The clear opening of the manhole cover (C1 x D1) should NOT be less than the one of manhole (C2 x D2). Should there be no duty required such as in walkway or heavy duty one to be used for medium duty function, two sides of opposite may be less (C1 < C2) while the other two have to be NOT (D1 ≥ D2) if the manhole covers of correct sizes would not be found. It's not recommended to have the manhole covers with shorter clear opening of all sides installed in any situations.
Our polymer concrete manhole covers, sewer and drain covers, trench covers, gully gratings and grids inlets have been classified into many duty types for different requirement. We convert this Duties Classification into the weight of vehicles (GVM) which allow to be driven over for easily understanding in practice. The clients should consider the heaviest vehicles may access unexpectedly and cause damage when they select the duty for normal situation.
When opening, moving, carrying and shipping the polymer manhole covers, do NOT throw the polymer manhole covers to the ground, avoid striking or crashing with other hard articles, as well as other polymer manhole covers, or the collision between covers and their frames, which may cause minor edge damage especially of the frames.
To open or lift the cover with the steel hooks through the keyholes, especially for heavy duty covers which are heavy while being opened regularly, we strongly recommend using two hooks to lift the cover through two keyholes at the same time, should it be done with one hook through one keyhole, lift one side of the cover just enough for the hands to hold it, then open the cover by hands, thus to avoid the hook damaging the keyhole. Doing carelessly may cause the holes worn out bigger and bigger.Read more
Most of lockholes and keyholes or lifting holes in our manhole covers are pre-closed, to open these holes, you have to break the closed holes with a screw driver from the back side (the closed side) to avoid chipping out the material surrounding the holes, driller is recommended doing so especially the pre-closed layer is thicker.
Incorrect installation may cause serious damage to the polymer manhole covers, sewer and drain covers, trench covers, gully gratings or grids inlets and their frames. For heavy duty manhole covers, especially in busy driveway, the ground base should be constructed strong enough to hold the manhole covers to avoid being pressed down by the vehicles, which may cause damage. The surrounding concrete should be repaired in time before further damage to the manhole covers.
Should the manhole covers be damaged, such as the above mentioned worn out key holes , lifting holes or the chipped out edges, cool tar or "bakkie back" is recommended to apply for the repairment.Read more