GB2217744A - Catch pit - Google Patents

Abstract

A catch pit (20) is provided which has a body (21) manufactured from helically wound high density polyethylene tubing the body walling being corrugated and a lower end of the body (21) being closed for example by a disc (22). Apertures (23) can be formed in the body (21) for the connection of inlet and outlet pipes and the upper end of the body can be cut-off square and can be provided with a lid (25). To create catch pits of different depths, a main body portion can be secured to a secondary body portion by a connector made from an internal or external sleeve, or an internal or external threaded connector engaging with the convolutions of the two portions. <IMAGE>

Description

CATCH PIT This invention relates to a catch pit for incorporation in a drainage system.

Such a catch pit will normally have an incoming pipe delivery liquid to the catch pit together with an outlet leading liquid from the catch pit. There is a closed body of the catch pit beneath a level of the outlet pipe which serves as a settling sump to accept and accumulate grit, gravel and comparable solid matter. Such catch pits are periodically cleaned out and function to collect solid matter to prevent accummulation of solid matter in pipes further down the system and possible blockage of the drainage/sewage system.

Heretofore, catch pits have been manufactured by constructing concrete or brick formations within the ground (extremely expensive and time consuming).

Recently, however, it has been usual to manufacture catch pits from unplasticised P.V.C. (U.P.V.C).

However, this material is relatively brittle and subject to stress cracking upon cutting or working of the material. Further, it is also subject to age hardening so that during use formed units gradually become more brittle and cannot be easily mended or worked if modification thereof (for example the introduction of a further pipe) has to be effected.

This age hardening also means that when a catch pit of variable depth has to be provided (and it will be appreciated that catch pits are of different depths depending upon the falls and the lie of the land in which they are buried). Conventionally, catch pits are provided in a standard relatively shallow depth of perhaps of half or one metre and a series of extension pieces are provided whereby the depth can be extended within a significant range. The extension of the connection pieces to an existing UPVC., type catch pit is quite difficult in that a unifying connector between a base of the catch pit and an extension piece, in the form of a shrouding sleeve, can often suffer from the generation of cracks therein after a period of time due to age hardening and stress cracking. Such cracks can lead to collapse of the upper portion of the catch pit.

It is in the nature of UPVC that upon cracking of an annulus, the parts of the annulus tend to move inwards rather than outwards and this allows the ingress of surrounding ground material, thus filling the catch pit and possibly blocking the drainage system.

It is an object of the present invention to provide an improved catch pit wherein the above described disadvantages are obviated or reduced.

Accordingly, the invention provides a catch pit in the form of a length of corrugated, helically wound polyethylene tube, closed at a bottom end thereof.

The top of the catch pit of the invention can be closed by a conventional metallic lid simply resting on the top open end of the body, but preferably is adapted to form a screw type union with the top end of the body.

For the introduction of entry/exit pipes simple circular apertures can be cut in the walls of the tube and the pipes being arranged simply to be a sliding fit therein. Any leaking gaps between the pipes and the body would simply be aiding drainage.

Any leak outward through such gaps would constitute a loss of the material drained, but would not be of any great significance.

Preferably, because of the significant weight advantage a single piece construction of the main body would be of advantage but the catch pit can have a further portion attached to its body to extend its height, said further portion also being in the form of a length of helically formed corrugated polyethylene material, a union between the two parts being provided which can be secured to at least one of the parts by screwing. For example, a union for the two parts can constitute a short length of a larger diameter complementarily threaded tube. The connector can be threadedly attached to both parts.

Alternatively, it can be welded to one part and screwedly attached to the other.

The connector can be a fully corrugated piece forming a tight seal. Alternatively, provided that the ends of the two pieces are formed square, the connector can be a cylindrical sleeve with inward projections forming helical formations engageable with the grooves in the surface of the two parts.

As a further alternative, an end portion of one of the two parts could be thermmally streched and expanded to be of larger diameter and screwed on to the portion beneath or above.

A particularly suitable lid of a tamperproof nature is described in our co-pending Application No.

8800592.

A base to the body can be formed by welding a disc of compatible material to the bottom of the body.

Alternatively, a base for the body can be formed by a cap consisting of a side wall of a larger diameter corrugated material and a flat disc intergrally moulded with or welded to such wall portion.

As a further alternative, the base can be a plastics disc with appropriate spigot adapted to be screwedly engaged with the lower end of the body.

The material of the body is preferably high density polyethylene (HDPE), that is to say polyethylene having a density higher than 0.941 gm/cm3.

The thickness of the plastics material can be from 6mm up to 15mm, but a wall thickness of from 8 to lOmm has been found quite satisfactory.

Because the body is of helical construction with a depth of thread, it enables the user the ability to use the undulating surface for toe hold when entering or exiting for maintainance.

