GB2283925A

GB2283925A - Meter and Manifold assembly

Info

Publication number: GB2283925A
Application number: GB9420431A
Authority: GB
Inventors: Gerald John Evans
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-10-11
Filing date: 1994-10-11
Publication date: 1995-05-24
Anticipated expiration: 2014-10-11
Also published as: GB9420431D0; GB2283925B

Abstract

A filter unit (12) is detachably secured between a meter unit (11) and a manifold (10). The filter unit has an inlet flow-in (33) leading into a casing (30) of the filter unit from the manifold, the interior of the casing (30) communicating with an inlet flow-way (22) of the meter unit (11). An outlet flow-way (23) of the meter unit (11) communicates with an outlet flow-way (31) of the filter unit (12), which extends to an outlet flow-way (18) of the manifold. To prevent components of the meter unit (11) being clogged with particles entrained in the fluid flow from the manifold (10), the filter unit (12) has a filter (35) therein, the outlet flow-way (31) extending through the filter (35). The filter (35) then prevents particles reaching the meter unit (11). The particles caught by the filter (35) may subsequently fall into one or more recesses (36) in the casing (30) below the filter (35). <IMAGE>

Description

METER AND MANIFOLD ASSEMBLY The present invention relates to an assembly of a meter unit and a manifold. It relates particularly, but not exclusively to the case where such an assembly incorporates a water meter.

It is well known for meter units, such as water meters, to be removably mounted on a manifold. The manifold is secured to inlet and outlet ducts, and thus, for water meters, is often located below the surface of the ground, and may contain a stop-cock to prevent flow to the meter. The meter unit is then mounted on the manifold so that the inlet to the meter unit is aligned with flow-ways in the manifold leading from the inlet duct, and the outlet from the meter unit is aligned with a flow-way leading to the outlet duct, Many different arrangements are known for interconnecting the meter unit and the manifold, including bayonet fittings and screw fittings. The meter must be suitably sealed to the manifold.

It has been found that water meters suffer a high failure rate due to particles of grit which interfere with the action of the metering components of the metering unit. Such particles of grit are entrained in the flow of water to the meter unit, but the path which they follow within the meter unit can cause them to be deposited. Many meter units contain a filter which seeks to prevent this.

However, if the pores of such a filter are large, small particles can pass and these may collect sufficiently to interfere with the metering components. If, on the other hand, the pores of the filter are small, the filter will rapidly become clogged. In this case, the meter has to be removed to enable the filter to be removed and cleaned.

Such removal and disassembly of the meter units then means that the meter unit must be re-calibrated before it can be re-used.

Therefore, the present invention proposes that a filter unit be detachably connected between the manifold and meter unit. The filter unit has a casing containing a outlet flow-way secured to the meter unit and manifold, and a filter. That filter is located so that the outlet flow-way extends therethrough, with the inlet from the manifold to the casing being on the opposite of the filter from the meter unit.

With such an arrangement, the filter in the filter unit can remove particles entrained in water passing from the manifold to the meter unit, thereby preventing clogging of the meter unit. At periodic intervals, the filter unit can be detached from the meter and manifold, to enable the filter to be cleaned, without any disassembly of the meter unit.

Preferably, one or more recesses are provided in the interior of the casing, on the opposite side of the filter from the meter unit, into which particles will fall. The flow from the manifold to the meter unit will tend to disturb particles adhering to the filter, and these can then fall into the recesses. In this way, particles will be removed from the filter, so that it will be necessary to clean it only at widely separated times. The or each recesses may be at least partially defined by internal walls within the casing of the filter unit.

The provision of such a recess or recesses, in a unit which is separable from the meter unit, represents a second, independent, aspect of the present invention. Whenever a filter is provided in the flow path to the meter components of the meter unit, particles which collect on the filter are likely to fall therefrom when the flow to the meter stops. This is true in the arrangements discussed above, in which the unit attached to the meter contains the filter, but also may occur using known metering arrangements in which the filter is built into the meter unit. When such particles fall, it is preferable to collect them and this is achieved by the or each recesses in the casing of the unit attached to the meter.

