Reasons for the decrease in pump outlet flow rate

Proceed as appropriate; everything is working normally. It’s possible that the amount of process medium has decreased, which in turn reduces the flow rate.

Is the inlet positive pressure or negative pressure? What is the pump inlet pressure, and what is the medium? Because it is only possible to determine based on these conditions whether there are blockages in the inlet pipeline or other similar issues

I wonder what medium the pump is transporting. If the pump is controlled by an inverter, then a decrease in speed will also result in a reduction in its output flow rate

Reason: 1. The temperature of the medium being transported increases, leading to cavitation, or the cooling effect of the rear heat exchanger is poor, resulting in an increased pressure drop； ⒉Backward pressure increases. This post was last edited by 156026692 on 2009-2-5 21:13]

Has the resistance in the pump outlet pipeline increased?

Reasons: 1. Insufficient inlet pressure. 2. Clogged inlet pipeline or filter. 3. Air leakage in the pump’s inlet pipeline. 4. Excessively high medium temperature, causing water to vaporize. 5. Clogged impeller or motor running in reverse. That’s about it.

1. How long has the pump been running? Is the medium highly corrosive? It may be due to impeller corrosion or erosion, resulting in an increased gap in the mouth ring. 2. Check the motor direction.

The pump inlet pressure is 13 KPa (absolute pressure); it is a vacuum tower, and the outlet leads to another tower whose pressure is 8.0 KPa (absolute pressure)； The medium temperature is around 155 degrees ； It’s impossible for the inlet pipeline to leak; otherwise, the vacuum wouldn’t be maintained ； The moisture content of the material is extremely low, at 0.01% ； The outlet flow was good before, but it has now decreased; therefore, reverse rotation of the motor can also be ruled out ； The medium is not corrosive ； The liquid level in the pump inlet tower is normal ； Cavitation cannot be ruled out at the moment; although the inlet filter is clean, an obstruction in the inlet pipeline still cannot be excluded ； The outlet filter is clean, but the outlet pipeline is blocked and cannot be removed ； Other mechanical failures of the pump cannot be ruled out. Thank you all for your analysis; I will continue to look for the real cause.

How can the liquid level in the tower remain normal when the flow rate is below a certain value? As for the tower downstream, if everything is working properly, the following points need to be considered: 1. Has your flow meter been calibrated? 2. Is the control valve at the pump’s outlet stuck? 3. Is the pump’s current within normal ranges? 4. There is a return line – what is its opening degree?

I would like to ask the original poster to provide the following information: 1. Does this pump have variable frequency control? 2. Has the flow meter been calibrated? 3. Have the parameter conditions of the conveyed medium changed? Such as density, operating temperature or pressure, and so on.

Back on the 11th floor, the pump is a simple centrifugal pump without variable frequency control. The flow meter has not been calibrated before or after use. Have the parameters of the medium being transported changed? Its density, operating temperature, and pressure are all the same as before. There is a return line, but both manual valves are fully closed. Since the pump is small, there is no ammeter. How can the liquid level in the tower remain normal when the flow rate is below a certain value? Previously, the outlet flow rate of this pump was 8500 kg/h with the control valve set at 75% open. To maintain this stable flow rate of 8500 kg/h, the automatic control valve was continuously opened further, until it reached 98% open to keep the flow rate at 8300 kg/h; making slight adjustments to other operating parameters was sufficient to ensure normal liquid levels.

By reviewing the analyses provided by the fellow sailors above, I believe that the decrease in efficiency is caused by mechanical issues with the pump, such as an increased gap in the sealing ring or wear and tear on the impeller.

When the flow rate decreases, does the head change if the valve remains open at its original setting of 75? Is it getting bigger? By increasing the valve opening to boost flow rate, is the head at this point close to that at an opening of 75%? If the head hardly changes before and after increasing the valve opening, it is very likely that there is a restriction somewhere in the piping outside the valve

Please ask LZ to explain the changes in the liquid level of the feed tower as well as the changes in the outlet pressure, so as to determine whether it is a problem with the flow meter or a decrease in pump flow. If the pump flow rate indeed decreases, in addition to the reasons mentioned, it could also be due to a faulty check valve or a loose impeller cover

Reply to floor 14: To ensure adequate flow, the valve was opened further, and the opening degree never dropped below 75%. Reply to floor 15: As the valve was increased from 75% to 98% open, the flow rate rose to a value close to the target level; therefore, the liquid level did not change much. The pressure at the pump outlet decreased from 0.4 MPa to 0.3 MPa. However, this pressure is still sufficient to provide the necessary driving force against the 8.0 KPa (absolute pressure) in the subsequent tower. From the thorough analyses provided by various forum members, it seems that the range of possible causes for the problem is gradually narrowing down. The issue is likely to lie within the pump itself – as mentioned by the forum members, it could be due to corrosion and erosion of the impeller, or a decrease in efficiency caused by an increased gap in the seal rings. We might find out the real reason in the day after tomorrow, as the pump has been switched to a backup pump; the pump needs to be taken apart for maintenance in order to identify the cause. I’ll let all the sea friends know then.

Reasons: 1. Obstructions in the inlet pipeline or filter. 2. The temperature of the medium is too high, causing water to vaporize. 3. If the medium is a cold material such as ethylene or propylene, check whether there is severe insulation loss in the pipelines, which leads to an increase in back pressure due to vaporization of the material. 4. A high back pressure in the system after the pump outlet can also result in a decrease in the pump’s flow rate.

Is there a problem with the flow meter? I encounter this situation in my workshop sometimes, especially in winter.

Could it be that there is a slight leak in the pump seal? Since it’s a vacuum tower, air is drawn in, so the leak isn’t visible.

There is no ammeter on site; an electrical specialist can go to the substation to measure it and compare it with the rated current. If possible, the pump can be disassembled to check the clearance of the ring seal

There might be a leak inside the pump, causing the fluid to flow back.