Again because of the helical construction the outer surface being corrugated it adis the backfill to grip the body of the catch pit so reducing the floating effect found with the UPVC catch pit.

The invention will be described further, by way of example, with reference to the accompanying drawings wherein Fig. 1 is a sketch illustrating a catch pit generally and its mode of use; Fig. 2 is a side elevation of a preferred catch pit of the invention; and Fig. 3 is a view similar to that of Fig. 2, but showing the modification.

Fig. 4 is an enlarged cross-sectional view illustrating an alternative method of joining two lengths of tube forming a catch pit of the invention; Fig. 5 is a reduced scale cross-sectional view on the line V-V of Fig. 4; Fig. 6 is an underneath plan view of an alternative lid for use with the catch pit; Fig. 7 is a cross-sectional view illustrating the lid of Fig. 6 in use; Fig. 8 is a plan view of a catch pit adapted to receive the lid of Figs. 5 and 6; Fig. 9 is a cross-sectional view illustrating a possible variation in a lower termination of the catch pit of the invention; Fig. 10 is a cross-sectional view illustrating a variation inside entry to the catch pit; Fig. 11 illustrates how a union between two lengths of tubing forming a catch pit of the invention can be created by cutting a length of tubing and removing a section therefrom; ; Fig. 12 shows that section after joining and re-welding to form a smaller diameter portion; and Fig. 13 illustratesa joint made using the section shown in Fig. 12.

Referring firstly to Fig. 1, a conventional catch pit 10 includes an upwardly open, downwardly closed body 11, which may be formed from concrete or plastics material. A number of inlet pipes, at least one and possibly three or more (two being shown at 12 and 13) enter the catch pit at positions at least level with and probably above the level of an outlet pipe 14. Liquid flow is in the direction of the arrows. The invert of outlet 14 is spaced above the base 15 of the body 11. Thus, the space between the invert of pipe 14 and the base 15 is normally filled with water and forms a sump into which inflowing waters enters. Solids, detus and the like carried by incoming water enters the relatively still water within the sump and heavier solid material settles out. This prevents the drain further along the system becoming choked with silt and the like.

Periodically such catch pits are opened and the deposit removed.

The depth of the catch pit 10 is sunk into the ground depends on the various folds, the slope of the ground and various other considerations. It will be apparent that the actual depth of the base 15 has to be chosen to the varying distances below ground level 16. Hence a single length of body 11 is not practical and a basic body length 11 is normally provided.

(This length may be half a metre or some comparable length). Thereafter, the use connects one or more extensions 17 to the top of the body 11 by means of a uniting collar, by welding (or cementing in the case of concrete). The top of the extension 17 is closed by a conventional lid 18 made of concrete, or, more usually, steel or cast iron. The extension 17 and the body 11 may have appropriate formations for engagement by a rim 19 of the lid 18.

Referring now to Figs. 2 and 3 which illustrate a preferred catch pit 20 of the invention, it will be seen that a body 21 is manufactured from helically wound high density polyethylene (HDPE) tubing of wall thickness between 4 and 15, preferably about 6mm.

The wall is corrugated as is best seen in Fig. 3.

A lower end of the body 21 is closed by welding to it a disc 22 of HDPE or other compatable plastics material. As an alternative, the lower end could be closed by a cap internally or externally screwable onto the body 21. Apertures 23 are formed in the body 21 for the connection of inlet and outlet pipe (not shown) comparable to pipes 12, 13, 14 in Fig. 1. The upper end of body 21 will be cut off square and can be attached to an extension piece 24 to increase its length to a value compatible with the sinkage depths desired and the position of the ground level.

For engagement with the top of extension 24 or the top of the body 21, there is provided a steel lid 25 (the lid can of course be of cast iron, plastics material, concrete or any other convenient material).

Lid 25 has a depending spigot 26 which can enter within the tubing constituting extension 24 or body 21 and there are two or more outwardly extending lugs 27. Lugs 27 are helically disposed in a manner complementary to the pitch of the tubing constituting extension 24 or body 21 and are positioned and dimensioned to be capable of entering in threaded relationship with the tubing of body 21 or extension 24. Once the lid 25 has been placed on top of the extension 24 or body 21, it is rotated about the axis of the body and the lugs 27 engage with the material of the body 21 or extension 24 and form a firm lock therewith.

Fig. 3 is a view comparable to that of Fig. 2 but illustrating union of the extension 24 and body 21 by means of external complementary sleeve 28 of larger diameter. Sleeve 28 can be a separated threaded part threadedly engaged with body 21 and extension 24.