In such an arrangement, the interior of the casing will normally have maximum internal transverse area which is greater than the area of the inlet flow-way into the casing. The effect of this is that the rate of flow of fluid flows as it emerges from the inlet flow-way into the interior of the casing. Such slowing of the flow may, in itself, cause particles to be deposited. Hence, even when there is no filter, the provision of upwardly-facing recesses permits particle entrapment and this presents a third, independent, aspect of the present invention.

It is important that such an entrapment unit, of the second or third aspect is releasable from the meter, to enable the particles in the recess, or recesses, to be periodically removed therefrom to prevent the recesses being filled. Preferably, the entrapment unit is also releasable from the manifold, as it is then easier to remove particles from the recesses than when the entrapment unit is mounted on the manifold.

In practice, it is preferable that such a recess or recesses are provided immediately outwardly of the inlet flow-way. Indeed, a wall of the casing defining the recesses may also form a wall defining the or each inlet flow-way. This minimises the risk that particles falling from the filter will enter the inlet flow-way, rather than being entrapped by the recesses. Such positioning of the recesses is even more important than when there is no filter, since particles are most likely to be deposited at the point at which flow slows as it emerges from the inlet flow-way into the larger area of the interior of the casing.

Embodiments of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Figs. 1 to 4 show a first embodiment of the present invention, Fig. 1 showing a meter, manifold and filter unit assembly shown partially in section, Fig. 2 being a cross-section along the line X to X in Fig. 1, Fig. 3 showing an alternative way of mounting the filter in the filter unit in Fig. 1, and Fig. 4 showing a further alternative for mounting the filter in the filter unit of Fig. 1; Figs. 5 to 7 show a second embodiment of the present invention, Fig. 5 showing the assembly of a meter, manifold and filter unit partially in section, Fig. 6 showing a sectional view through the filter unit along a line below the filter, and Fig.

7 being a sectional view of the upper part of the casing of the filter unit along a line above the filter; Fig. 8 shows another filter unit which may be used in a third embodiment of the present invention; Fig. 9 shows another filter unit which may be used in a fourth embodiment of the present invention; Fig. 10 shows another filter unit which may be used in a fifth embodiment; Fig. 11 shows a sectional view through a meter unit and filter unit for use in a sixth embodiment of the present invention; Fig. 12 shows a sectional view through a meter unit and a filter unit for use in a seventh embodiment of the present invention; Fig. 13 shows a sectional view through an eighth embodiment of the present invention, in which the particle entrapment unit has no filter; and Fig. 14 shows a sectional view through a ninth embodiment of the present invention, again where the entrapment unit has no filter.

A first embodiment of the present invention will now be described with reference to Figs. 1 to 4. Fig. 1 shows a meter and manifold assembly, having a manifold 10, a meter unit 11, and a filter unit 12. The manifold 10 of this embodiment is generally conventional, and has a shape corresponding approximately to the letter "H" with a stop-cock side 13 and a meter side 14 connected via a connection 10a. The stop-cock side 13 is connected to an inlet duct (not shown) and has a flow-way therein leading to an inlet flow-way 15 inthe meter side 14. In the region shown generally at 16, there may be a stop-cock valve (not shown) for closing the flow-way in the stop-cock side 13 leading to the inlet flow-way 15, that valve being controlled by a handle 17. The meter side 14 has an outlet flow-way 18 which, in this embodiment, contains a one-way valve 19.

The meter unit 11 is also generally conventional in this embodiment. The meter unit 11 has an outer casing 20 which, at its lower region, has a threaded part 21. Immediately, within that threaded part 21 is an inlet flow-way 22 which is coaxial with an outlet flow-way 23.

