Flow Metering Tips & Best Practices

water covers

Choosing the Right Flow Meter & How It Can Directly Impact Revenue

By Paul Alleman

Managing the operations of a water treatment plant requires making decisions that affect processes, employees and revenue. In an industry where time is critical and thousands of residents depend on your plant, it’s easy to fall into a re-purchase cycle for failing equipment without performing a thorough examination to ensure the right decisions are made.

When the meters began to fail at a 5 million gallons-per-day (MGD) municipal water plant, the lead plant operator made calls attempting to source replacement propeller meters for the raw water intakes. The meters had caused problems for years, and when the management team made room in the budget for replacements, the plant operator began the search for new, similar propeller meters.

The operator made a common assumption – that the meters already in place must be the correct meters for the job. After a bit of probing and discovery from the supplier, however, they learned propeller meters weren’t the best option. The key factors were:

  1. The meters measure flow from a river, which includes silt and debris. Propeller meters have moving parts, which are adversely affected by particles flowing through them.
  2. The meters were simply to monitor flow, and would not be used for billing purposes.
  3. The pipe was large – 20 in. in diameter. Installing propeller meters would be costly.
  4. Downtime was not an option, and any meter installation would need to happen without shutting down the plant. Installing propeller meters meant an inevitable disruption in operations.

Based on these factors, the supplier recommended a meter the plant operator hadn’t even considered. Magnetic sensor meters were far from what the plant operator had intended to purchase, but in the end proved to be more accurate, reliable, cost-effective and have a longer lifespan.

It Pays to Do the Research

When a water professional chooses the wrong meter, they can wind up with inaccurate readings and shortened meter life which can turn into revenue loss. Knowing how to choose the right meter based on the application is important for anyone responsible for transferring water, producing water or billing water consumption. There are several key questions to ask:

  • What does the meter need to do? An operator or manager should know what the meter needs to accomplish. Common goals for new meters include:
  • Detect unaccounted water to improve billing accuracy. If a plant is pumping 5 million gallons, but is only billing for 4.5 million, there’s a lot of revenue being left on the table.
  • Process control. Certain meters easily interface with SCADA for process control, monitoring and reporting purposes.
    Be reliable. Reliability through the life of the meter system should always be a goal, but it isn’t a guarantee with every meter choice.
  • Where will the meter be located? Is the meter inside the plant or is it outside, exposed to the weather? Will it be in an underground vault?
  • What are the flow conditions? Will the meter measure full-pipe, pressurized flow? What’s the velocity rate? Will the meter measure gravity flow, partially-filled pipe?
  • What’s the quality of the water flowing through the meter? Is the water flowing through the meter already treated and clean? Is it turbid? Or does it contain solids, like raw waste?
  • What is the pipe size and pipe type? Pipe diameter is a big factor in choosing the right meter, for both accuracy and cost efficiency. Knowing pipe type is important when considering insertion meters.
  • What type of flume or weir do you have? If you don’t already have one and you plan to measure open-channel flow, you’ll need to choose either a flume or a weir before making a meter choice.
  • How much straight run of pipe is within the system? Every joint, every valve, every turn in pipe has the potential to introduce turbulence. Know how much straight run of pipe there is and where the most uninterrupted flow is located. Some meter types can tolerate a certain amount turbulence and can be mounted in a variety of positions, but it’s important to know the system.
  • What installation obstacles exist? How much downtime can you manage? Depending on meter type, installation can take anywhere from a few minutes to a few hours. Knowing how much downtime your plant can manage may be the deciding factor for the meter type chosen, but there may be a trade-off between ease-of-installation and accuracy.

Officials responsible for making purchase decisions should reach out to the various personnel within the plant to get accurate answers to these questions. There are a countless number of potential scenarios that affect meter choice, and neglecting to gather the right information could result in failing to achieve the desired results, shortening the meter’s life and wasting money.

aerial view of water plant

Knowing how much downtime a plant can manage may affect meter choice, but there may be a trade-off between ease of installation and accuracy.

Scenario 1

A small county needed to comply with new reporting guidelines requiring they disclose well-water usage. Several factors led their distributor to recommend a mechanical paddlewheel flow meter:

  • The meter would need to ensure accuracy for reporting purposes
  • It would measure full-pipe, pressurized flow
  • The plant was small – only a few thousand gallons per day
  • The well water was clean
  • The pipe was only 6 in. in diameter
  • The meter would be installed close to the wellhead
  • The county couldn’t afford any downtime

The paddlewheel flow meter is an ideal choice in this scenario because it’s cost-effective, easy to install and would perform the necessary job well.

Scenario 1.5

If the above county discovered a discrepancy in the water they were pumping in versus billing out, they could consider a different meter to improve accuracy for billing purposes. Magnetic meters are verifiable and would result in fewer billing disputes, but they’re also more expensive and require a more-involved installation process.

Scenario 2

A wastewater treatment plant needed to replace a failing meter that measured the input of raw sewage. The meter was used for process control and needed to be compatible with the plant’s SCADA – specifically for chemical feed reporting.

  • This is a large plant, with high input and output volume.
  • It would measure partially-filled, open-channel flow from a Parshall flume.
  • The meter would measure flow that included solids.

A non-contact ultrasonic sensor is a top-contender in a scenario like this one, because it’s mounted above the water level and is highly accurate measuring flow from flumes and weirs.

Scenario 2.5

There are some instances where a flume or weir may not be practical, however, an accurate reading can still be obtained. Area velocity flow meters can be used for raw sewage, but are more ideal for irrigation and stormwater applications with large diameter pipe. They require, however, special knowledge to ensure they perform the way they’re supposed to. Knowing pipe diameter is critical with area velocity flow meters, but ultimately, they cost less to install and are accurate solutions in the absence of a flume or weir.

inside a water plant

Operators and workers who help maintain plant equipment know where there’s opportunity for improvement.

Consult with the Right People

Before a plant management team approves a meter replacement purchase, they can benefit from talking to their team on-the-ground, who has valuable insight that could influence final decisions. Operators and workers who help maintain the equipment often have intimate knowledge regarding pain points and where there’s room for process improvement. If improved billing is a goal, consult with the billing department, and possibly even the customer service team.

Additionally, lean on your supplier partner, who will know the right questions to ask and provide guidance towards the right meter solution. The best suppliers of metering products are more than just distributors – they’re problem solvers. They will know your goal, understand your system and your budget, and can match your challenge with a solution.

A reliable supplier partner will have a strong relationship with the metering manufacturer so you can obtain the best warranty and have easy access to repair parts. Your supplier should be your partner even after the purchase. Pollardwater, for instance, carries practically every meter type available and has the product experts to walk you through the decision-making and product support process.

Know What You Need

The most common mistake a plant makes when making big purchasing decisions is assuming they already know what they need because it’s what they’ve always used, or thinking they need the same equipment a neighboring municipality uses. But when it comes to measuring flow, a one size fits all approach just won’t do.

Paul Alleman is a product manager for Pollardwater, and has worked in the waterworks industry for more than 25 years. He is responsible for consulting customers on all aspects of level measurement (lift stations), well pump control, gauges and pressure and flow measurement within all areas of water and wastewater systems.

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