WO2013179045A2

WO2013179045A2 - Improvements in and relating to manhole covers

Info

Publication number: WO2013179045A2
Application number: PCT/GB2013/051441
Authority: WO
Inventors: Paul Spencer PRICE
Original assignee: Price Paul Spencer
Priority date: 2012-05-30
Filing date: 2013-05-30
Publication date: 2013-12-05
Also published as: GB201209627D0; GB2504452B; GB2504452A; WO2013179045A3

Abstract

A manhole cover comprising an upper face that is arrangeable in use to extend across manhole opening. The manhole cover further comprises a seat engaging portion that is arrangeable in use to rest on a manhole supporting seat; characterised in that the manhole cover seat engaging portion is set back from an outer edge of the upper face.

Description

Improvements in and Relating to Manhole Covers

Field of the Invention The present invention relates to manhole covers. The present invention further relates to parts and accessories for use with manhole covers.

Background Manholes are used in a number of fields, typically to provide access to sewers, drains or other openings or spaces below ground level. A manhole cover is used to stop things from falling through the manhole when access is not needed. For manholes in roadways, traditionally cast iron manhole covers have been used, as they were relatively easy to produce, long-lasting and provide suitable load-bearing characteristics. However, with the cost of raw materials, in particular metals, rising, theft of such manhole covers for their scrap value has become a problem.

A problem with cast iron manhole covers of traditional design is that although long- lasting due to their generally solid construction, corrosion does lower their service life and causes problems when they rest on support structures with which they can react, chemically.

Another problem with traditional designs, when installed flush with ground level, is that lifting a heavy manhole cover is difficult. Finally, traditional manhole designs are not well adapted to provide a water-tight, or other fluid-impermeable seal for the manhole, which would be advantageous in a number of installations.

It is an aim of example embodiments to address at least one of the problems identified above, or other related problems not identified above.

Summary of the Invention

In one aspect there is provided a manhole cover comprising:

an upper face that is arrangeable in use to extend across manhole opening; a manhole cover seat engaging portion that is arrangeable in use to rest on a manhole supporting seat; characterised in that the manhole cover seat engaging portion is set back from an outer edge of the upper face. Suitably, the manhole cover seat engaging portion is connected to the upper face by a depth-setting flange. Suitably, the manhole cover seat engaging portion extends inwardly from the depth-setting flange. Suitably, the manhole cover seat engaging portion comprises a generally flat surface, for example a generally flat surface extending parallel to the upper face. Suitably, the manhole cover seat engaging portion comprises a lowermost portion of the edge of the manhole.

Suitably, the depth-setting flange extends downwardly from the upper face. Suitably, the depth-setting flange extends inwardly from the upper face. Suitably, the depth-setting flange comprises an outward-facing surface. Suitably, the outward-facing surface is shaped so that in use only a portion of the outward-facing surface engages a manhole cover supporting seat. Suitably, the engaging port of the outward-facing surface is the port nearest to the outer edge of the upper face. Suitably, the engaging port of the outward-facing surface is where the depth-setting flange extends from the upper face. Suitably, the outward-facing surface is generally continuous around the manhole cover. Suitably, the depth-setting flange comprises a frusto-conical surface. Suitably, the depth-setting flange comprises a frusto- conical surface which is a portion of the surface of a right, circular cone. Suitably, the depth- setting flange comprises a frusto-conical surface which is a portion of a right, circular cone of aperture greater than 10 degrees, for example greater than 15 degrees. Suitably, the depth- setting flange comprises a frusto-conical surface which is a portion of a right, circular cone of aperture less than 40 degrees, for example less than 30 degrees. Suitably, the depth-setting flange comprises a frusto-conical surface which is a portion of a right, circular cone of aperture in the region 15 degrees to 30 degrees, for example 20 degrees plus or minus 2 degrees, for example 20 degrees.

In another aspect there is provided a manhole cover comprising a depth-setting flange, in combination with a manhole cover supporting seat, wherein the manhole cover supporting seat is arranged to cooperate with the manhole cover so that non-uniform separation from an outward-facing surface of the depth-setting flange is maintained down the depth-setting flange. Suitably, the manhole cover is as described in the aspect of the invention set out above.

In another aspect there is provided a manhole cover comprising a manhole cover seat engaging portion including a sealing member arranged to run around the manhole cover seat engaging portion and to in use form a seal against a manhole cover supporting seat.

