One particular problem associated with lifting manhole covers is the danger associated with gas build-up within the access conduit under certain circumstances. Removal of the manhole cover may cause ignition of the gas, resulting in an explosion. Any personnel who are in close proximity to the access conduit therefore face severe danger and the possibility of extreme injury. Accordingly, there is a need for an apparatus that provides efficient and convenient manhole cover removal and replacement and at the same time keeps personnel safe by allowing such removal and replacement to be performed by personnel from a sufficient distance from the manhole cover and access conduit. In particular, there is a need for an apparatus that may be used to remove and replace rectangular manhole covers.
The invention described herein is intended to addresses the above needs. In particular, it is an objective of the invention to provide an apparatus that facilitates the efficient and convenient removal and replacement of rectangular manhole covers. Another objective of the invention is to permit personnel to safely perform such removal and replacement from a sufficient distance from the rectangular manhole cover and the access conduit.
To achieve these and other objectives, the invention provides a hydraulic lifting apparatus that permits safe and convenient removal and replacement of a rectangular manhole cover. An embodiment of the invention provides a lifting member operably connected to a hydraulic actuation device and a plurality of lifting hooks. The hydraulic lifting device may be configured to be lifted by appropriate rigging equipment, such as a crane, and the hydraulic actuation device may be activated by personnel from a location that is not in close proximity to the rectangular manhole cover and access conduit. In operation, one embodiment of the invention provides for the activation of the hydraulic actuation device that causes the plurality of lifting hooks to securely interface with lifting blocks that are provided on the rectangular manhole cover. After the lifting hooks are securely interfaced with the lifting blocks, the hydraulic lifting apparatus and the rectangular manhole cover may be lifted by an appropriate rigging structure. When the rectangular manhole cover is replaced, the hydraulic actuation device may be de-activated to allow release of the lifting hooks from the lifting blocks of the rectangular manhole cover.
According to an alternate embodiment of the present invention, a lifting apparatus is disclosed for lifting a rectangular manhole cover, which includes an elongated frame having first and second end assemblies each supporting a hook adapted to engage a corresponding lifting block on a rectangular manhole cover. At least one end assembly is movable with respects to the other end assembly to expand a distance between the hooks. An actuator moves the movable end assembly to increase distance between the hooks and force the hooks into engagement with the lifting blocks on an adjacent rectangular manhole cover.