74 EMMET---THE CURTIS STEAM TURBINE. {April 2, 
better than those obtainable from the types of steam engines 
generally applied to the production of electricity. 
It should be noted that these curves show a very high efficiency 
at light loads, as compared with results obtainable from steam 
engines, and that the efficiency does not fall off at overload, as it 
must necessarily do with all engines which operate economically 
under normal full-load conditions. This light-load and overload 
economy is an important feature of the Curtis turbine, and arises 
from the fact that the functions of its working parts is virtually the 
same under all conditions of load. 
Curves 3, 4and 5 show the effect upon steam consumption of 
changes in the steam pressure, the degrees of superheat and in the 
vacuum. It will be observed that the superheat and vacuum curves 
are straight lines so inclined as to indicate a great advantage by the 
use of all degrees of superheat and also an immense advantage in 
the use of very high vacuum. The most important reason why the 
Curtis turbine so greatly surpasses the steam engine in economy is 
that it is adapted to use effectively the highest possible degrees of 
expansion, while in the steam engine it is practically impossible to 
provide for high degrees of expansion. As the exhaust pressure 
approaches a perfect vacuum, the volume naturally increases at a 
rapid rate—the volume of steam with a 29’’ vacuum being double 
that with a 28’’ vacuum. To handle high degrees of expansion, it 
would, therefore, be necessary to make cylinders of steam engines 
very large, and this increase of size and weight of parts fixes a prac- 
tical limit which cannot be passed without excessive cost and com- 
plication. In the turbine, the highest degrees of steam expansion 
are easily provided for, and consequently a much larger proportion 
of the total work in steam can be utilized by turbines than by steam 
engines. 
There are other conditions in the Curtis turbine which make high 
degrees of vacuum more easily attainable than they are under ordi- 
nary conditions. ‘The machine is so constructed that leakage of 
air into the vacuum chamber is easily rendered impossible. The 
leakage of air into condensing engines is considerable, and is gen- 
erally not checked owing to the small value of improved vacuum 
to an engine. 
With turbines of the type here described, no oil comes into con- 
tact with the steam, and consequently condensed water can be 
taken from surface condensers and returned to boilers. The use of 
a 