In another aspect there is provided a manhole cover supporting seat, comprising an upper edge region arranged to lie in the plane of a manhole received by the manhole cover supporting seat, and a seating region arranged below and inwardly of the upper edge region to in use engage and support a manhole cover, with depth between the upper edge and the seat provided to accommodate the thickness of a manhole cover; characterised in that a sealing member is provided running around the seating region to in use seal the manhole cover supporting seat against a manhole cover received by the seat. In another aspect there is provided a manhole cover arranged with a manhole cover supporting seat, comprising an upper edge region arranged to lie in the plane of a manhole received by the manhole cover supporting seat, and a seating region arranged below and inwardly of the upper edge region to in use engage and support a manhole cover, with depth between the upper edge and the seat region is provided to accommodate the thickness of a manhole cover; characterised in that a sealing member is provided between the manhole cover and the seat to in use seal the manhole cover supporting seat against the seat.

In another aspect there is provided a manhole cover including a pressure relief valve, arranged to remain closed while a pressure difference between faces of the manhole cover is below a predetermined threshold, and to open to enable passage of fluid from one face of the manhole cover to the other if the pressure difference exceeds the predetermined threshold.

Suitably, the pressure relief valve is arranged, while closed, to extend downward from the upper face of the manhole cover to the lower face of the manhole cover. Suitably, the pressure relief valve is arranged to extend above the upper face of the manhole cover only when open.

Suitably, the valve member is held against a valve seat by a biasing member when the valve is closed. Suitably, the valve member or valve seat comprises a sealing element which is compressed between the valve member and the valve seat while the valve is closed. Suitably, the sealing element is carried on the valve member. Suitably, the predetermined pressure difference is set according to a set bias tension applied to the valve member by the biasing member when the valve is closed. Suitably, the valve member and valve seat comprise tapering surfaces, complementary with one another. Suitably, the valve seat tapers such that the opening of the valve is wider toward the upper face of the manhole cover than toward the lower face of the manhole cover.

Suitably, the valve member is actuatable, for example accessible, from the upper face of the manhole cover, to permit opening of the valve independently of the pressures acting on the faces of the manhole cover. Suitably, a tool-engaging portion is provided accessible from the upper face of the manhole cover to enable actuation of the valve with the aid of a tool. In another aspect there is provided a manhole cover including a releasable locking assembly, the releasable locking assembly comprising a locking lever below the lower face of the manhole cover and arrangeable in an unlocked position to lie within the extent of the lower face of the manhole cover, and further arrangeable in a locked position to extend further toward the edge of the lower face of the manhole cover to in use engage with a manhole cover supporting seat and hold the manhole cover against the seat; characterised in that the locking lever is coupled to a lock bar that passes through the manhole cover and is accessible for actuation from both above and below the manhole cover to arrange the locking lever in the unlocked position and in the locked position to allow the manhole cover to be removed from the seat, and to hold the manhole cover against the seat respectively.

Suitably, the locking assembly comprises a stopper plate, such that rotation of the locking lever is restricted by engagement of the stopper plate when the locking lever is arranged in the locked position. Suitably, the lock bar is a threaded bar, and the locking lever is carried on the thread. Suitably, the relative rotation of the lock bar and the locking lever about the axis of the lock bar moves the locking lever along the lock bar. Suitably, rotation of the lock bar while the locking lever is in engagement with the stopper plate causes the locking lever to move along the lock bar. Suitably, rotation of the lock bar tightens the locking lever against the seat when the locking lever is in engagement with the stopper plate. Suitably, rotation of the lock bar in the opposite sense moves the locking lever out of engagement with the seat. Suitably, the locking lever is captive on the lock bar. Suitably, the lock bar is captive in the manhole cover. Suitably, the locking assembly further comprises a second stopper plate, such that rotation of the locking cover is restricted by engagement of the second stopper plate as the locking lever is moved out of engagement with the seat.

Suitably, the locking assembly comprises a handle, accessible from below the lower face of the manhole cover to allow manual actuation of the lock bar. Suitably, the locking assembly comprises a security head, accessible from above an upper face of the manhole cover to allow actuation of the lock bar using a security head tool. Suitably the security head is a bolt head, and the security head tool comprises matching socket for engaging the bolt head.

