GB2429486A

GB2429486A - Manhole cover assembly

Info

Publication number: GB2429486A
Application number: GB0516546A
Authority: GB
Inventors: John Walsh; Dan Wade
Original assignee: ENDERBY CONSTRUCTION Ltd
Current assignee: ENDERBY CONSTRUCTION Ltd
Priority date: 2005-08-12
Filing date: 2005-08-12
Publication date: 2007-02-28
Also published as: GB0516546D0; WO2007020398A1; EP1920115A1

Abstract

The manhole cover assembly, primarily for use as a temporary cover, comprises a cover plate 25 arranged, in use, to substantially close an opening in a manhole, wherein the cover plate comprises engagement elements 39,40 adapted to releasably engage corresponding receiving elements 61 within a side wall of the manhole. The engagement elements preferably comprise at least one protrusion that extends from the outer edge of the cover plate, preferably in a direction substantially parallel with the plane of the plate. The protrusion(s) may be fixed or movable, with there preferably being at least two protrusions extending in substantially opposite directions. The receiving elements preferably comprise one or more recesses in the side wall of the manhole, positioned to correspond with the position of the protrusion(s). The cover plate preferably comprises first and second sections 30,31 adapted to cooperate to close the opening of the manhole. The cover plate sections may be locked together and each include at least one fixed protrusion, with one of the sections including at least one movable protrusion. A housing may be attached to the underside of the cover plate which defines channels within which the or each movable protrusion is adapted to slide. The movable protrusions may be biased towards the position where they engage the recesses and may include a handle adapted to extend through the cover plate to aid extension or retraction. Also claimed is a method of attaching a manhole cover assembly to a manhole.

Description

MANHOLE COVER ASSEMBLY

The present invention relates to manhole cover assemblies. In particular, but not exclusively, the present invention relates to releasable temporary manhole cover assemblies.

Manholes, also known as inspection chambers, are used to allow maintenance personnel access to underground structures such as sewers and pipelines. This may be necessary, for example, for routine inspection and maintenance purposes. A manhole typically comprises an opening at ground level, for instance in a road or pavement, of a suitable size to allow an adult to pass through. The opening may then typically open out below the surface of the ground into a vertical shaft descending to the level of the underground structure.

Referring to Figure 1, this illustrates a cross sectional side view of a typical manhole. The manhole comprises a cylindrical concrete manhole ring 1, forming the side walls of shaft 2. Shaft 2 descends vertically downwards from ground level 3 towards the underground structure (not shown) to which access is required. Rungs 4 are arranged to assist maintenance personnel in descending the shaft 2.

At the upper end of manhole ring 1, the shaft 2 is capped by a cover slab 5, also known as a manhole biscuit. The cover slab 5 defines an opening 6 (illustrated in Figure 1 by the horizontal arrow) communicating with the shaft 2. In plan view, opening 6 is typically square or rectangular. Above the cover slab 5, there is typically provided one or more courses of brickwork 7. Two courses of brickwork 7 are illustrated in Figure 1. Supported upon brickwork 7 is a manhole cover 8 arranged to block access to the manhole. The manhole cover 8 may typically be formed from a sheet of metal or plastic material. The manhole cover 8 is designed to prevent access to the manhole, when the manhole is not in use, in order to avoid accidents.

During the construction of a manhole, after the manhole ring I and the cover slab 5 have been set in place a bricklayer is required to lay the brickwork 7 on top of the cover slab 5 around opening 6. This can be a dangerous operation because the bricklayer is required to work close to the opening 6, or even leaning over it.

Consequently, the bricklayer is at risk of injury through falling into the manhole.

Additionally, before manhole cover 8 has been set in place, it is possible for building debris to be dropped down shaft 2. This must be removed, otherwise it can block or damage the underground structure.

It is known to provide a temporary manhole cover formed from, for instance, a sheet of plywood. The sheet of plywood temporarily covers the manhole during the construction process, for instance if the brickwork 7 needs to be left overnight for the mortar to set. However, clearly this is an inadequate solution as it can be readily appreciated that such a temporary manhole cover is weak and easily displaced, either accidentally or deliberately, leaving an open shaft.

It is known to provide a temporary manhole cover assembly comprising a cover plate supported by a frame secured in position within the cover slab 5 by an extendable brace. Figure 2 illustrates a cross sectional side view of such a manhole cover assembly assembly. The temporary manhole cover assembly comprises first and second brackets 10, ii. Each bracket comprises a sidewall 12, 13, upper bracket shelves 14, 15 and lower bracket shelves 16, 17 respectively formed from welded sheet metal.

