What are the reasons for low outlet pressure in a pipeline pump (vertical centrifugal pump)?
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Hello everyone. Our company has recently purchased two new pipeline pumps, model DGDS100-250, with a head of 65m and a flow rate of 100 m3/h. The inlet and outlet diameters of these pipeline pumps are DN100; however, due to limitations in the pipeline installation on site, the inlet and outlet pipes use a diameter of DN80. (1) These pipeline pumps are used for transferring oil products, from tankers to storage tanks via these pumps. The inlet pressure of the pumps is 0.1 MPa, while the pressure in the pipeline system is approximately 0.1–0.3 MPa. The medium transported is oil, with a density of 800 kg/m3. (2) When the pump is started with the outlet valve still closed, the outlet pressure is 0.65–0.8 MPa. By gradually adjusting the outlet valve, the outlet pressure drops rapidly; when the valve is opened by 20%-30%, the outlet pressure falls to 0.15–0.2 MPa. (3) It is necessary to check that the inlet filter is not clogged and that the liquid level in the tanker is sufficient； Question: (1) Why is the opening of the outlet valve so small and the outlet pressure so low? (2) The valve is in a low position, so the flow rate does not reach the rated value; the current flow rate is approximately 40 m3/h (with a rated value of 100 m3/h) (3) Should the outlet pressure of a centrifugal pump be independent of the back pressure? Is it because of the low back pressure? I appreciate your advice! Thank you!
At the sites I visited, the pump inlets were all connected to the pump inlet after the large pipes had their diameter increased; I never saw any situation where a small pipe was converted into a larger one. According to the normal behavior of pumps, when the outlet valve is opened wider, the outlet pressure should decrease while the flow rate should increase. It’s necessary to check the pump’s performance curve to see whether these values fall within the range indicated by the curve. What will happen if the valve is opened even further? Will the flow rate increase as well?
The resistance in the outlet pipeline is low; what is the current and flow rate when the outlet valve is fully open?
The discharge pressure is related to the back pressure, and the flow rate point is the intersection of the pump’s performance curve and the pipeline resistance curve
Thank you! If the valve is opened further, the pressure will continue to drop! Continuing to open the valve will increase the flow rate, but the pressure drop remains high, and the rated flow rate is not yet achieved. The other pumps are operating normally. There is no overcurrent.
Were the medium parameters provided to the supplier when purchasing the pump? What is the viscosity of the oil? A value above 20 cP requires correction and conversion. The parameters on the pump are calculated based on water.
It’s provided, do I understand? Testing is always carried out using water as the medium at the factory.
1. A rapid drop in pressure indicates that the pressure in the outlet pipeline has not been established. The pipeline flow is insufficient and there is gas present; the pump can be run at a low flow rate for a while first, with the valves gradually opened thereafter. 2. Is the pump noisy and experiences significant vibration during operation? The inlet pipe is smaller in diameter than the pump outlet, making it difficult to achieve a sufficient flow rate.
1. Is the intake volume at the inlet sufficient? 2. Is it gaseous?
The inlet pipeline is too small; there’s no other reason.