In another aspect there is provided a lifting structure for a manhole cover, comprising a coupler attached to a manhole cover and a lifting head in engagement with the coupler, characterised in that the lifting head is coupled to the coupler so as to in use transmit a lifting force to the coupler, independent of the relative rotational arrangement of the coupler and the lifting head about a generally horizontal axis.

Suitably, the lifting head and couple engage one another at a plain bearing. Suitably, the axis of the plain bearing is generally horizontal. Suitably, the coupler provides a section of cylindrical surface to engage the lifting head, for example a convex cylindrical surface. Suitably, the lifting head comprises a section of a cylindrical surface to engage the coupler, for example a concave cylindrical surface. Suitably, the lifting head is arranged to engage two distinct portions of the coupler. Suitably, the lifting head is arranged to engage a projection extending from the coupler. Suitably, the lifting head comprises two distinct portions for engaging the coupler. Suitably, the coupler comprises projections extending in opposite directions from one another. Suitably, the coupler comprises cylindrical projections arranged to engage the lifting head. Suitably, the cylindrical projections define an axis about which relative rotation between the lifting head and the coupler may take place.

In other aspects there is provided a coupler, or a lifting head as described in relation to the lifting structure set out above, or a method of lifting a manhole cover using the same.

In another aspect there is provided method of raising a manhole cover using a lifting trolley comprising a handle coupled to a lifting head, the lifting head extending from the handle on a lifting arm, comprising

arranging the lifting head in a position beneath a coupler attached to a manhole cover; pressing down on the handle to cause the lifting trolley to rotate, thereby lifting the lifting arm into engagement with a coupler to lever up the manhole cover, while allowing relative rotation of the manhole cover about a horizontal axis through the lifting head as the manhole cover is lifted.

Brief Introduction to the Figures For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1A and Figure 1 B show a manhole cover according to an example embodiment of the present invention;

Figure 2A and Figure 2B show a manhole cover including a pressure relief valve, according to an example embodiment of the present invention; Figure 3A and Figure 3B show releasable locking assemblies for use in manhole covers according to an example embodiment of the present invention; and

Figure 4A to Figure 4D show a components of a lifting assembly and a lifting trolley according to example embodiments of the present invention. Description of Example Embodiments

Figure 1A and Figure 1 B show partial side sectional views of a manhole cover 100 according to an example embodiment of the present invention. In Figure 1A the manhole cover 100 is arranged on a manhole supporting seat 1 10 so as to extend across a manhole opening. The manhole cover 100 comprises a manhole cover seat engaging portion 102 which is set back from an outer edge 104 of the upper face 106 of the manhole cover 100. In this way the depth setting flange 108 which connects the upper face 106 to the seat engaging portion 102 can be spaced apart from the inward-facing side of the manhole cover supporting seat 1 10, for example in the shaded region S shown in Figure 1 B.

This is advantageous, as the space provided in this region can prevent the manhole cover from becoming stuck against the manhole cover supporting seat 1 10 in the event of a build-up of corrosion, rust and other debris between the manhole cover and the manhole supporting seat.

The depth-setting flange 108 extends downwardly from the upper face 106 of the manhole cover 100, with the depth-setting flange having an outward-facing surface 1 12 which extends inwardly as it extends from the upper face 106. This outward-facing surface 1 12 is generally continuous around the manhole cover 100, and in the embodiment of Figure 1 A and 1 B is a frusto-conical surface. The aperture of the cone that defines this frusto-conical surface is around 20 degrees, meaning that the angle shown in Figure 1A as angle alpha is around 10 degrees. In other embodiments, the outward-facing surface 1 12 may be arranged to sit away from the inward-facing side of the manhole cover supporting seat 1 10 in other ways, for example through cut-back sections, curved profiles or the like. However, the smooth taper of the frusto-conical section is particularly easy to manufacture, is compatible with existing manhole supporting seats without needing said seats to be modified, and does not provide any area where a build up of debris could cause the manhole to catch as it is raised. In other embodiments, the depth-setting flange may for example comprise the edge of the cover. For example, the flange may not have any cut-out region behind, or may not extend below the lower face of the manhole cover as a separate downward projection

In the embodiment of Figure 1A and 1 B the manhole cover seat engaging portion 102 extends inwardly from the depth-setting flange 108 and comprises a generally flat surface that extends parallel to the upper face 106 of the manhole cover 100. This flat surface rests on a sealing member 1 14 that runs around the manhole cover seat engaging portion 102 forms a seal against the manhole cover supporting seat 1 10. As will be appreciated, in other embodiments the sealing member 1 14 may comprise part of the manhole cover rather than part of the manhole cover supporting seat.