The filter unit 12 is positioned between the meter unit 11 and the meter side 14 of the manifold 10. It has an outer casing 30, which is hollow and contains an outlet flow-way 31 having a cylindrical wall 32 which interconnects the outlet flow-ways 23,18 of the meter unit 11 and the manifold 10. The cylindrical walls 32 are sealed to the meter unit 11 and manifold 10 by suitable seals, such as O-rings.

In this embodiment, the meter unit is secured to the filter unit by engagement of the threaded part 21 with the outer casing 30, and the outer casing is threadably secured to the meter side 14 of the manifold 10.

The filter unit 12 also has inlet flow-ways 33 which interconnect the inlet flow-way 15 of manifold 10 to the hollow interior 34 of the casing 30. As can be seen from Fig. 2, the inlet flow-ways 33 form a broken annulus which is located coaxially around the outlet of flow-way 31. Within the hollow interior 34 of the casing 20 is a filter 35 which extends across the casing 20. Hence, any water flowing from the inlet flow-way 33 of the filter unit to the inlet flow-way 22 of the meter unit 11 must pass through the filter 35. Thus, any particles entrained in that fluid will collect on the filter 35. They will then fall by gravity (particularly when fluid flow ceases) into a recess or recesses 36 within the interior of the casing 30, those recesses 36 being bounded by an upstanding wall 37. The wall 37 prevents particles which have collected in the recesses 36 from falling back into the inlet flow-way 33. Note that there may be a single recess 36 extending circumferentially around the outlet flow-way 31, or a plurality of recesses 36 separated by internal walls of the casing 20.

In this embodiment, the meter unit 11 can be removed from the manifold 10 and filter unit 12 by unscrewing it from its engagement with the filter unit 12. In a similar way, the filter unit 12 (with or without the meter unit 11 attached thereto) can be removed from the manifold 10 by unscrewing it therefrom. Hence, it is possible to remove the meter unit 11 for replacement, or to separate the filter unit 12 from the meter unit 11 and the manifold 10 to enable the filter 35 to be inspected.

In the arrangement of Fig. 1, the casing 30 comprises an upper part 38 and a lower part 39 threadably engaged together with a compression seal therebetween. The outer edge of the filter 35 is then clamped between the upper and lower parts 38,39. The filter has a hole therein through which the outlet flow 31 passes, and the edge 39 of that hole rests on a flange 40 on the cylindrical wall 32.

Since there will be upward pressure on the filter 35, it will need to be fixed to the flange 40.

Fig. 3 shows an alternative arrangement, in which the upper and lower parts 38,39 of the casing 30 are fixed together by e.g. adhesive, again with the outer edge of the filter 35 clamped therebetween. In this arrangement, the cylindrical wall 32 has a flange 41 which is above the filter 35, so that the flow from the inlet flow-way 33 via the filter to the meter unit 11 will force the filter 35 onto the flange 41.

Fig. 3 also illustrates an arrangement in which there are no recesses 36, due to the absence of the wall 37. Such an arrangement is not preferred.

When the fluid emerges from the inlet flow-way 33, into the larger area of the interior of the casing 20 its speed will slow and particles may be deposited. Thus, if arrangements are used without the recesses 36, particles both from the filter, and also deposited due to the slowing of the flow, may fall to the bottom of the casing, and pass into the inlet flow-way.

Fig. 4 shows a further alternative, in which the upper and lower parts 38,39 of the casing 30 are secured together by a bolt 42.

A second embodiment will now be described with reference to Figs. 5 to 7. This embodiment is generally similar to the first embodiment, and the same reference numerals are used to indicate corresponding parts.

In this embodiment, the recesses 36 are deeper than the first embodiment to enable the particles to collect therein. Furthermore, the recesses 36 are separated by vertically extending walls 50, seen more clearly in Fig. 6. Moreover, to prevent the filter being damaged by the upward pressure of fluid passing from the inlet flow-way 32 to the meter unit 11, walls 51 are provided on the upper part 38 of the casing 30, which extend downwardly to contact the upper surface of the filter 35 and thus provided support. A plurality of such walls 51 are provided extending around the outlet flow-way 31 as can be seen more clearly in Fig. 7, which shows a view into the upper part 38 of the casing 30 with the lower part 39 and the outlet flow way 31 removed.