Trench brace 18 is disposed laterally between the first and second brackets 10, 11. Trench brace 1 8 is extendable such that it can exert pressure on the sidewalls 12, 13 of brackets 10, 11 and hence on the sides of the opening 6 in cover slab 5. Each end of trench brace 18 is retained between the upper and lower shelves of the respective bracket 10, 11. The lateral pressure on the sides of opening 6 prevent the manhole cover assembly from moving. Each bracket 10, 11 further comprises a lip 19, 20 arranged in use to rest upon the upper edge 21 of cover slab 5. The lips 19, 20 in use will not pass through opening 6. The manhole cover assembly further comprises spacer 22, which rests upon upper bracket shelves 14, 15, and in turn supports cover plate 23, which is placed thereon.

However, the known temporary manhole cover assembly depicted in Figure 2 suffers from a number of problems. Firstly, the assembly comprises a large number of separate parts that in use, particularly during installation, move relative to each other.

These separate parts, namely the brackets, brace, spacer and cover plate, except when fully installed, are at risk of being dropped down shaft 2. The installation process can be difficult to achieve, particularly if the manhole cover assembly is being retrofitted into an existing manhole, which already has several courses of brickwork 7 impeding access to the cover slab 5. The brackets 10, 11 must be held in place against the edges of opening 6 in which the brace 18 is extended, otherwise they may easily be dropped.

It will appreciated that this is therefore a multiple person installation process, which is clearly undesirable.

Furthermore, to ensure a secure installation, this known cover requires specialised training. For instance, if the lips 19, 20 of brackets 10, 11 are not positioned such that they rest correctly on the edge 21 of cover slab 5, then the temporary manhole cover assembly may give the impression of being securely fitted, but in actual fact be liable to give way if, for instance, someone stands on it. The lips 19, 20 engaging the edge 21 of cover slab 5 can cause concrete corrosion due to the excess localised pressure applied to the cover slab 5.

Additional problems, which are ultimately due to the complex multiple part design of this manhole cover assembly, include the fact that the manhole cover assembly is sufficiently heavy that in some circumstances to install or remove the manhole cover safely requires mechanical lifting gear. When not in use, the manhole cover assembly can be difficult to store because of its bulk. The various moving parts, in particular the extendable brace require regular lubrication in order to function correctly. Perhaps most disadvantageously, the large number of separate moving parts makes this a relatively expensive solution.

It is therefore an object of the present invention to obviate or mitigate one or more of the problems of the prior art, whether identified herein or elsewhere.

Specifically, it is an object of the present invention to provide an improved manhole cover assembly having reduced number of separate component parts.

According to a first aspect of the present invention there is provided a manhole cover assembly comprising a cover plate, arranged in use to substantially close an opening in a manhole, wherein the cover plate comprises engagement means adapted to releasably engage corresponding receiving means within a side wall of the manhole.

An advantage of the present invention is that the engagement means and the receiving means allow for easy and efficient installation and removal of the manhole cover assembly within a manhole while providing a safe and secure temporary manhole cover when installed. The engagement means and receiving means provide a secure installation that is not liable to come free, even if the manhole cover assembly is installed into the manhole before the manhole is positioned in the ground during the construction process. Preferably, the manhole cover assembly is adapted to be used either temporarily or permanently as a means for closing the opening in the manhole.

Known manhole cover assemblies require large numbers of separate parts.

Advantageously, the manhole cover assembly according to the first aspect of the present invention comprises a relatively small number of separate component parts.

This makes the job of installing or removing the manhole cover assembly easier to achieve compared with known alternative solutions. Furthermore, the limited number of separate component parts means that storage of the manhole cover when not in use takes up less space than other known designs. Additionally, the cost is reduced compared with other known designs of manhole cover assemblies by the reduced numbers of separate moving components.

Preferably, the engagement means comprises at least one protrusion extending from an outer edge of the cover plate. Preferably, the at least one protrusion extends from the outer edge of the cover plate in a direction, which is substantially parallel to the plane of the cover plate. The at least one protrusion may be fixed or rigid. The at least one protrusion may be moveable.

More preferably, the engagement means comprises at least two protrusions extending from the outer edge of the cover plate, preferably in substantially opposite directions.