With the manhole cover 100 sealed against the manhole cover supporting seat 1 10, it may be desirable to include a pressure relief valve in the manhole cover 100 to release pressure from under the manhole cover 100 before a dangerous build-up occurs. Figures 2A and 2B show partial side sectional views of a pressure relief valve 200 according to an example embodiment mounted in a manhole cover 100, and arranged in closed and open conditions respectively.

The pressure relief valve 200 is arranged to remain closed while a pressure difference between faces of the manhole cover is below a predetermined threshold, and is arranged to open to enable passage of fluid from one face of the manhole cover 100 to the other if the pressure difference exceeds the predetermined threshold. The pressure relief valve 200 is arranged, while closed, to extend downward from the upper face 106 of the manhole cover 100, on the lower face of the manhole cover.

The pressure relief valve 200 comprises a valve member 202 held against a valve seat 204 by a biasing member in the form of a spring 206 when the valve 200 is closed. The valve member comprises a sealing element 208 which is compressed between the valve member 202 and the valve seat 204 while the valve is closed. A valve carrier 210 provides the connection between the valve member 202 and the lower face of the manhole cover 100, via a spring shroud 212 and spring securing nut 214. The valve carrier has passageways (not shown) formed through it to enable pressure to act on the underside of the valve member 202. The spring shroud 212 stabilises the valve member 202, protects the spring 206 and acts as a stop to limit valve opening by engaging the valve carrier 210. The predetermined pressure difference is set according to a bias tension applied to the valve member 202 by spring 206.

As shown in Figures 2A and 2B the valve member 202 and valve seat 204 comprise tapering frusto-conical surfaces, complementary with one another, to ease fluid flow therebetween when the valve 200 is open, and to reduce the potential for debris from on top of the manhole cover 100 to collect and block the valve 200.

Figure 3A shows a partial side sectional view of a manhole cover 100 including a releasable locking assembly 300. The releasable locking assembly 300 comprises a locking lever 302 below the lower face of the manhole cover 100 and arrangeable in an unlocked position to lie within the extent of the lower face of the manhole cover 100. Figure 3A shows the locking lever 302 in a locked position, which is rotated ninety degrees from the unlocked position. In the locked position the locking lever 302 extend furthers toward the edge of the lower face of the manhole cover to thereby engage with a manhole cover supporting seat 1 10 and hold the manhole cover 100 against the manhole cover supporting seat 1 10. The locking lever 302 is coupled to a lock bar 304 that passes through the manhole cover 100 and is accessible for actuation from both above and below the manhole cover to arrange the locking lever 302 in the unlocked position and in the locked position to allow the manhole cover to be removed from the manhole cover supporting seat 1 10, and to hold the manhole cover 100 against the manhole cover supporting seat 1 10 respectively.

The locking assembly 300 further comprises a stopper plate 306, such that rotation of the locking lever 302 is restricted by engagement with the stopper plate 306 when the locking lever 302 is arranged in the locked position. The lock bar 304 is threaded with the locking lever 302 carried on the thread such that relative rotation of the lock bar 304 and the locking lever 302 about the axis of the lock bar 304 moves the locking lever 302 along the lock bar 304. In this way, suitable rotation of the lock bar 304 while the locking lever 302 is in engagement with the stopper plate 306 causes the locking lever 302 to move along the lock bar 304 and tightens the locking lever 302 against the underside of the manhole cover supporting seat 1 10. Rotation of the lock bar 304 in the opposite sense moves the locking lever 302 out of engagement with the manhole cover supporting seat 1 10. A further stopper plate (not shown) may be provided to enable the locking lever 302 to be unscrewed down the lock bar 304, or the locking lever 302 may be able to engage two sides of the stopper plate 306. To prevent unwanted separation of the components of the locking assembly the locking lever 302 is captive on the lock bar 304 and the lock bar 304 is captive in the manhole cover 100. The locking assembly 300 of Figure 3A comprises a nut 308 which is fixed on the lock bar 304, not on the thread, by which the lock bar 304 may be rotated from below. In the embodiment of Figure 3B the locking assembly 300' comprises a handle 312, for example held in place on the lock bar 304 by a pair of lock-nuts, and arranged to be accessible from below the lower face of the manhole cover to allow manual actuation of the lock bar 304 if needed from below. In both embodiments the locking assembly 300 comprises a security head 310 for the lock bar 304, accessible from above an upper face of the manhole cover to allow actuation of the lock bar 304 only by operatives using a suitable, corresponding security head tool.

