Low Flow or No Discharge Centrifugal Pump Troubleshooting Guide

1. Problem description and scope

This guide is for troubleshooting centrifugal pump problems where there is reduced flow or a complete loss of output. These symptoms can occur in various types of equipment such as refrigeration systems, chemical processes, water supply and power plants. Problems are classified as critical if they lead to a stoppage of production, or as medium if they affect the efficiency or quality of products.

2. Preventive measures

Energy protection: All work must be performed after the power has been completely cut off and the electric drive has been secured. Use lockout and tagout (LOTO) tools to prevent contingencies.
Protection against hazards: Use personal protective equipment (PPE): work gloves, goggles, exclusively protective shoes and equipment for working at height if necessary.
Protection against hazardous materials: When working with chemical liquids, use protective clothing and ventilation.

3. Necessary diagnostic tools

4. The first checklist

5. Systematic diagnostic scheme

1. Symptom: The pump does not deliver liquid
   1. Check the inlet pressure (0-1 bar). If it's lower, follow the steps to diagnose intake problems.
   2. Check the outlet pressure (0-5 bar). If it's below, follow the steps to identify issues with the release.
   3. Check the pump temperature (≤ 60°C). If it is higher, take steps to detect overheating.
   4. Check for vibrations (≤ 4.5 mm/s). If it is higher, take action to detect vibration anomalies.
   5. Check the noise (≤ 85 dB). If it is higher, take steps to detect cavitation.
   6. Check for air in the system (0–5 %). If it is higher, take steps to detect air leaks.
2. Symptom: Pump discharges fluid at low flow
   1. Check inlet pressure (0-1 bar). If it's lower, follow the steps to diagnose intake problems.
   2. Check the outlet pressure (0-5 bar). If it's below, follow the steps to identify issues with the release.
   3. Check the pump temperature (≤ 60°C). If it is higher, take steps to detect overheating.
   4. Check for vibrations (≤ 4.5 mm/s). If it is higher, take action to detect vibration anomalies.
   5. Check the noise (≤ 85 dB). If it is higher, take steps to detect cavitation.
   6. Check for air in the system (0–5 %). If it is higher, take steps to detect air leaks.
3. Symptom: The pump discharges liquid with an unstable flow
   1. Check the inlet pressure (0-1 bar). If it's lower, follow the steps to diagnose intake problems.
   2. Check the outlet pressure (0-5 bar). If it's below, follow the steps to identify issues with the release.
   3. Check the pump temperature (≤ 60°C). If it is higher, take steps to detect overheating.
   4. Check for vibrations (≤ 4.5 mm/s). If it is higher, take action to detect vibration anomalies.
   5. Check the noise (≤ 85 dB). If it is higher, take steps to detect cavitation.
   6. Check for air in the system (0–5 %). If it is higher, take steps to detect air leaks.

6. Matrix of causes of defects

7. Analysis of the reasons for each defect

1. Cavitation

Cavitation occurs when the inlet pressure drops below the boiling point of the liquid, causing a void to form in the liquid. This causes noise, vibrations and unpredictable changes in the flow. If left unaddressed, cavitation can lead to vane wear, shaft spalling, or reduced pump efficiency.

2. Wear of the shaft or blades

Shaft or blade wear occurs due to constant friction, incorrect installation or high load. This leads to vibrations, reduced flow and possible failure. Failure to address this issue may result in catastrophic wear or failure.

3. Lack of flow

A lack of flow can be caused by a blocked line, lack of pressure, or improper system setup. This results in the pump not being able to work efficiently. If left unresolved, unexpected downtime or equipment damage occurs.

4. Air leakage

An air leak can be caused by improper system setup, leaking valves, or improper pump installation. This leads to an unexpected decrease in flow and unexpected changes in the operation of the pump. If this problem is not resolved, an explosion or damage to the equipment may occur.

8. Step-by-step troubleshooting procedures

1. Cavitation

1. Check the inlet pressure. If it is below 0.5 bar, perform actions to increase the pressure.
2. Check the fluid temperature. If it is higher, reduce the temperature.
3. Check for cavitation with a thermal imager. If found, take action to reduce exposure.
4. Increase the inlet pressure to 1.0 bar.
5. Check the vibrations. If it is higher than 4.5 mm/s, take action to reduce the vibration.
6. Reduce noise up to 85 dB.
7. Check for air. If it is above 5%, take steps to reduce the air leakage.
8. Perform diagnostic measurements to confirm the solution.

2. Wear of the shaft or blades

1. Check the vibrations. If it is higher than 4.5 mm/s, take action to reduce the vibration.
2. Check the noise. If it is higher than 85 dB, take steps to reduce the noise.
3. Check the temperature of the pump. If it is above 60°C, take steps to reduce the temperature.
4. Disassemble the pump to check the shaft and vanes.
5. Replace worn components with new or remanufactured components.
6. Install the components with the appropriate settings.
7. Check for vibration and noise after installation.
8. Perform diagnostic measurements to confirm the solution.

3. Lack of flow

1. Check the inlet pressure. If it is below 0.5 bar, perform actions to increase the pressure.
2. Check the outlet pressure. If it is below 0.5 bar, perform actions to increase the pressure.
3. Check the fluid temperature. If it is higher, reduce the temperature.
4. Check for cavitation with a thermal imager. If found, take action to reduce exposure.
5. Increase the inlet pressure to 1.0 bar.
6. Increase the outlet pressure to 5.0 bar.
7. Check the vibrations. If it is higher than 4.5 mm/s, take action to reduce the vibration.
8. Reduce noise up to 85 dB.
9. Check for air. If it is above 5%, take steps to reduce the air leakage.
10. Perform diagnostic measurements to confirm the solution.

4. Air leakage

1. Check for air in the system. If it is above 5%, take steps to reduce the leakage.
2. Check the inlet pressure. If it is below 0.5 bar, perform actions to increase the pressure.
3. Check the outlet pressure. If it is below 0.5 bar, perform actions to increase the pressure.
4. Check the fluid temperature. If it is higher, reduce the temperature.
5. Check for cavitation with a thermal imager. If found, take action to reduce exposure.
6. Increase the inlet pressure to 1.0 bar.
7. Increase the outlet pressure to 5.0 bar.
8. Check the vibrations. If it is higher than 4.5 mm/s, take action to reduce the vibration.
9. Reduce noise up to 85 dB.
10. Perform diagnostic measurements to confirm the solution.

9. Prevention methods

10. Production components and spare parts

For more information on parts and components, visit our e-catalog.

11. Links

• DSTU 3049-95: Requirements for production equipment
• EN 12952-3: Water pumps
• ISO 9906: Pumps, turbines, compressors
• ISO 5199: Equipment requirements for production
• OEM technical relatives
• UNITEC-D Maintenance Guides