Discussion on Some Problems in Axial Flow Pump Test

(1) Blade hub side clearance on the performance

For example, the JMT-08-8.5 model, with 0-degree angle sealing the gap with wax, has an efficiency of 87.35% and an increase of 2.16%. In JMT-20-6.5 model, the gap is closed with wax at 0 degree with an efficiency of 86.69% 1.4%. It can be seen that it is beneficial to take improvement measures and to use as much as possible without adjusting the fixed blades.

(2) Deceleration test flow, head in line with similar laws

In the axial flow pump model test, into the unstable area, in order to prevent damage caused by the test equipment and model pumps , usually using the deceleration test. Verification tests showed that the results of the low-speed test conversion were the same as those of the high-speed test.

(3) The influence of pre-spin on the test results

Axial flow pump pre- centrifugal centrifugal pump import large, more obvious when the small flow. During the axial flow pump test, the pressure at the wall of the impeller before the inlet was higher than the pressure at the center of the tube due to the effect of pre-rotation, so that the measured head was lower than the actual head. This effect is usually negligible at large and design flows, but can be quite noticeable in the vicinity of small flows, especially shut-off flows. In this test, the dead lift of the test was only 13m compared with the model with the speed of 800, and the curve shape in the unstable area was abnormal. The same specific speed model pump in the device test, the shut-off point lift up to 21m, the lift should be the true pump head, because the inlet pressure measuring point installed in the tank wall, there is no pre-rotation effect. It is recommended that during the test of the model pump to measure the head of the unstable area, the inlet pressure-measuring point should be taken forward as far as possible and can even be taken on the water tank because the measurement accuracy of this section has nothing to do with the trend of the measured curve.

As the import of pre-spin to increase the inlet pressure, thereby increasing NPSH, the optimal efficiency conditions and high flow conditions have any impact, pending further study.

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