Figures 4A-4D show a lifting structure for a manhole cover, comprising a coupler 400 arrangeable to be attached to a manhole cover 100 and a lifting head 500 that can be brought into engagement with the coupler 400 to thereby transmit a lifting force to the coupler 400. The coupler 400 can rotate relative to the lifting head 500 as lifting takes place so that the lifting force is applied independent of the relative rotational arrangement of the coupler 400 and the lifting head 500 about a generally horizontal axis, so that no rotation about that axis is imparted by the lifting force, thereby preventing the lifting force from causing the manhole to impinge on the manhole cover supporting seat 1 10 and potentially jam against the seat.

In essence, the lifting head 500 and coupler 400 engage one another at a plain bearing, with the axis of the plain bearing being generally horizontal and provided by cylindrical projections 402. The coupler 400 has a generally T-shaped body, and comprises two projections 402 extending in opposite directions from one another and the back 404 of the T. The coupler comprises a threaded lower portion 406 to enable the coupler 400 to be removably secured in a corresponding threaded socket 600 that is provided in the manhole cover 100. Ideally the socket is provided above the centre of gravity of the manhole cover. The projections 402 are formed from a tubular element, the inner passageway of which can be used to help tighten the coupler 400 in the socket 600, and release it.

Raising the manhole cover 100 using the coupler 400 and the lifting head 500 is facilitated by use of a lifting trolley 700. The lifting trolley 700 comprises a handle 702 coupled to the lifting head 500, the lifting head 500 extending from the handle 702 on a lifting arm 704.

In use the lifting head 500 is arranged in a position beneath a coupler 400 that is attached to a manhole cover 100. Pressing down on the handle 702 causes the lifting trolley to rotate, thereby lifting the lifting arm 704 and bringing the lifting head 500 into engagement with the coupler 400. Continuing rotation of the trolley 700 levers up the manhole cover 100, while relative rotation of the manhole cover 100 and the coupler 400 about a horizontal axis through the lifting head 500 allows the manhole cover 100 to be lifted without twisting. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS:

1 . A manhole cover comprising:

an upper face that is arrangeable in use to extend across manhole opening; a manhole cover seat engaging portion that is arrangeable in use to rest on a manhole supporting seat; characterised in that the manhole cover seat engaging portion is set back from an outer edge of the upper face.

2. The manhole cover of claim 1 , wherein the seat engaging portion is connected to the upper face by a depth-setting flange, and wherein the manhole cover seat engaging portion extends inwardly from the depth-setting flange.

3. The manhole cover of claim 2, wherein the depth-setting flange comprises an outward-facing surface that extends downwardly from the upper face and inwardly from the upper face.

4. The manhole cover of claim 3, wherein the outward-facing surface is shaped so that in use only a portion of the outward-facing surface engages a manhole cover supporting seat, and the engaging portion of the outward-facing surface is the portion nearest to the outer edge of the upper face.

5. The manhole cover of claim 3 or 4, wherein the manhole cover supporting seat is arranged to cooperate with the manhole cover so that non-uniform separation from an outward-facing surface of the depth-setting flange is maintained down the depth-setting flange.

6. The manhole cover of claim 4 or 5, wherein the engaging portion of the outward- facing surface is where the depth-setting flange extends from the upper face.

7. The manhole cover of any one of claims 2 to 6, wherein the depth-setting flange comprises a frusto-conical surface which is a portion of a right, circular cone of aperture greater than 10 degrees, and less than 30 degrees.

8. The manhole cover of any preceding claim, wherein the manhole cover seat engaging portion comprises a generally flat surface extending parallel to the upper face.

9. The manhole cover of any preceding claim, wherein the manhole cover seat engaging portion includes a sealing member arranged to run around the manhole cover seat engaging portion and to in use form a seal against a manhole cover supporting seat.

