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For operators who use them, Fiberglass Packaged Metering Manholes are a great solution to the problem of measuring piped flows below grad. They provide a safe, convenient place in which accurate flow measurement can take place.

Concrete shoulder poured around a 6-inch Parshall flume in a Fiberglass Packaged Metering Manhole


Factory integration eliminates the problems caused by incorrect installation.  Most plant personnel are responsible for many area of a plant – not just the flow metering portion.  As a result, the operators using a flume may only have a cursory knowledge of their operation – and that’s fine!  Factory integration allows operators to focus on their flow data…and not how the data was collected!


With tens of thousands of standard and flow monitoring installations throughout North America, fiberglass manholes have demonstrated extremely long service lives.  Installations going as far back as the 1960’s are still going strong – almost 50 years since they were originally installed! 

Reduced Inflow

The unique construction of fiberglass packaged metering manholes make the units watertight and not subject to inflow in the same way that concrete manholes are.  The monolithic nature of the manhole means that there are no seams to leak and the available watertight tops mean that water can’t enter through the top of the manhole. 

While a certain amount of I&I is inevitable in a collection system, packaged metering manholes are not contributing factors to it.  For operators this means fewer demands on their collection and treatment infrastructure. 


As a single-piece, monolithic structure, packaged metering manholes are watertight and not subject to the corrosion and eventual leaks that concrete manholes are subject to. 

This can be of particular importance when monitoring manholes need to be place near creeks or streams or where ground water is high.  An unintentional leak due to corrosion into these bodies of water can contaminate drinking water supplies and damage aquatic life. 

By isolating the wastewater being metered, packaged metering manholes serve as a long-term means of protecting the environment and reducing risk / liability for the industry or municipality.


Over time, the cost of concrete manholes increases as there is a constant (and ever growing) need for regular inspection, maintenance, and rehabilitation to keep a concrete manhole in good repair. 

The cost of fiberglass manholes, on the other hand, decreases over time.  The manholes do not corrode; there is no need for rehabilitation or maintenance; and no infiltration.


Fiberglass packaged metering manholes provide a superior working environment for operators and are highly customizable - maximizing the usability of the installation.  Customization included a variety of manhole diameters, top styles, and accessories.  

Flow metering manholes are entered much more frequently than ordinary inspection manholes in order to maintain and calibrate flow metering and sampling equipment.  Most manholes are considered to be confined spaces – ones in which bulky harnesses and other safety equipment may be required.  With the wide variety of manhole diameters and top styles available, each manhole can be customized to provide the right amount of working room at the flume.

Additionally, the fiberglass construction means that there is little in the way of maintenance required other than periodic inspections of integral access ladder.  The walls of the packaged metering manhole are smooth and highly resistant to biological growth and corrosion. 

Integral fiberglass manhole benches and grating over the flume, provide a safe, convenient place from which to operate and can also serve as convenient storage for sampling equipment in the manhole.

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