The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

66 THE STEAM ENGINE.
into the bottom of the cylinder, so that on turning the cock
the pressure of the water in the pipe H, from the level of the
water in the cistern N, would force the water to rise as a jet
into the cylinder, and would instantly condense the steam.
This method of condensing by a jet formed a very important
improvement in the engine, and is the method still used.
(41.) Having taken a general view of the parts of the
atmospheric engine, let us now consider more particularly
its operation.
When the engine is not working, the weight of the pumprod D draws down the beam A, and draws the piston to the
top of the cylinder, where it rests. Let us suppose all the
cocks and valves closed, and the boiler filled to the proper
depth. The fire being lighted beneath it, the water is boiled
until the steam acquires sufficient force to lift the valve v.
When this takes place, the engine may be started. For this
purpose the regulating valve R is opened. The steam rushes
in and is first condensed by the cold cylinder. After a short
time the cylinder acquires the temperature of the steam,
which then ceases to be condensed, and mixes with the air
which filled the cylinder. The steam and heated air, having
a greater force than the atmospheric pressure, will open a
valve placed at the end x of a small tube in the bottom of
the cylinder, and which opens outwards. From this (which
is called the blowing valve*) the steam and air rush in a
constant stream until all the air has been expelled, and the
cylinder is filled with the pure vapour of water. This process is called blowing the engine preparatory to starting it.
When it is about to be started, the engine-man closes the
regulator a, and thereby suspends the supply of steam from
the boiler. At the same time he opens the condensing
valve H;t and thereby throws up a jet of cold water into the
cylinder. This immediately condenses the steam contained
* Also called the snifting valve, from the peculiar noise made by the air and
steam escaping from it.
t Also called the injection valve.