Common Causes of Low Pressure in Multistage Pumps

When it comes to multistage pumps, maintaining optimal pressure performance is critical. These pumps are widely used across industries—from water treatment plants to oil and gas processing facilities—because they efficiently move fluids under high pressure. However, even a minor drop in pressure can disrupt system operations, reduce efficiency, and lead to costly downtime.

But what exactly does【low pressure】mean in real-world applications? It typically refers to a pump's inability to achieve the required pressure level to support system demands. This can result in inadequate fluid delivery, lower system performance, or even complete operational failure. Understanding the root causes behind low pressure in multistage pumps is essential for diagnosing the issue and implementing effective solutions.

Below, we'll break down the most common causes of low pressure in multistage pumps and provide actionable insights for addressing them.

1. Mechanical and Installation Issues

Mechanical and installation-related factors often contribute to low pressure in multistage pumps. Even minor setup or alignment problems can severely affect pump performance.

a. Improper Pump Sizing or Selection

Selecting the wrong pump for an application is a frequent cause of low pressure. A pump must match the operational requirements, including flow rate, head, and system pressure. A pump that's undersized or not suited for the application will fail to maintain optimal pressure, resulting in subpar performance.

Practical Example:

A manufacturing plant selects a smaller pump to save costs, but the pump cannot meet the pressure demands of its production system. Performance drops, forcing costly retrofit adjustments.

b. Incorrect Pump Motor Rotation 

The direction of motor rotation directly impacts how the pump impellers perform. Improper rotation can reduce the efficiency and pressure output of a multistage pump.

Quick Fix:

Verify motor rotation during installation and consult the pump manual to ensure it aligns with the manufacturer’s specified direction.

c. Shaft Misalignment or Mechanical Wear

Shaft misalignment, whether from improper installation or wear over time, creates inefficiencies in the pump. Friction increases, leading to reduced flow rates and pressure. Pumps must be inspected regularly to identify signs of wear or alignment issues.

d. Leakage in Seals, Gaskets, or Fittings

Even small leaks in seals or fittings can bleed pressure from the system. These often develop due to wear-and-tear or improper installation practices. Keeping seals and gaskets in good condition is necessary to maintain pressure integrity.

2. Hydraulic Problems

Hydraulic issues often arise within the pump itself, particularly under challenging operating conditions. These problems can significantly affect the pump’s ability to deliver consistent pressure.

a. Air Entrainment or Cavitation

When air enters the pump or low-pressure zones form near the impellers, cavitation occurs. This not only reduces pressure but can also cause long-term damage to internal components.  

Solution: Minimize cavitation by eliminating restrictions in the suction line and ensuring proper NPSH (Net Positive Suction Head).

b. Blocked or Partially Clogged Impellers

Particles or debris in the fluid can clog impellers, disrupting fluid flow and lowering pressure performance. Install filters and clean impellers regularly to prevent clogs.

c. Excessive Clearance Between Impellers and Casing

Wear or poor machining can increase the clearances between impellers and casings, reducing their efficiency. Regular inspections and proper machining during repairs help maintain the right tolerances.

d. Worn-Out Wear Rings or Diffusers  

Components like wear rings and diffusers experience abrasion during operation, leading to inefficiencies and pressure loss. Replace these components promptly when visible damage occurs.

3. Suction Side Issues

Most pressure-related problems in multistage pumps start on the suction side. Ensuring proper suction conditions is crucial for maintaining stable performance levels.

a. Low Water Level in the Source Tank

If the water level in a tank or well is too low, it can restrict fluid flow and result in a drop in pressure. Keep tanks filled to the appropriate levels or implement level monitoring systems.

b. Suction Pipe Leaks Allowing Air Entry

Leaks in the suction piping system can introduce air, causing cavitation and disrupting the pump's pressure balance. Regularly inspect piping for leaks and repair faults as needed.

c. Blocked Suction Strainer or Clogged Filters

A clogged suction strainer restricts fluid entry into the pump, diminishing the flow rate and pressure output. Cleaning or replacing filters at intervals is vital to prevent this.

d. Incorrect Suction Lift  

Exceeding the pump's suction lift capability causes performance degradation. Match the pump model to the specific suction conditions of your system for optimal results.

4. Discharge Side Problems

Pressure issues on the discharge side are another common culprit.

a. Discharge Piping Leaks

Leaks in the discharge piping can cause pressure drops across the system. This compromises fluid delivery to downstream applications. Routine inspections and leak repairs are essential.

b. Partially Closed or Malfunctioning Valves

Valves that remain partially closed or malfunction will impede fluid flow, causing a drop in pressure. Ensure all valves are fully opened during normal operations and address faults promptly.

c. Excessive System Demand

When the demand within a system exceeds what the pump can supply, the pressure will drop. Consider upgrading to a higher-capacity pump or splitting the load across multiple pumps to resolve this.

d. Pressure Gauge Errors

Calibration errors in pressure gauges can lead to inaccurate readings, creating the illusion of low-pressure conditions. Regularly calibrating gauges ensures reliability.

5. Motor and Power Supply Factors

The pump motor is the heart of the system. When issues arise in the motor or power supply, they inevitably impact pressure performance.

a. Insufficient Motor Speed

Delayed or inadequate motor speed, often due to electrical faults, will cause pressure drops. Troubleshoot speed controls and motor settings as part of regular diagnostics.

b. Voltage Fluctuations

Fluctuating voltage can underpower motors, affecting pump operation. Install voltage stabilizers to provide consistent power and improve reliability.

c. Motor Overload or Failure

Overloading the motor reduces its efficiency, directly affecting the pressure capacity of the pump. Avoid running the pump under conditions that exceed its rated specifications.

6. Maintenance and Operational Errors

Finally, a lack of regular maintenance or operational oversights can contribute to low-pressure issues.

a. Lack of Inspections

Without regular maintenance checks, worn components and leaks can go unnoticed. Implement a proactive maintenance schedule that includes inspections, lubrication, and cleaning.

b. Operating Outside Recommended Range

Running a pump outside its design specifications leads to poor pressure performance. Always adhere to manufacturer recommendations regarding speed, flow rates, and pressure levels.

c. Poor Lubrication or Cooling

Heat buildup in motor bearings due to inadequate lubrication or cooling will affect performance and efficiency. Regularly check lubrication systems and cooling mechanisms.

Conclusion

Low pressure in multistage pumps can stem from a variety of issues, including mechanical faults, hydraulic inefficiencies, suction or discharge problems, motor issues, and inadequate maintenance. Addressing these challenges begins with understanding the root causes and implementing targeted solutions.

Key Takeaways:

• Conduct regular inspections to identify wear or leaks.

• Maintain proper alignment, lubrication, and cooling.

• Match your pump to your system’s operational requirements.

• Avoid cavitation by ensuring optimal suction conditions.

• Monitor both suction and discharge pressure regularly.

By prioritizing preventive maintenance, accurate diagnostics, and proper installation practices, engineers and maintenance professionals can enhance pump reliability and system performance while preventing costly downtime. Solving low-pressure problems starts with a systematic approach—step by step.