Preferably, the receiving means comprises at least one recess arranged to receive the engagement means. Preferably, the at least one recess is provided in the side wall of the manhole in a position, which corresponds with the position of the or each protrusion. Hence, preferably, the engagement means is adapted to releasably engage corresponding recesses within substantially opposite side walls of the manhole. This is advantageous as it braces the cover plate across the opening within a manhole, thereby improving the security of the temporary manhole cover assembly.

Preferably, the cover plate comprises first and second cover plate sections, which are adapted to mutually cooperate to close the opening in the manhole. Having at least two cover plate sections is advantageous as it makes the manhole cover assembly easier to install as each section may be manoeuvred into position separately.

Preferably, the first and second cover plate sections are adapted to be locked together. Locking the cover plate sections together makes it harder to accidentally or deliberately interfere with the manhole cover assembly.

Preferably, each cover plate section comprises at least one fixed protrusion.

This allows each cover plate section to be independently engaged with the sidewalls of the manhole.

Preferably, either the first cover plate section and/or the second cover plate section comprises at least one moveable protrusion. Preferably, the at least one moveable protrusion is moveable between a retracted position in which it does not substantially extend beyond the outer edge of the cover plate and an extended position in which the moveable protrusion extends beyond the outer edge of the cover plate. It will be appreciated that when in position in the manhole, the or each moveable protrusion is arranged to releasably engage a corresponding recess within the side wall of the manhole. The moveable protrusions are desirable as they allow engagement in the receiving means to be provided on all sides of the cover plate.

Preferably, the cover plate comprises first and second moveable protrusions attached to the first cover plate section and extending from the outer edge of the cover plate in substantially opposite directions, said directions being substantially transverse to the direction of the at least one fixed protrusion attached to the first cover plate section. As the directions of the moveable protrusions are transverse to the directions of the fixed or rigid protrusions, it is not possible to accidentally remove the manhole cover by knocking it sideways along the axis of one or more of the protrusions.

Preferably, the assembly comprises a housing attached to the underside of the cover plate, which housing defines a channel in which the or each moveable protrusion is adapted to slide. Hence, the or each moveable protrusion is preferably adapted to slide within the channel. The channel constrains the movement of the or each moveable protrusion.

The cover plate may further comprise biasing means adapted to bias the at least one moveable protrusion to its extended position. The biasing means may be a spring, for example, a helical spring or a torsion spring. The biasing means may be supported within the channel.

The or each moveable protrusion may comprise a handle portion adapted to aid the extension or retraction of the moveable protrusion. The or each handle portion may comprise an upturned portion of an end of the moveable protrusion distal to the end which engages the receiving means. The upturned portion may be arranged to pass through a slot within the cover plate. This advantageously allows the handle portions to be manipulated by a user positioned above the cover plate.

The second cover plate section may comprise an overlap portion arranged such that when the first and second cover plate sections are brought together the overlap portion impedes movement of the or each handle portion preventing the or each moveable protrusion from being retracted. The overlap portion may be attached to an upper surface of the second cover plate section. The overlap portion may extend beyond an outer edge of the second cover plate section. This improves the security of the design by preventing the moveable protrusions from disengaging from the recesses.

The first cover plate section may further comprise a locking lug, which may be attached to an upper surface of the first cover plate section. The overlap portion may comprise a slot through which the locking lug may extend when the first and second cover plate sections are brought together. Preferably, the locking lug is arranged to receive locking means to prevent the locking lug from passing back through the slot.

The locking means may be a padlock or a combination lock.

The cover plate may further comprise a support plate attached to the underside of the first cover plate section. The support plate may extend beyond an outer edge of the first cover plate section. The support plate may be adapted to support an edge of the second cover plate section.

According to a second aspect of the present invention there is provided a method of attaching a manhole cover assembly to a manhole, the method comprising the steps of: (i) positioning a cover plate such that it substantially closes an opening in a manhole, the cover plate comprising engagement means, and (ii) releasably engaging the engagement means in corresponding receiving means within a side wall of the manhole.

Preferably, the method according to the first aspect comprises use of the assembly according to the first aspect. Hence, preferably, the engagement means comprises at least one protrusion extending from an outer edge of the cover plate.

Preferably, the receiving means comprises at least one recess in the manhole side wall. The method may comprise providing the receiving means in the side wall of the manhole. For example, if the receiving means is a recess, then the method may comprise cutting out a suitable recess in the side wall. Preferably, the step of releasably engaging the engagement means comprises receiving the at least one protrusion within the at least one recess.

More preferably, the cover plate comprises at least two protrusions.

Preferably, the two protrusions extend from the outer edge of the cover plate in substantially opposite directions.

