GB2415007A

GB2415007A - Lifting device for manhole covers

Info

Publication number: GB2415007A
Application number: GB0511911A
Authority: GB
Inventors: Kobus Jacobus Hendrik Cilliers
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-06-12
Filing date: 2005-06-13
Publication date: 2005-12-14
Also published as: GB0511911D0; GB0413280D0

Abstract

The lifting device comprises a pair of lifting elements 12, each lifting element having a lifting bar or bars, a key locatable upon the lifting bar(s) and engageable with a key slot in the manhole cover, and support elements 22 for engaging the ground adjacent to the manhole cover, with the lifting device having a lifting mechanism 26 to move the lifting bar relative to the support elements. The lifting elements are separable from each other but can be used together to lift a manhole cover. Preferably at least one of the lifting elements has a foot which in use engages the upper surface of a manhole cover. The lifting mechanism may comprise a mechanical system, preferably a screw mechanism 56, and a set of links 46,52 which can pivot relative to one another in a 'scissor' action. The support elements preferably comprise a pair of wheels. The lifting bar(s) remain spaced from a manhole cover in use, at a distance determined by leg elements connected to the lifting bar(s) upon which a system for interconnecting lifting elements may be carried.

Description

1 241 5007

LIFTING DEVICE FOR A MANHOLE COVER

FOLD OF TEE INVENTION

This invention relates to a lifting device for a manhole cover.

BACKGROUND OF THE INVENTION

Many services and facilities are provided underground. To enable a service engineer or the like to gain access to those services and facilities vertical shafts are provided at periodic intervals, the shafts being large enough to accommodate the service engineer. A manhole cover is typically used to close the top of the shaft. The manhole cover is typically made of metal and is substantially rigid so that it can support the weight of pedestrians or motor vehicles (for example) passing over it.

The manhole cover is therefore necessarily heavy, which has the advantage that inadvertent or unauthorised lifting or removal of the manhole cover is made more difficult.

To further reduce the likelihood of the manhole cover being lifted and/or removed, and so further restricting unauthorised access to the shaft and the underground services and facilities, the manhole cover will typically have two or more key slots so that it can be lifted only by the insertion of correctly dimensioned keys.

The keys and the corresponding key slots are not particularly complex as it is not intended to provide a totally secure system, but the provision of special means to lift the manhole cover, and the weight of the manhole cover, renders the unauthorised lifting or removal of the manhole cover very unlikely in practice.

When it is desired to lift the manhole cover so that the service engineer for example can gain access to the underground services or facilities, the engineer can use a set of keys to lift the manhole cover manually.

Because of their considerable weight, it is only practicable for a service engineer manually to liD smaller manhole covers. Also, health and safety legislation limits the maximum weight which can be lifted safely, and for example European legislation requires the maximum weight which can be lifted by one person to be 25 kg, and the vast majority of manhole covers exceed this weight.

DESCRIPTION OF THE PRIOR ART

To allow a service engineer or the like to lift a heavier manhole cover, it is known to provide one or more levers, the levers comprising long rigid bars which can engage the manhole cover directly, or can engage the keys fitted thereto. Whilst the levers can reduce the force required to lift the manhole cover the levers are themselves necessarily heavy, their weight and length making them difficult to store and transport.

Mechanical lifting devices are also known, which can significantly reduce the manual force required to lift a manhole cover. These devices typically utilise either a screw mechanism or a hydraulic mechanism. Such devices typically utilise a pair of lifting bars which can accommodate a part of the key, the lifting bars being placed upon the top surface of the manhole cover and the key(s) inserted between the lifting bars and into the key slots in the manhole cover. The devices have lifting means which can subsequently be used to lift the lifting bars and hence also the manhole cover.

Typically, the lifting means, comprising a screw mechanism or a hydraulic mechanism, is manually operated, so that the service engineer has to provide the force to lift the manhole cover, the screw mechanism or the hydraulic mechanism providing a mechanical advantage so that the force required is considerably less than the weight of the manhole cover. Alternatively, the force can be provided by a motor.

