GB2219984A

GB2219984A - A manhole cover lifter

Info

Publication number: GB2219984A
Application number: GB8914175A
Authority: GB
Inventors: Peter David Irish
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-06-21
Filing date: 1989-06-20
Publication date: 1989-12-28
Anticipated expiration: 2009-06-20
Also published as: GB8914175D0; GB2219984B; GB8814691D0

Abstract

A manhole cover lifter comprises a mobile frame (12) and a lifting frame (11), movable attachment means (14, 16) on the lifting frame for engaging manhole covers of different sizes, and a power drive (30) connected between the two frames which enables the lifting frame with the attached manhole cover to be raised relative to the mobile frame, wherein after lifting, the mobile frame allows the cover to be easily moved away to give access to the manhole. A suitable power drive is a hydraulic jack. The mobile frame and power drive are collapsible for ease of storage and transportation. Frame (11) is pivoted at (24) (25) and (27) so that when jack (30) is collapsed, wheels (26) are roughly level with frame (12). <IMAGE>

Description

Manhole Cover Lifter This invention relates to a manhole cover lifter.

Conventionally, manhole covers are lifted manually.

Each manhole has a recessed handle or aperture which enables the cover to be engaged by a tool or hook, at opposite ends. The upward pull required is often very great, since the cover may have become rusted into its frame, or jammed by dirt and stones. A manually applied vertical pull is difficult and in some circumstances can cause back injury. After lifting, the cover must then be moved sideways to allow access to the manhole.

The invention aims to provide means for lifting manhole covers without the danger of injury and by mechanically applied forces preferably employing a mechanical advantage.

Accordingly the invention proposes a manhole cover lifter comprising a mobile frame and a lifting frame, movable attachment means on the lifting frame for engaging manhole covers of different sizes, and a power drive connected between the two frames which enables the lifting frame with the attached manhole cover to be raised relative to the mobile frame. After lifting, the wheels allow the cover to be easily moved away to give access to the manhole.

In a preferred arrangement a linkage between the two frames is arranged to provide a mechanical advantage in application of the power drive to lifting of a manhole cover.

Preferably, the mobile frame has wheels mounted thereon.

Preferably, the mobile frame comprises one or more lifting units, each unit comprising a pair of first and a pair of second elongate members, wherein the first members have a wheel mounted on their first ends and are pivotably mounted on the lifting frame, the second members are pivotably connected to the power drive by their first ends, and the second ends of the first and second members are linked such that mechanical stresses are transmitted through the lifting unit.

Preferably, the mobile frame is collapsible when the lifter is not in use.

Preferably, the power drive comprises a hydraulic jack that is also collapsible.

In order that the invention shall be clearly understood, an exemplary embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the lifter according to the invention in a lowered position; Figure 2 shows the lifter in a raised position; Figure 3 shows a plan view of the lifter illustrated in Figure 2; Figure 4 shows an end view of the lifter shown in figure 2; and Figure 5 shows the lifter collapsed for transport.

Referring to Figures 1 and 2, the lifter is seen to comprise a lower, rectangular, lifting frame 10 and an upper, collapsible frame 11. The rectangular frame 10 is rigid, and has fixed side members 12 rigidly joined by a cross member 13. Across the two ends of the lower frame are two support beams 14 (see Fig.3) which are arranged to be slidable along the side members 12, as indicated by arrows 15. On each support beam 14 are two attachment means 16 in turn slidable in the direction of the arrows 17. Each of the attachment means carries a hooked or otherwise shaped member 18 for engaging a handle or aperture in a manhole cover.

The collapsible upper frame 11 has a single transverse beam 20 which connects four pairs of links 21. Each pair consists of an upper link 22 and a lower link 23, with an elbow joint 24 between them. The upper links pivot on a common axis 25 while the lower end of each lower link 23 carries a wheel 26. In addition, each lower link is pivotted on the side members 12 of the lifting frame at pivot points 27. Between the cross member 13 and the transverse beam 20, and controlling the distance between them, is a hydraulic ram 30.