Preferably, the cover plate comprises first and second cover plate sections arranged to cooperate to substantially close the opening in the manhole. Preferably, each cover plate section comprises at least one protrusion adapted to releasably engage a corresponding recess within a side wall of the manhole. Preferably, the method further comprises positioning the first cover plate section within the opening and engaging a protrusion attached to the first cover plate section within a first recess within a sidewall of the manhole.

Preferably, the method comprises positioning the second cover plate section within the opening and engaging a protrusion attached to the second cover plate section within a second recess within a sidewall of the manhole.

The method may further comprise locking the first cover plate section to the second cover plate section.

The cover plate may further comprise at least one moveable protrusion attached to the first cover plate section. The method may comprise moving the or each moveable protrusion from a retracted position, in which it does not substantially extend beyond the outer edge of the cover plate, to an extended position in which it extends beyond the outer edge of the cover plate. The method may further comprise releasably engaging the or each moveable protrusion in a corresponding recess within a side wall of the manhole.

The method may further comprise biasing the or each moveable protrusion towards its extended position.

The weight of manhole cover assembly in accordance with embodiments of the present invention is designed such that no mechanical lifting gear is required to install it. Furthermore, it is envisaged that no specialised training is required to fit the manhole cover. Alternatively, and particularly advantageously, the manhole cover assembly may be factory fitted into a cover slab prior to delivery to the building site.

Due to the design of the manhole cover assembly it is immaterial which way up the cover slab is stored before installation, as the manhole cover assembly will not fall out in any orientation. Due to the engagement of the protrusions with the corresponding recesses within the sides of the manhole there is a much reduced risk of concrete corrosion compared with previous known designs designed to engage the cover slab using lateral pressure.

All of the features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: - Figure 1 illustrates a cross sectional side view of a typical manhole; Figure 2 illustrates a cross sectional side view of a known manhole cover assembly; Figure 3A illustrates a plan view of an upper elevation of a first section of a manhole cover plate, in accordance with an embodiment of the present invention; Figure 3B illustrates a plan view of an upper elevation of a second section of a manhole cover plate, in accordance with an embodiment of the present invention; Figure 4A illustrates a plan view of a lower elevation in partial cross section of the first section of the manhole cover plate shown in Figure 3A; Figure 4B illustrates a plan view of a lower elevation of the second section of the manhole cover plate shown in Figure 3B; Figure 5A illustrates a side view of the first section of the manhole cover plate shown in Figures 3A and 4A; Figure 5B illustrates a side view of the second section of the manhole cover plate shown in Figures 3B and 4B; Figure 6 illustrates a side view of both the first and second sections of the manhole cover plate engaging each other; Figure 7 illustrates a cross sectional plan view of a manhole cover slab in accordance with an embodiment of the present invention; Figure 8 illustrates a cross sectional side view along line A-A of the manhole cover slab shown in Figure 7; Figure 9 illustrates in partial cross section a plan view of the manhole cover plate of Figures 3A to 8 installed in the manhole cover slab of Figures 7 and 8; and Figure 10 illustrates a cross sectional side view along line B-B of the manhole cover plate and manhole cover slab shown in Figure 9.

Figures 1 and 2 illustrate a manhole and a known temporary manhole cover assembly, respectively.

Figures 3 to 8 illustrate the various parts of a temporary manhole cover assembly in accordance with the invention, and Figures 9 and 10 show such a manhole cover assembly fitted into a modified manhole. The manhole cover assembly consists of a manhole cover plate 25 formed from first and second cover plate sections 30, 31. The cover plate 25 engages with a manhole cover slab 5 to thereby substantially close off opening 6 in the manhole, as shown in Figures 9 and 10.

Hence, when in position, the manhole cover assembly ensures that the opening 6 is blocked, thereby preventing anyone from accidentally falling down the manhole.

Referring to Figures 3-6, there are shown various views of the first and second cover plate sections 30, 31. The cover plate sections 30, 31 are arranged in use to mutually cooperate with each other such that when they are brought together, they form a single cover plate 25 as shown in Figure 6. The cover plate sections 30,31 are formed from sheets of a suitably strong material, for instance, steel.

Referring to Figures 3A, 4A, and 5A there are shown upper, lower and side views respectively of the first cover plate section 30. The first section 30 is substantially rectangular in shape. Welded to an underside of the cover plate section 30, and extending beyond a peripheral edge 33 thereof, there is provided a support plate 36 formed from a separate sheet of steel. As shown in Figure 3A, the first cover plate section 30 is provided with a locking lug or eyelet 37, which is attached approximately centrally to an upper surface thereof. The locking lug 37 is either ring or U-shaped, and is formed from metal welded to the upper surface of the cover plate section 30.

