A platform for sliding vane pump and centrifugal pump tests is installed to study the series operation of them under different characteristics of pipeline. Firstly, the sliding vane pump and the centrifugal pump work independently, and the performance is recorded. Then, the two types of pumps are combined together, with the sliding vane pump acting as the feeding pump. Comparison is made between the performance of the independently working pump and the performance of series operation pump. Results show that the system flow rate is determined by the sliding vane pump. In order to ensure the stability of the series operation pumping system, the energy consumption required by the pipeline under the system flow should be greater than the pressure energy centrifugal pump can generate. Otherwise, the centrifugal pump can not operate stably, with reflux, swirl, gas-liquid two-phase flow in the runner and strong vibration and noise. The sliding vane pump can be in serial operation with the centrifugal pump under limited conditions.
In china, some oil devices are equipped with sliding vane pumps (such as the fixed refueling vehicles), and some are equipped with centrifugal pumps (such as the delivery pumps in oil pipeline). In order to complete the mission of transporting oil for emergency, there is a strong demand for combining these equipments together under current equipment system, thus leading to the series operation of the two types of pumps.
However, the working principles of sliding vane pump and centrifugal pump are completely different. The former belongs to positive displacement pumps, while the latter belongs to dynamic pumps [
In order to investigate the series operational properties of them and guide their application, an experimental platform is designed and installed [
The experimental process and equipments of the independent operation of sliding vane pump and centrifugal pump are shown in Figure
Parameters of pumps.
Model | Type | Differential pressure (MPa) | Rated flow (m3/h) | Rotational speed (r/min) |
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SUB50-15/40 | Sliding vane pump | 0.4 | 15 | 1440 |
IH50-32-200 | Centrifugal pump | 0.5 | 12.5 | 2900 |
Flowchart of the independent operation of sliding vane pump and centrifugal pump.
To take a sliding vane pump at a rotational speed of 1490 r/min and a centrifugal pump at 2940 r/min, for example, through the parameters gained from the experimental records and calculation, the performance curves of two pumps are drawn (Figures
Performance curve of sliding vane pump.
Performance curve of centrifugal pump.
Based on the above single pump experiment, an experiment on the series operation of sliding vane pump and centrifugal pump is adapted, as shown in Figure
Series operation flowchart of sliding vane pump and centrifugal pump.
(1) Shut down the by-pass butterfly valve, open all the gate valves in pipeline, start data collection at 0 s, and start the sliding vane pump at 9 s.
(2) After the system is running steadily, open centrifugal pump at 140 s, and the two pumps operate in series. Shut down the centrifugal pump and sliding vane pump at 1012 s and 1046 s successively. Stop data collection at 1060 s.
(3) Open the sliding vane pump and centrifugal pump again. When the two pumps operate in series, open the butterfly valve of the by-pass pipeline on the outlet of centrifugal pump. Observe the liquid flow through sight glass.
(1) It is the same as Step 1 in experiment I.
(2) When the liquid flow is stable, start the centrifugal pump (at 98 s). The two pumps then operate in series. When the pressure of centrifugal pump outlet is stabilized at 0.02 MPa, adjust valve 19 of centrifugal pump outlet (at 260 s) to change the pipeline friction loss. Narrow down the opening of valve 19 to increase the outlet pressure of centrifugal pump by 0.05 MPa each time until the valve is fully closed (1764 s). The outlet pressures of centrifugal pump and its corresponding time are shown in Table
Outlet pressures of centrifugal pump versus time.
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|
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272 | 0.07 | 833 | 0.47 | 1345 | 0.87 |
376 | 0.12 | 890 | 0.52 | 1408 | 0.92 |
442 | 0.17 | 962 | 0.57 | 1460 | 0.97 |
504 | 0.22 | 1023 | 0.62 | 1524 | 1.02 |
582 | 0.27 | 1085 | 0.67 | 1590 | 1.07 |
646 | 0.32 | 1148 | 0.72 | 1640 | 1.12 |
702 | 0.37 | 1213 | 0.77 | 1705 | 1.17 |
770 | 0.42 | 1285 | 0.82 | 1764 | 1.19 |
Note:
(3) Open gate valve 19 quickly until it is fully opened, and stop the centrifugal pump and sliding vane pump, stop data collection.
In experiment I, the system is stable when the sliding vane pump is working alone. All parameters have good stability. But after the centrifugal pump is turned on, the centrifugal pump and its pipeline begin to vibrate and obvious noise and severe calorification can be observed. The changes of all parameters are shown in Figures
Variation trend of
Variation trend of flow and differential pressure in experiment I.
As shown in Figure
As shown in Figure
Compared with the independent working condition of the two pumps, the flow and differential pressure changes of the sliding vane pump follow the rule which is suggested in Figure
Based on experiment I, we close the outlet valve of the centrifugal pump gradually to make a further study in experiment II. The variation of the system parameters in the experiment is shown from Figures
Variation trend of
Variation trend of flow and differential pressure in experiment II.
The working status of the system before closing the outlet valve and after opening the outlet valve is the same as that in experiment I. So, emphases are put on the dynamic variation regularity of each parameter during the valve closing process in experiment II. The outlet valve of the centrifugal pump is closed gradually with
Figure
Comparison of performances of sliding vane pump.
Comparison of performances of centrifugal pump.
Through the analysis and comparison of the results in experiment I and experiment II, the following conclusions can be drawn.
(1) The system flow rate is determined by the characteristics of the feeding sliding vane pump. The working performance of the two pumps and the characteristics of the pipeline are crucial for normal and steady system operation. In the serial use, the corresponding relation between the system flow and the differential pressure of the sliding vane pump fits its independent working characteristics well. The operation of the centrifugal pump effectively changes the differential pressure of the sliding vane pump by sharing the pressure energy of the system, thus leading to the change in the system flow.
(2) The centrifugal pump works under the flow determined by the sliding vane pump. If the energy it provides is larger than the energy consumed by flow, then fierce unsteady such as reflux, swirl, gas-liquid two-phase flow will occur inside the centrifugal pump to consume the superfluous energy.
(3) During different periods, the change of the pipeline characteristics has different impacts on the working status of the two pumps. When the centrifugal pump is under abnormal operation, changing the pipeline friction loss causes nearly no sliding vane performance variation and no flow rate change. The centrifugal pump changes the operation parameters and slowly comes near to or far away from the normal working status. After the centrifugal pump works steadily and before the safety valve opens, the change in the characteristics of the pipeline exerts a major influence on the operation of the sliding vane pump. As a consequence, the system flow has a small-scale change. After the safety valve opens, both of the two pumps change the operation parameters to adapt to the change in the characteristics of the pipeline.
Series operation experiments for sliding vane pump and centrifugal pump are conducted. Sliding vane pump is used as the preceding-stage pump and the centrifugal pump as the secondary pump. By changing the friction loss of the pipeline, results are gained under different operational conditions. Experimental results show that the system rate of flow is determined by the sliding vane pump. The centrifugal pump works under the flow rate restricted by the sliding vane pump. Only when the friction of the pipeline is greater than the pressure energy that the centrifugal pump can provide, the system can operate normally. Otherwise, the system will work unsteadily with calorification, vibration, and noise. So, the sliding vane pump can be in serial operation with the centrifugal pump under limited conditions.
This paper is supported by the Academic Innovation Fund of Logistical Engineering University.