Willie Williams | Burns & McDonnell

Pump designers and consultants excel at guiding system owners toward optimal design based on hydraulic requirements, equipment preference, available space and end user familiarity. They preach the gospel of selecting the right pump for the duty point, sizing pipes and valves correctly and adhering to the Hydraulic Institute’s intake design standards. This foundational work is critical. A system built on these principles is engineered for success. But without the right instrumentation, it is also operating blind, risking inefficient operation and noncompliance with stringent Environmental Protection Agency (EPA) discharge permits.

A correctly selected pump and correctly sized piping system are only half the story. They represent the “muscle” of the system, ready to perform the work. But muscle without a nervous system is useless, unable to sense its environment, control its output or protect itself from harm. In a pumping system, instrumentation is that nervous system. It provides monitoring, control and protection that transform a collection of high-quality components into a smart, efficient and resilient system. Overlooking instrumentation is not just a missed opportunity; it is an invitation for inefficiency, downtime and premature failure.

| IMAGE 1: Monitoring system performance (Image courtesy of Burns & McDonnell)

Monitoring: The Eyes & Ears of the System

“You can’t manage what you don’t measure.” This old business adage is the fundamental truth of system optimization—a primary goal of pump industry professionals. Without real-time, actionable data, operators are merely guessing at system health and performance. Monitoring instrumentation provides the critical feedback needed to move from guesswork to informed management.

Several key parameters serve as the vital signs of a pumping system:

Pressure: Pressure gauges and transmitters are arguably the most common and vital instruments. They do more than just confirm the system is pressurized. A discharge pressure reading that is lower than expected can indicate a worn impeller, an internal leak or an upstream blockage. On the suction side, a vacuum gauge can alert operators to a clogged strainer, preventing pump cavitation and the severe damage it causes. In long force mains, pressure monitoring is also critical for detecting and mitigating damaging water hammer or pressure transients.
Flow: While pressure shows the system’s potential to do work, flow shows the work actually being done. A nonintrusive magnetic flow meter (magmeter) is an efficient and reliable way to know for sure that a system is delivering the required volume, as it has no moving parts to get clogged with the rags and debris common in raw sewage. It confirms the pump is operating at its desired point on the performance curve.
Level: For any application involving a tank, sump or wet well, level is the most important process variable. Whether it is a noncontact ultrasonic or radar transmitter to avoid issues with foam and corrosion or a robust submersible pressure transducer, this continuous data is crucial for sophisticated pump control strategies. Monitoring the rate of level change can also provide an indirect measure of inflow and outflow, helping to identify upstream or downstream issues.
Temperature: Heat is a primary byproduct of inefficiency and a major symptom of mechanical distress. Temperature sensors on motor windings and pump bearings serve as an invaluable early warning system. A gradual rise in bearing temperature over weeks can flag a lubrication issue or impending failure long before it becomes catastrophic, turning an emergency shutdown into a scheduled maintenance task. Temperature monitoring typically comes standard on pumps used in the industry.
Vibration: Every rotating machine has a unique vibration signature. Modern vibration sensors can detect minuscule changes in this signature that are imperceptible to human touch. These changes are direct indicators of developing mechanical problems like bearing wear, shaft misalignment or impeller imbalance. By trending vibration data over time, operators can implement a truly predictive maintenance strategy. Vibration monitoring typically comes standard on pumps used in the industry.

Control: Taking Action on the Data

Monitoring provides awareness, but control creates a response. Control instrumentation uses the data gathered by sensors to automatically adjust system operation, optimizing for efficiency, stability and longevity.

By integrating a level transmitter with a variable frequency drive (VFD), a more elegant solution is created. The level transmitter provides a continuous, real-time signal of the wet well level to the VFD or a programmable logic controller (PLC). The control system then precisely adjusts the pump’s speed to match the rate of inflow, maintaining a nearly constant level in the well. The benefits are:

Energy savings: According to the pump affinity laws, power consumption is related to the cube of the speed change. Reducing a pump’s speed by just 20% can reduce its energy consumption by nearly 50%.
Reduced wear and tear: The VFD provides a “soft start,” gradually ramping the pump up to speed. This eliminates the massive inrush current and mechanical shock of across-the-line starting, which extends the life of the motor, couplings and seals.
Process stability: By automatically adjusting to demand, a VFD-controlled system can maintain a constant pressure, flow or tank level with a precision that is impossible to achieve with on/off control. In a wastewater lift station, this is critical for keeping solids and grease suspended, reducing odors and the need for expensive manual cleanouts. In pressure systems, this is one tool in mitigating transients.

