What to Do If the Flow Rate of a Horizontal Multistage Centrifugal Pump Is Insufficient?

In industrial and high-rise water supply systems, Omron Tech Pumps horizontal multistage centrifugal pumps are the core power source. However, many engineers find that the pump flow rate gradually "drops" after a period of operation and fails to reach the calibrated parameters.

Combining the theoretical research of fluid machinery and frontline operation and maintenance experience, this article will thoroughly solve the problem of insufficient flow rate from three dimensions: tightness, system resistance and power source performance.

Multistage pump performance check

1. Improper Design and Selection

Cause Analysis:

Mismatch between pump selection and actual working conditions: The rated flow rate and head of the pump fail to accurately match the actual system requirements, for example, the selected pump has an excessively small flow rate or insufficient head to overcome the system resistance. This usually stems from deviations in the calculation of system resistance in the initial design stage, or failure to adjust the pump selection in a timely manner when the actual working conditions change.
Defects in pipeline system design: Factors such as an overly long suction pipeline, small pipe diameter, excessive elbows and high valve resistance will significantly increase the system resistance, causing the actual operating point of the pump to deviate from the high-efficiency zone and thus leading to a drop in flow rate.

Diagnosis and Solutions:

Verify design parameters and performance curves: Recalculate the system head and flow rate requirements accurately, and compare them carefully with the pump performance curve to ensure the pump operates stably in the high-efficiency zone. If necessary, resolutely consider replacing the pump with one that is more suitable for the current working conditions.
Optimize the layout of the pipeline system: Conduct a comprehensive inspection and optimization of the suction and discharge pipelines, minimize unnecessary elbows and valves, and ensure the pipe diameter meets the optimal requirements for fluid transportation, thereby effectively reducing pipeline resistance.

2. Installation and Commissioning Issues: Key Points for On-site Troubleshooting

Cause Analysis:

Air leakage at the suction pipeline and valve base: This is a common and key cause of insufficient flow rate. Poor sealing of the suction pipeline or valve base will cause air to continuously enter the pump chamber, trigger cavitation, and seriously weaken the water absorption capacity and flow rate of the pump. It is imperative to inspect the suction pipe and valve base to ensure no air leakage occurs.
Clogging of the foot valve or suction filter: The foot valve fails to open fully, or the suction filter is severely clogged with debris (such as sediment, fibers, etc.), which will cause a sharp increase in suction resistance and prevent the pump from drawing enough liquid.
Incorrect motor rotation direction: Incorrect motor wiring may cause the pump impeller to rotate in the reverse direction. In this case, although the pump is running, it can hardly generate an effective flow rate or the flow rate is extremely low.
Poor alignment between the pump and the motor: Poor alignment accuracy of the coupling will cause abnormal vibration of the pump unit, accelerate the wear of bearings and seals, and thus affect the operating efficiency and flow stability of the pump.

Diagnosis and Solutions:

Conduct a strict inspection of the tightness of the suction pipeline: Perform a rigorous air tightness test on the suction pipeline and all connection points, and repair any air leakage points in a timely manner. Ensure all connections are fastened reliably, especially the connection between the suction pipe and the valve base.
Clean the foot valve and filter regularly: Establish a system for regular inspection and cleaning of the foot valve and suction filter to ensure they are always unobstructed and avoid debris accumulation.
Confirm the correct motor rotation direction: By jogging the motor, carefully observe whether the rotation direction of the pump is consistent with the direction indicated by the arrow clearly marked on the pump body. If inconsistency is found, adjust the motor wiring immediately.
Perform precise alignment calibration: Use professional alignment tools (such as laser alignment instruments) to conduct high-precision alignment of the pump and motor, fundamentally reducing vibration and component wear.

3. Improper Operation and Rotation Speed Optimization

Cause Analysis:

Inadequate priming of the pump: If the air in the pump chamber and suction pipeline is not completely exhausted before startup, the pump will fail to absorb water normally or the flow rate will be severely insufficient.
Insufficient rotation speed caused by low system voltage: Unstable or continuously low power supply voltage will directly cause a drop in motor rotation speed, thereby significantly reducing the pump performance (including flow rate and head). Insufficient rotation speed is an important cause of insufficient flow rate for horizontal multistage centrifugal pumps.
Insufficient opening of the outlet valve: After the pump is started, if the outlet valve is not fully opened, the flow output will be artificially restricted.
Cavitation: Severe suction conditions (such as excessively high suction lift, high suction pipeline resistance, excessively high liquid temperature) cause the pressure at the pump inlet to be lower than the vaporization pressure of the liquid, generating a large number of bubbles and triggering cavitation. Cavitation will cause a sharp drop in flow rate, accompanied by abnormal noise and violent vibration.

