134 SECTIONAL ADDRESSES 
efficiency at heads which had hitherto been thought quite outside the 
range of this pump. 
In the pioneer days of centrifugal pump development, when the method 
of calculation for design was somewhat rudimentary, a number of basic 
facts were discovered experimentally, from which empirical relationships 
were devised to meet the various conditions imposed. Later on, the 
advances made in the design of high-speed prime movers, particularly 
of steam engines and electric motors, gained for this type of pump a pre- 
eminence which it has maintained ever since and seems likely to enjoy 
for some time to come. ‘To-day, although we have still much to learn, 
centrifugal pump design has become a highly specialised study, and 
characteristics can be forecast, for numerous combinations of conditions, 
with a reasonable degree of accuracy. Compared with the plunger type, 
the centrifugal pump has the advantages of much lower capital and main- 
tenance cost, with concomitant economy in space and weight, which 
renders it particularly suitable for use on board ship. It can be run in 
special cases with a shut-off head. It has a reasonable measure of un- 
chokeability, while its delivery at constant pressure makes it peculiarly 
applicable to boiler feed and similar duties. 
A striking application of this pump has been in the handling of coal, 
sands, gravels, and the like, where, in spite of the abrasive nature of the 
materials, maintenance costs can be kept comparatively low, while lined 
pumps of special construction are capable of passing stones and boulders 
up to the size of the delivery branch. 
The much improved efficiency now obtainable from centrifugal turbo- 
pumps has led to a marked increase in their use for waterworks installa- 
tions, where the high speed enables large quantities of water to be de- 
livered from a comparatively small bore-hole. ‘The pump is suspended, 
often many hundred feet below the surface, from a rising main, the 
impellers being driven by vertical shafting supported in bearings fitted 
to the rising main itself, or, occasionally, by an electric motor which runs 
submerged. 
A comparatively recent development is the axial-flow type of pump, 
and this, with its advantages of reduced weight and space, and higher 
speed, may—when dealing with low heads—be said to carry the low cost 
of construction and installation a stage further. Because the flow is uni- 
directional, the pump being merely an incident in the pipe, higher speeds 
can be obtained with lighter prime movers. Intermediate types, partly 
centrifugal and partly axial-flow, have also been devised. While no one 
dare prophesy as to the future of the pump, it would appear that both 
centrifugal and axial-flow types are in essence so simple that it is difficult 
to see how any future improvement can be expected, except in detail. 
These technical developments have amazingly increased the field of 
application of the centrifugal pump, particularly for graving and floating 
docks, impounding for wet docks, and in the drainage of watery wastes 
and the irrigation of barren deserts, so as to bring large areas of ground 
previously unproductive into a state of high fertility—often affording, 
indeed, a sure means of subsistence to peoples whose very existence had 
hitherto been precarious. In our own country, before the beginning of 
