Without
such spray connections, it is safe to say that this compressor has
scarcely any cooling advantages at all, so far as air cooling is
concerned. Water is not a good conductor of heat. In this case only one
side of a large body of air is exposed to a water surface, and as water
is a bad conductor, the result is that a thin film of water gets hot in
the early stage of the stroke and little or no cooling takes place
thereafter. The compressed air is doubtless cooled before it gets even
as far as the receiver, because so much water is tumbled over into the
pipes with it, but to produce economical results the cooling should take
place _during compression_.
Water and cast iron have about the same relative capacity for heat at
equal volumes. In this water piston compressor we have only one cooling
surface, which soon gets hot, while with a dry compressor, with water
jacketed cylinders and heads, there are several cold metallic surfaces
exposed on one side to the heat of compression, and on the other to a
moving body of cold water.
But the water piston fraternity promptly brings forward the question of
speed.
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