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For a Flume or Weir to work correctly, the flow must be sub-critical and tranquil.  Many times, however, site conditions don’t allow the development of this type of flow.  For those occasions Openchannelflow has developed fiberglass Energy Absorbing Manholes.

Openchannelflow - fiberglass manhole sloganFiberglass Energy Absorbing Manholes are a way on slowing the velocity of water through a pipe system in a way that's cost effective and which requires little in the way of line downtime.  

Energy Absorbing Manholes can be placed directly upstream of Packaged Metering Manholes.  The flow is slowed and conditioned in the Energy Absorbing Manhole and then smoothly flows into the Packaged Metering Manhole to be measured.  

Energy Absorbing Manholes eliminate the need for costly line excavations, replacement, or resloping.  Installation can also be concurrently with a Packaged Metering Manhole – reducing labor and machinery costs.

Strength Built In

At the core of each Openchannelflow Energy Absorbing Manhole is our fiberglass manhole tube.  While manhole configurations may differ, all Openchannelflow manhole tubes are designed to meet or exceed both ASTM D3753 and AASHTO H-20 standards.  The interior of these tubes is smooth and corrosion resistant.  The light tan coloration of the tube helps to maximize visibility inside the manhole.

To the barrel that we add a cover, base, mounting flange, and, most importantly, the energy absorbing structure.

ASTM D3753 Compliance

Unlike competing Flume Metering Manholes which claim to meet ASTM D3753, the interiors of Openchannelflow Energy Absorbing Manholes are pigment / gel coat free – allowing for visual inspection and quality control of the tube during and after production and meeting D3753.


While Energy Absorbing Manholes aren't usually as customized as our other manhole types, there are a variety of top styles are available:

Energy Absorber manholes are available in sizes from 48 to 96-inches [1.22 to 2.44 m] in diameter and in depths up to 35-feet [10.7 m].

More About Energy Absorbing Manholes

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