Referring to Figures 3B, 4B and 5B, there are shown upper, lower and side views respectively of the second cover plate section 31. The second cover plate section 31 is also substantially rectangular in shape, such that when the two cover plate sections 30, 31 engage each other, they form the complete cover plate 25, which is approximately the same shape as the manhole opening 6, as shown in Figure 9.

Referring to Figure 3B, the second cover plate section 31 is provided with a steel overlapping flange 32, which is welded onto an upper surface thereof, and which extends over peripheral edge 34 of the second cover plate section 31. When the first and second cover plate sections 30, 31 are brought together, peripheral edge 33 of the first cover plate section 30 abuts peripheral edge 34 of the second cover plate section 31. The peripheral edge 34 of the second cover plate section 31 rests on top of the plate 36 of the first section 30, and the overlapping flange 32 of the second section 31 bears against an upper surface of the first cover plate section 30.

As shown in Figure 3B, the overlapping flange 32 of the second cover plate section 31 includes a slot 38 suitably sized such that when the cover plate cover plate sections 30,31 are brought together, the locking lug 37 of the first section 30 passes through the slot 38 of the second section 31. A padlock or combination lock (not shown in Figure 3B) may then be attached to the locking lug 37, thereby locking the two cover plate sections 30, 31 together, as shown in Figure 6.

As shown in Figure 9, in use, the outer edge 35 of the combined cover plate 25 is arranged to fit in and engage with the inner side walls of the cover slab 5, which is shown in detail in Figures 7 and 8. The cover slab 5 has an opening 6, which is shown in Figure 7 as a square. However, it will be appreciated that opening 6 could be any shape, with the dimensions of the temporary manhole cover adapted accordingly. In the centre of each of the side walls 60 of the cover slab 5 there is provided a recess 61, which is arranged in use to receive a protrusion provided on the complete cover plate formed by first and second sections 30, 31.

As shown in Figures 3A to 8, each cover plate cover plate section 30, 31 includes a rigid protrusion or rod 39, 40, respectively, extending outwardly therefrom.

The rigid rods 39, 40 are formed from a steel bar and are welded to the underside of the respective cover plate section 30, 31 and extend beyond the peripheral edge 35 of their respective cover plate section 30, 31.

As shown in Figures 3A, 4A and 5A, the first cover plate cover plate section further includes two moveable rods 41, 42, which are formed from a steel bar. The rods 41, 42 are slideably mounted within a housing 50, which is welded to the underside of the cover plate section 30. As shown in Figures 5A and 6, the housing 50 forms a V-shaped channel along which the two rods 41, 42 may slide. The housing 50 is illustrated in partial cross section in Figure 4A by dashed lines, at the points at which it is welded to the underside of the first cover plate section 30.

The motion of the moveable rods 41, 42 is constrained such that they may only move along the axis of the V-shaped channel, as indicated by arrows 51, 52 respectively in Figure 4A. The rods 41, 42 are arranged to slide along the housing 50 between an extended position (as illustrated in Figure 3A and 4A) in which they extend beyond the outer edge 35 of the cover plate 25, and a retracted position, in which they do not substantially extend beyond the outer edge 35 of the cover plate 25.

When in the extended position, the slideable rods 41, 42 extend into and engage with corresponding recesses 61 in the side walls of the cover slab 5, as shown in Figure 9.

As shown in Figures 3A and 4A, inner ends of the moveable rods 41, 42 (i. e. the opposite end to that of the outer edge 35 of the cover plate) are attached to a helical spring 46, which is also disposed inside the Vshaped channel of the housing 50. The spring 46 biases the two rods 41, 42 outwardly such that they are normally biased to the extended position as shown. At the inner end of the moveable rods 41, 42, there are provided upwardly facing handles 43, 44, which extend through an elongate slot 45 in the first cover plate section 30. The handle portions 43, 44 may be manipulated by a user in order to extend or retract the moveable rods 41, 42 between the first and second positions. The moveable rods 41, 42 can be temporarily moved from the extended position to the retracted position by applying sufficient inwards force to the handles 43, 44 in order to overcome the biasing force provided by the spring 46. The user may then let go of the handles 43, 44 to allow the biasing effect of the spring 46 to urge the rods 41, 42 back to the extended position.

