5 Reasons Your Pump Might Be Running Inefficiently
What Is Pump Efficiency?
Pump efficiency is the ratio of useful hydraulic energy a pump delivers to the fluid compared to the mechanical energy it consumes to do so, usually expressed as a percentage. A pump running below its rated efficiency wastes energy, increases operating costs, and often signals an underlying mechanical or system design issue rather than normal wear.
A pump’s performance curve, which is included in the documentation provided by the manufacturer, allows you to measure your pump’s performance, including energy, flow and pressure that it should be providing under a specific set of circumstances. If your pump is running, but not operating at peak efficiency, the excessive energy required will cost you money – sometimes more than the initial cost of the pump! So, what could cause your pump to run inefficiently?
This applies just as much to water pump efficiency in municipal and commercial systems as it does to chemical or industrial process pumps — the underlying causes of poor pump performance are largely the same across applications. So, what could cause your pump to run inefficiently?
Signs your pump may be running inefficiently include:
- Rising energy costs without a corresponding increase in output
- Lower-than-expected flow or pressure compared to the performance curve
- Unusual noise, such as popping or knocking sounds
- Excessive vibration during operation
- More frequent seal, bearing, or impeller wear than expected
Common Causes of Inefficient Pump Performance (retain structure, expand each point)
1. Oversized pump
It is essential to select the right sized pump for the application – yet many engineers choose pumps that generate more flow and head than the application requires. Over time the pumped fluid will cause the casing and impeller to deteriorate and the worn pump will eventually operate within an acceptable performance range. However, the pump discharge must be throttled until the wear occurs, which is a waste of energy. If an engineer were to choose a smaller pump, which has a protective coating to minimise the effects of corrosion and erosion, they would be able to save on this loss of energy.
Many issues can also occur if the pump remains the same but the design point changes, such as increased energy costs and cavitation.
Undersized (low capacity) pumps have the opposite problem: a pump that’s too small for the application will run at or beyond its maximum capacity continuously, leading to excessive wear, higher energy draw per unit of flow, and a shortened service life. Matching pump size to the actual system curve — not just peak demand — is critical to avoiding both oversizing and low-capacity pump issues.
2. Motor wired incorrectly
If the motor is wired incorrectly, the motor can cause the pump shaft to rotate counter to its required direction – indicated on the pump’s bearing frame. While the pump will still run, it will run at a fraction of the flow and head indicated by the performance curve. If you find that your pump is not generating the rate of flow expected, check that the shaft is rotating in the right direction.
3. Degraded bearings or contaminated lubricant
If a bearing is failing it causes a drag on the motor, requiring more current to rotate at the designed speed – thus costing more energy to get the correct flow. So although your pump may generate the specified flow and pressure, more energy is required to rotate the shaft.
Washing down industrial pumps can also cause bearing lubricant to become contaminated – eventually degrading the bearing. Protecting bearings from degrading and bearing lubricants from moisture is critical in maintaining the reliability and efficiency of your pump.
4. Eroded or corroded impeller and casing
The shape of the impeller and its casing are critical for the correct functioning of the pump, affecting its ability to impart energy to the fluid. Erosion, corrosion and instances where solids in the fluid flow at high speed can change the shape of the impeller and/or its casing – affecting the efficiency of the pump over time. Although pumps are designed with an allowance for corrosion, anything beyond these limits can affect the efficiency of the equipment. If possible, choose pumps which are made of corrosion and erosion resistant materials, contain enclosed impellers and wear rings, or which offer hard casing, protective materials for the impeller, or rubber linings to prevent erosion.
5. Cavitation
Clogged filters or strainers, blockages in the pipe, or poor piping design can lead to cavitation – which is usually indicated by a popping sound. Pump cavitation can lead to excess energy use and severe issues for your pump system, such as damage to the impeller and/or the pump housing and decreased flow and/or pressure. The excessive vibration can also lead to early seal and bearing failure if left untreated. Check for clogged filters or strainers or blockages in the pipe, or if the pump is running too far right on the pump curve (suction cavitation) or too far left (discharge cavitation).
Symptom, Cause, and Fix — Quick Reference Table
| Symptom | Likely Cause | Recommended Fix |
|---|---|---|
| Higher energy bills, normal flow | Oversized pump, throttled discharge | Right-size the pump or trim the impeller |
| Low flow/pressure vs. performance curve | Incorrect motor wiring, wrong rotation | Check shaft rotation direction |
| More current draw at same flow | Degraded bearings or contaminated lubricant | Inspect and replace bearings; protect lubricant from moisture |
| Gradual efficiency loss over time | Eroded or corroded impeller/casing | Use corrosion-resistant materials, wear rings, protective linings |
| Popping/knocking noise, vibration | Cavitation | Clear clogged filters/strainers, check piping design and pump curve position |
| Constant max-capacity operation, frequent wear | Undersized (low capacity) pump | Re-evaluate system curve and select appropriately sized pump |
How to Reduce Pump Flow Rate (When That’s the Goal)
Not every flow issue is a problem to fix — sometimes reducing pump flow rate intentionally is the goal, such as when a system was originally oversized. Common methods include:
Throttling the discharge valve: Simple but wastes energy, since the pump still works at full capacity against added resistance
- Installing a variable frequency drive (VFD): Adjusts motor speed to match actual demand, improving energy efficiency compared to throttling
- Trimming the impeller: Physically reduces impeller diameter to lower flow and head output, matching the pump more closely to the system curve
- Installing a smaller pump or a multi-pump staged system: Addresses chronic oversizing at the source rather than compensating for it after installation
Of these methods, impeller trimming and VFD installation are generally the most energy-efficient long-term solutions, while throttling should be considered a temporary or last-resort measure.
If you’d like more information, please call our toll-free number 1-800- 367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.
For related guidance, see our posts on pump cavitation and how to catch pump issues before they become emergencies.