Also, to prevent the filter 35 moving upwardly due to fluid pressure, a collar 52 may be provided extending around the cylindrical wall 32, against which the inner edge of the filter 35 abuts.

In the embodiments described above, the inlet flow-ways 33 in the filter unit are arranged immediately outside the cylindrical wall 32 of the outlet flow-way 31. Such a concentric arrangement is not necessary, however, and Fig. 8 shows a further alternative in which the filter unit 12 has an inlet flow-way 60 which is at the side of, but parallel to the outlet flow-way. Alternatively, the inlet flow-way could extend in a completely different direction, as shown by flow-way 61. The specific arrangement of the inlet and outlet flowways of the filter unit 12 thus depends on the shape of the manifold 10 to which the flow-ways are secured. The concentric arrangement of the embodiments of Figs. 1 to 7 is preferred, since it enables the filter unit to threadably engage the manifold 10 with the inlet and outlet flow-ways positioned simultaneously. In the arrangement of Fig. 8, a more complex arrangement is needed since the outlet flow-way 31 may be threadably secured to the manifold 10 via the wall 32, but a different threading arrangement will then be needed to enable a further flow-way of the manifold 10 to engage the inlet 60 or the inlet 61.

Apart from the inlet arrangement, a filter unit 12 of Fig. 8 is similar to that of earlier embodiments, and will not be described in further detail. Corresponding parts are indicated by the same reference numerals.

As was mentioned earlier, the filter unit may be formed by upper and lower parts threadably secured together. Fig. 9 shows a further filter unit arrangement, in which the filter unit has upper and lower parts 70, 71 which are threadably engaged together and clamp the filter 35 therebetween.

Again, parts of the arrangement of Fig. 9 which correspond to those of earlier embodiments are indicated by the same reference numerals. Fig. 9 shows in more detail the seal 72 which prevents leakage between the upper and lower parts 70,71 of the casing of the filter unit 12, and how a flange 73 of the upper part 70 may co-operate with a step 74 in the cylindrical wall 32 to clamp the inner edge of the filter 35 therebetween, so that the filter 35 is firmly held in place and thus will resist pressure from water entering via the inlet flow-way 33. The seal 72 could be replaced by a compression seal, as in the embodiment of Fig. 1.

In the arrangement of Fig. 9, the upper part 70 of the casing of the filter unit 12 has a downwardly extending collar 73 which makes threadable engagement with the meter unit (not shown), the downward movement of the meter unit being limited by a further step 76 in the inner wall 32. Similarly, there is an upstanding collar 77 on the upper part 70, which threadably engages a sleeve 78 on the lower part 71.

Fig. 10 shows a modification of the arrangement of Fig. 9, in which the upper and lower parts 70,71 of the casing of the filter unit 12 are connected together by one or more bolts 80. The arrangement of Fig. 10 is otherwise similar to that of Fig. 9 and the same reference numerals are used to indicate corresponding parts.

In the embodiment of Fig. 1, the meter unit 11 had a threaded part 21 which engaged the filter unit 12, but the outlet flow-way 23 was sealed to the cylindrical wall 32 by a resilient seal. There are some meter units in which the outlet flow-way is threaded, and an embodiment of the present invention where this occurs is shown in Fig. 11. Again, components which correspond to those of earlier embodiments are indicated by the same reference numerals.

In this embodiment, the meter unit 11 has an outer casing 90 with a downwardly extending rim 91 which threadably engages an upstanding rim 92 of the casing 30 of the filter unit 12. Within the outer casing 90 of the meter unit is an inner casing 92 which has a collar 93 which defines the outlet flowway 23, and which engages threadably or via a sealing means the cylindrical wall 32 of the outlet flow-way 31 of the filter unit 12. A plate 94 then connects the inner and outer casings 90,92 to hold the inner casing in place in the outer casing 90.

The plate 94 has apertures 95 therein which permits water to pass from the interior of the casing 30 of the filter unit to the space 96 between the outer and inner casings 90,92 of the meter unit 12. The water then passes through the top 96 of the meter piston 97 and then through an aperture 98 at the bottom of the meter piston 97 into a space 99 within the inner casing 92, and from thence to the outlet flow-way 23.

Fig. 11 also shows that the outer casing 90 has a lid 100 containing the meter display 101.

In this embodiment, rotation of the meter unit 11 will unscrew the rim 91 of the casing 90 of the meter unit 11 from the rim 92 of the casing 30 of the filter unit 12, and will also simultaneously lift the collar 93 from the cylindrical wall 32.

The meter unit 11 can therefore be removed from the filter unit 12 as a single component, and does not have to be disassembled.

Fig. 11 also shows a further modification of earlier embodiments, in which the recesses 36 are partially covered by an additional filter 102. That filter is mounted on the outstanding wall 37, and particles caught by the filter 35 will fall onto the filter 102 where turbulence will move them around the edge 103 thereof into the recesses 36. Since the turbulence in the recess 36 will then be less than in the arrangement of Fig. 1, there is less chance of particles being disturbed from the recesses 36 at a later time.

Fig. 12 shows a further embodiment. In the embodiment of Fig. 11, the rim 91 of the casing 90 of the meter unit 11 extends outside of the rim 92 of the casing 30 of the filter unit 12, and the sleeve 93 defining the outlet flow-way 23 of the meter unit is received within the cylindrical wall 32. Fig. 12 shows an alternative arrangement, in which the rim 110 of the casing 90 of the meter unit 11 is received within the rim 111 of the casing 30 of the filter unit 12 with a seal 112 therebetween.

The inner casing 92 has a downwardly extending sleeve 113 defining the outlet flow-way 23, which extends around the top of the cylindrical wall 32.

The advantage of this arrangement is that the meter unit 11 may then help to secure the filter unit 35 in place within the filter unit 12, since the downwardly extending rim 110 of the outer casing 90 may force the outer edge of the filter 35 onto a step 114 on the casing 30, and the downwardly extending sleeve 113 may force the inner edge of the filter 35 onto a flange 115 on the cylindrical wall.

Such an arrangement has not only the advantage of simplicity of construction, but also it is easy to remove the filter 35 from the casing 30 of the filter unit 12 e.g. for cleaning, once the meter unit 11 has been removed from the filter unit 12.

It can be seen that, with the meter unit 11 removed, the filter unit 12 can be inverted and the filter 35 will then fall therefrom.

In the embodiments of Figs. 10 to 12, the manifold 10 is not shown. It may be similar to that shown in Fig. 1, but other constructions are also possible. In each case, a threaded region 116 is provided at the lower part of the casing 30 which will threadably engage the manifold. Also, in the embodiment of Fig. 12, a strengthening ring is provided around the rim 91 of the casing 30 of the filter unit.

With the embodiments of the present invention described above, the filter prevents particles entrained in the water supply to the meter from clogging the meter. However, unlike existing designs where the filter is incorporated into the meter, it is then possible to remove the filter unit 12 from both the meter unit 11 and the manifold 10, so that the filter 35 can be cleaned either on-site, or at another location. In the latter case, a used filter unit 12 can be replaced with a new one, to enable the meter to continue its function. The time for which the water supply needs to be stopped (e.g.

by stop-cock valve shown in the embodiment of Fig.

1, can be very short, unlike known arrangements, since the meter does not need to be replaced by a new meter, or re-calibrated.

In the above embodiments, the recesses 36 entrap particles which are deposited from the fluid flow onto the filter 35, which fall therefrom when the flow stops. However, as mentioned previously, the fact that the casing has a maximum internal cross-section area which is greater than the greater cross-sectional area of the inlet flow-way 33 will, in itself, cause particles to be deposited from the flow. When the flow emerges from the inlet flow-way 33, its speed will slow and this slowing will tend to release particles entrained in the flow. This effect may be used in arrangements in which there is no filter, as well as in the embodiments described above, or when conventional meters incorporating filters therein are used.