10. The manhole cover of any preceding claim, including a pressure relief valve, arranged to remain closed while a pressure difference between faces of the manhole cover is below a predetermined threshold, and to open to enable passage of fluid from one face of the manhole cover to the other if the pressure difference exceeds the predetermined threshold.

1 1 . The manhole cover of claim 10, wherein the pressure relief valve is arranged, while closed, to extend downward from the upper face of the manhole cover to the lower face of the manhole cover, and wherein the pressure relief valve is arranged to extend above the upper face of the manhole cover only when open.

12. The manhole cover of claim 10 or 1 1 , wherein the valve member is held against a valve seat by a biasing member when the valve is closed, with the predetermined pressure difference set according to a set bias tension applied to the valve member by the biasing member when the valve is closed.

13. The manhole cover of any preceding claim, including a releasable locking assembly, the releasable locking assembly comprising a locking lever below the lower face of the manhole cover and arrangeable in an unlocked position to lie within the extent of the lower face of the manhole cover, and further arrangeable in a locked position to extend further toward the edge of the lower face of the manhole cover to in use engage with a manhole cover supporting seat and hold the manhole cover against the seat; characterised in that the locking lever is coupled to a lock bar that passes through the manhole cover and is accessible for actuation from both above and below the manhole cover to arrange the locking lever in the unlocked position and in the locked position to allow the manhole cover to be removed from the seat, and to hold the manhole cover against the seat respectively.

14. The manhole cover of claim 13, wherein the locking assembly comprises a stopper plate, such that rotation of the locking lever is restricted by engagement of the stopper plate when the locking lever is arranged in the locked position.

15. The manhole cover of claim 13 or 15, wherein the locking assembly further comprises a second stopper plate, such that rotation of the locking cover is restricted by engagement of the second stopper plate as the locking lever is moved out of engagement with the seat.

16. The manhole cover of claim 13, 14 or 15, wherein the locking assembly comprises a handle, accessible from below the lower face of the manhole cover to allow manual actuation of the lock bar.

17. A manhole cover supporting seat, comprising an upper edge region arranged to lie in the plane of a manhole received by the manhole cover supporting seat, and a seating region arranged below and inwardly of the upper edge region to in use engage and support a manhole cover, with depth between the upper edge and the seat provided to accommodate the thickness of a manhole cover; characterised in that a sealing member is provided running around the seating region to in use seal the manhole cover supporting seat against a manhole cover received by the seat.

18. A manhole cover arranged with a manhole cover supporting seat, comprising an upper edge region arranged to lie in the plane of a manhole received by the manhole cover supporting seat, and a seating region arranged below and inwardly of the upper edge region to in use engage and support a manhole cover, with depth between the upper edge and the seat region is provided to accommodate the thickness of a manhole cover; characterised in that a sealing member is provided between the manhole cover and the seat to in use seal the manhole cover supporting seat against the seat.

19. A lifting structure for a manhole cover, comprising a coupler attached to a manhole cover and a lifting head in engagement with the coupler, characterised in that the lifting head is coupled to the coupler so as to in use transmit a lifting force to the coupler, independent of the relative rotational arrangement of the coupler and the lifting head about a generally horizontal axis.

20. The lifting structure of claim 19, wherein the lifting head and coupler engage one another at a plain bearing.

21 . The lifting structure of claim 19 or 20, wherein the coupler provides a section of cylindrical surface to engage the lifting head, for example a convex cylindrical surface, and the lifting head comprises a section of a cylindrical surface to engage the coupler, for example a concave cylindrical surface.

22. The lifting structure of claim 19, 20 or 21 , wherein the lifting head is arranged to engage two distinct portions of the coupler.

23. The lifting structure of claim 22, wherein the lifting head comprises two distinct portions for engaging the coupler.

24. The lifting structure of claim 22 or 23, wherein and the coupler comprises projections extending in opposite directions from one another

25. The lifting structure of claim 24, wherein the projections are cylindrical projections that define an axis about which relative rotation between the lifting head and the coupler may take place.

26. A coupler, or a lifting head as described in relation to the lifting structure set out in any one of claims 19 to 25.

27. In another aspect there is provided method of raising a manhole cover using a lifting trolley comprising a handle coupled to a lifting head, the lifting head extending from the handle on a lifting arm, comprising

28. A manhole cover, or lifting structure substantially as herein-described, with particular reference to the accompanying drawings.

29. A method of raising a manhole cover using a lifting trolley, the method substantially as herein-described.