GB2222536A

GB2222536A - Filter assembly

Info

Publication number: GB2222536A
Application number: GB8821240A
Authority: GB
Inventors: George Sherwood Hunter; Michael John Hawker
Original assignee: Process Scientific Innovations Ltd
Current assignee: Process Scientific Innovations Ltd
Priority date: 1988-09-09
Filing date: 1988-09-09
Publication date: 1990-03-14
Also published as: GB8821240D0

Abstract

A filter assembly comprises a filter bowl (10) and a head (11) enclosing a filter cartridge (12) which carries a spigot (54) engaging in inlet/outlet port (52) and carrying axially spaced O-rings (56, 58) defining between them a space (65). If the cartridge is absent or incorrectly mounted, leakage of fluid into space (65) and through port (66) actuates a signal. The bowl and cartridge fit to the head (11) as one unit, and if they are incorrectly fitted a valve (38) opens to provide a second audible signal. In Fig. 5 the flange (18) which connects the cartridge to the bowl is frangible and breaks if the pressure drop across the cartridge rises, to allow leakage from port (66). <IMAGE>

Description

FILTER ASSEMBLY AND CARTRIDGE THEREFOR This invention relates to a filter assembly and to a filter cartridge adapted to form part of such an assembly.

It is well known in' the gas and liquid filtration art to provide a filter housing in the form of a filter bowl and a filter head and to provide a separate consumable filter cartridge for fitting into the bowl. An object of the invention is to provide a way of determining when a cartridge is present and correctly mounted to the filter head when enclosed in a bowl which is normally of metal or other optically opaque material.

In one aspect the invention provides a filter assembly comprising a filter head and a filter cartridge mountable to the filter head, wherein correct mounting of the cartridge on the filter head establishes a fluidtightly isolated space and a port opens into said space for determining by the state of gas in or the flow of gas from said space whether a cartridge is present and correctly mounted.

Means may be connected to the port for determining a gas flow therethrough, or a a pressure transducer may be connected to the port.

The filter cartridge and the filter head preferably fit together by a spigot and socket connection, the spigot and socket preferably being sealed by a pair of axially spaced seals (preferably O-ring seals) between which is defined a the fluid-tightly isolated space.

The assembly preferably further comprises a filter bowl releasably mounted to the filter head, the filter head and the filter bowl having bayonet formations for connecting them together. Preferably means establishes a mechanical connection between the filter bowl and the filter cartridge so that the filter bowl and the filter cartridge are together mountable to and demountable from the filter head. The top inner face of the bowl may have seat means on which a projection of the cartridge fits, and may have internal buttresses, the cartridge projection being shaped to pass the buttresses in one angular position and to be trapped beneath the buttresses in other angular positions.

The filter bowl may carry a pressure relief valve and may have latch means that snaps into a recess in the filter head at one angular position at which the bayonet connection is made to prevent relative rotation of the filter head and the filter bowl but is prevented from engagement at other angular positions, the latch means being decoupled from the valve when in its engaged state but being operatively coupled to the valve when in a disengaged state to open the valve, fluid flow through the valve giving a warning of pressure in the filter bowl.

The invention further provides a filter cartridge for use with a filter head having a port into which a spigot of the cartridge is a push fit, wherein the spigot carries a pair of axially spaced O-rings that when the cartridge is correctly positioned on the filter head fluid tightly isolate a space with which a second port communicates.

The casing of the cartridge is advantageously of moulded plastics and the filter bowl and filter head may be moulded or cast in aluminium or light alloy. The cartridge may contain a moulded or pleated microporous element and may be adapted for coalescing droplets from a gas stream.

Alternatively it may contain an adsorbent element and may be adapted for removal of vapour from a gas stream by adsorption.

In an alternative aspect, the invention provides an assembly comprising a filter head and a filter cartridge fluid-tightly mounted to the filter head to establish a gas flow path from or to the filter head through the cartridge, wherein the cartridge is held to the filter head by frangible mounting means arranged to break at a predetermined pressure difference across the 'cartridge to permit the cartridge to move away from the filter head and enable the gas flow to by-pass the cartridge.

The frangible mounting means may comprise one or more projections extending from the cartridge that shear when the predetermined pressure difference is exceeded. The cartridge may have means co-operating with the filter head to establish a fluid-tightly isolated space and a port may then open into the space for determining by the state of fluid in the flow of fluid through said space whether the cartridge is correctly mounted and sealed.

