Inspection pit, lid and inspection pit assembly

Abstract: An inspection pit assembly (10) comprises an inspection pit (14) and a lid (12), the lid (12) and body portion (16) of the pit (14) each being integrally moulded of a suitable rigid plastics material. The pit (14) has a bottom (18) and continuous side walls (20) projecting upwardly therefrom to an outwardly projecting flange (24) from which a rim (26) upstands; reinforcing ribs (28, 30) extend, respectively, between the flange (24) and the wall (22) and rim (26). The lid (12) comprises a cover portion (44) complimentary in shape with the rim (26). From an underface (48) of the cover portion (44) a circular rim portion (46) projects and a plurality of ribs (50, 52) project. The ribs (50) extend radially from the central boss (56) to the rim portion (46) and provide reinforcing ribs for the lid. The inspection pit assembly (10) is especially suitable for use in earthing electrical conductors.

Description: This invention relates to a lid, particularly a lid suitable for use with an inspection pit assembly and especially with an inspection pit assembly suitable for use in the provision of an earth in association with lightning conductors and the like. For example, as described in our copending UK Patent Application Publication No GB-2226343 A. In the earthing of conductors associated with buildings, for example, it is necessary to have an earthing rod or other earthing medium to which access can be gained for connection of conductors to provide a suitable electrical path. To facilitate such access, it is common practice to provide an inspection pit recess into the ground around the earthing rod. Known inspection pits may be made of various materials, for example cast concrete, galvanised iron or the like and are supplied by the applicants. Whilst such inspection pits are satisfactory, generally, in performance, the concrete inspection pits are heavy and bulky and thus difficult to handle and transport, whilst the galvanised steel inspection pits may, over a period of time, corrode. Lids, especially lids to inspection pits, are also commonly cast from reinforced concrete or galvanised metal; similar weight and/or possible corrosion problems may arise. The US patent US-A-3 858 755 discloses a meter box with a lid integrally moulded of a rigid plastics material, whose structure comprises an outer portion, a continuous rim portion projecting from an under face of the outer portion and extending substantially around the periphery of the outer portion, and a plurality of reinforcing ribs projecting from the under face of the outer portion. It is one of the objects of the present invention to provide an improved lid, suitable for use with an inspection pit. The invention provides a lid comprising a structure integrally moulded of a rigid plastics material comprising an outer portion, a continuous rim portion projecting from an under face of the outer portion and extending substantially around the periphery of the outer portion and a plurality of reinforcing ribs projecting from the under face of the outer portion, the ribs comprising a plurality of first ribs extending radially from a boss projecting from the under face at a central region of the structure to the rim and a plurality of second ribs extending towards the rim from a junction region of a first rib between the boss and the rim, two such second ribs extending from each junction region one at either side of the first rib and each of said two second ribs being positioned at the same angle relative to the associated first rib. Preferably in a lid in accordance with the invention the junction regions are situated at the same radial distance from the central boss and second ribs radiating from the junction regions of adjacent first ribs meet at a meeting position between the central boss and the rim, the lid further comprising a plurality of third ribs extending from the meeting positions to the rim, preferably extending radially to the central boss. Preferably the periphery of the outer portion projects slightly beyond the rim and in that case some, at least, of the ribs extend beyond the rim. In one embodiment a lid in accordance with the invention comprises a generally rectangular cover portion, e.g. a square cover portion, and the rim is elliptical or circular in plan. Preferably a lid in accordance with the invention is suitable use in an inspection pit assembly and has at least one first opening in a cover portion adapted to receive a fastening bolt for use in securing the lid to an inspection pit, the bolt having a shank and a head, and at least one key-hole shaped second opening having a first portion through which the head of the bolt can pass and a second portion into which the shank of the bolt can slide, the head dimension being such that the head cannot pass through the second portion, whereby the bolt can be used to lift the lid out of engagement with the inspection pit. In another aspect the invention may be considered to provide a method of making a lid according to the invention comprising procuring a mould assembly comprising a first mould part having a cavity defining the outer surface of the outer portion of said lid structure and meeting a second mould part having a cavity defining the under surface of the outer portion and the remained of the lid structure, injecting a plastics material in flowable condition into the part of the mould cavity defining the central boss, to fill the mould cavity, causing or allowing the injected material to harden, and removing the structure from the mould assembly. The lid in accordance with the invention is moulded from a suitable rigid plastics material; conveniently the plastics material is reinforced by a suitable fibre, for example glass fibre. The plastics material may comprise any suitable rigid polymer, for example polypropylene. There now follows a detailed description to be read with reference to the accompanying drawings of an inspection pit assembly, comprising a lid embodying the invention. It will be realised that this inspection pit assembly has been selected for description to illustrate the invention by way of example. In the accompanying drawings:- Figure 1 is a plan view of an inspection pit assembly, showing the inspection pit and lid embodying the invention; Figure 2 is a view in section on the line A-A of