By
increasing the initial pressure of the air, much better results can be
obtained, and future attention in practice should be devoted to this
point. The amount of work required to compress air does not increase
in the same ratio as the pressure, and for this reason considerable
economy can be effected at the first stage, and the loss in the mains
will be reduced.
Passing to another point of the same subject, Professor Riedler
considers the best dimensions that should be given to the mains.
Resistance decreases with an increase in the diameter of these and in
direct ratio to their diameter; for this reason--still assuming a
pressure corresponding to a velocity of 20 ft. per second--with a fall
of one atmosphere, a length of 40 kilometers could be succesfully
worked.
The mains of the new _reseau_ for the Quai de la Gare station are
19.69 in. in diameter; they are built up of steel plates riveted, and
this Professor Riedler considers to have been a serious error on
account of the extra resistance offered by the large number of rivet
heads.
The following may be taken as a brief summary of Professor Riedler's
conclusions: Recent improvements in central station practice have
resulted in an increased efficiency of about 30 per cent. in the
compressors, but this benefit can only be realized when the new
station is in operation.
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