Fig. 13 illustrates an embodiment of such an arrangement. The embodiments of Fig. 13 is generally similar to that of Fig. 1, and the same reference numerals are used to indicate corresponding parts. However, in the embodiment of Fig. 13, there is no filter 35. Nevertheless, the upwardly facing recess or recesses 36 will still entrap particles. Fig. 13 shows clearly that the cross-sectional area of the main internal void 120 of the casing 30 of what is now a particle entrapment unit 121, rather than a filter unit 12, is greater than the cross-sectional area of the inlet flow-way 33. This can also be appreciated from Fig. 2. Hence, as the flow of fluid emerges from the inlet flow-way 33 it will slow and particles will be deposited. The particles will fall into the upwardly opening recess or recesses 36, to be entrapped therein. Periodically, the recess or the recesses 36 may be cleaned by removal of the filter unit 11, and the upper part 38 of the casing 30. This permits access to the recess or recesses 36. In the embodiment of Fig. 13, the lower part 39 of the casing is also removable from the manifold, to make cleaning easier. Fig. 13 also shows the metering components of the meter unit 11, in which a turbine 1 to 3 is positioned above the outlet flow-way 23 of the meter unit 11, so that fluid flows around the outside of that turbine 123 within the casing 30, downwardly through the turbine 123 turning it, and out of the outlet flow-way 23.

The turbine turns a spindle 124, which then drives the meter display 101.

As was mentioned above, the embodiment of Fig.

13 corresponds to that of Fig. 1, but without the filter 35. Fig. 14 illustrates another embodiment which is similar to that of Fig. 12, but again without the filter 35. Again, therefore, the casing 30 is a casing of a particle entrapment unit 121, rather than a filter unit 12. Again, as the fluid flow emerges from the inlet flow way 33, its speed will slow and particles entrained therein will tend to be deposited. Hence, such particles will collect in the recesses 36 and prevent it from falling back into the inlet flow-way 33 by the wall 37. Removal of the meter unit 11 from the particle entrapment unit 121 again permits access to the recess or recesses 36, to remove the particles therefrom at suitable periodic intervals.

Hence, in the embodiment of Figs. 13 and 14, there need be no filter at all. The embodiment of Fig. 13 may, however be used with arrangements in which a conventional meter unit 11 is used, which incorporates a filter therein. In such cases, particles will fall out of the casing 20 of the meter unit 11 through the inlet flow-way 22, into the casing 30 of the particle entrapment unit 121, and hence into the upwardly-opening recess or recesses 36.

In all the embodiments described above, the fluid is water, and the invention may be applied to other fluids.

Claims

1. An assembly having a filter unit detachably connected between a manifold and a meter unit, the filter unit having an outer casing, an outlet flowway extending within the casing and sealed to the meter unit and the manifold, a filter in the casing with the outlet flow-way extending therethrough, and an inlet flow-way extending from the manifold into the casing on the opposite side of the filter from the meter unit.

2. An assembly according to claim 1 wherein the outer casing of the filter unit defines at least one recess below the filter.

3. An assembly according to claim 1, wherein said at least one recess is arranged radially outwardly of the inlet flow-way.

4. An assembly according to claim 2 or claim 3, wherein said at least one recess is at least partially covered by a further filter.

5. An assembly according to any one of the preceding claims, wherein the casing and the outlet flow-way define a further flow-way communicating with an inlet flow-way of the meter unit.

6. An assembly according to any one of the preceding claims, wherein the meter unit has a collar which clamps a radially inner part of the filter to the outlet flow-way of the filter unit.

7. An assembly according to any one of the preceding claims, wherein the meter unit has a rim which clamps a radially outer part of the filter to the outer casing of the filter unit.