It should be appreciated that the two cover plate cover plate sections 30, 31 may only be brought together when the moveable rods 41, 42 are in the first extended position, otherwise the overlap portion 32 on the second section 31 is obstructed by handle portions 43, 44. In addition, when the moveable rods are extended, the overlap portion 32 prevents the moveable rods 41, 42 from being retracted by blocking the motion of the moveable rods 41, 42. Such features improve the security and hence safety of the assembly when in use.

As shown in Figure 9, when the temporary manhole cover assembly is installed in a manhole, the rods 39, 40 each engage a corresponding recess in the inner side wall of the cover slab 5. Figure 9 also shows that the corners of the outer edge 35 are chamfered in order to make it easier to install the temporary manhole cover assembly in the manhole.

Referring to Figures 4A and 4B, these respectively illustrate the underside of the first cover plate section 30 and the second cover plate section 31. The fixed rods 39 and 40 are shown partially extending beneath first and second cover plate sections 30, 31, respectively. The fixed rods 39, 40 are formed from sections of a metal bar, and are welded in place to the cover plate sections 30, 31. The plate 36 is shown partially extending beneath the first cover plate section 30, where it is welded in place. The portion of overlap between the first cover plate section 30 and the plate 36 is arranged such that it does not interfere with the moveable rods 41, 42.

Referring to Figures 5A and SB, these respectively illustrate side views of the cover plate sections 30, 31, together with the relative positions of the fixed rods 39, 40, the plate 36 and the overlapping flange 32. The moveable rod 42 is shown in position within the V-shaped channel formed bythe housing 50. Handle portion 44 is attached to the moveable rod 42, and comprises an upturned portion of the rod.

Locking lug 37 extends above the upper surface of first cover plate section 30.

Figure 6 illustrates a side view of the two cover plate sections 30, 31 brought together to form the whole cover plate 25. Overlapping flange 32 passes between the handle portions 43, 44 (only handle portion 44 visible in Figure 6) and locking lug 37 passes through the slot 38 (not visible in Figure 6).

Figure 7 illustrates a cross sectional view of the cover slab 5. Opening 6 is shown as a square. However it will be appreciated that opening 6 could be any shape, with the dimensions of the temporary manhole cover adapted accordingly. In the side walls 60 of opening 6 there are four recesses 61. Recesses 61 are arranged to each receive a protrusion 39, 40 or a moveable protrusion 41, 42. Figure 8 is a cross sectional view of the cover slab 5 of Figure 7 along the line A:A.

Figure 9 illustrates in partial cross section the temporary manhole cover assembly installed in a cover slab 5. Each recess 61 receives either a fixed rod 39, 40, or a moveable rod 41, 42 of the cover plate sections 30, 31. The first cover plate section 30 is supported in the opening 6 by the fixed rod 39 and the two moveable rods 41, 42. The second cover plate section 31 is supported in opening 6 by the fixed rod 40, the plate 36 (not visible in Figure 9) attached to the under side of the first cover plate section 30, and also by the overlapping flange 32 which bears down on the upper surface of first cover plate section 30. A padlock 70 is attached to the locking lug 37 such that the second cover plate section 31 is securely attached to the first cover plate section 30. Overlap portion 32 prevents handle portions 43, 44 from being used to retract moveable protrusions 41, 42, when the two sections 30, 31 are secured together.

Figure 10 illustrates in partial cross section the arrangement of Figure 9 along the line B:B. In Figure 10 recesses 61 are shown receiving the protrusions 39, 40 attached to the first and second cover plate sections 30, 31 respectively. Padlock 70 can be seen in this side view passing through the locking lug 37 securing the manhole cover assembly in place.

One method of installing a temporary manhole cover will now be described.

The first cover plate section 30 and the second cover plate section 31 are separately inserted into the opening 6 of the manhole. Referring to Figures 9 and 10, handle portions 43, 44 on the first cover plate section 30 are first manipulated to move the moveable rods 41, 42 against the biasing action of the spring 46 in to their respective retracted positions. The first cover plate section 30 is then lowered into position within opening 6 of the cover slab 5 and the protrusion 39 is lined up with, and inserted into, a recess 61 in the slab 5. The two moveable protrusions 41, 42 are then aligned with two further recesses 61 in the cover slab 5, and handle portions 43, 44 are released such that the moveable protrusions 41, 42 are urged by the spring 46 into the recesses 61. At this point, the first cover plate section 30 is securely fitted in place in the cover slab 5.