Protection: The System’s Insurance Policy

While monitoring and control optimize performance, protection instrumentation acts as the ultimate failsafe. Its job is to detect dangerous conditions and take immediate action by shutting down equipment or triggering high-priority alarms to prevent a minor issue from escalating into disaster. This is the system’s insurance policy, and a small investment here can prevent six-figure losses.

Essential protective instruments include:

Pressure switches: A high-pressure switch can shut down a pump in a dead-head condition, preventing the massive temperature buildup that can flash the liquid to steam and cause a casing explosion. A low-pressure switch can stop a pump that has lost its prime, preventing it from running dry and destroying its mechanical seal.
Level switches: In any application involving a tank or sump, level switches are nonnegotiable. A low-level switch is an effective way to prevent a pump from running dry, the single most common cause of catastrophic pump failure. A high-level switch can prevent a costly and hazardous sanitary sewer overflow (SSO), protecting the environment and saving the utility from significant fines and negative publicity.

| IMAGE 2: Sewer overflow (Image courtesy of Burns & McDonnell)

Validating Performance: From Factory Curve to Field Reality

A manufacturer’s pump performance curve is a promise. It represents how the pump performed under controlled, ideal laboratory conditions. By using a few key instruments, an owner can perform a simple field verification test. At minimum, pressure gauges on the discharge piping and level instruments to detect basin level can allow a draw-down test to be performed. Adding a flow meter to the discharge side of this arrangement adds another, more trustworthy data point.

By calculating the total dynamic head (discharge head minus suction head) and recording the flow rate, it is possible to plot a real-world operating point directly onto the factory curve. This test definitively answers the critical question: “Is the problem with the pump, or is it with the system?” It empowers owners to hold manufacturers accountable, diagnose system issues accurately and move maintenance from a reactive guessing game to a data-driven science.

llustrating the Stakes: A Tale of 2 Lift Stations

Consider a typical municipal wastewater lift station.

Lift Station A was specified with a focus on minimizing upfront capital cost. It uses simple float switches for on/off pump control. The pumps slam on at full speed, creating a hydraulic shock that rattles the check valves and stresses the force main. They run for a short period and slam off. This hard cycling happens dozens of times an hour, causing extreme wear on the motor contacts and mechanical seals. One night, a float gets tangled in rags and fails to activate. The wet well overflows, causing a reportable SSO into a local creek. The result: emergency cleanup costs, a hefty fine from the state EPA and a loss of public trust.

Lift Station B was specified with a focus on total life cycle cost. It features a noncontact radar level transmitter that provides a smooth signal to the pumps’ VFDs. The pumps gently speed up to match the rate of inflow, maintaining a consistent level in the wet well. The system runs quietly and efficiently, keeping solids suspended and reducing the need for pump-clogging manual cleanouts. Vibration sensors on the pumps trend data to the central supervisory control and data acquisition (SCADA) system, and an alert is generated when a bearing’s vibration signature begins to degrade, allowing maintenance to be scheduled weeks in advance with no service interruption. A redundant high-level float switch is tied to the alarm dialer, providing a final layer of protection against an overflow.

The initial cost for Lift Station B was 30% higher. Its reliability, lower energy bills and reduction of emergency call-outs and SSO fines paid back that difference in just two years.

| IMAGE 3: Life cycle cost (Image courtesy of the Hydraulic Institute)

An Investment, Not an Expense

Instrumentation is not a luxury or a collection of optional add-ons. It is the intelligence that unlocks the full potential of a well-designed pumping system. It ensures the system is efficient, protects it from self-destruction and provides the visibility needed for proactive management.

The responsibility of industry professionals extends beyond simply providing a pump that meets a duty point. They must educate end users on the crucial difference between initial price and total cost of ownership.

Willie Williams is a mechanical engineering manager at Burns & McDonnell. He may be reached at wgwilliams@burnsmcd.com or 816-349-6864. For more information, visit burnsmcd.com.

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