GB2328198A - Lifting device - Google Patents

Abstract

A device for lifting a manhole cover (5) comprises: a bar (1); a castor wheel (4) provided at each end of the bar (1) and offset from its axis; an elongate handle (2) connected to the bar (1) for rotating it about its axis and, a connector (3 Fig 3) for connecting to the bar (1) to the manhole cover (5) to be lifted. Preferably the castor wheels (4) are provided on the ends of the legs (7) and two handles (2) are also provided. As the device is supported by a wheel (4) at each end of the bar, the device straddles the manhole cover (5). By applying a force to the elongate handle(s)(2), the bar (1) rotates and rotates the legs (7). The vertical component of this rotation of the legs (7) is applied to the manhole cover (5) through the connector (3) causing it to be lifted. Preferably, the bar is telescopic and formed off freely rotatable tubes. Preferably the handles are telescopic and pivoted to form a compact storage arrangement. Preferably the connectors (3, Fig 3) are T-pieces with twin hook portions - either of which can be connected to the bar depending on the advantage required.

Description

LIFTING DEVICE The present invention relates to a lifting device, and in particular to a device suitable for lifting manhole covers.

Typically a manhole includes a frame around its opening, the frame being set into the ground with concrete.

A manhole cover is provided within the frame to close the hole. Manhole covers come in a variety of shapes and sizes, and may be of a weight such that it is difficult for a person manually to lift the cover from the frame. A further problem is that when the manhole cover has not been removed for a long time, the cover becomes set within the frame and a very high initial force is required to release the manhole cover.

A device for removing manhole covers is known which comprises a sturdy heavyweight frame which is positioned adjacent one end of the manhole and has supports extending along two opposed sides of the manhole cover, and which includes a plate arranged to be bolted to the manhole cover. The plate is connected to the main frame by a hydraulic lifter, and this is actuated to raise the manhole cover. Such manhole lifters have not achieved great commercial success for a number of reasons. Firstly the equipment is expensive requiring heavy components and a hydraulic lifting mechanism. Further, due to the heavyweight nature of the lifter it is cumbersome to transport, and its weight may be almost as high as the manhole cover to be removed. With such devices, it is difficult to adjust for different size manholes. The device includes wheels to allow the lifter to be moved away from the manhole with the cover after the cover has been removed. This removal is difficult due to the weight of the lifter.

A manual lifter for manhole covers is also known.

This lifter includes a single wheel provided on a stem, to the other end of which is provided an elongate handle extending in one direction and a hook extending in the opposite direction. In use, a bar is bolted across the diagonal of the manhole cover, and one end of this bar is attached to the hook of the lifter. By applying downward pressure on the handles, the lifter pivots around the single wheel causing the hook and the end of the bar attached to the hook to be raised, thereby releasing the manhole cover. Such a lifter gives a small mechanical advantage of between 2 to 1 and 3 to 1 thereby giving the user some assistance in the lifting of the manhole cover.

Nevertheless, the system is unstable since it rests on a single wheel, and does not allow easy removal of the manhole cover from over the opening. Because the cover is lifted from a corner, the user must balance the entire weight of the cover.

According to the present invention, a device for lifting a manhole cover comprises: a bar; a castor wheel provided at each end of the bar and offset from its axis; an elongate handle connected to the bar for rotating its axis; and, a connector for connecting the bar to the manhole cover to be lifted.

With a device according to the present invention, the manhole cover to be lifted is connected to a bar supported on a pair of castor wheels. As the device is supported by a wheel at each end of the bar, the device can straddle the manhole cover allowing the manhole cover to be lifted at its centre of gravity. This means that, when lifted, the manhole cover is balanced. This compares to the prior art manual lifting device in which the device must be provided at one side or corner of the manhole cover, and this side or corner must be lifted so the user must balance the entire weight of the cover. With the present invention, by applying a force to the elongate handle, the bar pivots about its axis urging the wheels to move forwards generating a vertical component of movement of the bar is applied to the manhole cover through the connector causing the manhole cover to be lifted. During this lifting, the wheels move forwards and into line with the connection point between the device and the manhole cover, thereby balancing the load of the manhole cover. Once lifted clear of the frame, the manhole cover can be moved away from the manhole using the wheels of the device.

