SECT. II.]
PROPERTIES OF STEAM.
95
Multiply the length of the stroke by the number of strokes per minute, and
divide the product by 2400; the square root of the quotient multiplied by the
diameter of the cylinder is the diameter of the pipe.
Example. To find the diameter for the steam pipe of an engine of which the
diameter of the cylinder is 2 feet, the length of the stroke 2‘5 feet, and the
number of strokes per minute 38 ;
38 x 2-5 _ 95 _ 1
2400 2400 25’
and the square root of sV is one-fifth ; hence the diameter of the steam pipe in this
case is one-fifth of that of the cylinder.
The same rule applies to both high pressure and low pressure steam engines,
and both to the steam passages and the passages to the condenser; and the excess
of force necessary to produce the velocity is very nearly one-144th part of the
force of the steam.
Of the Loss of Force by the Cooling of the Cylinder.
155. The steam after it gets within the cylinder is liable to a loss of force
by cooling. It is, in large engines, usually inclosed by a case called a jacket, and
steam is introduced between this case and the cylinder to keep the latter hot; but
the loss in fuel by this mode is the same as with a naked cylinder, and there is
clearly no advantage in preserving the force of the steam by adding this case,
unless it be supplied with steam by a separate pipe. (See art. 147.)
156. The investigation for the loss of force in the steam pipe applies in the
case of a naked cylinder with a very slight alteration. The steam in this case is
progressively exposed to the sides of the cylinder; hence the loss will be some
and when we use the length of the stroke l, and the number per minute m; 2 l m = 60 V, and we
may take
Aim
U ~ 90 n/459 +7
When t' = 220°, it becomes
Aim
a “"2400
which is the same as the rule. If t' = 320°, then
Aim ,
a ~ 2520
showing that a rather smaller aperture will do for high pressure steam. A is the area of the
cylinder, and a the area of the pipe, in superficial inches.