner face 88 of the support ring 86 having a frusto-conical shape. The inner face 88 of the support ring 86 and the diaphragm support 42 are generally of a similar angle with a radial outer part 90 of the support ring 86 extending forward beyond the diaphragm seat 30. In use, the support ring 86 provides additional support to the diaphragm 82 between the diaphragm support 42 and the diaphragm seat 30. The support ring 86 further includes radially spaced mounting apertures 92 (best seen in Figs. 10 and 12) which corresponds to the second set of radially spaced apertures 54.2. In use, suitable fasteners extend through the second set of radially spaced apertures 54.2 and are received within the radially spaced mounting apertures 54.2 to secure the support ring 86 to the housing. The support ring 86 also include a deaeration cavity 94 (best seen in Fig. 13) which includes an elongated slot 94.1 in the front face 96 of the support ring 86 which is in fluid communication with a cavity 94.2 extending through the support ring 86. In the illustrated example the cavity 94.2 extends towards a rear face 98 of the support ring 86. In an alternative example not shown, the cavity 94.2 may extend towards an outer cylindrical face of the support ring 86 and be in fluid communication with the radial outer portion of cavity 32.1. The diaphragm housing assembly 55 is secured to a driving unit to pump abrasive (and sometimes corrosive) slurry mixtures. The diaphragm 82 is provided with a diaphragm shaft (not shown) which is movably accommodated in guides (not shown) disposed in a pressure chamber (not shown). The pressure chamber (not shown) is filled with a working fluid, which can be pressurised by means of a piston (not shown) that is connected to the driving unit (not shown) by means of a piston rod (not shown). The reciprocating movement of the piston (not shown) within the cylinder (not shown) effected by the driving unit leads to the working fluid being pressurised and consequently to the diaphragm 82 being moved between a discharged position and a suction position in the diaphragm housing 10. The reciprocating movement of the piston (not shown) and the resulting movement of the diaphragm 82 comprises a suction stroke or suction period in which piston (not shown) and the diaphragm 82 undergo a rearward movement or to the right (when viewing Fig. 6), and a delivery or discharge stroke in which the piston (not shown) and the diaphragm 82 undergoes a forward movement or to the left (as seen in Fig. 6). The diaphragm housing assembly 55 is mounted in a pipe system (not shown) that forms part of a more extensive network of pipes (not shown). The inlet 48 and outlet 50 of the diaphragm housing 10 are in fluid communication with a inlet pipe portion (not shown) and an outlet pipe portion (not shown) respectively. Mounted in the inlet pipe portion (not shown) is a suction one-way valve (not shown) whilst a discharge one-way valve (not shown) is mounted in the outlet pipe portion (not shown). The one-way valves are mounted in the pipe system in such a manner that the discharge one-way valve remains closed and the suction valve is open during the suction stroke (when the working fluid moves to the right and forces the diaphragm into the chamber) thus enabling the intake of a certain amount of slurry into the pumping chamber 62 through the inlet 48. During the subsequent discharge stroke (working fluid moves to the left and pulls the diaphragm out of the chamber) the suction one-way valve automatically closes under the influence of the action of a spring and the discharge one-way valve automatically open under the influence of the delivery pressure, so that the amount of slurry that has collected in the pumping chamber 62 is forced into the discharge pipe via the outlet 50. It is to be appreciated that the annular cavity 32, and more specifically the radial limit of the annular cavity, may have different forms as shown in Figs. 14A-14C. As shown in Fig. 14A the radial limit of the annular cavity may be defined by the rear side arc 33 which extends rearward from the rear face 30.3 of the diaphragm seat and the transition arc 40 which extends from the rear side arc 33 towards the internal rear wall 27. Alternatively as shown in Fig. 14B the rear side arc 33 and the transition arc 40 may be separated by a substantially cylindrical portion of the annular sidewall 29. Further alternatively as shown in Fig. 14C, the rear side arc 33 may be omitted with the transition arc 40 extending from the rear face 30.3 or substantially from the radially inner wall 35 of the diaphragm seat towards the internal rear wall 27. The diaphragm housing and diaphragm housing assembly described above have several advantages over existing