What is pump dry running and how can you protect against it?

Dry running is one of those phenomena that, in installation practice, can destroy a device worth several hundred or several thousand złoty from one day to the next. At Dambat, we regularly see its effects – in service requests and conversations with installers seeking effective protection for their customers. Below, we explain exactly what dry running is, what its consequences are, and how to prevent them.

Note: This article is technical and informational in nature. Always verify detailed data against the documentation for the specific model or with our technical department.

What is dry running?

Dry running (in English, dry run) is a condition in which the motor operates while the device has no access to water – or the flow is so low that it cannot perform its cooling and lubricating functions. In submersible pumps, water serves a dual purpose: it is the transported medium, while also cooling the winding and lubricating the mechanical seals. When the water level in the well drops below the inlet – or when air is drawn in instead of water – this entire system ceases to function properly.

In pressure-boosting systems, the mechanism is identical: the device draws water from a tank or water source, and if the tank runs empty or the suction pipeline is leaking, the impeller rotates without a medium. The temperature rises rapidly, resulting in damage.

Most common causes

• Drop in the water level. This may be seasonal – summer droughts in Poland are becoming increasingly severe – or result from excessive withdrawal exceeding the capacity of the water source.
• Device capacity exceeding the well’s capabilities. An oversized device depletes the water source faster than it can regenerate. The operating state then changes cyclically: full capacity → dry running → restart → dry running. Each such episode shortens the installation’s service life.
• Leak in the suction pipeline. Even a minor leak at the connections or a damaged check valve causes air to be drawn in instead of water – an effect similar to dry running.
• Error during initial start-up. A unit started without first filling the system runs without a cooling medium – damage occurs immediately.
• Emptying of the pressure tank. An undersized diaphragm tank or intensive use can empty the tank before the well has time to refill it.

Consequences – what happens inside?

Operating without water triggers a cascade of physical phenomena that quickly lead to costly failure. The sequence of events is almost always the same:

• Overheating and cracking of mechanical seals. The so-called mechanical seal is designed for submerged operation—without water, friction increases rapidly, the temperature rises within seconds, and the seals are destroyed. This is the most common and usually the first visible effect.
• Motor winding overload and burnout. Without a hydraulic load, the pump operates outside the optimum point of its performance curve. Current draw increases, and without thermal protection, the windings burn out.
• Impeller seizure. Under the influence of high temperatures, components deform or fuse to the housing.
• Hidden hydraulic damage. Plastic impellers and diffusers deform thermally. The result is a permanent loss of efficiency and noisy operation—even when the device appears to be “working” after a dry-running incident.

In practice, the cost of repairing or replacing a pump after seizure is many times higher than the cost of proper protection installed from the outset. A long service life for the installation is entirely achievable—and with relatively simple technical measures. We describe them below.

Dry-running protection methods

Pressure switches

The most common protection used in pressure-boosting installations. A pressure switch responds to a pressure drop below the set threshold and cuts off the power supply—operation resumes once the pressure returns to the starting value. Pressure switches are inexpensive and reliable, but they respond to the effect (lack of pressure), not the cause (lack of water in the well).

Our IBO range includes the IBO PRESS 10 controller—an electronic pressure switch designed to reliably protect against dry running and overcurrent. Detailed technical specifications, including the maximum power of the devices it supports, can be found in the product data sheet.

Water-level sensors and relays

Probes, electrodes, and float water-level relays monitor the medium directly in the well or tank. Shutdown occurs before damage can happen—this is the key difference compared with a pressure switch, which reacts only after the event. Operation can resume only after the water source has been replenished. Our range includes both many pumps with this type of switch and independent devices that perform these functions.

An important practical note: the installation of the device and the sensor activation threshold should take the dynamic water level into account – that is, the level during operation at full flow, not the static level. The difference can reach several metres and directly affects the effectiveness of the entire system.

Thermal motor protection

Temperature sensors built into the winding, also known as thermal protectors, respond when the limit is exceeded – they cut off the power supply and initiate shutdown. Restarting is possible after the motor has cooled down. However, this protection should be treated as the last line of defense, not as a substitute for water-level sensors or pressure switches.

Controllers and inverters

Pump controllers integrate multiple protective functions into a single module: pressure monitoring, operating status, supply voltage parameters, and protection against overload and dry running. This solution is intended for professional applications: farms, irrigation systems, and anywhere operational continuity is critical.

Inverters (variable frequency drives) are another level of protection and also an optimization tool. They regulate the motor’s rotational speed according to current demand, reduce the number of start-stop cycles, and monitor power consumption in real time. A sudden drop in power consumption when there is no flow is an unambiguous signal for the inverter to shut down – the response occurs within seconds. Compatible devices and control equipment for IBO and IPRO pumps can be found on our website under inverters and accessories.

Warning signs – when should you respond?

Not every dry-running incident occurs suddenly. Often, the installation deteriorates over several weeks under borderline conditions – too little water, but not yet a complete lack of water. The following symptoms should prompt an immediate inspection:

• Irregular or pulsating water flow from the taps – a typical sign of air intake.
• A noticeable increase in operating noise or new sounds (vibrations, grinding) – the impeller is operating without being fully submerged.
• Shorter cycles with unchanged demand – more frequent starts and faster shutdowns may indicate incomplete water intake.
• Automatic shutdowns by the thermal protection—operation outside the rated parameters.
• A noticeable drop in pressure during peak consumption hours—a classic symptom of the water source running dry.

Each of these signals requires immediate diagnosis. Ignoring them almost always ends with replacing the entire device. If you have any doubts about the operation of your pump, contact a specialist or our technical department.

Dambat—a trusted manufacturer of pumps and hydrotechnical equipment with quality certificates.

Frequently asked questions—dry running and protection of IBO and IPRO submersible pumps