Maintenance Guides 1 min read

A guide to detecting and correcting low flow or no suction in a centrifugal pump

Technical analysis: Troubleshooting centrifugal pump low flow or no discharge: cavitation, impeller wear, air lock, suct

Гід для виявлення та виправлення низького потоку або відсутності відкачування у центрифігальному насосі - UNITEC-D Industrial MRO
Цей гід надає систематичний підхід до виявлення та виправлення низького потоку або відсутності відкачування у центрифігальному насосі. Він включає діагностичні тести, кореневі причини та конкретні дії

1. Problem description and scope

This guide displays a low flow or no pump problem in a centrifugal pump that can be caused by cavitation, vane fatigue, air entrapment, intake problems, or system curve analysis. Violations are critical production conditions because they can lead to process stoppages, product loss, and increased risk of security breaches.

2. Preliminary safety measures

Use personal protective equipment (PPE): gloves, glasses, special work clothes, mask for protection against chemical liquids.
Lockout and tagout: Before performing any work on the pump, turn off power, install lockouts and tags to prevent unintended activation.
Check for stored energies: in the case of pumps with hydraulic or electric systems, ensure complete shutdown and discharge of batteries.
Attention to hazardous conditions: in the presence of aggressive liquids, gases or high temperatures, observe the assumptions for working in such conditions.

3. Necessary diagnostic tools

Name of the tool Model/Specification Measuring range The goal
Multimeter Fluke 289 0-2000 V, 0-200 A Checking electrical connections and voltage
Thermography FLIR T650 -20°C to 1400°C Detection of overheated elements
Vibration analyzer Brüel & Kjær 4390 0-100000 mm/s Detection of vibration anomalies
Pressure sensor Transite T100 0-10 bar Checking the pressure in the system

4. Check before starting diagnostics

Name action Meaning
Ambient temperature Record the temperature in the room and in the work area 20–30°C
Pressure in the system Measure the pressure in the inlet and outlet lines 0.5–10 bar
Presence of air Check for air in the system There is none
Changes in the system Record any system and hardware changes There is none
A history of anxiety Record the alarms displayed in the system There is none

5. Systematic diagram of diagnostics

  1. Symptom: Low flow or no pumping
    1. Measure pressure in inlet and outlet lines
    2. If the inlet pressure is less than 0.5 bar, check for air
    3. If the inlet pressure is normal, check the fluid level
  2. Symptom: Air Blockage
    1. Use thermography to detect uneven temperatures
    2. Check for air in the system
    3. If air is present, bleed
  3. Symptom: Cavitation
    1. Measure the temperature in the system
    2. If the temperature is above 60°C, check the pressure
    3. If the pressure is less than 0.5 bar, check the inlet line
  4. Symptom: Blade fatigue
    1. Use vibration analyzer to detect high values
    2. If the vibration is greater than 10 mm/s, check the blades
    3. If the blades are tired, replace them
  5. Symptom: System curve
    1. Measure flow and pressure
    2. Construct the system curve
    3. Check that the curve meets the design parameters

6. Matrix of causes of defects

Symptom A possible reason Diagnostic test Answer
Low flow Cavitation Measure temperature and pressure Temperature > 60°C and pressure < 0.5 bar
Low flow Blade fatigue Vibration analysis Vibration > 10 mm/s
Low flow Air blockade Thermography Uneven temperature
Low flow System curve Construct a curve The curve deviates from the design curve

7. Analysis of root causes

7.1 Cavitation

Reason: Cavitation occurs due to low pressure in the inlet line, which causes a void in the liquid. This can be caused by a decrease in inlet pressure, high temperature or insufficient fluid level.

Confirmation: Measure the temperature and pressure in the system. If the temperature is greater than 60°C or the pressure is less than 0.5 bar, cavitation is the most likely cause.

Consequences: Cavitation can cause vanes to collapse, reduce efficiency and damage the pump. If not addressed, a complete shutdown may occur.

7.2 Blade fatigue

Reason: Blade fatigue occurs due to prolonged use, high vibrations or improper installation. This results in reduced flow and increased vibration.

Confirmation: Use the vibration analyzer. If the vibration is greater than 10 mm/s, blade fatigue is the most likely cause.

Consequences: Blade fatigue can lead to increased vibration, reduced efficiency, and equipment damage.

7.3 Air blockade

Reason: Airlock occurs due to air entering the system, resulting in reduced flow and increased vibration.

Confirmation: Use thermography. If uneven temperatures are detected, air blockage is possible.

Consequences: Air entrapment can lead to increased vibration, reduced efficiency and damage to the pump.

7.4 System curve

Reason: The system curve deviates from the design parameters due to changes in the system or incorrect settings.

Confirmation: Plot the system curve. If the curve deviates, this may indicate a problem with the system curve.

Consequences: An incorrect curve system can lead to reduced efficiency, product loss and increased energy costs.

8. Correction sequence

8.1 Cavitation

  1. Measure the temperature and pressure in the system
  2. If the temperature is higher than 60°C or the pressure is lower than 0.5 bar, do the following:
  3. Check the inlet line pressure
  4. Increase the liquid level or decrease the temperature
  5. Check that the pressure is within design parameters
  6. Run diagnostics and fixes

8.2 Blade fatigue

  1. Use a vibration analyzer
  2. If the vibration is greater than 10 mm/s, do the following:
  3. Check the condition of the blades
  4. Measure the dimensions of the blades
  5. If the blades are tired, replace them
  6. Install new blades
  7. Check for vibration after installation

8.3 Air blockade

  1. Use thermography
  2. If uneven temperatures are detected, do the following:
  3. Check for air in the system
  4. Flush the system
  5. Measure the pressure after bleeding
  6. Check that the pressure is within design parameters
  7. Run diagnostics and fixes

8.4 System curve

  1. Construct the system curve
  2. If the curve deviates, do the following:
  3. Check the system settings
  4. Measure flow and pressure
  5. Check that the curve meets the design parameters
  6. Make adjustments or corrections
  7. Check the curve after adjustment

9. Preventive measures

The root cause Prevention strategy Monitoring method Recommended interval
Cavitation Ensure adequate pressure in the inlet line Thermography, pressure measurement Weekly
Blade fatigue Perform scheduled maintenance Vibration analysis monthly
Air blockade Perform regular pumping of the system Thermography Weekly
System curve Checking the system parameters Construction of the system curve monthly

10. Production components

Description of the component Specification When to replace UNITEC-D category
shovels Material: stainless steel, size: 100–500 mm In case of fatigue or damage Pump Components
Filters Material: polypropylene, size: 50–200 mm When clogging Filter Components
Pipelines Material: steel, diameter: 50–300 mm In case of corrosion or wear Pipeline Components
Pressure sensors Material: stainless steel, range: 0–10 bar In the event of a malfunction Pressure Sensors

To get components, go to: https://www.unitecd.com/e-catalog/

11. Links

  • ISO 9906:2012 – Pumps. Technical conditions
  • EN 12189:2003 – Pumps. Diagnostics and repair
  • DSTU 2842:2021 – Equipment diagnostics
  • UNITEC-D Technical Manual for Centrifugal Pumps

Related Articles