diaphragm housing designs. During the discharge stroke, the pressure in the pumping chamber 62 is sufficiently high to cause the annular sidewall 29 to splay radially outwards to some extent. The diaphragm housing cover 74 is provided to mitigate this, but it cannot entirely prevent it. The result is that stresses are introduced into the annular sidewall 29. In the previous designs, these pressures were the most severe in (concentrated at) the equivalent feature of the front side arc 31 which is located in the abrasive slurry being pumped. Such cyclic (suction and discharge pressure introduces cyclic stresses and strains) stresses resulted in fatigue loads, and ultimately failure of the diaphragm housing. In addition, the equivalent feature of the front side arc 31 (31a and 31b as shown in Figs. 14D and 14E) is located within the abrasive, and sometimes corrosive, slurry being pumped. In contrast, the embodiments described above include an annular cavity behind the diaphragm seat which is located in the clean fluid chamber not in contact with the slurry. The results of this is that when such stresses are introduced into the annular sidewall 29 (which is inevitable) these stresses are directed to, and concentrated in the annular cavity, (more specially at the transition arc 40) (rather than the front side arc 31). This is shown in Fig. 14F where the normalized stress in the front side arc 31 (shown by line 100) is significantly reduced by the annular cavity 32 as compared to the normalised stress in the front side arc 31a and 31b (shown by lines 102 and 104 respectively). The annular cavity 32 ensures that these stresses are lower, thereby limiting fatigue failure of the diaphragm housing. Furthermore, the transition arc 40 is located in the clean fluid chamber 83, not in the pumping chamber 62. As such, those smaller stresses experienced by the transition arc 40 are less harmful in the clean than being subjected to abrasive, sometimes corrosive, slurry. Further benefit could be obtained were the radius R2 of the transition arc 40 is larger than the radius R1 of the front side arc 31 as shown in Figs. 14B and 14C. The above embodiments may also mitigate any stress concentration that is generated in or at the outer diameter of the clamping member and the housing. Various modifications to the above described embodiments may be made within the scope of the present invention. For example, although the arc 31, 40 are described as having a radius, there may not be a single radius but the arc may be generally curved. LIST OF REFERENCE NUMERALS Diaphragm housing 10 Diaphragm housing body 12 Front end 14 Rear end 16 Inner chamber 18 Front portion of chamber 18.1 Rear portion of chamber 18.2 Entrance 20 Outer surface of housing 22 Front face 24 Rear face 26 Profiled internal rear wall 27 Shoulder formation (of internal sidewall) 28 Profiled annular sidewall 29 Diaphragm seat (annular stub) 30 Sealing area of diaphragm seat 30.1 Diaphragm sealing face (stub front face) 30.2 Rear face (of diaphragm seat) 30.3 Axial thickness of diaphragm seat 30.4 Front side arc (of internal sidewall) 31 Front side arc of prior art diaphragm housing 31a Front side arc of prior art diaphragm housing 31b Annular cavity 32 Radial outer portion of cavity 32.1 Radial inner portion of cavity 32.2 Axial length of annular cavity 32.3 Rear side arc (of internal sidewall) 33 Outer diameter of cavity 34 Radially inner wall 35 Diameter of radially inner wall 36 Diameter of sealing area 36.1 Generally cylindrical surface (of rear portion) 37 Cylindrical protrusion 38 Transition surface / Transition arc 40 End (of cylindrical protrusion) 41 Diaphragm support 42 Narrow end of diaphragm support 44 Bore 46 Inlet 48 Outlet 50 Radially spaced apertures in front face of diaphragm housing 52 First set of apertures in rear face of diaphragm housing 54.1 Second set of apertures in rear face of diaphragm housing 54.2 Diaphragm housing assembly 55 Clamping member 56 Cylindrical body of clamping member 58 Internal sidewall (of diaphragm clamping member) 59 Outer rim of clamping member 60 Peripheral wall 61 Pumping chamber 62 Flange of clamping member 64 Frusto-conical portion of clamping member 66 Straight surface 68 Inlet clamping member 70 Outlet of clamping member 72 Housing cover 74 Cylindrical body of housing cover 75 Flange of housing cover 76 Annular rear face 78 Radially spaced opening in housing cover 80 Diaphragm 82 Radial outer portion of the diaphragm 82.1 Clean fluid chamber 83 Connection arrangement 84 Clamping zone 85 Support ring 86 Inner face of support ring 88 Radial outer portion of support ring 90 Radial spaced mounting apertures 92 Elongated slot 94.1 Cavity 94.2 Front face of support ring 96 Rear face of support ring 98