The invention yet further provides a filter cartridge for removably mounting to a filter head via frangible mounting means that is arranged to break when the pressure difference across the filter head exceeds a predetermined value.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view of a filter head in horizontal section; Figure 2 is a view of the filter head and upper portions of a filter bowl and of a filter cartridge in the bowl, the view being taken in vertical composite section on the lines O-A and O-A' of Figure 1; Figure 3 is a side view of upper parts of the filter cartridge; Figures 4a and 4b are plan views of the filter cartridge showing a fragment of the outer wall of the filter bowl in a first relative position of the bowl and filter head corresponding to unlocking of the filter bowl from the head and in a second relative position corresponding to locking of the filter bowl to the filter head; and Figure 5 is a view of the filter head and upper portions of a filter bowl and of a filter cartridge in the bowl, the view being taken in vertical composite section on the lines O-A and O-A' of Figure 1, but with a second form of the filter cartridge which has a frangible mounting flange. The position of the cartridge is shown after breakage of the mounting flange by reason of excess pressure across the filter; In the drawings, a filter bowl 10 is mountable to and demountable from a filter head 11 and houses a consumable filter element or cartridge 12 which may be a vapour coalescing filter of the general kind described in our Patent No's GB-A-1603519 and 1557821 or may be an activated carbon filter element as described in our Patent No. GB-A2019068 or may be a dust removal filter or may be a combined filter and adsorption element.The working parts of the cartridge 12 are housed in a casing of plastics or other suitable material having an upper portion 14 attached by adhesive or other suitable means to a lower portion 16.

The upper portion 14 is formed with a flange 18 projecting radially outwards therefrom and reinforced at intervals about the periphery of the upper portion 14 by upper and lower vertical webs 22,24 of triangular form extending part-way across the flange 18. It is also reinforced on its upper face with four generally rectangular top webs 20. As seen in Figures 4a,4b, the flange 18 is formed with a first cut-out 26 of relatively large angular extent and with three second cut-outs 28 of relatively small angular extent, the four cut-outs,being disposed symmetrically at equi-angular intervals about the periphery of the flange 18 and extending the full distance across the flange 18. The relatively large first cut-out 26 allows the cartridge to enter a bowl having a pressure relief valve generally indicated by the reference numeral 38.The four rectangular top webs 20 occur at the ends of the first cut-out 26 and midway between each pair of second cut-outs 28 (Figures 4a,4b). If the valve 38 were omitted, the cut-outs could all be of the same angular extent, and there could be three such cut-outs or more than for with corresponding formations (described below) in the inner face of the filter bowl 10.

As seen in Figure 2, the filter bowl 10 has a lower region 30 connected at a transition region 31 to a radially enlarged top region 32 by a horizontal step 34 which defines a seat on which the flange 18 rests and thereby supports the cartridge 12 in an intended axial position relative to the bowl 10. The outer face of the top region 32 is formed with a groove 40 in which an O-ring 42 fits and is retained during mounting of the bowl 10 to and during demounting of the bowl 10 from the filter head 11.

Internally of the top region 32 there are formed three vertically directed horizontally interrupted buttresses 0 disposed at 90 intervals about the axis of the bowl 10.

Each buttress 44 is formed with a lower part 44b that arises at a small clearance above the horizontal step 34 and acts firstly as an abutment limiting axial travel of flange 18 and secondly as a physical stop limiting angular travel of the bowl 10. Each buttress 44 is also formed with an upper part 44a that acts as a bayonet ramp follower. A first groove 46 is defined between the buttress lower parts 44b and the step 34 and receives the flange 18. Thus the second cut-outs 28 are dimensioned and positioned so that when the cartridge 12 is in an angular position such that they align with the buttresses 44 the cartridge 12 can pass axially downwards into the bowl 10 until flange 18 seats onto step 34.Displacement of the cartridge 12 in either angular direction engages flange 18 into groove 46 and the lower part 44b of each buttress then limits upward travel of the cartridge 12 which is therefore mounted to and demounted from the filter head 11 as a unit with the bowl 10. It is understood that the grooves 46 at the buttresses 44 are of the same height, have a common datum and are directed parallel to the step 34. The upper pat 44a of each buttress acts as a bayonet ramp follower and defines a second groove 48 with the lower part 44b. Again the second grooves 48 are of the same height, have a common datum and are directed parallel to the step 34.Each buttress 44 has a relatively small angular extent (about 240), the corresponding intervals being relatively large (about 660), these intervals not being critical but being selected to provide an effective and robust interface.

Referring now to the the structure of the filter head 11, a first threaded or bayoneted port 50 leads to the interior of the cartridge 12 via a vertical port 52 which receives a spigot 54 upstanding from the upper casing portion 14. The port 52 is stepped at 60. An upper cartridge O-ring 56 seals against an upper smaller diameter portion 62 of the port 52 and a lower cartridge O-ring 58 seals against a lower larger diameter portion 64 thereof.

