[Illustration: Stirling Water Tube Boiler.]
Q. How is a water tube boiler constructed?
A. The Stirling Water Tube Boiler as illustrated, has three upper or
steam domes, the steam space of all of which is connected, while the
water space of the two front domes is connected. All of these three
domes are connected with a lower or mud drum, which is not bricked in,
but is left free to expand and contract.
The three upper domes are supported on wrought iron beams, which are
entirely free and independent from the brick work. The feed water
enters the rear upper dome, and descends gradually to the lower or
mud drum, being heated in its descent by the escaping gases to a
sufficiently high degree to cause precipitation in the mud drum of all
of the solid or scale bearing matter that the feed water contains.
The water then in the front bank of tubes is chemically pure, and all
danger of scale reduced to a minimum.
Q. What advantages have the water tube boilers?
A. One of the great advantages of this style of boilers is its distinct
circulation, being up the front bank of tubes across from the front
upper dome to the middle dome, down the middle bank of tubes to the
lower or mud drum, and up again the front bank of tubes, and so on in
circuit. It also has great steaming capacity, and is economical in
fuel. Steam is taken from the middle dome.
This marked circulation is a desideratum in boiler practice, and the
Stirling may be said to be the first that has accomplished it to so
great a degree.
Q. What disadvantages have the water tube boilers?
A. Expensive first cost of setting them up in brick work.
[Illustration: J. I. Case Traction Engine.]