The single-ended return tube Scotch marine boiler consists of a cylindrical boiler shell of large diameter and short length, provided with two or more furnaces i.e. corrugated fire-tubes. Each furnace ends in a combustion chamber, surrounded by water. The gases pass through a bank of flue-tubes from the combustion chamber to the smoke-box at the boiler front.
A Scotch marine boiler contained large quantity of water, about six times more
than a water-tube boiler, and was therefore slow to steam up and to change the
output capacity. Due to the Scotch boiler's stiff construction it required also
a long steaming up period to avoid leaks caused by thermal expansion of the material.
The Scotch boiler was a very common marine boiler, used in steamships from many nations.
steamships still sails with Scotch marine
boilers, some of them with new-built old fashion Scotch boilers.
Double-ended Scotch marine steam boilers
These types of boilers were normally used in ships with many
Scotch boilers. Space was saved even though two stokeholes were required.
Normally a pair of furnaces shared one combustion chamber.
In older double-ended boilers were often vertical Galloway tubes built into the
combustion chamber. They were intended to promote water circulation in the
boiler and thus contribute to reducing tensions in the material.
Twenty-four double-ended Scotch marine steam boilers with
three furnaces at each end and five single-ended Scotch boilers with three
furnaces each were installed onboard R.M.S. Titanic. Electrically operated
stoking indicators were used in the stokeholds to prevent that opposite furnace
doors were open at the same time. These indicators also helped to minimize the
total number of simultaneously open boiler furnace doors.
When the furnace door was open, cold air could hit the combustion chamber's
opposite wall and cause tube leakage. To prevent that, a high baffle of
firebrick was installed in the middle of the combustion chamber.
The three pass Scotch marine steam boiler
The flue gases passes three times through the water space in stead of two
times that was common in the old Scotch boilers. It is a further development of
the Scotch fire tube boiler, often referred to as the Scotch boiler.