Domed Tops for Fiberglass Packaged Metering Manholes

For installations where a Packaged Metering Manhole will be located away from vehicle and pedestrian traffic, Openchannelflow offers domed fiberglass tops. These tops are lightweight, structurally strong, and provide excellent operator access.

Access

Unlike traditional tops that are supported by rod-and-pin or lift arm supports, Openchannelflow domed tops are supported by stainless steel gas struts. While these struts do cost more than cheaper rod-and-pin designs, they dramatically increase operator safety.

Moving the struts to opposite the ladder allows the operator maximum access to the interior of the manhole. The entire manhole interior is accessible as the top opens to nearly 90º.

fully open domed top on Openchannelflow fiberglass packaged metering manhole

Also, there is no longer the need to maneuver around a support arm or worry about accidentally moving the arm (and inadvertently knocking the lock pin loose, closing the top).

To increase operator safety, the struts have been sized so the domed top “fails open”. This means that an operator can’t become inadvertently trapped inside the manhole and it also serves as a safety reminder for passing crews as the manhole will open unless secured.

Construction

While structurally sound, fiberglass does retain a certain amount of plasticity and can deform under load. To alleviate this, a core material is encapsulated in the domed top. This core material greatly increases the stiffness of the top while adding minimal weight.

Although not designed for traffic applications, tests by Openchannelflow have shown that our domed tops can withstand repeated vehicle overruns without structural damage.

Sizing Considerations

Packaged Metering Manholes with domed tops should be sized so that the top of the manhole barrel is 12-18 inches above the surrounding surface grade. This distance reduces the likelihood of inflow into the manhole. Operator access is easy and natural, with the lip of the manhole provides a convenient handhold to steady the operator as they enter / exit the manhole.

open domed top on an Openchannelflow Packaged Metering Manhole with Parshall flume factory integrated

For sites where water may pond around the manhole opening, the top of the barrel may be raised above the recommended distance, but keep in mind that too tall and the operator will have difficulty entering / exiting the manhole. Overstretching to enter the manhole may make the operator unstable which could result inadvertent injury. For these installations steps, regrading the surround area, or access platforms may be required.

a domed top Packaged Metering Manhole installation where the top is set too high above the surrounding grade for each operator access

Openchannelflow offers domed top for 48, 60, 72, and 92-inch diameter manholes. Mounted with a stainless steel piano hinge at the rear of the cover, replacement tops can also be provided if necessary.

replacement 48-inch domed top