Figure 1; Figure 3 is an underneath view of the lid embodying the invention; Figure 4 is a plan view showing part of the inspection pit; and Figure 5 is a view in section on the lines B-B and C-C of Figure 4. The inspection pit assembly (10) comprises a lid (12) and an inspection pit (14). The inspection pit comprises a body portion (16) integrally moulded of a rigid plastics material, e.g. glass fibre reinforced polymer, e.g. polypropylene, for example by injection moulding. The body portion (16) having a bottom (18) and an opening (20) in the bottom (18) to provide access to the interior of the pit, for example for an earth rod (not shown). A continuous wall (22) is upstanding from the bottom (18) to an open, upper end. At the open upper end, remote from the bottom (18), a flange (24) projects outwardly from the wall (22). Within the outer periphery of the flange (24), a rim (26) which is also continuous, extends around the opening. Reinforcing strut means comprising first reinforcing struts (28) extending between the wall (22) and flange (24), and second reinforcing struts (30) extending between the flange (24) and rim (26) are provided. The struts (28, 30) are planar members which are positioned perpendicular to the flange (24) and to the wall (22) and rim (26), respectively. Two pockets (32) are formed adjacent the opened end of the body portion at opposite sides of the body portion (16) providing recesses in the rim (24) and in the wall (22) opening into the interior of the body portion (16). End portions of an earth bar (34), which extends across the body portion (16) from one side to the other, are slidingly received in the pockets (32) whereby to position the earth bar (34) in the body portion. The earth bar (34) may suitably provide means for connecting a plurality of conductors to an earth rod entering the inspection pit through the opening (20). The body portion (16) further comprises recesses (36) opening to the flange at an upper surface at one end and opening below the flange at the other end, the recesses (36) having nuts (38) received therein for cooperation with bolts (40) which are used to retain the lid (12) in position. Caps (42) may be a press fit in the recess (36) to prevent entry of dirt into the recess (36). The lid (12) comprises a structure integrally moulded of a rigid plastics material (of a composition which may be similar to the material from which the inspection pit (14) is moulded; the lid is moulded by a method embodying the invention as will be discussed below. The lid comprises an outer, cover portion (44), a rim portion (46) projecting from an underface (48) of the cover portion (44), and extending substantially around the periphery of the cover portion (44). A plurality of reinforcing ribs (50, 52, 54) projecting from the underface (48) of the cover portion (44). The ribs comprise a plurality of first ribs (50) extending radially from a central boss projecting from the underface (48) of a central region of the lid structure. The first ribs (50) extend from the boss to the rim (46). A plurality of second ribs (52) extend generally towards the rim (46) from junction regions (53) of the first ribs (50). The junction regions (53) are situated at the same radial distance from the central boss (56). Two second ribs (52) extend from each junction region (51) at either side of the first rib (50); each of these two second ribs are positioned at the same angle relative to the first rib. Second ribs (52) radiating from the junction regions (52) of adjacent first ribs meet at a meeting position (55) between the central boss (56) and the rim (46). The third ribs (54) extend radially of the boss (56) from the meeting positions (55) to the rim (46). Certain of the first ribs (50) and third ribs (54) have portions (50 a ) respectively, which project beyond the rim (46). As can be seen viewing Figure 3, the cover portion (44) is generally square in plan, while having rounded corners, and the rim (46) is circular in plan. A desired number of tags (72) of a suitable rigid material, e.g. similar to the material of the pit (10), may be secured to the bottom (18) of the pit (10). The tags (72) may be secured by any suitable means, e.g. rivets. In the illustrative pit (10), holes (70) are formed in corner regions of the bottom and the tags (72) are moulded with integral plastics pegs (74) dimensioned to be a snap fit in the holes (70) (see Figure 2); if desired, the part of the peg (74) within the pit may be treated by heat and pressure after installation, forming a head (not shown) preventing removal. Each tag (72) may be swung about the axis of its peg (74) between an outwardly projecting position (shown in Figure 2) for use and an inwardly directed position in which it is positioned beneath the bottom of the pit: in that position the tags (72) do not interfere with the stacking of pits (10) one within another which is convenient for supply purposes. As can be seen from the drawings the wall (22) flares (slightly) outwardly from the bottom (18) thus facilitating stacking. In the manufacture of the illustrative lid (12), a mould assembly (not shown) is used, the assembly comprising a first mould part having a cavity defining an outer surface (47) of the cover portion (44) of the lid structure (12) and meeting a second mould part at a parting line, the second mould part having a cavity defining the underface (48) of the cover and the remainder of the lid structure including the ribs (50, 52, 54), boss (56) and rim (46). In further carrying out the method a suitable rigid plastics material, for example similar to that used for the inspection pit, is injected in flowable condition into the part of the mould cavity which defines the central boss (56), thus to fill the cavity. The injected material is thereafter caused or allowed to harden and the structure removed from the mould assembly. As can be seen viewing Figure 1, the outer periphery of the cover portion (44) of the lid (12) is complementary with the inner wall of the rim (26) of the inspection pit so that the lid seats on the flange (24), within the rim (26), with the outer periphery of the cover portion (44) closely spaced from the internal wall of the rim (26). The portions (50 a , 54 a ) of the ribs projecting beyond the rim (46) of the lid (12) serve to support the part of the cover portion (44) projecting