The known mechanical devices for lifting manhole covers have a rigid frame which rests upon the ground around the manhole cover to be lifted. The presence of the frame presents three major disadvantages. Firstly, there may be limited access to the manhole cover, for example the manhole cover may be close to a wall or other physical obstruction which precludes the correct positioning of the frame. Secondly, the size of manhole cover which can be lifted is limited by the size of the frame, so that larger frames are required for larger manhole covers. Thirdly, the frame, and the lifting device of which it is a part, is necessarily sufficiently robust to support the weight of the lifted manhole cover and so is itself heavy.

To overcome the second disadvantage outlined above it would be possible to make the frame large enough to accommodate the largest manhole covers, since such a frame would then be usable with smaller manhole covers. However, that would impact negatively upon the first and third disadvantages, since a larger frame and lifting device would necessarily be more likely to foul adjacent obstructions, and be heavier and more cumbersome.

As regards the third disadvantage, the health and safety legislation referred to above not only applies to the manhole covers but to the lifting device, since the lifting device must be transported to and from the location of use, and at least part of the journey will usually require the lifting device to be manually carried. One known hydraulic lifting device is made up of separable components so that the weight of each component is transportable by hand, but that device must be assembled around the manhole cover before it is lifted (and disassembled around the manhole cover after it has been replaced), which considerably increases the time taken to lift the manhole cover. In addition, care must be taken during storage and transportation of the device to ensure that none of the components are lost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lifting device for a manhole cover which avoids or reduces the disadvantages of the prior art lifting devices described above.

According to the invention, there is provided a lifting device for a manhole cover, the device comprising a pair of lifting means, each lifting means having a lifting bar or bars, a key locatable upon the lifting bar(s) and engageable with a key slot in the manhole cover, support means for engaging the ground adjacent to the manhole cover, and a lifting mechanism to move the lifting bar(s) relative to the support means, the lifting means being separable from each other but being usable together to lift the manhole cover.

The present invention therefore provides a lifting device for a manhole cover comprising a pair of separate lifting means. Each lifting means has its own support means for engaging the ground. A rigid frame connected to both lifting means is not provided. This allows each lifting means to be positioned adjacent to the manhole cover independently of the other lifting means, so that obstructions can be more easily avoided. Also, the lifting means can be placed close together when lifting a small manhole cover, and far apart when lifting a large manhole cover, the same lifting device being used for a large range of sizes of manhole cover The inventor has therefore realised that a rigid frame for the lifting device is not required, so that a cumbersome, heavy and limiting part of the prior art lifting devices is avoided.

Nevertheless, the pair of lining means of the present lifting device can cooperate to lift a manhole cover by virtue of the rigidity of the manhole cover, i.e. when in use the manhole cover provides a part of the structural rigidity of the lifting device.

Preferably, the lifting mechanism comprises a mechanical means, preferably a screw mechanism. Desirably, the lifting mechanism comprises a set of links which can pivot relative to one another, the links providing a "scissor" action. Thus, it is arranged that the screw mechanism acts through the links so as to provide a mechanical advantage for the lifting mechanism and reduce the force required to lift a manhole cover to considerably less than the weight of the manhole cover.

Desirably, the support means comprises a pair of wheels. In the preferred embodiment the support means is required to move across the ground as the lifting bar(s) are moved relative thereto, and the provision of wheels reduces the resistance to such movement. In addition, once the manhole cover has been lifted, the wheels allow the lifting device and manhole cover easily to be moved away from the shaft to provide unhindered access to the shaft. l

Preferably, in use the lifting bar(s) remain spaced away from the manhole cover. As above indicated, with prior art lifting devices the lifting bars lie upon the manhole cover and a (short) key connects the manhole cover to the lifting bars. The present inventor has realised that this is not required, and that spacing the lifting bar(s) from the manhole cover facilitates engagement of the key with the key slot (since accurate positioning of the lifting bar(s) above the key slot is not required), and the longer key required to connect the manhole cover to the lifting bar(s) can also be used for manually lifting manhole covers when required.