The second cover plate section 31 is then lowered into position within opening 6 of the cover slab 5, and slightly angled such that overlap portion 32 clears the first cover plate section 30, while protrusion 40 is inserted into the final recess 61 in the slab 5. At the same time, the second cover plate section 31 is lowered such that the peripheral edge 34 rests upon the plate 36 of the first cover plate section 30. The overlap portion 32 comes to rest against the upper surface of the first cover plate section 30, and the locking plate 37 of the first section 30 passes through the slot 38 of the second section 31. At this point, the complete cover plate 25 consisting of both first and second sections 30, 31 is fully fitted into position within opening 6 as shown in Figure 9. A padlock 70 can then be attached to the locking lug 37 to prevent the cover plate 25 from being lifted up or removed.

In order to remove the assembly, padlock 70 (if present) must first be removed from locking lug 37. The installation process is then reversed. The second cover plate section 31 is lifted up slightly, angling it such that it will clear the first cover plate section 30. The second cover plate section 31 is then moved sideways such that the protrusion 40 is disengaged from recess 61. The second cover plate section 31 may then be lifted out of the manhole and removed.

Handle portions 43, 44 on the first cover plate section 30 are then brought together, retracting moveable protrusions 41, 42 against the biasing action of the spring 46. The first cover plate section 30 is then moved sideways such that the protrusion 39 is disengaged from recess 61, and the first cover plate section 30 removed from the manhole.

The manhole cover assembly in accordance with the invention is designed such that it may be factory fitted into a cover slab 5 at the factory that manufactures the cover slab 5 itself. This is advantageous because as soon as the cover slab 5 is placed in position over the manhole ring 1, the temporary manhole cover assembly provides protection for construction personnel preventing them from falling in.

Alternatively, the manhole cover assembly can be retro-fitted into an existing manhole by drilling recesses into the cover slab 5, or into the brick work, for instance.

The manhole cover assembly can also be used to provide a temporary cover in other holes or openings provided with suitable recesses. The size and shape of the cover plate may be adjusted accordingly.

Further advantages of the assembly reside in fact that there are relatively few moving parts. This allows for simple installation and removal of the manhole cover assembly, and also simple maintenance and storage. Due to the simplified design of the assembly compared to known products mechanical lifting aids are not required to install the assembly, making it much safer for the users. Furthermore, the weight of the assembly is greatly reduced such that there are no manual handling issues.

Accordingly, the assembly may be installed by one person in contrast to existing designs, which require at least two men to install safely.

Factory installation of the manhole cover assembly prior to delivery of the manhole improves the safety of the product as there is no point in time at which the manhole presents an unguarded open shaft. Additionally, due to the positive engagement between the protrusions or rods and the recesses within the sidewalls of the manhole there is a reduced risk of the manhole cover assembly working free over time, compared with known designs which rely upon applied lateral pressure.

Overlap portion 32 positively prevents the moveable protrusions from being retracted.

This further improves the safety and security of the design, by reducing the risk of accidental or deliberate interference with the manhole cover assembly, specially when the second cover plate section 31 is locked to the first cover plate section 30.

Other objects and advantages of the present invention will be readily apparent to the appropriately skilled person, without departing from the scope of the appended claims.

Claims

1. A manhole cover assembly, comprising: a cover plate, arranged in use to substantially close an opening in a manhole; wherein the cover plate comprises engagement means adapted to releasably engage corresponding receiving means within a side wall of the manhole.

2. A manhole cover assembly according to claim 1, wherein the engagement means comprises at least one protrusion extending from an outer edge of the cover plate.

3. A manhole cover assembly according to claim 2, wherein the at least one protrusion extends from the outer edge of the cover plate in a direction, which is substantially parallel to the plane of the cover plate.

4. A manhole cover assembly according to either claim 2 or claim 3, wherein the at least one protrusion may be fixed or moveable.

5. A manhole cover assembly according to any preceding claim, wherein the engagement means comprises at least two protrusions extending from the outer edge of the cover plate, preferably in substantially opposite directions.

6. A manhole cover assembly according to any preceding claim, wherein the receiving means comprises at least one recess arranged to receive the engagement means.

7. A manhole cover assembly according to claim 6, wherein the at least one recess is provided in the side wall of the manhole in a position, which corresponds with the position of the or each protrusion.

8. A manhole cover assembly according to any preceding claim, wherein the cover plate comprises first and second cover plate sections, which are adapted to mutually cooperate to close the opening in the manhole.

9. A manhole cover assembly according to any preceding claim, wherein the first and second cover plate sections are adapted to be locked together.

