Common problems and solutions during the installation of centrifugal pumps

Centrifugal pumps, as core equipment for fluid transportation, are widely used in fields such as petrochemicals, electric power, municipal water supply, and sewage treatment. The quality of their installation directly impacts operational efficiency, energy consumption, and equipment life. However, in practical applications, centrifugal pumps often suffer from problems such as excessive vibration, leakage, and bearing overheating due to improper installation, construction errors, or design flaws. This article analyzes common problems encountered during centrifugal pump installation, drawing on typical project cases, and proposes solutions to improve the quality of practical applications.

 

 

1. Foundation Installation Issues

Case 1: Heavy Oil Transfer Pump at a Refinery

1.1 Installation Issues:

1) Insufficient foundation strength (cured for only three days), causing the pump body to sink and tilt.

2) Anchor bolts not tightened, and anti-loosening measures inadequate.

1.2 Engineering Practice:

1) According to the concrete manufacturer's instructions: Foundation curing time ≥ 7 days.

2) The thickness of the secondary grouting layer must be no less than 25mm.

1.3 Problem Symptoms and Consequences

1) 0.5mm cracks appeared in the foundation after two months of operation.

2) Vibration increased from 2.8mm/s to 6.5mm/s (45% above the standard).

3) Bearing life was reduced to 30% of the design value.

1.4 Cause Analysis:

1) Insufficient foundation stiffness (measured at only 65% ​​of the design value).

2) Grouting layer shrinkage caused voids (ultrasonic testing showed 20% of the area was void).

1.5 Solution:

1) Use a high-strength, shrinkage-free concrete foundation with a curing period of at least 7 days.

2) Use a level to calibrate the pump base, ensuring a level deviation of ≤0.1 mm/m.

3) Use the correct secondary grouting process to ensure the anchor bolt tightening torque meets specifications.

 

2. Pipe Installation Issues

Case 2: Cooling Water Pump (Equipped with Inlet Filter) at a Pharmaceutical Factory

2.1 Installation Issues:

1) The horizontal section of the inlet pipe was tilted upward by 5° (causing air pockets)

2) Three short-radius elbows were installed in the inlet pipe.

2.2 Engineering Practices:

1) There should be no high points in the inlet pipe that could easily cause air pockets.

2) The straight section after the elbow should be ≥ 3 pipe diameters; the slope of the eccentric reducer must face downward.

2.3 Problem Symptoms and Consequences:

1) Operating current overload of 42%, resulting in motor burnout.

2) Periodic air-binding shutdowns (flow loss ≥ 25%), resulting in a 30% decrease in system efficiency.

2.4 Cause Analysis:

1) The upward tilt of the pipe and the excessive number of elbows caused air accumulation (causing air pockets), reducing the effective flow cross-section.

2) The filter's filtration area was too small, resulting in insufficient NPSH safety margin.

2.5 Solution:

1) Reroute the pipes (eliminate high points prone to air pocket formation and remove redundant elbows)

2) Increase the length of the straight pipe after the elbows

3) Increase the filter area to 3-4 times the pipe cross-sectional area to reduce resistance

 

3. Pipe Stress Issues

Case 3: Acid Pump at a Chemical Plant

3.1 Installation Issues:

1) Inlet and outlet pipes were installed using forced butt joints.

2) No pipe supports were installed.

3.2 Engineering Practices:

1) Pipeline stress ≤ 0.1 times the pump weight (confirm that the pipe load is within the pump's load capacity).

2) Pipeline displacement ≤ 0.15 mm/m.

3.3 Problem Symptoms and Consequences:

1) Flange leakage rate increased by 200%.

2) The average life of the mechanical seal was only 1,800 hours.

3) The pump body exhibited a permanent deformation of 0.2 mm.

3.4 Cause Analysis:

1) Thermal expansion of the pipe generated an additional force of 1.8 kN.

2) Flange bolt stress exceeded the specified value (reaching 85% of the yield strength).

3.5 Solution:

1) Install spring supports on the pipe near the pump inlet and outlet flanges.

2) Use flexible connections (metal bellows compensation ≥ 10 mm).

