What can cause insufficient flow in a centrifugal pump?

First, check whether the flow meter and pressure gauge show significant deviations. If they are normal, then determine how long the centrifugal pump has been in use; after prolonged use, could the gaskets and other components have worn out, resulting in increased gaps that lead to a decrease in performance?； If it is a new pump, has it undergone performance testing at the factory? The new system should not have such problems; the supplier can be approached to resolve them.

The inlet pressure is low, resulting in a low suction volume.

The flow meter has not been inspected； The pressure gauge checks out normally ； The centrifugal pump has been in use for about a year ； It has undergone performance tests upon leaving the factory and meets the design requirements ；

The root inlet pressure is related to temperature.

The actual flow rate depends on factors such as the installation of the pipes and pumps, as well as the inlet pressure. What does it mean to \"check that the inlet filter is in good condition\"? Just because it’s not blocked doesn’t necessarily mean it meets the required circulation area for the entrance.

The pressure gauge shows normal readings; however, the actual head indicated by the gauge is low. The pump has been in use for a year, and the fluid contains solid particles, so the decrease in flow rate is likely due to wear. But whether the flow rate has decreased by 20 m3/h cannot be determined with certainty, as the flow meter has not been calibrated; therefore, an estimation can only be made based on actual operational conditions. If inspection of the pump reveals significant wear, it is recommended to consider using more wear-resistant materials.

Today the pump was disassembled for inspection; the impeller flow channels were in good condition, and the mouth ring showed no signs of wear.

NPSH: net positive suction head. Check whether the pump is installed in the designated location.

It is necessary to examine the performance curve of the pump to determine whether the operating point falls within the acceptable range under these process conditions; this is related to the selection of the appropriate pump model.

When the pump is first started, its flow rate can be adjusted to the normal level, but after it has been running for some time the flow rate decreases. Even after adjusting it to the normal level using the outlet valve, the flow rate drops again after a while! (The flow meter and the outlet pressure gauge are both accurate.)

Based on what you said about being able to adjust it with an outlet valve, it’s possible that the outlet is set too wide, which causes vaporization of the pump fluid and leads to a decrease in flow rate; this is related to the selection of the pump.

Is this a test run, or regular production? If other media are used as substitutes, it will definitely be different ； If it’s the same medium, check what the current drawn by the pump is and compare it with the rated current specified in the design to determine the result ； It could be due to differences in the medium (even if they are minor), or it might be an issue with the pump selection ； Of course, whether the flow meter being used is accurate also needs to be taken into consideration!

1 Cavitation or gas entrapment 2 Blockage or air leakage in the inlet pipeline 3 Wear of the impeller 4 Wear of the outlet ring or excessive clearance 5 Presence of gas inside the pump and in the suction pipe

It might be a problem with the medium; centrifugal pumps are designed for clean water, and using them as slurry pumps is certainly caused by the high density and poor fluidity of the medium. You can try using a larger pump.

I analyze that there might be two reasons: 1. The filter is clogged, but you don’t notice the dirt because the suction force decreases when the pump is turned off, allowing the dirt to float away from the filter; thus it’s not visible when you clean it. Once the pump is started again, the pressure near the filter drops, and the dirt is drawn back in. Handling method: Keep the pump running and the outlet valve open; do not make any changes. Slowly close the inlet valve, and as soon as the pressure gauge shows a drop in pressure due to vacuum formation, close the inlet valve completely. Then stop the motor, and finally close the outlet valve. Clean the filter again; there’s definitely a reward, I’ve done it myself. 2. If this trick doesn’t work, it’s likely that there was an issue with the initial selection of the pump – it was chosen to be too small. At the beginning of pumping, the back pressure is low, meaning H is small; according to the pump’s performance curve, Q is high and the flow rate is sufficient. But once the back pressure increases as the system fills up, it becomes problematic.

Check the flow meter; if there are no issues, it is recommended to disassemble it for major repairs and adjust the assembly clearances

1. Check the current of the pump; there are several scenarios. a If the current is below the pump’s set value and remains stable, it indicates that the pump’s capacity is insufficient. At this point, it is necessary to check whether the inlet and outlet are unobstructed (whether the inlet filter and outlet pipe valves are in place, whether the outlet pipe has a too small diameter that affects flow rate, and whether the outlet pipe is clear). If the current is low but fluctuates greatly, and if the pump heats up and vibrates significantly, it indicates that the pump has vaporized; in such cases, the pump must be stopped to allow proper venting. It is also necessary to check whether the pump’s seals are intact, and whether the temperature of the fluid being pumped is too high, resulting in vaporization of the fluid. If the current of pump c remains close to or above the design value, it indicates that the pump was selected improperly and does not have sufficient capacity. 3. Check the pressures of the medium at the pump’s inlet and outlet; if the inlet pressure of the centrifugal pump is too low and the pressure difference across the pump has reached the designed value, it indicates that the pump is operating properly. If the pressure of the equipment connected to the pump’s outlet pipe is lower than the pressure required by the pump, then the pump’s maximum pressure can only reach that of the equipment. Because it’s impossible to use a single pump to power the subsequent equipment.

The inlet pressure is low, resulting in a low suction volume.

The allowable suction vacuum degree of the pump is too low, resulting in difficulty in suction!