10. A manhole cover assembly according to claim 9, wherein each cover plate section comprises at least one fixed protrusion.

11. A manhole cover assembly according to either claim 9 or claim 10, wherein either the first cover plate section and/or the second cover plate section comprises at least one moveable protrusion.

12. A manhole cover assembly according to claim 11, wherein the at least one moveable protrusion is moveable between a retracted position in which it does not substantially extend beyond the outer edge of the cover plate and an extended position in which the moveable protrusion extends beyond the outer edge of the cover plate.

13. A manhole cover assembly according to any one of claims 10-12, wherein the cover plate comprises first and second moveable protrusions attached to the first cover plate section and extending from the outer edge of the cover plate in substantially opposite directions, said directions being substantially transverse to the direction of the at least one fixed protrusion attached to the first cover plate section.

14. A manhole cover assembly according to any preceding claim, wherein the assembly comprises a housing attached to the underside of the cover plate, which housing defines a channel in which the or each moveable protrusion is adapted to slide.

15. A manhole cover assembly according to any preceding claim, wherein the cover plate comprises biasing means adapted to bias the at least one moveable protrusion to its extended position.

16. A manhole cover assembly according to any preceding claim, wherein the or each moveable protrusion may comprise a handle portion adapted to aid the extension or retraction of the moveable protrusion.

17. A manhole cover assembly according to claim 16, wherein the or each handle portion comprises an upturned portion of an end of the moveable protrusion distal to the end which engages the receiving means.

18. A manhole cover assembly according to claim 17, wherein the upturned portion is arranged to pass through a slot within the cover plate.

19. A manhole cover assembly according to any one of claims 16-18, wherein the second cover plate section comprises an overlap portion arranged such that when the first and second cover plate sections are brought together the overlap portion impedes movement of the or each handle portion preventing the or each moveable protrusion from being retracted.

20. A manhole cover assembly according to any one of claims 8-19, wherein the first cover plate section comprises a locking lug, which is attached to an upper surface thereof

21. A manhole cover assembly according to claim 20, wherein the overlap portion comprises a slot through which the locking lug may extend when the first and second cover plate sections are brought together.

22. A method of attaching a manhole cover assembly to a manhole, the method comprising the steps of: (i) positioning a cover plate such that it substantially closes an opening in a manhole, the cover plate comprising engagement means, and (ii) releasably engaging the engagement means in corresponding receiving means within a side wall of the manhole.

23. A method according to claim 22, wherein the engagement means comprises at least one protrusion extending from an outer edge of the cover plate.

24. A method according to claim 23, wherein the receiving means comprises at least one recess adapted to releasably engage the at least one protrusion.

25. A method according to claim 24, wherein the step of releasably engaging comprises receiving the at least one protrusion within the at least one recess.

26. A method according to any one of claims 22 to 25, wherein the cover plate comprises first and second cover plate sections arranged to cooperate to substantially close the opening in the manhole.

27. A method according to claim 26, wherein each cover plate section comprises at least one protrusion adapted to releasably engage a corresponding recess within a side wall of the manhole.

28. A method according to claim 27, wherein the method further comprises the steps of positioning the first cover plate section within the opening and engaging a protrusion attached to the first cover plate section within a first recess within a sidewall of the manhole.

29. A method according to claim 28, wherein the method further comprises positioning the second cover plate section within the opening and engaging a protrusion attached to the second cover plate section within a second recess within a sidewall of the manhole.

30. A method according to any one of claims 26 to 29, wherein the method further comprises locking the first cover plate section to the second cover plate section.

31. A method according to any one of claims 26 to 30, wherein the cover plate comprises at least one moveable protrusion moveable between a retracted position, in which it does not substantially extend beyond the outer edge of the cover plate and an extended position in which it does extend beyond the outer edge of the cover plate, the at least one moveable protrusion being attached to the first cover plate section.

32. A method according to claim 31, wherein the method comprises releasably engaging the or each moveable protrusion in a corresponding recess within a side wall of the manhole.

33. A method according to either claim 31 or claim 32, wherein the method comprises biasing the or each moveable protrusion towards its extended position.

34. A method according to any one of claims 22-33, wherein the cover plate assembly is as defined in any one of claims 1-21.

35. A manhole cover assembly, substantially as hereinbefore described, with reference to the accompanying drawings 3A to 10.

36. A method of attaching a manhole cover assembly to a manhole, substantially as hereinbefore described, with reference to the accompanying drawings 3A to 10.