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fiberglass domed top weir metering manholes measuring dam seepageThe Domed Top style is the most popular type of manhole cover offered by Openchannelflow for our fiberglass manholes.

Domed Top manholes offer great access to the manhole interior and are extremely easy to enter / exit.

Suitable Locations

Extending above the surrounding surface grade, Domed Top manholes are only suitable for grassy, non-traffic installations. If pedestrian traffic is anticipated, then an Aluminum Top manhole should be used.  In traffic areas (roads, parking lots, loading dock areas) a H-20 Traffic Reducer manhole should be used.

If a Domed Top manhole is going to be installed near an area frequented by vehicular traffic, bollards or other protection may be needed to protect the manhole.

Sizing Domed Top Manholes

Domed Top manholes should be sized so that it's 12 to 18-inches [30.48 to 45.72 cm] above the surrounding surface grade.  Operator access is easy and natural, with the lip of the manhole providing a convenient handhold to steady the operator as they enter / exit.

By extending the top above grade, the Domed Top manhole:

  • Easiest to enter / exit
  • Keeps inflow out of the manhole
  • Keeps the top from being damaged by ground crews
  • Allows the pad lock staple to be accessed

Should a manhole be incorrectly sized and the cover be at or below grade, Openchannelflow offers manhole extensions to help bring the top back up to its desired height.

Repair and Replacement

Fiberglass standoff for securing the base of a stainless steel gas strut on a Domed Top manhole manufactured by OpenchannelflowA Domed Top is secured to the manhole barrel with a stainless steel piano hinge and gas strut.  The is secured with quick-release clips should the top ever need to opened further than normal or replaced.

At the manhole barrel the base of the strut is mounted to a custom-built fiberglass standoff top optimize the action of the strut.

Replacement of the Domed Top is simple:

  • Unclip the gas strut from the top
  • Unbolt the Top from the heavy duty stainless steel hinge securing it to the manhole barrel
  • Remove the damaged Top
  • Reverse the process with the new Top

Fail Safe Design

Openchannelflow has carefully sized the gas strut(s) with our Domed Tops. The strut(s) have been sized so that they have sufficient lifting force to allow the manhole to open completely unless secured by a padlock.

The result is a Top that will always remain open unless the operator has secured it.  This "fail open" design means that an operator can't be accidentally trapped in a manhole by a top that inadvertently closed.

Top Strength

While not intended for use in vehicular traffic applications, the Domed Top has proven to be quite strong and resistant to damage and has been tested and survived repeated vehicle overruns without damage.