FPI Mag installed in pipe.
Water and wastewater utilities rely on accurate flow measurement for important process controls. These may include recycle streams, chemical dosing systems, and other operational functions. In addition, regulators require utilities to measure certain flows, such as treatment plant influent and effluent and potable water pumping. Accurate flow measurement is also important for monitoring and reducing unaccounted-for water.
Flow Meter Choices
Many types of flow meters are available, and the selected meter depends on the matrix, temperature, pipe size, pressure, location, and other factors. While ultrasonic and propeller meters have been used in the water industry, electromagnetic meters have become a meter of choice when considering accuracy, cost, and maintenance requirements.
Electromagnetic meters, also called mag meters, measure water velocity using Faraday’s Law of Electromagnetic Induction. Faraday’s Law states that a conductor (water) moving through a magnetic field produces a voltage directly proportional to the velocity of the water moving through the field. These meters have a wide flow-range capability. Also, as mag meters have no moving parts, maintenance costs are minimal.
Flow Meter Installation Challenges
Flow meter installation is typically not a problem during construction of new pumping stations or treatment facilities. Contractors on-site can install flanged, full-bore mag meters as specified in the design.
However, some installations prove more difficult. Treatment plants are often upgraded or modified, requiring new or relocated flow meters in existing pipework. New regulatory permits may require additional flow meter installations at existing facilities. Or utilities may wish to monitor flows in the distribution system to check for leaks.
In these cases, flow meter installation may be problematic. To install a full-bore mag meter, the pipe must be cut, flanges installed, and the flow meter positioned and welded. For meters larger than 12 inches, a crane is needed to lift and place the meter. The process is labor intensive, time-consuming, costly, and often requires heavy equipment.
Perhaps more importantly, the treatment process or water distribution system must be taken out of service. Interrupting a wastewater treatment system risks upstream sewer overflows or disturbance of the downstream biological process. The potential result is environmental damage and regulatory citations or fines.
Taking a water plant process out of service risks incomplete treatment or a possible water outage. Cutting into a water distribution main mandates a water outage and precautionary boil water orders. These issues can endanger the public health and result in regulatory fines. At a minimum, they greatly inconvenience the affected community. Water outages and boil notices may also cause temporary closures of businesses and schools.
Installing Mag Meters with Hot Taps
Fortunately, options are available to install mag meters using a hot tap process, also called wet tapping. Hot tapping is a procedure that allows connection to a pipe under pressure, without taking the line out of service. Hot taps can be used for inserting meters and probes, adding valves, or for new pipe connections. Hot taps require specialized equipment and must be performed by highly trained technicians.
The process begins with a tapping sleeve being sealed around the pipe. A permanent valve is attached to the sleeve. The hot tap machine is attached to the valve. The machine cuts a hole through the pipe and lifts the removed section, known as the coupon, back out. This allows insertion of the flow meter.
Installing mag meters with hot taps avoids problematic outages or system shutdowns. The process avoids inconveniencing citizens and businesses. The utility continues to protect public health and the environment while maintaining regulatory compliance. In addition, the utility saves the cost of labor and heavy equipment needed for typical full-bore, flanged meter installation.
Options for Flow Meters Installed with Hot Taps
Single Point Insertion Mag Meters
In the past, only “single point” insertion mag meters could be installed with hot taps. They provide one point of measurement in the velocity profile. These flow meters are very cost-effective for water and wastewater flow measurement.
Unlike full-bore mag meters, pipe size does not affect their cost. They can measure a wide flow range with a high degree of accuracy, ±2 percent of full range. This accuracy range is often sufficient to meet regulatory requirements for monitoring influent and effluent wastewater flows or drinking water pumping volumes.
Full Profile Insertion Mag Meters
Advanced technology is now available that allows the enhanced accuracy of a full-bore mag meter, installed with the convenience and cost savings of a hot tap.
A full profile insertion meter is placed in the middle of the flow stream through a hot tap. An array of coils and electrodes measure multiple points across the pipe diameter. This provides an entire velocity profile to obtain improved accuracy of ±0.5 percent with third-party testing.
These meters also have no moving parts and a single piece design. No pipe or system shutdown is needed for calibration or maintenance. Also, they can be used for pipe sizes ranging from 4 inches to 138 inches in diameter.
Accurate Flow Measurement Without Service Interruption
Utilities can save installation costs without the need for system downtime with hot tap mag meter installation. Treatment plants remain in compliance. And customers avoid troublesome water outages and boil water notices. Breakthrough technology allows utilities to select the best option for their system, including full profile flow measurement with extreme accuracy where needed.
