The centrifugal pump (OH2) isn’t producing sufficient flow – please help analyze the issue
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Two centrifugal pumps in parallel (one in use and one as backup), with each pump having a rated flow rate of 21 m3/h, a head of 50 m; the fluid is ethylene glycol at 154°C, with a density of 0.942. After starting up, the flow rate cannot be increased. The situation is as follows: 1. When two pumps are started, a flow rate of 12.1 m3/h can be achieved, with a pressure reading of 0.5 MPa on the pressure gauge on the main outlet pipe. Then, when the outlet valve was opened further, there was basically no change in the flow rate or outlet pressure. Since the device was in operation, the outlet valve wasn’t opened to its maximum position; it was turned a few notches, yet neither the flow rate nor the outlet pressure changed. 2. Slowly close the outlet valve of one of the pumps (Pump B). At first, there is basically no change in flow rate; once the outlet valve of Pump B is fully closed, the flow rate becomes 8.8 m3/h and the pressure gauge on the main outlet pipe reads 0.48 MPa. 3. The pump operates smoothly during valve opening and closing, without issues such as noise or vibration. 4. By looking at the manufacturer’s performance curve, it can be seen that the maximum flow rate of this pump is around 30 m3/h.
I’m not sure if this is happening for the first time with the new device or after it has been in use for some time In a situation like this, it’s likely that there isn’t enough material supplied. I’m not sure what the concentration of ethylene glycol is in your case – could cavitation be a possibility?
Is the inlet pipeline or inlet filter clogged?
The inlet filter has been checked and is fine. The new device is being operated for the first time.
Many valves are like this: within a certain range of opening, they are not sensitive to the rotation of the valve stem. Is the back pressure too high? When the back pressure exceeds the head, there may be a situation where opening the valve has no effect; check whether the process parameters match those specified at the time of ordering. Furthermore, the fact that the maximum flow rate on the pump curve is 30 m3/h does not mean that this flow rate can necessarily be achieved under your operating conditions. The person who mentioned it earlier is right: if the outlet pressure is low (i.e., the head is low) and the backpressure is high, it will result in an inability to increase the flow rate no matter what, as the flow rate at the intersection of the pump curve and the system curve is always below 30 m3/h
I agree with the comment above; it is recommended to check whether the back pressure in the subsequent stages of the process can be adjusted. Sometimes, when problems occur, it’s not sufficient to focus solely on the pump itself.
It runs smoothly, with no noise or vibration. Could it be a problem with the flow meter? Also, does the pump have a return pipe, and is the return valve open?
It should be a magnetic pump; its pressure is similar to ours. It operates in a negative-pressure environment, requires frequent exhaust, and frequent filter cleaning. Every time we start operation, we repeat the process of switching pumps and cleaning filters. Until the pressure stabilizes and the outlet valve is fully open.
The actual head of the pump is insufficient; there is at least a negative deviation.