beyond the rim portion (46) and also to guide the lid as it is inserted into the opening defined by the rim (26) of the inspection pit. As can be seen viewing Figures 3 and 4, the rim (46) and the wall (22) of the inspection pit are both circular in plan; it will, however, be understood that the rim (46) and wall (22) may be of any desired shape in plan. However it is preferred that the wall (22) of the inspection pit and the rim portion (46) of the lid have the same shape as one another, in plan. The lid (12) is provided with openings (60) extending through the lid (12) and positioned to be in alignment with the recesses (36) in the inspection pit, when the lid is correctly located on the inspection pit within the opening defined by the rim (26). The inspection pit assembly (10) comprising the lid (12) and the inspection pit (14) are secured together by means of bolts (40) having a shank (39) and head (41), the head (41) being accommodated in a part (61) of the opening (60) of larger diameter than the remainder of the opening (60). The lid (12) is provided with two key-hole shaped second openings, each having a first portion (62) through which the head (41) of the bolt (40) can pass, and a second portion (64) into which the shank (39) of the bolt can slide. The dimensions of the head (41) are such that the head (41) cannot pass through the second portion (64). Thus, when it is desired to remove the lid (12) from engagement with the inspection pit (14), the bolts (40) are first unscrewed and removed from the openings (60) and then inverted so that the heads (41) are facing downwardly. The heads (41) are then inserted through the first portions (62) of the key-hole shaped openings and the bolt slid sideways so that the shank passes into the second portion (64) of the key-hole shaped openings. The bolts can then be used to lift the lid (12) out of engagement with the inspection pit (14). The inspection pit is relatively light compared with many previously known inspection pit assemblies and sufficiently strong for use in many purposes. It is readily manufactured by two simple injection moulding operations and is corrosion resistant. Furthermore, the body portion of the inspection pit itself is substantially resistant to penetration by moisture and can be used in apparatus as described in our above mentioned copending patent application. The configuration of reinforcing ribs on the inspection pit provides substantial support for the flange (24) and for the rim (26). The reinforcing ribs of the lid (12) are so arranged as to give rigidity to the lid, resisting bending or damage even under substantial loads and, furthermore, are arranged so that the lid can be manufactured very simply using a relatively simple two-part mould, in an injection moulding operation. In use, the inspection pit (10) is received in a hole of suitable depth in the ground. Suitably concrete is poured around the pit and allowed to harden to secure the pit in position. Suitably the concrete is level with the uppermost edge (26 a ) of the rim (26) and the flange (24) and ribs (28, 30) are encompassed by the concrete so that the rim (26) is given very strong support by the concrete and the pit (10) is firmly secured. To ensure stability during pouring of the concrete, if necessary, the tags (72) may be positioned projecting outwardly as shown in Figure 2: sufficient weight is initially placed on the tags (72) to prevent the pit (10) "floating" in the concrete as concrete is poured round the pit (10).

Claims: A lid (12) comprising a structure integrally moulded of a rigid plastics material comprising an outer portion (44), a continuous rim portion (46) projecting from an under face (48) of the outer portion (44) and extending substantially around the periphery of the outer portion and a plurality of reinforcing ribs projecting from the under face of the outer portion (44), the ribs comprising a plurality of first ribs (50) extending radially from a boss (56) projecting from the under face at a central region of the structure to the rim (46) and a plurality of second ribs (52) extending towards the rim from a junction region (53) of a first rib (50) between the boss (56) and the rim, two such second ribs (52) extending from each junction region (53) one at either side of the first rib (50) and each of said two second ribs (52) being positioned at the same angle relative to the associated first rib (50). A lid according to claim 1 wherein the junction regions are situated at the same radial distance from the central boss and second ribs radiating from the junction regions of adjacent first ribs meet at a meeting position between the central boss and the rim, the lid comprising a plurality of third ribs extending from the meeting positions to the rim. A lid according to claim 2 wherein the third ribs extend radially to the central boss. A lid (12) according to any one of the preceding claims suitable for use in an inspection pit assembly the lid having at least one first opening (60) in a cover portion adapted to receive a fastening bolt (40) received in the first opening for use in securing the lid to an inspection pit (14), the bolt having a shank (39) and a head (41), and at least one key-hole shaped second opening (62,64) having a first portion (62) through which the head of the bolt can pass and a second portion (64) into which the shank of the bolt can slide, the head dimension being such that the head cannot pass through the second portion, whereby the bolt can be used to lift the lid out of engagement with the inspection pit. A method of making a lid according to any one of the preceding claims comprising procuring a mould assembly comprising a first mould part having a cavity defining the outer surface of the outer portion of said lid structure and meeting a second mould part having a cavity defining the under surface of the outer portion and the remainder of the lid structure, injecting a plastics material in flowable condition into the part of the mould cavity defining the central boss, to fill the mould cavity, causing or allowing the injected material to harden, and removing the structure from the mould assembly.

Inventors: BILBIE JOHN LESLIE, HALL TREVOR, BILBIE, JOHN LESLIE, HALL, TREVOR
Applicants: FURSE W J & CO LTD, W.J. FURSE & CO. LTD.
Application year: 1992
Main classification: H02G9
IPC codes: H02G9