Why flow measurement is critical to achieving pump system efficiency.
by Cheryl Ades Anspach
September 17, 2019

For water and wastewater plant operators, opportunities to better manage the energy use of pump systems is an area of great interest. This equipment accounts for a large share of a facility’s total electricity consumption.

The following article describes how advancements in ultrasonic flow meter technology provide an enhanced solution for monitoring flow rate in water distribution systems, for pump efficiency checks and in sewage pumping stations, among other applications.

Demands on Plant Operators

In today’s uncertain economic environment, water and wastewater plants strive to be efficient, cost-effective and reliable. Every facility needs to maximize performance and availability. Environmental regulations have become more rigorous, operating costs have increased and technology has advanced.

Some of the specific demands on operations include:

  • maximize pumping reliability
  • minimize energy consumption
  • optimize maintenance procedures
  • reduce life cycle costs
  • ensure environmental compliance
  • achieve long-term sustainability

Critical Role of Pump Systems

Pump systems play a significant role in a wide range of water and wastewater operations. Ideally, they should always operate at the flow rate at the point of highest efficiency—but that is almost never the case. The average pump efficiency in industrial applications is estimated to be below 40 percent. By evaluating the actual operating point of pumps and correcting performance problems, plant operators can improve availability and reduce maintenance and repair costs.1

Pumps tend to consume large amounts of electricity, so it is important that they run at the required speed and not any faster. A study by the Electric Power Research Institute (EPRI) estimated that, on average, pumping accounted for 80 percent of total electricity use in public water systems. Additionally, raw water pumping to a treatment facility, along with treated water pumping to distribution systems, are large energy-consuming processes.2

Importance of Flow Measurement

Pumping, lift and well stations are integral parts of water and wastewater networks. Flow measurement at these sites is crucial, as the quantities fed to the treatment plant or delivered through the distribution system have to be monitored. As heavier rainfall becomes more widespread, sewage levels at pumping stations can rapidly reach critical levels and monitoring pump flow rates can help operators take appropriate measures.

All too often, water and wastewater plants lack the right tools to accurately measure flow. Many facilities are fitted with outdated flow meters, which no longer function properly due to age, condition and other factors. The effort and cost to remove these devices from the line can be prohibitive. In order to determine whether flow exceeds the capacity within any of their pumps, operators may rely on course flow data derived from calculating the rate of change in sump levels.

In a perfect world, flow measurements could be obtained on all pumps. This often proves impractical, yet vital for understanding overall pump efficiency. Most facilities have two primary flow measurement challenges: accuracy and cost. The goal is to correctly match the right flow meter to the right application to achieve the best performance for the lowest purchase price and total cost of ownership.

Flow meters installed downstream of pumping stations can provide valuable real-time data, which is processed to yield actionable information to operators and engineers.

For instance, comparing flows at various points in the system can show if a major leak has occurred. Data from flow meters can also be used to balance loads during pump operation, as it is often found that pump speed set points can be lowered while still maintaining sufficient flow—saving energy, reducing maintenance and increasing pump life.

Why Use Ultrasonic Meters?

Many plant operators now choose noninvasive ultrasonic flow measurement solutions. Ultrasonic meters can work whenever contact with the measured fluid is not possible. Designed for easy clamp-on installation, these instruments can be used for metering points on sewage networks and wastewater treatment plants, especially for retrofit situations. They are designed to have no moving or wetted parts, no pressure loss, offer a large turndown ratio and may provide maintenance-free operation.

Transit time ultrasonic flow meters are used in the vast majority of liquid flow application due to their ability to obtain accuracy. This technique measures the difference between the travel time of an ultrasound wave going with the fluid flow and against the fluid flow. The time difference is used to calculate the velocity of the fluid traveling in a closed-pipe system. The transducers employed in transit time measurements operate alternately as transmitters and receivers. Transit time measurements are bidirectional and are most effective for fluids that have low concentrations of suspended solids and are sonically conductive.

Transit-time ultrasonic flow meters also have diagnostic capabilities that other meter designs lack.

Clamp-on ultrasonic flow meters can be quickly installed without cutting or tapping the pipe. They reside outside the process line and can make it easier to perform routine monitoring of pump efficiency, which helps staff to identify maintenance concerns such as worn impellers or blockages.

Clamp-on ultrasonic flow meters can be an alternative to traditional mechanical meters, which may be subject to deteriorating accuracy caused by wear and tear.