When the cartridge 12 is correctly fitted to the filter head 11 the O-rings 56,58 define an annular space 65 bounded by spigot 54 and vertical port 52 that is isolated from the prevailing pressure of fluid (usually gas) within the bowl 10 and head 11. A port 66 which conveniently is formed by post-drilling downwardly at a small angle communicates with the space 65 and may be threaded as shown for connection thereto of a pressure transducer (not shown) or other pressure-sensitive device. In the absence of a cartridge 12 in the bowl 10 or if the cartridge 12 is incorrectly fitted or if the O-ring 56 and/or 58 fails during service (e.g. due to chemical attack) the state of the transducer or other device connected to the port 66 is determined by line pressure, and differs from the state when a cartridge is present.Thus by altering the size of the orifice entering the annular space 65 between the two O-rings 56,58 a high pitched whistle or hiss can be induced indicating a malfunction. By this means an indication of the presence or absence of the cartridge 12 may be given either on the side of the filter head 11 or at a remote location. An outer chamber 68 is defined between the cartridge 12 and the bowl 10 and leads via a radially offset vertical port 70 in the filter head 11 to a second threaded or bayonet port 72. The ports 50,72 are interchangeably inlets and outlets to the cartridge 12 depending on the intended direction of fluid flow.

A depending cylindrical wall 75 is formed about the vertical port 52 on the under-side of the filter head 11 at an intermediate radial position. At its lower edge the wall 75 carries on its outer face radially projecting bayonet locking elements 77 each complementary to the buttresses 44. As shown in our patent application No. EP-A-0278771 (the disclosure of which is incorporated herein by reference) each locking element 77 has a lead-in ramp along its top edge leading to a horizontal region, and has at its end opposite to the ramp a depending lock tooth 79.

Externally of the wall 75 a solid annular underface of the head 11 leads to a depending outer cylindrical wall 80, a lower portion of whose inner face is formed with a lead-in portion 82.

The filter bowl 10 is formed at one angular position with a protuberance 84 having a relieved inner face 86 that enables the pressure relief valve 38 to be fitted without the valve 38 intruding into the envelope of the outer chamber 68, the structure and method of fitting of the valve 38 being as described in our patent application No.

EP-A-0278771. A buttress 44 occurs on the inner face of the protuberance 84 and has an upper portion 44a and an abbreviated lower portion 44b above valve 38, but the step 34 is locally absent. Thus the bowl 10 is held to the head 11 at four positions 900 apart. The horizontal step 34 is present for most of the periphery of the flange 18 to support the cartridge 12 against down-load, but upward force on the cartridge 12 is taken at three angular positions 900 apart corresponding to the other three lower buttress parts 44b. A pivoted locking lever or handle 88 which is of generally rectangular form when viewed from outside the bowl 10 is pivoted to the bowl 10 at 90 and is arranged to co-operate with a pintle 92 of the valve 38 so that the valve 38 is open when the handle 88 is pivoted outwardly from the vertical position shown.When the bowl 10 is other than rotated fully home, a head 93 of the handle 88 rides on the outer cylindrical surface of the wall 80, maintaining the handle 88 in its outwardly pivoted attitude and maintaining the valve 38 open. But when the bowl 10 reaches its fully home position, the head 93 snaps into recess 94 under the action of spring 96, de-coupling handle 88 from valve 38 which then closes by the action of an internal spring to enable the bowl 10 to be pressurised.

The bowl 10 and head 11 can be connected together by relative rotation to engage bayonet coupling means 44,77 thereof. When they are connected together, an outer wall 80 of the head 11 overlaps top portion 32 of the bowl 10 with a fluid-tight O-ring seal 42 therebetween. The handle 88 acts as a spring latch that engages at one angular position of the bowl and head when the bayonet coupling has been established to prevent relative rotation of the bowl and head, but the handle 88 cannot engage at other angular positions. The handle 88 is de-coupled from the valve 38 when it has engaged into, the recess 94, but when it is disengaged from the recess 94 it becomes operatively coupled to the valve 38 to open the valve 38. Fluid flow through the valve 38 when it is open provides an audible warning when a pressure differential exists across the valve 38.

