Airlock in water pumps: the silent polluter

Airlock in water pump systems is a common yet often overlooked challenge—especially for wastewater and sewage utilities managing remote, submerged, or unmanned assets. These trapped air pockets can silently halt pumping and forward flow, disrupting operations at the most critical points. Beyond reducing efficiency and triggering costly callouts, airlocks often evade detection by traditional monitoring tools like SCADA, vibration sensors, or pressure switches.

The reason airlocks frequently go undetected is simple: their symptoms closely mimic other pump faults. Flow is disrupted, but the pump keeps running. Pressure and vibration readings may seem normal. As a result, the true cause remains hidden, and teams spend time and resources chasing symptoms.

However, with the rise of advanced condition monitoring techniques—especially electrical signature analysis (ESA)—utilities can now identify and address airlock issues remotely, accurately, and before they escalate.

What causes airlock in water pumps?

An airlock forms when air becomes trapped inside a section of pipe or the pump casing, creating a blockage that prevents water from moving freely. This typically happens after maintenance or pump restarts, when air enters the system and isn’t fully purged. However, one of the most common causes in the field is poorly controlled pumps—particularly when operators allow wet well levels to drop too low, drawing air into the system. Poor system design can further exacerbate the issue, especially in vertical risers or low-flow sections where air tends to collect. Turbulence or vortexing at inlets can also contribute, pulling air into the pipework and increasing the risk of entrapment.

In wastewater applications, submersible pumps are particularly vulnerable. After wet well cleaning or pump reinstallation, air pockets often remain inside the pump or piping unless actively removed. These scenarios are so common that airlocks have become one of the most persistent hidden threats to pump performance.

Signs of airlock in water pumps and how they impact operations

The symptoms of an air-locked pump can be subtle but costly. You may notice a sudden drop in flow or, in some cases, a complete loss of output. The pump continues running, but little or no water moves downstream. This inefficiency drives up energy use as the motor works harder to overcome internal resistance. Meanwhile, the pump heats up, experiences unnecessary wear, and critically cannot pass flow forward, causing the wet well to fill and potentially overflow into the environment.

These performance issues are not always obvious in telemetry data. SCADA systems may show normal motor operation. Vibration and pressure readings may fall within expected ranges, especially if the airlock is partial rather than total. This makes it challenging to detect the problem until it causes a failure or triggers a compliance risk.

The most reliable signs of an airlock include unexplained drops in flow, increased energy consumption without an obvious cause, and repeat site visits to resolve what seems like a mechanical fault. Without proper tools, airlocks are easy to misdiagnose.

Understanding pump cavitation vs airlock

It’s important to distinguish between airlocks and cavitation. Although both involve trapped gases and impact flow, they have different causes and consequences.

Cavitation occurs when vapor bubbles form due to low pressure and then collapse violently inside the pump. This collapse produces shockwaves that damage internal components, often causing noise, vibration, and wear. Cavitation is more likely in high-speed systems or where inlet pressure drops too low.

Airlock, by contrast, involves real air trapped in the system, physically preventing fluid movement. It tends to be quieter and doesn’t always produce the characteristic vibration or damage that cavitation does. That’s why knowing how to detect airlock in water systems requires more nuanced monitoring tools that go beyond conventional vibration or pressure-based systems.

Why standard monitoring tools miss airlocks

Traditional monitoring setups rely on mechanical data. Vibration, pressure, and flow sensors are excellent at identifying worn bearings, misalignment, and seal failures. But they’re not designed to pick up hydraulic issues without mechanical consequences.

An airlocked pump may still spin, generate acceptable vibration levels, and appear fine in the control room. In fact, many utilities discover airlocks only after repeated performance drops or through manual inspection.

This is particularly true for submerged and unmanned sites. In these environments, where access is limited and extra sensors are impractical, airlocks can persist for days or weeks without detection.

Condition monitoring for pumps: a new approach

The emergence of condition monitoring based on electrical signature analysis offers a much-needed solution. SAM4 from Samotics uses ESA to continuously analyze the high-frequency electrical signals from the motor’s control cabinet. This allows it to detect patterns that mechanical sensors miss.

When an airlock is present, the motor experiences a drop in torque and load. Efficiency decreases as energy is consumed but not effectively turned into flow. Subtle harmonic distortions in the electrical current also indicate abnormal pump behavior. These patterns are detectable even when the pump is fully submerged or located at an unmanned station.

Importantly, SAM4 can distinguish between different types of faults. Airlocks, for example, reduce torque and create unstable load conditions. Blockages, on the other hand, tend to cause torque spikes. Cavitation produces its own signature, often involving rapid drops in efficiency and more erratic behavior. Being able to tell these apart in real time allows teams to take the right action without guesswork.

How to remove airlock in water pump systems

Once an airlock has been confirmed, the next step is removal. The right approach depends on the system setup. In many cases, air can be vented manually through air release valves. In others, utilities may use backflushing to force the air out of the system. Cycling the pump in specific sequences can also help purge trapped air.

For more severe or persistent airlocks, the pump may need to be removed and the system re-primed. This is labor-intensive, especially at remote or underwater installations, which makes accurate diagnostics critical. With SAM4’s real-time data, teams can pinpoint the issue, confirm the presence of air, and decide on the best course of action without repeated trial and error.

The value of early detection

Detecting airlocks early brings clear operational and financial benefits. Teams can restore full flow before the issue impacts performance or triggers overflows. Emergency callouts are reduced, as fewer visits are needed to diagnose recurring faults. And because pumps operate under optimal conditions, they last longer and require less maintenance.

Beyond cost savings, early detection also supports regulatory compliance. In wastewater systems, flow reductions caused by airlocks can lead to untreated discharges or exceedances. These events carry fines, environmental consequences, and reputational risks. Proactive monitoring minimizes these threats and keeps systems running reliably.

A smarter strategy for pump performance

Utilities are under growing pressure to improve efficiency, reduce environmental impact, and modernize infrastructure. Including airlock detection in your condition monitoring strategy is a practical step toward achieving those goals.

SAM4 gives you visibility into issues that would otherwise go unnoticed. It fits seamlessly into existing electrical infrastructure and helps operators move from reactive maintenance to proactive management.

If you’re wondering whether airlocks are affecting your pump performance, it’s time to take a closer look.

Request a performance review or book a live demo to see how SAM4 detects hidden issues like airlocks—and gives your team the insights needed to act quickly and confidently.