Diagnosis and Solutions:

Perform thorough air exhaust and pump priming operations: Before each startup, ensure that the pump chamber and suction pipeline are completely filled with liquid and all residual air is exhausted thoroughly.
Inspect and stabilize the power supply voltage: Inspect the power supply voltage regularly to ensure it is stable and meets the rated voltage requirements of the motor. If necessary, consider installing a voltage stabilizer to effectively increase the rotation speed of the multistage pump.
Check the opening of the outlet valve: Confirm that the outlet valve is fully opened and adjust it to the optimal operating opening according to the actual process requirements.
Improve suction conditions and water entry depth: Increasing the water entry depth of the horizontal multistage centrifugal pump can effectively increase the suction pressure of the pump, thus solving the flow problem caused by insufficient water pressure. At the same time, the suction lift should be reduced as much as possible, the suction pipeline resistance should be decreased, and the transportation of overheated liquid should be avoided. If necessary, consider installing a booster pump or optimizing the design of the suction pipeline.

4. Improper Maintenance and Component Wear: Timely Replacement of Wearing Parts

Cause Analysis:

Impeller wear or damage: During long-term operation, the impeller may be damaged due to corrosion, wear or jamming by debris, and the impeller flow channel may be deformed, which seriously affects the work capacity of the pump and leads to a significant drop in flow rate.
Internal leakage caused by wear of the sealing ring: The gap between the sealing ring and the impeller increases with the use time, leading to an increase in the backflow of liquid inside the pump, a sharp reduction in volumetric efficiency, and thus a decrease in effective flow rate.
Bearing wear: Bearing wear will increase the friction between the rotor and the stator, reduce the mechanical efficiency of the pump, and may even cause vibration and shaft seal leakage, indirectly affecting the flow rate.
Leakage of packing or mechanical seals: Wear or improper installation of seals (such as packing or mechanical seals) will cause liquid leakage, which not only affects the normal operation of the pump but may also lead to insufficient flow rate.

Diagnosis and Solutions:

Inspect and replace the impeller regularly: Establish a system for regular inspection of the impeller condition, clean up debris in a timely manner, and repair or replace worn and damaged impellers. For pumps that have been used for a long time, the worn impellers should be replaced in a timely manner.
Replace the sealing ring in a timely manner: Inspect the gap of the sealing ring regularly, and replace it with a new one immediately once an excessive gap is found to ensure the gap is within the design allowable range and maintain the volumetric efficiency of the pump. The performance of some sealing rings will decline after long-term use, so we need to replace them in a timely manner.
Inspect and replace bearings: Inspect the lubrication condition and wear degree of bearings regularly, and replace damaged bearings in a timely manner to ensure the smooth and efficient operation of the pump.
Inspect and replace seals: Inspect the wear and leakage of packing or mechanical seals regularly, and adjust or replace them as needed to prevent liquid leakage from affecting pump performance.

Conclusion

Solving the problem of insufficient flow rate of a horizontal multistage centrifugal pump is not difficult; the key is to identify the root cause accurately. Remember our mnemonic: "Prevent air leakage and check the foot valve, clean up debris and unclog pipelines, stabilize voltage to ensure rotation speed, replace parts in time to eliminate wear".

By increasing the water entry depth to raise water pressure, ensuring stable voltage to maintain a high rotation speed, and resolutely replacing aging sealing rings and impellers, you can not only quickly restore the rated flow rate of the pump but also extend the service life of the equipment and reduce operating energy consumption.

If you need a replacement tutorial for the sealing ring of a specific model of horizontal multistage pump, solutions for unstable voltage or professional selection and calculation support, please feel free to contact us. It is our common pursuit to make every drop of water flow efficiently with Omron Tech Pumps.