Desirably, the lifting mechanism has a leg means connected to the lifting bar(s), the length- of the leg means determining the spacing between the lifting bar(s) and the manhole cover in use. The leg means preferably includes a foot which in use engages the upper surface of the manhole cover.

Preferably, the leg means carries interconnecting means by which the pair of lifting means may be (temporarily) connected together. Thus, as above indicated the pair of lifting means can work together by way of a structural link provided by the manhole cover, but it may in addition be desirable or necessary to provide interconnecting means by which the lifting means may be connected when appropriately positioned.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a front view of a lifting means used as part of the lifting device of the present invention; Fig.2 shows a side view of the lifting means of Fig. 1; Fig.3 shows a plan view of the lifting means of Fig 1; Fig.4 shows a perspective view of the leg of the lifting means; Fig.5 shows a lifting device according to the present invention, comprising a pair of lifting means according to Figs. 1-3, in a first position relative to a first manhole cover; Fig.6 shows the lifting device of Fig.5 in a second position relative to a second manhole cover, and Fig.7 shows the lifting device of Fig.5 in a third position relative to a third manhole cover.

DETAILED DESCRIPTION

A lifting device 10 (Figs. 5-7) for a manhole cover according to the present invention comprises a pair of lifting means 12, a lifting means 12 being shown in Figs. 1-3. Each lifting means 12 has a pair of lifting bars 14, a key 16 locatable upon the lifting bars 14 and engageable with a key slot (not shown) in the manhole cover 20, support means 22 engageable with the ground 24 adjacent to the manhole cover 20, and a lifting mechanism 26 to move the lifting bars 14 relative to the support means 22.

In common with the lifting bars provided on prior art lifting devices, the two lifting bars 14 together define an open slot 30 which can accommodate a part of the key 16.

Specifically, the key 16 comprises an elongated rod 32 which terminates in a key profile 34 which is of a size and shape suited to the particular key slot (not shown) in the manhole cover 20. The open slot 30 is sufficiently wide to allow the key profile 34 and rod 32 to pass therethrough, the slot allowing the rod to slide therealong to a position above the key slot in the manhole cover.

In use the support means 22 lies outside the periphery of the manhole cover 20. Since the key slot may be a variable distance from the edge of the manhole cover 20 the open slot 30 is designed to be a length sufficiently great to allow the key 16 to engage the key slot for substantially all manhole covers. In practice, lifting bars having a length of around 400 mm will permit the lifting means 12 to be used with substantially all manhole covers.

As shown in Fig.2, one end of the lifting bars 14 are connected to a leg means 36. The leg means 36 has a foot 38 which in use engages the surface of the manhole cover 20. The leg means 36 serves to maintain the separation between the lifting bars 14 and the manhole cover 20. In this regard, it will be appreciated that spacing the lifting bars 14 from the manhole cover 20 facilitates fitment of the key profile 34 into the key slot of the manhole cover. Thus, the key 16 is freely movable along the lifting bars 14 and has significant freedom of movement laterally relative to the lifting bars by virtue of the relatively loose fitment of the rod 32 within the open slot 30 which permits some lateral pivoting of the rod. Accordingly, whereas with the prior art lifting devices in which the lifting bars would have to be positioned very accurately over the key slot to allow the key to be inserted through the lifting bars and into the key slot, with the present invention only approximate positioning of the lifting bars 14 is required. In addition of course, with the present invention the key slot is visible during insertion of the key profile 34, whereas with the prior art devices the key slot was at least partially obscured by the lifting bars.

Notwithstanding the ability of the operator to position the lifting bars 14 only approximately relative to the key slot, a diligent operator will nevertheless typically seek to position the lifting bars accurately since that will avoid any lateral force upon the manhole cover during lifting thereof.