However, preferably it only slightly overlaps one part (for example the extension 24 and is welded thereto). Thus, each individual extension 24 (because one or more such extensions may be needed to put the upper level of the catch pit to ground level) will be provided with a downwardly extending large diameter threaded collar 28 which can form a strong union with the body 21 beneath.

As a variation, the corrugated threaded member 28 could be replaced by a plain sleeve 29 which has inwardly directed members which could form a helical array complementary to the grooves in the body 21 and extension 24 so as to be threadably engage able therewith. Provided that the body 21 and extension 24 were suitably finished such a union could form a firm bond between them.

As a further alternative, the two parts 20, 24 could be provided with complementarily welded on annulae at their mating surfaces and be united by conventional solvent weld or the like.

It will be appreciated that the provision of a helically wound body (with or without extensions) of high density polyethylene gives significant advantages in relation to -chemical and stress related corrosion cracking, resistance to wear and age hardening. In addition, it is also significantly lighter and easier to install than concrete or brick constructions. For example, HDPE has a specific gravity of 0.9, UPVC has a specific gravity of 1.4 and concrete has a specific gravity of 2.7. A normal concrete catch pit has a 50mm wall thickness and a normal UPVC catch pit has a wall thickness of 15 to 18mm. The HDPE catch pit of the invention has a corrugated wall which gives extreme strength at 6mm thickness. Therefore, a wall part 900mm square has the following approximate weights for the three materials. Concrete 12.5 kilograms, UPVC 2.34 kilograms, HDPE 1 kilogram.

It will be appreciated that the savings to be made in the storage, transportation and installation of such light weight strong materials is a significant advantage in relation to the construction of drainage systems.

Further, the helical winding of the material gives great advantages in the ease of connection and the durability and the replaceability of joints.

The invention is not limited to the foregoing and variations may be made thereto.

For example, the diameters of the various catch pits can range from as low as perhaps 300mm up to a metre or more. The closures for the tops of the catch pits can be of metal, plastics, or even of concrete material if circumstances so demand. Although a screw thread is desirable on the lid, there can be a further fitting wherein a rim is secured to the existing top of the catch pit (by threading of by welding or simply by setting into locally poured cement or concrete) and an internal liftable lid of metal or other material is provided within the rim.

such a lid could be lockable to prevent entry and/or damage.

Referring now to Figs. 4 and 5 it will be seen that a join between a lower section 30 and an upper section 31 can be made utilizing three fingers 32 arranged, as will be seen from Fig. 5, at respective angles of 1200 about the axis of the tube. The lower section 30 has secured to the top thereof an annulus 33 and the lower end of the upper section 31 has an outer splayed cylinder 34 welded thereto. Each finger 32 has a lower base portion which includes a pair of projections 35 which are dimensioned to be a close fit within the convolutions of the lower section 30 to which they are welded. A main body 36 extends upwardly and mounts an outwardly extending projection 37. The projection 37 is dimensioned and disposed to be a sliding fit within the convolutions of the upper portion 31. As the fingers 32 are arranged at spaced positions around the circumference, the projections 37 are arranged in a helical disposition and can be engaged with the convolutions of the upper section 31.

Thus, the upper section 31 can simply be screwed into position by engagement of its inner convolutions with the projections 37. The annulus 33 and the cylinder 34 ensure a smooth inter-engagement and a sturdy connection. This inter-connection can be used to apply a lid to a catch pit or to add an extension piece to the lower end of a catch pit.

Referring now to Figs. 6, 7 and 8, it will be seen that a catch pit 38 can have its upper end formed from a length of convoluted tube 39 as aforesaid to which is applied an L-sectioned annulus 40. As best seen in Fig. 8, the annulus 40 has formed therein a pair of (for example) diametrically opposed slots 41 which allow entry into the convolutions of the tube 39.

Adjacent each slot 41 is a stop 42. This top formation is suitable for use with a lid 43 which can be made either of metal or plastics material. The lid 43 has a main disc 44, a depending skirt 45 and transverse reinforcing ribs 46. Apertures 47 are provided in the disc 44 to enable the lid to be gripped and placed into position. At positions on the skirt complimentary to the positions of the slots 41, diametrically placed in this position the skirt is formed with outwardly projecting lugs 48. It will be seen that one of the lugs is lower than the other.

This disposes the lugs on an imaginery helical surface extending around the skirt 45.

When the lugs 48 are passed through the slots 41, they engage the convolutions of the tube and the lid 43 can then be turned to screwedly lock it to the tube.

Many variations are possible within the scope of the invention.

Claims (32)

1. A catch pit having a body in the form of a length of corrugated, helically wound polyethylene tube, closed at a bottom end thereof.

2. A catch pit as claimed in claim 1 wherein the top of the catch pit is closed by a metallic lid resting on the top open end of the body.

