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Case Study

Dislodged Manhole Cover

Relieving Gas Pressure with an Innovative Design 

When the city of Fort Wayne, Indiana, discovered a manhole cover that was dislodged due to gas pressure, NEI delivered the solution.

Cross section view of retrofit vent
Project Description

Gas pressure in a Fort Wayne, Indiana, sanitary sewer dislodged a manhole cover. The dislodged cover created a hazard to both pedestrian and vehicular traffic. Bolting the manhole cover to the frame was not an option as it would either damage the underground infrastructure or relocate the issue to another manhole. A vented cover with open holes was not an option, as limiting infiltration into the system was a priority. The City of Fort Wayne contacted Neenah Foundry for an economical solution. 

Cast iron sanitary manhole cover
Installed 1772 manhole cover with new venting (courtesy, City of Fort Wayne, IN)
Project Actions

Neenah Foundry engineers worked with the City of Fort Wayne to design a modified manhole cover that could be retrofitted into the existing frame. 

Neenah recommended an R-1772 manhole cover drilled with eight holes and fitted with elevator bolts and angle washers. As positive pressure built up, the elevator bolts would rise to disperse the pressure and prevent the manhole cover from being dislodged. Additionally, an angle washer and lock nut allowed venting of the gas pressure, preventing the elevator bolt from being dislodged.

  • The manhole cover was installed and consistently performs as expected
  • Retrofitting the manhole cover allowed for easy and fast replacement
  • The need for costly construction or system modifications was reduced.
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