It will be seen from Fig.2 that the key 16 is provided with a hand-grip 40. Whilst the hand grip 40 is not required with the present invention it makes the key 16 easier to manipulate, and also allows the key 16 to be used for manually lifting a manhole cover in the event that the lifting device is not required or desired to be used.

A part of the rod 32 is threaded, and carries a combined wing nut and washer 42 which is larger than the open slot 30 and so cannot pass therethough. In use, when the key profile 34 has been inserted into the key slot (and rotated into a secured position with the manhole cover as required), the combined wing nut and washer 42 is moved downwardly along the rod 32 into engagement with the top edge of the lifting bars 14, to temporarily secure the key 16 in position, and temporarily secure the manhole cover 20 to the key 16.

The ends of the lifting bars 14 opposed to the leg 36 are connected to a top block 44.

Pivotably connected to the top block 44 are a pair of arms 46, the end of the arms opposed to the top block 44 being connected to the support means 22. In this embodiment each support means is a wheel 22 having an axle SO by which it is rotatably connected to a respective arm 46.

Intermediate the connection to the top block 44 and the axle 50, each arm 46 is pivotably connected to a link 52, a link connecting a respective arm 46 to a bottom block 54. The bottom block 54 is connected to an end of a screw mechanism 56, which screw mechanism also passes through the top block 44 and terminates in a handle 60.

The screw mechanism 56 is mounted to be freely rotatable relative to the bottom block 54, but substantially immovable longitudinally relative thereto. The screw mechanism 56 passes through a threaded section of the top block 44, so that rotation of the screw mechanism causes the top block 44 to move relative to the screw mechanism 56 in the longitudinal direction of the screw mechanism.

Accordingly, as the screw mechanism 56 is rotated by way of the handle 60, the bottom block 54 is caused to move towards or away from the top block 44, depending upon the direction of rotation of the handle 60. It will be understood that as the bottom block 54 moves away from the top block 44 from the position shown in solid outline in Fig. l, the links 52, and consequently the arms 46, pivot towards a more vertical orientation such as that shown schematically in dotted outline in Fig.l. Since in use the wheels 22 will engage the ground, such relative movement of the arms 46 will act to lift the top block 44 away from the ground.

As indicated, the top block 44 is connected to the lifting bars 14, and so lifting of the top block 44 causes lifting of the lifting bars 14 and consequently lifting ofthe manhole cover connected thereto.

It will be understood that if only a single lifting means 12 is used to lift a manhole cover, the lifting means 12 will tilt as the top block 44 is lifted upwards, the manhole cover pivoting about its opposed edge which is not lifted. It is not usually desired to lift only one side of the manhole cover, and so as above indicated two lifting means 12 are used together as a lifting device to lift the manhole cover 20. A second lifting means 12 will be connected to another key slot of the manhole cover (preferably a key slot at the opposite corner or edge of the manhole cover so that the centre of gravity of the manhole cover lies between the two key slots used) and both lifting means operated together so that the manhole cover remains substantially horizontal as it is lifted, and neither of the lifting means is caused to tilt significantly.

It will be understood, however, that a single lifting means 12 could be used with the small class of manhole covers which are hinged and therefore must be pivoted into the open posltlon.

Notwithstanding the desirability of lifting the manhole cover in a substantially horizontal orientation, it may be desirable initially to lift only one side of the manhole cover so as to break the seal created between the manhole cover and its surround. Such a seal may arise because of dirt and debris entering into the gap between the manhole cover and its surround, and can require a significant force in addition to the weight of the manhole cover. It will be understood that lifting one side of the manhole cover first, perhaps only by a few millimetres, can cause the seal to be broken gradually, so reducing the maximum force required. The present invention can accommodate that by allowing rotation of the screw mechanism 56 of one of the lifting means 12 before the other.