The operation of the device will now be described. The lifter is manoeuvred into position above the manhole cover with its upper frame 11 in the position shown in Fig.l, with the hydraulic ram 30 retracted. The support beams 14 and the attachment means 16 at each end of the lifter are manoeuvred to bring two or four attachment means 16 into position above handles or apertures of a manhole cover to be lifted. The hooks 18 are engaged with the manhole cover and the hydraulic ram 30 is then operated, either manually employing a mechanical advantage as is usual, or by pressure from a compressor.

The upward force on the cross member 20 tends to straighten each pair of links 21, at the same time swinging each of the lower links 23 about their pivot points 27. Since the wheels 26 are resting on the ground 28, such a movement tends simultaneously to cause the lower rectangular frame 10 to rise. This has the affect of exerting an upward pull on the manhole cover which is thus raised out of its frame at ground level.

The ram 30 can only be extended to a length sufficient to bring the upper and lower links 22,23 into a straight line, at which the whole of the lifter, including the wheeled frame 11 and the lifting frame 10, reach a stiff, rigid state. This also produces a sufficient rise in the level of the lifting frame 10 to lift the manhole cover clear of the ground. In that state, the lifter with the cover can be wheeled out of the way.

Contraction of the ram 30 causes lowering of the manhole cover.

In order to make the lifter more compact for the purpose of transport to and from a working site, the upper frame is arranged to be collapsible, as shown in Fig.5. The corresponding upper links 22 at opposite sides of the lifter are arranged to be detachable at the axis 25 by release of spring bolts or catches, so that those upper and lower links 22,23 can be positioned almost horizontal. The lower link 23 rests upon a stop member 35, and the upper link 22 in each case is supported by a stud 36 which engages on the topof the lower frame. The hydraulic jack 30 is pivotted at 37 can be swung over and extended until it too also lies almost horizontal.

This ensures that the lifter is considerably reduced in overall height for transport.

When the hydraulic jack is actuated by application of fluid pressure from an external compressor this can produce very large forces which might be so great as to bend the frame if the manhole cover is firmly embedded.

Thus, a relief valve is preferably included in the jack to limit the force it can apply.

It will be clear that other arrangements of an upper and lower frame may be adopted in order to provide the advantages of the arrangement just described. The mechanical linkages are preferably arranged to provide a substantial mechanical advantage so as to reduce the manual forces which need to be applied. The structure is mechanically simple and will contribute considerably to work place safety.

Claims

1. A manhole cover lifter comprising a mobile frame and a lifting frame, movable attachment means on the lifting frame for engaging manhole covers of different sizes, and a power drive connected between the two frames which enables the lifting frame with the attached manhole cover to be raised relative to the mobile frame, wherein after lifting, the mobile frame allows the cover to be moved away to give access to the manhole.

2. A lifter according to claim 1, wherein a linkage between the two frames is arranged to provide a mechanical advantage in application of the power drive to lifting of a manhole cover.

3. A lifter according to claims 1 or 2, wherein the mobile frame has wheels mounted thereon.

4. A lifter according to any preceding claim, wherein the mobile frame comprises one or more lifting units, each unit comprising a pair of first and a pair of second elongate members, wherein the first members have a wheel mounted on their first ends and are pivotably mounted on the lifting frame, the second members are pivotably connected to the power drive by their first ends, and the second ends of the first and second members are linked such that mechanical stresses are transmitted through the lifting unit.

5. A lifter according to any preceding claim, wherein the mobile frame is collapsible when the lifter is not in use.

6. A lifter according to any preceding claim, wherein the power drive comprises a hydraulic jack.

7. A lifter according to claim 6, wherein the hydraulic jack further comprises a relief valve to limit the force the jack can apply.

8. A lifter according to any preceding claim wherein the power drive can be folded adjacent to the lifting frame when the lifter is not in use.

9. A manhole cover lifter substantially as herein described, with reference to the accompanying drawings.