It is preferred that the bar is extendable, and this may be achieved by forming the bar from two coaxial tubes which are telescopic and advantageously freely rotatable with respect to each other. In this way, it is possible to adjust the length of the bar so that each of the wheels rests directly on the frame of the manhole cover or on the concrete bedding the frame to the ground. In this way, when the force is applied to the handles of the device to rotate the main bar around its axis, the lifting force on the manhole cover opposes the downward force through the wheels onto the frame, and therefore ensures that the manhole cover is separated from the frame. This is important since there is otherwise the risk, especially where the manhole cover has become set within the frame, that the entire frame is lifted from the ground if, as in the prior art, the downward force is applied not directly to the frame but to the ground surrounding the frame.

It is preferred that the lifter includes two connectors for connecting the manhole cover to the bar. In this case the cover can be supported at two points across its width, thereby ensuring the cover is balanced as it is lifted.

It is also preferred that the device includes two elongate handles one extending from each end of the bar.

This assists a two handed operation by the user, and is also particularly advantageous where the device includes two connectors, and where opposed ends of the main bar are rotatable. This allows the handles to be operated independently, and therefore allows the user to compensate for any unevenness in the surface surrounding the manhole cover, for any non-uniform distribution of the weight on the manhole cover by applying a greater force to one of the handles than to the other, or to apply a greater force to one side of the cover than the other to release that side.

It is preferred that the or each handle is telescopic.

Preferably the handle is pivotally connected to the main bar about a pivot perpendicular to the longitudinal axis of the main bar to allow the handles to be folded generally parallel to the main bar to reduce the overall size of the device for transportation. Especially where the main bar is rotatable, the handles can be folded to overlie each other by rotation of the main bar.

It is preferred that the or each connector has at least two different connection points, each for connecting the bar to the manhole cover with a predetermined spacing.

In this way, the length of the connection between the bar and the manhole cover can be varied. The length of the interconnection in relation to the spacing of the wheels from the main bar determines the mechanical advantage and maximum lift height obtainable by the device. This is advantageous as it allows in a first position a high mechanical advantage, advantageously of 30 to 1 with a relatively small lift height which allows the initial release of a set manhole cover, and in a second position a lower mechanical advantage, typically 10 to 1 but with a greater lift height sufficient to lift the manhole cover from the frame to allow its removal. The connecting points on the connector may be in the form of hooks which clip over a bar, which are rotatable with respect to the bar thereby ensuring that the connectors always hang below the bar.

The connection between the connectors and the manhole covers are preferably formed by a T-connector which connects with a conventional key hole slot in the manhole cover.

The elongate handles and bar of the device are advantageously of a light weight metal alloy. Such a material gives the necessary strength of the device, whilst ensuring the device remains portable. The wheels are preferably of nylon, and preferably have a diameter of at least 100mm thereby spreading the force applied through the lifter.

A preferred example of the present invention will be described in respect to the accompanying drawings, in which; Figure 1 shows a side view of the device in accordance with the present invention when lifting a manhole cover; Figure 2 shows a plan view of the device according to claim 1; Figure 3 shows a side view of the connector; and, Figures 4 and 5 show the variation of the vertical component of force depending on the length of the connector.

As shown in Figures 1 and 2, the device includes a main bar 1 formed from two coaxial tubes la, ib which are rotatable and slidable with respect to each other. The tubes la, ib are steel or a lightweight alloy tubes, and can extend to give a maximum length of about 1200mm, or be shortened to a minimum length of about 700mm, depending on the size of the manhole cover. A leg 7 is connected to each end of the main bar 1, and a castor 4 is mounted on each leg 7. The castors 4 are of nylon, and the overall length of the castor 4 and the leg 7 is 250mm. A handle 2 is connected to each end of the main bar 1 by a plate and a pivotal connection. A stop pin on the plate limits the movement of the handles. Each of the handles 2 are formed from two alloy coaxial elongate members 2a, 2b which are slidable with respect to each other allowing the telescopic extension of the handles 2. When not in use, the handles 2 can be shortened by telescoping the in free ends 2b into the main section 2a, and may be pivoted to lie generally parallel to the main bar 1. By rotation of the parts la, lb of the main bar 1 with respect to each other, the arms 2 can lie side by side. This gives a small overall package size.

In use, the main bar 1 is extended so that the wheels 4 rest on or close to the frame 6 of the manhole cover.

Two connectors 3 are hooked onto the main bar 1 and are connected to the manhole cover 5. Manhole covers 5 typically include key hole slots, and accordingly the connector 3 provided is with a T-piece 8 at one end which slots into the key hole slot. The connectors 3 also include a plate 9 which is biased by a spring 10 towards the T-piece 8. This bias forces the plate onto the upper surface of the manhole cover 5 thereby securing the connector to the manhole cover. The other end of the connector 3 includes two hook portion 11,12 either of which are able to hook onto the main bar 1 of the lifting device.