When two lifting means 12 are used and the manhole cover is maintained substantially flat, rotation of the screw mechanisms 56 upon the respective lifting means 12 will cause the top block(s) 44 to be lifted rel$ive to the wheels 22. As the manhole cover 20 is maintained substantially horizontal the lifting arms 14 will also be maintained substantially horizontal, and the leg(s) 36, the lifting bars 14 and the top block(s) 44 will be lifted together with the manhole cover.

It will therefore be understood that the manhole cover itself forms a part of the lifting device and it is not necessary for the two lifting means 12 to be connected together. The two lifting means 12 are effectively connected together by way of the manhole cover and the engagement thereof by their respective leg means 36. Alternatively stated, each of the lifting means 12 provides an unbalanced force at one side of the manhole cover, which forces would separately result in pivoting movement of the manhole cover. The structural rigidity of the manhole cover, and the engagement thereof by each of the lifting means, ensures that the pivoting forces of each lifting means oppose each other and substantially cancel out so that (substantially) only a lifting force remains, so that the manhole cover acts to balance the applied forces.

Once the manhole cover 20 has been lifted above ground level the operator can push the lifting device 10 and the manhole cover 20 across the ground by virtue of the wheels 22, until the manhole cover is moved clear of the shaft it was covering.

Replacing the manhole cover 20 requires a reversal of the above steps.

As above indicated, it is not necessary that the two lifting means 12 used as a lifting device 10 (Fig.5) be interconnected in use other than by the manhole cover 20. However, in some applications it may be desirable to interconnect the lifting means themselves, and the leg means 36 provides for such interconnection. As better shown in Fig.4, each leg means 36 carries a bracket 62 and a bracket 64, the brackets 62, 64 being adapted to embrace a part of the leg of another lifting means when the legs of two lifting means 12 are placed together. It will be understood that the brackets 62, 64 when used provide structural integrity for the lifting device in use.

It will be noted from Fig.2 that a part of the bracket 64 is flush with the underside of the foot 38 and so provides an extension of the foot. The foot 38 and the bracket 64 together provide a large area of contact with the manhole cover 20 and make the lifting means 12

very stable in use.

It will also be understood that the lifting means 12 with a leg means 36 is not handed, so that the two lifting means used as a lifting device can be identical.

Figs. 5-7 show the lifting device in use with different manhole covers. In Fig.5 the manhole cover 20a is relativy small and the legs 36 are interconnected In Fig.6 the manhole cover 20b is relatively large and the lifting means 12 are necessarily spaced apart. Also shown in Figs. 5 and 6 is a respective obstruction 66 which limits the positioning of the lifting means 12. Such obstructions 66 could prevent a prior art lifting device being used for the manhole covers 20a and 20b, but it will be understood that with the present invention the lifting means 12 can be positioned as shown so as to avoid the respective obstruction. It will be understood that without the obstructions 66 the lifting means 12 could be positioned relative to the manhole covers at any desired angle.

In Fig.7, the manhole cover 20c is of a particular form comprising a substantially square shape, but formed as two separate substantially triangular manhole covers 20d and 20e.

Since each manhole cover 20d and 20e is separate lifting them both together requires them to be interconnected in some way. The present invention achieves this by the first lifting means 12a having its key 16 connected to a key slot of the manhole cover 20d and its leg means 36 engaging the other manhole cover 20e, and vice versa for the second lifting means 12b. When the lifting means 12a and 12b are operated together the manhole covers 20d and 20e will be lifted together as would a complete (square) manhole cover 20c.

The lifting device can similarly be used with manhole covers of any shape, since all non- hinged manhole covers will have at least two key slots to permit the lifting thereof.

It will be understood that different manhole covers can require different key profiles, and to accommodate different profiles the engineer can have available different keys, it being necessary only to change the keys for the different manhole covers, the remainder of the lifting device being unchanged.