3. A catch pit as claimed in claim 1, wherein the lid is adapted to form a screw type union with a top end of the body.

4. A catch pit as claimed in claim 1, 2 or 3 wherein for the introduction of entry/exit pipes simple circular apertures are formed in the wall of the tube, pipes being arranged to be a sliding fit therein.

5. A catch pit as claimed in claim 1, 2 or 3 wherein flow connection to the catch pit is via one or more ports formed by forming an aperture in the wall of the body and positioning therein a spigot to receive an end of a length of pipe.

6. A catch pit as claimed in any of claims 1 to 5, wherein the catch pit is of single piece construction.

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7. A catch pit as claimed in any of claims 1 to 5, wherein the body consists of a main body portion and a further portion attached to the main body portion to extend its height, said further portion also being in the form of a length of helically formed corrugated polyethylene material, a union between the two portions being provided which can be secured to at least one of the parts by screwing.

8. A catch pit as claimed in claim 7 wherein a union for the two parts is constituted by a short length of a larger or smaller diameter complementarily threaded tube.

9. A catch pit as claimed in claim 8, wherein the connector is threadedly attached to both portions.

10. A catch pit as claimed in claim 8 wherein the connector is welded to one portion and screwedly attached to the other portion.

11. A catch pit as claimed in claim 8, 9 or 10 wherein the connector is a fully corrugated piece forming a tight seal.

12. A catch pit as claimed in any of claims 8, 9 or 10 wherein ends of the two pieces are formed square and the connector is a cylindrical sleeve with inward projections forming helical formations engageable with the grooves in the surfaces of the two portions.

13. A catch pit as claimed in any preceding claim wherein the lid is tamperproof and as as described in -co-pending Application No. 8800592.

14. A catch pit as claimed in any preceding claim wherein a base to the body is formed by welding a disc of compatible material to a lower end of the lower portion of the catch pit.

15. A catch pit as claimed-in any of claims 1 to 13 wherein a base for a lower portion of the body is formed by a cap consisting of a side wall of a larger diameter corrugated material and a flat disc united with such side wall.

16. A catch pit as claimed in any of claims 1 to 13 wherein the base is a plastics disc having an appropriate spigot adapted to be screwedly engaged with a lower portion of the body.

17. A catch pit as claimed in any preceding claim wherein the material of the body is high density polyethylene (HDPE).

18. A catch pit as claimed in claim 17 wherein the 3 polyethylene has a density higher than 0.941 gm/cm

19. A catch pit as claimed in any preceding claim wherein the thickness of the plastics material is from 6mm to 15mm.

20. A catch pit as claimed in claim 19 wherein the wall thinness is from 8mm to 10mm.

21. A catch pit as claimed in claim 1 and consisting of a pair of aligned portions of corrugated tube, one of said portions having a plurality of spaced apart fingers providing outwardly extending projections arranged in a helical configuration to be screwedly engagable with the convolutions of the other portion.

22. A catch pit as claimed in claim 21 wherein one or both of the portions so joined has an annular locating portion secured thereto.

23. A catch pit as claimed in claim 22 wherein said locating portion is either a cylindrical portion extending beyond the end of that portion or a washer portion forming a seat.

24. A catch pit as claimed in claim 21, 22 or 23 wherein the fingers are three in number and are equally spaced about the circumference of the one portion.

25. A catch pit as claimed in claim 1, wherein a main upper portion thereof has an annulus at its upper end forming a sealing seat, said annulus having one or more slots therein, a lid being provided which has a body and a depending skirt which is a fit within the annulus, the skirt having outstanding therefrom one or more projecting lugs each complementary to a slot, and adapted to pass through the slot and screwedly engage with convolutions of the main body portion of the tube therebeneath.

26. A catch pit as claimed in claim 25 wherein said lugs are two or more in number and are helically arranged on the skirt.

27. A catch pit as claimed in claim 26 or 27 wherein a stop is provided within the internal convolutions of the walling immediately adjacent each slot, disposed to allow travel of an entrant lug only in one direction.

28. A catch pit as claimed in claim 8, 9 or 10 and made up of two portions, said two portions being united by means of an internal sleeve of comparable material screwedly engaged with both portions, said sleeve having been made from a length of the same convoluted tubing by removing a portion of the circumference of such tubing and re-connecting the two edges together to form a sleeve of smaller diameter.

29. A catch pit as claimed in claim 28 wherein the edges of the section are united by welding.

30. A catch pit as claimed in claim 28 or 29 wherein the internal sleeve is secured to one of the portions.

31. A catch pit as claimed in claim 28, 29 or 30 wherein the free end of the or each portion is provided with an annular face flange.

32. A catch pit substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 13 of the accompanying drawings.