Consultation of publications on the testing of centrifugal pumps seems to show that while much experimental work has
been carried out, yet the work has been confined mainly to overall
Overall tests of a pump may show slight changes in
efficiency with alterations in the proportions of one component
part of the pump, but it is not possible to make definite conclusions
as to whether this change is entirely due to the alteration in
that one part of the pump. For new conditions of flow introduced
by the alteration in proportion may affect the efficiency of and the
losses in other component parts. A change in curvature of impeller
blades or in the rate of change of cross sectional area of the
passages between the impeller vanes - without alteration of the
angles or radial areas at entry or exit - may affect the actual
angle of discharge from the impeller tip and hence also the losses
in the guide passages; and thus the change in overall efficiency
may not be due entirely to the alteration in the impeller.
The total losses in the pump at any delivery may be known
but their allocation among impeller, guide.passages etc., is very
much a matter of conjecture from analogy with results from flow
through stationary passages; and in the case of shock loss, deductions from such analogy are very uncertain.
Experiments were carried out by Dr. Stanton on the
efficiency of a vortex chamber with and without guide vanes and with
various types of impellers; and this seems to be the only published
record of experiments carried out to determine separately the
efficiency of a certain component part of a centrifugal pump.
The experiments described in the present paper were undertaken primarily to determine the separate losses and efficiencies
of the impellers, guide passages, volute, and the various connecting passages of a turbine pump, and how these losses and efficiencies
varied with the discharge and the impeller speed. But during the
analysis of the results it was found necessary to consider other
questions. For the ordinary theory of the centrifugal pump, while
indicating the general .laws connecting discharge, head, speed and
power and explaining the effect of various factors in design, is
admittedly not quite in accordance with actual test results as
regards the relative proportions of these items.
The additional matters considered are, the amount of
leakage, the pressure in the casing at the side of the impeller,
the manner of flow through the impeller, and the relation of the
ordinary theory to the experimental results. In addition, the
pump tested presents a peculiarity in the abrupt rise (with increasing discharge) of the head quantity curve at constant speed. (See
Fig. 9). Additional tests were therefore made at the discharge
at which the abrupt rise takes place( termed the "critical" discharge hereafter); the results have been analysed and a possible
explanation of this detrimental feature put forward.