Reasons for the drop in outlet pressure of a vertical multistage centrifugal pump (booster pump)

Reasons for Reduced Outlet Pressure of Vertical Multistage centrifugal pumps (Booster Pumps)

There are many reasons why the outlet pressure of stainless steel vertical multistage centrifugal pumps drops. Once I understand these reasons, I can take corresponding measures based on the specific situations encountered on-site to solve the issue with the stainless steel vertical multistage pumps.

The specific reasons are as follows:

1. Motor Reversal
Due to wiring problems, the motor may rotate in the opposite direction of what the Pump requires. Usually, when starting, power the motor briefly to observe whether the Pump's rotation direction matches the required direction. If the rotation is reversed, simply swap any two wires on the motor terminals.

2. Internal Leakage of the Pump
When the gap between the rotating and stationary parts inside the Pump exceeds the design range, internal leakage occurs, showing as a drop in the Pump's discharge pressure. This can happen at places like the impeller eye clearance or the inter-stage gaps in multistage Pumps. At this point, the Pump should be disassembled and inspected, and parts causing excessive gaps should be repaired or replaced.

3. Reduced Pump Speed
The impeller diameter and Pump speed are critical factors affecting the Pump head. Under other constant conditions, the Pump head is proportional to the square of the speed, so speed has a significant impact on head. Sometimes, due to external causes, the Pump speed drops, which in turn lowers the Pump head. In such cases, check the Pump speed and investigate the reason to resolve it properly.

4. Cavitation at the Pump Inlet
If the suction pressure is too low, below the saturation vapor pressure of the medium, cavitation will occur. In this case, check for blockages in the inlet piping or whether the inlet valve opening is too small, or increase the liquid level in the suction tank.

5. Operating Point Shifts to Higher Flow
Typically, vertical multistage centrifugal pumps have a continuously downward-sloping performance curve, meaning the flow increases as the head decreases. During operation, if for some reason the pump pressure drops, the operating point passively shifts along the system curve to a lower head and higher flow point, resulting in reduced head. This is usually caused by external factors like changes in the system rather than the pump itself. Increasing the back pressure on the pump, such as slightly closing the outlet valve, can resolve the problem.

6. Clogging of Pump Impeller Passages

7. If part of the impeller passage is blocked, it will affect the pump's performance, causing the outlet pressure to drop. In this case, the pump should be disassembled to remove any foreign objects. To prevent this issue from recurring, if the cleanliness of the inlet medium cannot be guaranteed, a filter device can be installed before the pump inlet.