Claims

1. A diaphragm housing comprising:a body having a front end, an axially spaced rear end, an inner chamber extending axially from an entrance in the front end towards an internal rear wall opposite and axially spaced from the front end, and an annular sidewall surrounding the inner chamber between the front end and the internal rear wall;an annular diaphragm seat laterally spaced from the entrance and extending radially inward from an interior of the annular sidewall into the inner chamber, the annular diaphragm seat including a front face oriented towards the entrance, against which a diaphragm sealingly sits, the diaphragm seat terminates at a radially inner wall which is radially inwardly spaced from the interior of the annular sidewall; andan annular cavity extending rearward from a rear face of the diaphragm seat, wherein an outer diameter of the annular cavity is larger than the diameter of the radially inner wall of the diaphragm seat.

2. The diaphragm housing according to claim 1, wherein the annular diaphragm seat defines a diaphragm sealing area where the diaphragm sealingly sits against the front face of the diaphragm seat and wherein the outer diameter of the annular cavity is larger than the diameter of the diaphragm sealing area.

3. The diaphragm housing according to claim 1 or 2, wherein an axial length of the annular cavity is larger than an axial thickness of the annular diaphragm seat.

4. The diaphragm housing according to any one of claims 1 -3, wherein a radial limit of the annular cavity is defined by a transition arc (in cross-section) which extend from the rear face side of the diaphragm seat at least partially towards an internal rear wall.

5. The diaphragm housing according to claim 4, wherein the radial limit of the annular cavity is further defined by a rear side arc (in cross-section) at the rear face side of the diaphragm seat and wherein the transition arc extends from the rear side arc at least partially towards the internal rear wall.

6. The diaphragm housing according to claim 5, wherein the rear side arc and the transition arc are separated by a cylindrical portion.

7. The diaphragm housing according to any one of claims 4 to 6, wherein the interior of the annular sidewall defines a front side arc (in cross-section) extending between the annularsidewall towards the front face side of the diaphragm seat and wherein the transition arc has a larger radius than the front side arc.

8. The diaphragm housing according to any one of claims 4 to 6, wherein the interior of the annular sidewall defines a front side arc (in cross-section) extending between the annular sidewall towards the front face side of the diaphragm seat and wherein the transition arc has a similar radius to the front side arc.

9. The diaphragm housing according to any preceding claim, wherein the annular cavity includes a radial outer portion which is defined by the portion of the annular cavity radially outward from the radially inner wall of the diaphragm seat and a radial inner portion defined by the interior rear wall.

10. A diaphragm housing assembly comprising:a diaphragm housing according to any one of the preceding claims;a housing cover arranged and dimensioned to be secured to the front end of the diaphragm housing and seal the entrance;a diaphragm clamping member receivable in the inner chamber;a diaphragm housed within the inner chamber with an outer periphery of the diaphragm clamped between the diaphragm clamping rim and the diaphragm seat to create a seal between the diaphragm and front face of the diaphragm seat at the diaphragm sealing area; anda support ring seated within a portion of the annular cavity, the support ring positioned radially inward from the diaphragm seat to support a portion of the diaphragm.

11. The diaphragm housing assembly according to claim 10, wherein the diaphragm clamping member includes a cylindrical portion with an outer rim extending rearward from an outer periphery of the cylindrical portion to define a pumping chamber inside the outer rim.

12. The diaphragm housing assembly according to claim 11, wherein an outer radial portion of the diaphragm is clamped between a rear face of the outer rim and a front face of the diaphragm seat so that the diaphragm creates a fluid tight seal at the diaphragm seat to divide the inner chamber into a pumping chamber and a clean fluid chamber and wherein an area between the rear face of the outer rim and a front face of the diaphragm seat in which the outer radial portion of the diaphragm is clamped defines a clamping zone and wherein a volume of the annular cavity is larger than a volume of the clamping zone.

13. The diaphragm housing assembly according to claim 12, wherein the volume of the outer portion of the annular cavity is larger than the clamping volume.

14. A diaphragm pump comprising:a diaphragm assembly according to any one of claims 10 to 13; and5          a driving unit which is arranged in communication with the diaphragm via a propellingfluid to displace the propelling fluid and diaphragm between a first condition wherein the propelling fluid and diaphragm is withdrawn from the pumping chamber to suck slurry into the pumping chamber via an inlet and a second condition wherein the propelling fluid and diaphragm is displaced into the pumping chamber to displace the slurry out of the pumping 10 chamber via the outlet.

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