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ARTICLE IX.
OF THE CONDENSER.
THE weight of the atmosphere resists the motion of the piston of our engine, when we work without a condenser, with a power equal to 15 pounds to the inch of its area; the use of the condenser is to take off this resistance, and is very useful when we work with weak steam, (see No. 4 in the table, article 6.)
In its usual form it consists of a metal vessel, air tight,
immersed in cold water, to receive the steam as it leaves the engine. The
steam is first let in plentifully to drive out all the air through a valve
fixed for that purpose. A cock is then opened to let a continual jet of
cold water enter, meeting the steam, which it condenses into water again,
and forms a vacuum in the condenser for the steam to enter freely, which
takes off the resistance of the atmosphere from the piston of the engine:
and if the vacuum be made perfect, it increases the effect of the engine
15 pounds for every inch area
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of the piston. But the air which arises from the first boiling of water would immediately fill the condenser, again destroy the vacuum and stop the engine; to keep the vacuum perfect, therefore, the air pump becomes necessary to extract this air, as well as the jet water, and that made by the condensed steam, and part of this water is returned into the boiler to supply it, and as there is a continual admission of fresh water by the jet, there is a continual generation of air, by boiling, to obstruct the vacuum, also a continual accumulation of sediment, forming a non-conductor of heat on the bottom of the boiler, which obstructs the passage of the heat from the fire into the water, causing the boilers to burn out; besides much trouble and expense in cleansing them.
To avoid all which, we improve the condenser by making
a jet vessel of metal, purposely for receiving and cooling our jet water;
immersing it in cold water, under or near the condenser. Out of this vessel
the jet rises into the condenser as before. The air pump, which serves also
for our supply pump, extracts the water and air from the condenser, and
forces back into the jet vessel as much water as it will receive; keeping
it always full; the residue (after the air is suffered to escape through
a valve for that purpose fixed in the top of an air vessel, which is fixed
in the pipe leading the water from the pump into the supply boiler) is forced
into the the boiler to supply it. A small air vessel is attached to the
jet vessel, the spring of which keeps up a continual jet. The water enters
the jet vessel at one end and the jet issues at the other, which gives the
water time to cool, to fit it for the purpose of condensing. By these
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means we admit no fresh water, but continue to work with the same quantity with which we begin; distilling it over and over repeatedly, we soon get rid of the air, and our vacuum becomes more perfect: from water distilled many times over no sediment can accumulate to cause our boilers to burn out, nor air to obstruct our vacuum. Our boiler may be said to be inexhaustible, and will last much longer, and require less fuel.
In some situations it may suit better to make the condenser
sufficiently capacious to expose so much surface to cold water, as to condense
the steam without a jet; laying it in running water, and (when it can be
done conveniently) so fixed that the water can be turned off at pleasure,
which would enable us to expel the air more completely before we begin to
work. The water formed by the steam in this condenser being driven back
into the supply boiler by the air pump, makes it inexhaustible as before.