For assembly of the bowl 10, cartridge 12 and head 11, the cartridge 12 is first dropped into the bowl 10, the cut-outs 28 being aligned with the buttresses 44. If desired the cartridge 12 can then be rotated manually to engage the flange 18 into the groove 46. The bowl 10 and cartridge 12 are then offered to the head 11, engaging the spigot 54 into the vertical port 52, the bowl 10 being at an angular position offset from the working position and defined by sight marks so that the buttresses 44 enter gaps between the bayonet locking elements 77. The bowl 10 is then rotated to engage the bayonet locking elements 77 into the grooves 48. The upper parts 44a ride up the ramps onto the horizontal parts and travel is limited by abutment of the lock teeth 79 with the lower parts 44b of the buttresses, at which time the lever 88 also snaps to the vertical position. As the bowl 10 is offered up, the O-ring 42 seals against the inner face of wall 80. The piston seal configuration of O-ring 42 between walls 75,80 gives excellent long-term performance at high operating pressures and standard O-rings can be used, the overlap preventing the O-ring 42 from being extruded between walls 75,80 by the elevated internal pressure of the bowl 10. When it is desired to remove the bowl 10, the first action is to depress the lower part of handle 88 by finger pressure, thereby opening valve 38 and de-pressurising the bowl 10.

The bowl can be rotated in the release direction, and as is apparent from Figures 4a and 4b which show the position of of the buttresses 44 in the locking and release positions respectively, the buttress rotates through register with the cut-out 28 but then rerengages onto the flange 18, the rectangular webs 20 serving as stops. It will be appreciated that rotation of the bowl 10 does not bring about simultaneous rotation of the cartridge 12 because of the tight fit of the O-rings 56,58 in the vertical port 52.

When the bowl 10 has been rotated to the release position, it is pulled downwards and mechanical engagement of the lower buttress parts 44b with the flange 18 ensures that the cartridge 10 descends as the bowl 10 descends.

Accordingly, when the cartridge 12 is placed in the bowl 10 and the bowl 10 is presented to the head 11, the neck of the spigot 54 will automatically engage into the vertical port 52 as the filter bowl 10 locks. On uncoupling, the cartridge 12 will move in such a way as to be withdrawn with the bowl 10, automatically disengaging the spigot 54 from the vertical port 52. The bowl 10 need only travel down until the spigot 54 is clear of the wall 75, after which the bowl 10 together with the cartridge 12 can be withdrawn sideways. Consequently mounting and removal of the bowl 10 and cartridge 12 can be carried out with a minimal amount of free space. Even under slight internal pressure, gas escaping through the valve 38 gives rise to a clearly audible hiss, and the valve 38 remains open with continuing hiss of any escaping gas until the bowl is removed.Accordingly there is a warning against accidental removal of the bowl 10 when it is under pressure. An advantage of the above arrangement is that shallow lead-in ramps on the bayonet locking elements 77 provide a lowtorque connection between the bowl 10 and the head 11 also gradually engaging the spigot 54 into the vertical port 52, and requiring only a quarter turn to lock and unlock. The handle 88 gives a positive mechanical lock between the bowl 10 and the head 11. The casing of the cartridge 12 may conveniently be injection moulded in plastics and the head 11 and bowl 10 may be cast or moulded in aluminium or in light alloy or in zinc or other convenient metallic or non-metallic material.

In Figure 5 there is shown a second form of the cartridge 12 in which the flange 18 is frangible e.g. by incorporation of lines or zones of weakness (not shown).

The flange 18 is designed to break when the pressure difference or drop across the cartridge 12 exceeds a given limit e.g. above 10 psi which corresponds to a significant level of blockage of the filter cartridge and preferably in the range 25-30 psi. It has been found that solids in the airline cause the pressure drop across the filter to increase slowly during the working life of the filter, but when the filter approaches saturation at the end of its working life the pressure drop accelerates rapidly. The flange 18 is designed to break at a pressure drop that is above what is encountered during the normal service life of the filter but below a level corresponding to substantial interference with gas flow through the filter.If the flange 18 is arranged to break at a pressure drop corresponding to a pressure in the steeper portion of the curve, manufacturing tolerances can be accommodated without the cartridge either failing significantly too soon or (more damagingly) significantly too late. In Figure 5 the flange 18 is shown broken, and the cartridge 12 has descended from the filter head 11, breaking the seal between the spigot 54 and vertical port 52. Accordingly port 66 is now in a gas stream that by-passes the cartridge 12 and its altered state may be detected as described above. For breathing air, flow of dirty air by-passing the cartridge 12 is more tolerable than choking off the air flow because of excessive pressure drop across a blocked cartridge.

The assemblies shown may be provided as a parallel pair with one working filter and housing and one stand-by filter and housing connoted by change-over valves. The valves may be controlled by a sensor in the port 66 of the working cartridge and housing to change the flow path to the stand-by filter and housing in the event of failure of the flange 18 of the working filter cartridge. A remote sensor may also give an audio/visual warning on a control panel that a spent filter cartridge needs servicing. Such an arrangement may be used where a continuous flow of fluid is essential as in breathing air lines or aircraft hydraulic systems.

