1. Description of the problem and scope of application
This guide is intended to systematically diagnose and troubleshoot common centrifugal pump malfunctions that manifest as low flow or no discharge. Such symptoms can lead to significant production disruptions, equipment damage and increased operating costs. The guide covers a wide range of centrifugal pumps used in industry: cantilever, multistage, submersible and other types used in the automotive, aerospace, food, chemical and energy industries.
Classification of severity:
- Critical: Complete absence of discharge resulting in immediate shutdown of production line or critical process. Requires immediate intervention.
- Significant: A significant reduction in flow that causes reduced productivity, impaired product quality, or overloading of other systems. Potential damage to the pump or system.
- Minor: A small but noticeable decrease in flow, periodic pressure fluctuations, or unusual noises, indicating the initial stage of the malfunction. Requires routine diagnostics to prevent further problems.
2. Precautions
WARNING! Before beginning any diagnostic or repair work on pumping equipment, the following precautions MUST be observed to ensure the safety of personnel and equipment. Failure to do so could result in serious injury or death.
- LOCKOUT/TAGOUT (LOTO): Always perform the Lockout and Tagout (LOTO) procedure in accordance with internal plant standards and DSTU requirements EN 1037. Disconnect all power sources (electrical, hydraulic, pneumatic) and lock them in the off position.
- Stored Energy: Ensure that all sources of stored energy (fluid pressure in piping, compressed air, springs, rotating masses) are discharged or safely locked. Open the drain valves to relieve system pressure.
- Personal Protective Equipment (PPE): Always use appropriate PPE: safety glasses or shield, protective gloves (chemically resistant or mechanical, depending on the fluid), protective clothing, protective shoes with metal toe caps, hearing protection (at high noise levels).
- Hazardous liquids: If the pump is pumping hot, corrosive, toxic or flammable liquids, make sure the system is completely drained, flushed and safe to service. Use appropriate means to collect and dispose of used liquids.
- Hot surfaces: Pumps and motors can have hot surfaces. Be careful to avoid burns.
- Rotating parts: Never work near rotating shafts, couplings or impellers without proper protection or when the equipment is energized.
3. Necessary diagnostic tools
The following set of tools is required for effective diagnosis:
| Name of the tool | Specification/Model | Measuring range | Purpose |
|---|---|---|---|
| Multimeter | True RMS, CAT III 1000V | Voltage (0-1000V AC/DC), Current (0-10A AC/DC), Resistance (0-50 MΩ) | Checking electric circuits, engine, sensors |
| Manometers (input/output) | The range corresponding to the system pressure, the accuracy class is not lower than 1.6 | 0-10 bar (vacuum), 0-25 bar (pressure) | Measurement of suction and discharge pressure |
| Flow meter | Portable ultrasonic or stationary | 0.1 - 100 m³/h, ±1% accuracy | Measurement of the actual volume flow of liquid |
| Vibration analyzer | With FFT function, 2-channel | 0.1 - 25.4 mm/s RMS (velocity), 0 - 20 kHz (frequency) | Detection of cavitation, imbalance, misalignment, bearing problems according to ISO 10816 |
| Thermal imager (thermal camera) | Resolution 320x240, sensitivity 0.05°C | -20°C to +350°C | Detection of overheating of bearings, engine, coupling, problems with seals |
| Tachometer | Optical/contact | 0-99999 rpm, ±0.05% | Checking motor/pump rotation speed |
| Noise meter (decibelometer) | Class 2, range A | 30 - 130 dB | Quantification of anomalous noises |
| Set of probes (Feeler gauges) | 0.02 - 1.00 mm | 0.02 - 1.00 mm | Measurement of axial and radial clearances |
| Torque wrench | Appropriate range (e.g. 10-200 Nm) | 10-200 Nm | Tightening of fasteners according to specifications |
4. Initial evaluation checklist
Before starting detailed diagnostics, perform the following preliminary check. Record all observations and data.
| Check element | What to observe/record | Expected Value/Status |
|---|---|---|
| Working conditions | ||
| Suction pressure | Manometer readings | According to design data (NPSHa > NPSHr) |
| Injection pressure | Manometer readings | According to the design data for the operating point |
| Fluid temperature | Thermometer or sensor reading | Within the operating range of the pump |
| Liquid level in the tank | Visual inspection, readings of the level sensor | Above the minimum level to ensure NPSHa |
| Visual/Audio Review | ||
| Unusual noises | Creaking, gurgling, crackling (characteristic of cavitation), buzzing | Normal operating noise, no extraneous sounds |
| Vibration | Tactile evaluation, vibration analyzer (if available) | Permissible level according to ISO 10816 (eg < 2.8 mm/s RMS for category II, group 2) |
| Origins | Around shaft seals, flanges, housings | Absent |
| Overheating | Bearing assemblies, engine, clutch (by hand or thermal imager) | Bearing temperature < 70°C, motor < 90°C |
| History and changes | ||
| Alarm/Accident Log | Checking the SCADA/DCS system | Records indicating the problem |
| Recent changes/repairs | Did the components, operating modes, pipeline configuration change? | Information about potential sources of the problem |
5. Systematic flow of diagnostics
This section presents a step-by-step diagnostic algorithm that allows you to systematically identify the root cause of the problem.
- Initial assessment: Low flow or no discharge
- Does the pump work?
- If NO:
- Power check:
- Use a multimeter to check the voltage on the motor.
- Expected result: The voltage corresponds to the passport data of the motor (for example, 380V ±10%).
- If the voltage is absent or low: Check the circuit breaker, fuses, cables, contactors. ATTENTION: Working with electrical installations requires qualification and compliance with electrical safety standards.
- Checking the motor:
- Measure the resistance of the motor windings with a multimeter (after LOTO).
- Expected result: The resistance of the windings is uniform (±5%) and corresponds to the passport data.
- If the resistance is uneven or open: Probable motor malfunction.
- Coupling inspection:
- Visually check the coupling for damage, wear, disconnection.
- Expected result: The clutch is intact, reliably connecting the motor and pump shaft.
- → Probable cause: Motor failure, power supply problems, clutch damage.
- → Go to Section 8 (Solutions) for motor/coupling electrical/mechanical faults.
- Power check:
- If YES (pump running but low/no flow): Go to step 2.
- If NO:
- Does the pump work?
- Evaluation of the hydraulic system
- Pressure measurement:
- Record the pressure gauge readings on suction (Pvs) and discharge (Pnagn).
- Expected result: Pvs should be positive (or a small vacuum not exceeding NPSHr), Pnagn should be close to the design value.
- If Pvs is too low (high vacuum) or negative:
- Inspect suction line:
- Visual inspection: Clogging of filter/mesh, foreign objects in pipeline.
- Check for tightness: Air leaks in the suction line (bubbles in the liquid, hissing sounds).
- → Probable cause: Suction problems (clogging, air leakage).
- → Go to Sections 7 (Root Cause Analysis) and 8 (Solutions).
- Inspect suction line:
- If Ppressure is low or zero and Pvs is normal:
- Check valve:
- Check the discharge line check valve for sticking or malfunction.
- Expected result: The valve should be open while the pump is running.
- Checking shutoff valves:
- Make sure all shutoff valves on the discharge line are fully open.
- → Probable cause: Closed valve, defective non-return valve.
- → Go to Section 8 (Solutions).
- Checking for an air plug:
- Was the pump correctly filled (primed)? Can you hear the sound of the pump?
- Check valve:
- Pressure measurement:
