Boiler House.
Boilers
The original Young and Summers engines had been supplied with steam at 100lb/sq.in.
from a Lancashire boiler installed in 1898 after being delivered to the site
on a trolley, hauled by a steam traction engine. A Babcock & Wilcox water
tube boiler working at 160lbs/sq.in augmented this in 1903 and in 1905 a
second Babcock & Wilcox boiler was installed to replace the Lancashire
boiler. A third Babcock & Wilcox boiler was ordered in 1916 to meet the
increased demand for water arising from the First World War.
The boiler house built for the original Lancashire boiler was used to accommodate the first
two Babcock & Wilcox boilers but when the third of these was installed
in 1916, the boiler house was extended to provide space for it.
The Babcock and Wilcox boilers.
The three boilers are “water tube” boilers based
on a design of two Americans, George Herman Babcock and Stephen Wilcox, patented
in 1867. It became the most successful water tube boiler with over four million
n.h.p. installed world wide by 1904. The three at Twyford represent the classic
Babcock and Wilcox boiler of the period 1900-14. Our 1916 boiler is now the
oldest one of its type which is steam able.
Looking at the boiler, the steam drum A at the top is supported
by straps from steel columns set in walls lined with refractory bricks. The
water tubes, from which the boiler gets its name, are mounted between two sets
of headers.
The rear set B nearly touch the boiler floor and
are fed by large tubes from the bottom of the drum.
The front set C connect
with the front of the drum by a short manifold so that the group of sixty 4
inch diameter tubes slopes up towards the front over the fire grate F.
This layout promotes good water circulation by thermo-syphon action. You can
see the front headers on the unrestored boilers, “saturated” steam
is taken direct from the top of the steam drum via a stop valve at the rear
of the drum.
Steam for the engine, however, is “superheated” by
being collected through two tubes high in the steam space and fed through twenty
U-shaped tubes D below the drum where the steam picks up extra
heat energy from the flue gases before passing to the main stop valve E.
The front of the steam drum has a pressure gauge and two gauge glasses to monitor
the water level. The original working pressure was 160 p.s.i. but we now operate
at 100 p.s.i. ( 7 bar or 0.7 MPa).
The water level is maintained by one or
more of the engine driven feed pump, auxiliary steam feed pumps or an electric
pump. The boiler feed water comes from condensed steam in the hot well, Since
steaming recommenced we have introduced an additional water storage tank beside
the chimney, which is used to hold treated boiler water whilst the boiler is
in use or in a dry storage condition. Steam grate blowers keep the boiler airways
free of ash and induced air is forced up through the grate. Any solids deposited
in the water tubes during steaming tend to collect at the bottom of the “downcomers”,
the headers at the rear of the tube stack.
Here, there is a special drain called
the “blowdown” which, when operated during steaming, dumps water
and deposited sludge in the blowdown pit outside. Steam plus hot water at 175 °C
is violent and dangerous.
Control of the furnace is by a damper, a sliding trapdoor, in the passage from
the boiler to the chimney G. The damper is counterbalanced and operated by
a large weight hanging to the right of the fire doors. The operating chain
passes over guide pulleys at the top of the boiler frame.