Claims

1. A filter assembly comprising a filter head and a filter cartridge mountable to the filter head, wherein correct mounting of the cartridge to the filter head establishes a fluid-tightly isolated space and a port opens into said space for determining by the state of gas in or the flow of gas from said space whether a cartridge is present and correctly mounted.

2. An assembly according to claim 1, wherein means is connected to the port for determining a gas flow there through.

3. An assembly according to claim 1, wherein a pressure transducer is connected to the port.

4. An assembly according to any preceding claim, wherein the filter cartridge and the filter head fit together by a spigot and socket connection.

5. An assembly according to claim 4, wherein the spigot and socket are sealed by a pair of axially spaced seals between which is defined the fluid-tightly isolated space.

6. An assembly according to claim 5, wherein the spigot and socket connection is fluid-tightly sealed by means of O-ring seals.

7. An assembly according to any preceding claim further comprising a filter bowl releasably mounted to the filter head.

8. An assembly according to claim 7, wherein the filter head and the filter bowl have bayonet formations for connecting them together.

9. An assembly Fcording to claim 8, wherein there are four bayonet connections disposed at 900 intervals about the filter bowl.

10. An assembly as claimed in any of claims 7-9, wherein means establishes a mechanical connection between the filter bowl and the filter cartridge so that the filter bowl and the filter cartridge are together mountable to and demountable from the filter head.

11. An assembly according to claim 10, wherein the top inner face of the bowl has seat means on which a projection of the cartridge fits, and has internal buttresses, the cartridge projection being shaped to pass the buttresses in one angular position and to be trapped beneath the buttresses in other angular positions.

12. An assembly according to claims 4 and 10 or 11, wherein the filter bowl carries a pressure relief valve and also carries latch means that snaps into a recess in the filter head at one angular position at which the bayonet connection is made to prevent relative rotation of the filter head and the filter bowl but is prevented from engagement at other angular positions, the latch means being decoupled from the valve when in its engaged state but being operatively coupled to the valve when in a disengaged state to open the valve, fluid flow through the valve giving a warning of pressure in the filter bowl.

13. A filter assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A filter cartridge for use with a filter head having a port into which a spigot of the cartridge is a push fit, wherein the spigot carries a pair of axially spaced O-rings that when the cartridge is correctly positioned on the filter head fluid tightly isolate a space with which a second port communicates.

15. A filter cartridge according to claim 14, having a casing of moulded plastics.

16. A filter cartridge according to claim 14 or 15, containing a moulded or pleated microporous element and adapted for coalescing droplets from a gas stream.

17. A filter cartridge according claim 14 or 15, containing an adsorbent and adapted for removal of vapour from a gas stream.

18. A filter cartridge substantially as hereinbefore described with reference to and as illustrated in Figures 2, 3 and ta,4b of the accompanying drawings.

19. An assembly of a filter cartridge, bowl and head wherein the bowl and cartridge are removable together once the bowl has descended a short distance from the head.

20. An assembly comprising a filter head and a filter cartridge fluid-tightly mounted to the filter head to establish a gas flow path from or to the filter head through the cartridge, wherein the cartridge is held to the filter head by frangible mounting means arranged to break at a predetermined pressure difference across the cartridge to permit the cartridge to move away from the filter head and enable the gas flow to by-pass the cartridge.

21. An assembly according to claim 20, wherein the frangible mounting means comprises one or more projections extending from the cartridge that shear when the predetermined pressure difference is exceeded.

22. An assembly according to claim 20 or 21, wherein the cartridge has means co-operating with the filter head to establish a fluid-tightly isolated space and a port opens into the space for determining by the state of fluid in or the flow of fluid from said space whether the cartridge is correctly mounted and sealed.

23. An assembly according to claim 20, 21 or 22, wherein the cartridge and head fit together by a spigot and socket connection and are fluid-tightly sealed when the cartridge is correctly mounted by means of a pair of axially spaced O-ring seals.

24. An assembly according to any of claims 20-23, further comprising a filter bowl releasably mounted to the filter head through bayonet formations.

25. A filter cartridge for removably-mounting to a filter head via frangible mounting means that is arranged to break when the pressure difference across the filter head exceeds a predetermined value corresponding to the onset of clogging of the cartridge.

26. A modification of the assembly claimed in claim 20, wherein the cartridge is held to the filter head by a detent, snap release formations:orother non-reversible holding means that releases the hold of the cartridge to the head at the predetermined pressure difference.