It will be understood from Figs. 5-7 that the wheels 22 of the respective lifting means 12 should be substantially aligned. This allows for the lifted manhole cover to be rolled away from the shaft relatively easily. It will, however, be understood that alignment of the wheels 22 is not required, and misalignment will not prevent removal of the lifted manhole cover but only make such removal more difficult as one or both sets of wheels 22 are required to slide across the ground rather than roll The preferred embodiment of the present invention utilises a screw mechanism 56 in which the screw mechanism is substantially vertically oriented in use. This has the advantage that the handle 60 is readily accessible and the operator can rotate the handle 60 of each lifting means 12 together. Other arrangements utilising a screw mechanism could clearly be provided, one alternative having the screw mechanism mounted substantially horizontally (for example driving the connections between the links 52 and arms 46 together and apart).

In most arrangements in which a screw mechanism acts upon links in a "scissor" type arrangement such as that shown the mechanical advantage will vary during movement of the screw mechanism as the angle of the links varies. It can if desired be arranged that the screw mechanism provides the greatest mechanical advantage when this is most needed, i. e. during the initial lift of the manhole cover as any seal is broken.

Alternative mechanical arrangements can of course be used, such as hydraulic or pneumatic actuators, or motor-driven arrangements, as required, perhaps dependent upon the size and weight of the manhole covers to be lifted.

In the embodiment shown, the length of the arms 46 and the links 52 define the maximum distance by which the manhole cover can be lifted, and in this embodiment the maximum distance is around 225 mm. If (exceptionally) the manhole cover was more than 225 mm deep then the lifting means could be altered to provide a greater lifting distance.

The lifting means 12 shown in the preferred embodiment is made from steel, though in alternative embodiments aluminium, carbon fibre or composite materials could be used.

The lifting means occupies a relatively small volume and so can be stored relatively easily (it will be noted that the handle 60 is pivoted at 70 to facilitate storage). In preferred embodiments two lifting means 12 can together weigh less than 25 kg and so can safely and easily be carried by one person from a vehicle to the position of use. No on-site assembly is required and the lifting device can be connected to the manhole cover and used very quickly. Furthermore, the device is mechanically very simple and robust and is relatively easy to service, either by the operator or by the manufacturer. Notwithstanding its mechanical simplicity and relative light weight, a lifting device similar to that shown and described has been used to lift a manhole cover weighing over 650 kg, and clearly larger size or scale lifting means could be used with heavier manhole covers if required.

Claims

A lifting device for a manhole cover, the device comprising a pair of lifting means, each lifting means having: a lifting bar or bars, a key locatable upon the lifting bar(s) and engageable with a key slot in the manhole cover, and support means for engaging the ground adjacent to the manhole cover, the lifting device having a lifting mechanism to move the lifting bar(s) relative to the support means, the lifting means being separable from each other but being usable together to lift the manhole cover.
2. A lifting device according to Claim l in which at least one of the lifting means has a foot which in use engages the upper surface of the manhole cover.
3. A lifting device according to Claim 1 or Claim 2 in which the lifting mechanism comprises a mechanical means, preferably a screw mechanism.
4. A lifting device according to Claim 3 in which the lifting mechanism comprises a set of links which can pivot relative to one another.
5. A lifting device according to Claim 4 in which the links provide a "scissor" action.
6. A lifting device according to any one of Claims 1-5 in which the support means comprises a pair of wheels.
7. A lifting device according to any one of Claims 1-6 in which the lifting bar(s) remain spaced away from the manhole cover in use.
8. A lifting device according to Claim 7 having a leg means connected to the lifting bar(s), the length of the leg means determining the spacing between the lifting bar(s) and the manhole cover in use.
9. A lifting device according to Claim 8 in which the leg means carries interconnecting means by which the pair of lifting means may be (temporarily) connected together.
10. A lifting means for a manhole cover, having: a lifting bar or bars, a key locatable upon the lifting bar(s) and being engageable with a key slot in the manhole cover, support means for engaging the ground adjacent to the manhole cover, a lifting mechanism to move the lifting bar(s) relative to the support means, and a foot for engaging the surface of the manhole cover.
11. A lifting device for a manhole cover constructed and arranged substantially as described with reference to the accompanying drawings.