8. An assembly according to any one of claims 1 to 5 wherein the outer casing of the filter unit comprises two casing parts secured together, and one casing part has a collar which clamps a radially inner part of the filter to the outlet flow-way of the filter unit.

9. An assembly according to any one of claims 1 to 8, wherein the outer casing of the filter unit comprises two casing parts secured together, with a radially outer part of the filter being clamped between the two casing parts.

10. An assembly according to any one of the preceding claims, wherein the inlet flow-way of the filter unit comprises a plurality of flow-way sections arranged circumferentially around the outlet flow-way of the filter unit.

11. An assembly according to any one of the preceding claims, wherein the filter unit is threadaby secured to the manifold.

12. An assembly according to any one of the preceding claims, wherein the filter unit is threadably secured to the meter unit.

13. An assembly having a filter unit detachably connected between a manifold and a meter unit substantially as herein described with reference to and as illustrated in Figs. 1 to 4, or Figs. 5 to 7, or any one of Figs. 8 to 12 of the accompanying drawings.

14. A filter unit having: an outer casing, the casing having first means for detachably connecting the filter unit to a meter unit and second means for detachably connecting the filter unit to a manifold; an outlet flow-way extending in the casing and sealable to the meter unit and to the manifold; a filter in the casing, the outlet flow-way extending therethrough; and an inlet flow-way into the casing on the opposite side of the filter from the second means.

15. A meter and manifold assembly having a particle entrapment unit detachably connected between a manifold and a meter unit, the entrapment unit having an outer casing, an outlet flow-way extending within the casing and sealed to the meter unit and the manifold and an inlet flow-way extending into the casing from the manifold; wherein the maximum internal transverse area of the casing is greater than the transverse area of the inlet flow-way; and there is at least one upwardly facing recess i the casing of the entrapment unit.

16. A meter and manifold assembly having a particle entrapment unit connected between a manifold and a

16. A meter and manifold assembly having a particle entrapment unit connected between a manifold and a meter unit containing metering components, the entrapment unit having an outer casing, an outlet flow-way extending within the casing and sealed to the meter unit, and an inlet flow-way extending into the casing from the manifold; wherein: there is a filter between the inlet flow-way of the entrapment unit and the meter components; there is at least one recess for entrapping particles in the casing of the entrapment unit below the filter; and the entrapment unit is detachably connected to the meter unit.

17. An assembly according to claim 15 or claim 16, wherein a wall of the at least one recess is also a wall of the inlet flow-way.

18. An assembly according to any one of claims 15 to 17 wherein the at least one recess is at least partially covered by a further filter.

19. An assembly according to any one of claims 15 or claim 18, wherein there are a plurality of recesses.

20. An assembly according to any one of claims 15 to 18, wherein the at least one recess is radially outwardly of the inlet flow-way.

21. A meter and manifold assembly having a particle entrapment unit substantially as herein described with reference to and as illustrated in Fig.13 or Fig. 14.

Amendments to the claims have been filed as follows and as illustrated in Figs. 1 to 4, or Figs. 5 to 7, or any one of Figs. 8 to 12 of the accompanying drawings.

14. A filter unit having: an outer casing, the casing having first means for detachably connecting the filter unit to a meter unit and second means for detachably connecting the filter unit to a manifold; an outlet flow-way extending in the casing, the outlet flow-way being defined by a tube which extends within the casing and having seals for sealing the tube to the meter unit and to the manifold whilst permitting fluid flow through the tube, the seals of the tube being separate from the first and second means; a filter in the casing, the tube defining the outlet flow-way extending therethrough; and an inlet flow-way into the casing on the opposite side of the filter from the second means.

15. A meter and manifold assembly having a particle entrapment unit detachably connected between a manifold and a meter unit, the entrapment unit having an outer casing, an outlet flow-way extending within the casing and sealed to the meter unit and the manifold and an inlet flow-way extending into the casing from the manifold; wherein the maximum internal transverse area of the casing is greater than the transverse area of the inlet flow-way; and there is at least one upwardly facing recess in the casing of the entrapment unit.