Wuzland® and Primus® Manhole Covers

There is nothing special to install our BMC/Polymer concrete manhole covers, sewer and drain covers, trench covers, gully gratings and grids inlets, comparing with the installation of iron cast or other types of manhole covers. However due to LESS FLEXIBILITY OF POLYMER MANHOLE COVERS, the installation has to be done more strictly than the cast iron ones for the manhole covers to work better and last longer:

1. The brick base on the manhole should be made to follow the shape and size of the manhole cover or frame, the clear opening of the manhole cover should not be less than the one of manhole.
2. There should be a 40cm width of concrete to be filled around the manhole cover or frame for support and protection. A 20cm width of concrete may be acceptable when the manhole cover is installed on the cement surface road with reinforced bars (Read below Installation Improvement). A layer of concrete is recommended to fill between the frame and base bricks to hold the manhole covers tightly. In practice the filling width and STRENGTH of the concrete to be made depends upon how busy and heavy the vehicles access to the covers.
3. The surface of the manhole cover must be at the same level as the surrounding concrete should the manhole cover to be installed be expected for the access of the vehicles.
4. While installing on the asphalt road, ensure that the construction vehicles will not be driven over the basement of the manhole cover.
5. For better appearance, the installed manhole cover can be covered by something such as a sheet of plastics during the road construction work.
6. After the cement surface road work is completed, open the manhole cover and clean it, and ensure the cover would not be stuck. Wash and clean the cover surface as well.
7. Keep the manhole cover not to be accessed for 10 days by sign and blockage device before open the access to the public.
8. The incorrect installation described below should be avoided.

The polymer manhole covers have to be installed properly, especially in busy walkway and driveway. Unfortunately we do not provide the installation services for our manhole covers sold.

The above image shows five kinds of incorrect installation of polymer manhole covers. There may not be any problems if no vehicles access to the places, should the vehicles be driven over the manhole covers installed in such ways, the manhole covers would be damaged and not last longer.

Polymer or BMC manhole covers are not as flexible as cast iron ones, without the support and protection of the surrounding concrete the edges of the cover and frame may be damage if they expose to high "point force", when the wheels "hit" or crash them. When the wheels of vehicle start to move, stop suddenly, or "jump" onto the covers as crash, the wheels apply higher point force to the cover or frame than they roll over as usual. Should such a crash force be over the load capacity of the manhole cover, or the force limitation it can stand, the damage may be caused.

1. Incorrect 1: Clear opening of the manhole cover is less than the one of manhole, this makes the part of frame which holds the cover hanging over the manhole, and without the support of the base, the frame may be damaged while the vehicles passing over.
2. Incorrect 2 & 5 : The surrounding concrete is higher than the surface of the manhole covers, the wheels will "jump" and crash onto the cover and may cause damage if the duty of the manhole cover selected is not high enough to resist such "crash", especially when the vehicle is speeding up.
3. Incorrect 3 & 4: The manhole cover is higher than the surrounding concrete, when the vehicle is passing over, the wheel will act as digging then jumping, and may damage the frame and cover. It may happen for the wheel to crash directly to the edges of cover and frame while the vehicle is speeding up.

Grid inlets are usually placed together for the long open trench. The load capability of each grid inlet decreases because two sides of the inlet do not get the support from the ground. Incorrect installation of the grid inlets may cause its load capacity to be even less, to our recommended vehicle GVM figure.

The orientation of the grids is important when they are placed on the trench, wrong direction may cause damage as shown in the above image:

1. Main reinforced steel bars are thicker than minor reinforced steel bars, so the main steel bars should be placed in the way to be the main support for the load.
2. In the steel framework, the main steel bars were weirded on the top of minor steel bars (in the image the inlet was placed up side down), the force from the vehicle wheel was at last transferred onto the minor bars. Certainly the minor steel bars may not placed in the way to be main support for the force.
3. In the case shown in the image, there are 3 minor steel bars of the inlet in verticle direction against 11 major steel bars. More steel bars apparently hold more weight.

Therefore all the above-mentioned three points indicates the major steel bars should be placed in the way to cross over the trench. The concrete bars may be installed under the grid inlets where they join with each other in order to have their full load capability. There is no orientation problem for single grid inlet.

In the above image, the left picture indicates the distribution of force when the wheel rolls over the manhole cover. We find 30% of the force go sidewards, this may explain why the concrete surrounding the manhole covers usually start to be broken earlier, this make the manhole covers not be protected and easily be damaged as shown in the right pictures of the above image. The duty of the concrete mix to be made should be well considered.

A steel framework is recommended to be made and placed along with the manhole cover to strengthen the surrounding concrete, especially for the manhole covers installed in heavy traffic areas such as filling stations. (Shown in the middle pictures of the above image)

There is no maintenance required for the polymer manhole cover itself but the surrounding concrete and the base holding the frame which should be repaired in time if damaged or loosen, before the manhole cover would be broken without its protection and support.