By applying a force to the handles 2 of the device, the main bar 1 is rotated around the hook portions 11,12 causing a forwards movement of the wheels 4 to generate a vertical lifting component as the legs 7 move into an upright position. This vertical lifting component is applied through the connectors 3 to the manhole cover 5, thereby lifting the manhole covers. As the manhole cover 5 is lifted, the wheels 4 move towards a position vertically below the main bar 1 and in line with the connection to the manhole cover. When the manhole cover 5 is lifted clear of the frame 6. The device is then pulled on the wheels 4 removing the manhole cover 5 from the opening of the frame 6.

The mechanical advantage given by the device depends on the length of the handles 2 on the length of the connection between the main bar 1 and the manhole cover 5 and the length of the legs 7. Figures 4 and 5 show the amount of movement of the bar for a given amount of rotation depending on the length of the connection. As shown in Figure 4, where the main bar 1 is connected to the manhole cover 5 by a short connection 3, the leg 7 lies at a shallow angle to the cover 5 with the wheel 4 well behind the connection point. In this case, any pivoting of the main bar 1 around the wheel 4 gives a large vertical movement Ahl. However, as shown in Figure 5, with a longer connection 3 between the main bar 1 and the manhole cover 5, the leg 7 lies at a much steeper angle, with the wheel 4 much closer to the connection point. In this case, pivoting the main bar 1 around the wheel 4 by the same angle as with the short connection, namely for the same movement of the handles 2, gives a much smaller vertical movement ash2. Accordingly, the mechanical advantage, which is dependent on the amount of movement, is significantly greater for a longer connection, applying a greater lifting force to the manhole cover. For a connection of 225mm, the mechanical advantage is typically around 30:1 compared to only 10:1 for a 100mm connection.

The connector 3 includes two hook portions 11,12, either of which can be hooked over the main bar 1 to connect the bar 1 to the manhole cover 5 and change the mechanical advantage of the device.

In use, the connector 3 is first connected to the manhole cover 5 by the key hole slots and T-piece 8. The plate 9 is biased onto the top of the manhole cover 5 retaining the connectors in place. The main bar 1 of the lifter is adjusted so that the wheels lie immediately beside the manhole cover 5 and the device is positioned to hook the main bar 1 under the appropriate hook 11 or 12 of the connector 3. A downward force is applied to the handles 2 to causing the manhole cover 5 to be lifted from the frame 6. When the manhole cover 5 is clear of the frame 6 the device including the manhole cover hanging on the main bar 1 can be wheeled away using the wheels 4.

Claims (12)

1. A device for lifting a manhole cover comprising a bar; a castor wheel provided at each end of the bar and offset from its axis; an elongate handle connected to the bar for rotating it about its axis; and, a connector for connecting the bar to the manhole cover to be lifted.

2. A device according to claim 1, in which the bar is extendable.

3. A device according to claim 2, in which the bar is formed from two coaxial tubes which are telescopic and freely rotatable with respect to one another.

4. A device according to any one of the preceding claims, which includes two connectors for connecting the manhole cover to the bar.

5. A device according to any one of the preceding claims, in which the or each connector has at least two different points, for connecting the main bar to the manhole cover with a predetermined and different spacing to enable the length of the connection between the main bar and the manhole cover to be varied.

6. A device according to claim 5, in which the connecting points on the connector in the form of hooks which clip over the bar and, which are rotatable with respect to the bar thereby ensuring that the connectors always hang below the bar.

7. A device according to any one of the preceding claims, in which the connection between the connectors and the manhole covers are formed by a T-connector which connects with a conventional key hole slot in the manhole cover.

8. A device according to any one of the preceding claims, in which the device includes two elongate handles one extending from each end of the bar.

9. A device according to any one of the preceding claims, in which the or each handle is telescopic.

10. A device according to any one of the preceding claims, in which the or each handle is pivotally connected to the bar about a pivot perpendicular to the longitudinal axis of the main bar to allow the handles to be folded generally parallel to the bar to reduce the overall size of the device for transportation.

11. A device according to any one of the preceding claims, in which the elongate handles and the bar of the device are made of a light weight metal alloy.

12. A device substantially as described with reference to the accompanying drawings.