Skip to main content

Openchannelflow fiberglass Packaged Metering Manholes (PMMs) solve the difficult problem of how to measure piped flows below grade.  Starting with our industry leading fiberglass manhole tube, Openchannelflow integrates a flow device, cover, base, and access ladder.  

Openchannelflow - dig it- drop it - done - fiberglass manhole slogan

The result is a single-piece, watertight, and corrosion resistant structure from which operators can accurately (and safely) measure and sample flows.


Openchannelflow Packaged Metering Manholes can be manufactured with a variety of different flow devices to measure both open and closed pipe flows.  

Strength Built In

At the core of each Openchannelflow Packaged Metering 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.

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


A variety of top styles are available with Openchannelflow Packaged Metering Manholes, including:

Openchannelflow Packaged Metering Manholes are available in diameters from 48 to 96-inches [1.22 to 2.44 m] and in depths up to 35-feet [10.7 m].

packaged metering manhole components

  • Cover 

  • OSHA-complaint fiberglass ladder

  • Thru-wall coupling

  • Integral base / mounting flange

  • Flow device (flume, weir, etc.)

  • Inlet / outlet piping

As always, Openchannelflow has developed series of accessories for our Packaged Metering Manholes, including:

More About Packaged Metering Manholes

Related Articles