 

4. Cavitation Issues

Case 4: Boiler Feedwater Pump at a Power Plant 

4.1 Installation Issues:

1) Sharp 90° Bend in Suction Pipeline

2) NPSH Safety Margin Not Calculated

4.2 Engineering Practice:

1) NPSHa ≥ 1.3 × NPSHr

2) Suction Inlet Velocity ≤ 2 m/s

4.3 Problem Symptoms and Consequences:

1) Impeller Cavitation (Pit Depth Reaches 3 mm After 6,000 Hours of Operation)

2) 15% Efficiency Drop

3) Periodic Vibration Fluctuations (±2 mm/s)

4.4 Cause Analysis:

1) Actual NPSHa is Only 5.1 m (Required 6.6 m)

2) Local Resistance Loss Reaches 0.35 MPa

4.5 Solution:

1) Modify the suction line (use a long-radius elbow R=5D)

2) Raise the liquid level by 2.5m (NPSHa increased to 7.3m)

 

5. Alignment Issues

Case 5: Circulating Water Pump at a Steel Plant

5.1 Installation Issues:

1) Cold Alignment Fails to Consider Thermal Expansion

2) Alignment Using a Standard Dial Indicator

5.2 Engineering Practices:

1) Cold Alignment Requires Allowance for Thermal Expansion

2) Coupling Radial/Angular Deflection is Typically Required to Be ≤ 0.05mm

5.3 Problem Symptoms and Consequences:

1) Vibration Rise to 8mm/s at Operating Temperatures of 80°C

2) Coupling Bolts Fracture (Replace Every 3 Months)

3) Bearing Temperature Reaches 95°C

5.4 Cause Analysis:

1) Thermal Expansion Leads to Angular Deflection of 0.12mm/m

2) Alignment Error Causes Additional Load (Up to 150% of Design Value)

5.5 Solution:

1) Use a Laser Alignment Tool for Hot Compensation Alignment

2) Use a Diaphragm Coupling (Permits 0.3° Angular Deflection)

 

6. Lubrication Issues

Case 6: Solvent Pump at a Chemical Plant (2019)

6.1 Lubrication Issues:

1) Over-grease the bearing housing (up to 80% of capacity)

2) No grease drain port is provided.

6.2 Engineering Practice:

1) Grease filling volume should be ≤ 50% of the bearing space.

2) Grease should be relubricated every 2,000 hours of operation.

6.3 Problem Symptoms and Consequences:

1) Operating temperature continuously above 85°C.

2) Grease carbonization.

3) Average bearing life is only 4,000 hours.

6.4 Cause Analysis:

1) Overlubrication causes churning heat (temperature rise up to 35K).

2) Excess grease cannot be drained (contamination level reaches ISO 4406 Class 20/18).

6.5 Solution:

1) Install an automatic lubrication system (5cc of grease per injection).

2) Switch to synthetic grease (applicable temperature range -30°C to 150°C).

 

7. Accessory and Foundation Issues

Case 7: Acid Pump

7.1 Installation Issues:

1) The flange gasket inner diameter was 1.5mm smaller than the pipe diameter, resulting in throttling.

2) Foundation level deviation was 0.25mm/m (150% above the standard).

7.2 Engineering Practice:

1) Gasket inner diameter = pipe diameter + 1mm

2) Foundation level ≤ 0.1mm/m

7.3 Problem Symptoms and Consequences:

1) Flow rate decreased by 35%

2) Acid corrosion and leakage from seals

3) Failure to re-grout anchor bolts caused resonance cracking

4) Pump body displacement exceeded the standard.

7.4 Cause Analysis:

1) The throttling effect increased the local flow velocity

2) Superimposed foundation vibration stress accelerated fatigue cracking

7.5 Solution:

1) Replace the gasket with a qualified one and re-measure the levelness after foundation grouting.

2) Perform hot alignment and re-measurement every 2,000 hours to prevent misalignment.

 

The installation quality of a centrifugal pump directly impacts its operational reliability and service life. Standardized foundation construction, precise alignment, optimized installation, and cavitation prevention measures can significantly reduce the failure rate. After installation, we recommend conducting a no-load test run (≥2 hours) and a loaded test run (≥4 hours), and regularly monitoring parameters such as vibration and temperature to ensure long-term stable operation.