IMPROVE- MENTS IN STEAM ENGINES
Year: 1854

page_text: PROVISIONAL SPECIFICATION left by Thomas Main at the Office of the
Commissioners of Patents, with his Petition, on the 3rd May 1854.
I, THOMAS MAIN, of Glasgow, in the County of Lanark, North Britain,
Engineer, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN STEAM ENGINES " to be as follows:-
This Invention relates to a mode or modes of arranging and constructing
steam engines so as to secure the power of running them at a high speed,
whilst they are peculiarly compact and of great simplicity in their details.
The two steam cylinders of a double engine, such as would be suitable for
actuating a screw propeller for marine purposes, are each set at or about an
angle of 45° with the vertical line, their lower ends being towards each other.
A triangular bracket or brackets with the ridge upwards, and running in a
line coincident with the keel line of the ship, carries the two cylinders, which
are held down or steadied from three several points; the bottom flanges of the
cylinders are bolted to the inclined sides of the hearing brackets or base
pieces. The outer overhanging upper ends of the cylinders are supported
either by pillars from the base plates or beams carrying the brackets, or by
angular cast-iron brackets, and a triangular cast-iron bracket or brackets is
inserted between the cylinders above, with its ridge downwards, being bolted to
both cylinders. This central bracket also answers for carrying the valve gear

page_text: connections. The two piston rods work out at the upper ends of the cylinders,
each rod having a long cross head with guide blocks fitted to inclined slotted
guide brackets bolted to the cylinder covers. From the two ends of each of
these cross heads side connecting rods pass down direct to two cranks on the
screw shaft, each two connecting rods on one side from the opposite cylinders
being jointed to one crank. The screw shaft runs along through the bottom
bearing bracket carrying the cylinders, and it is close to the lower ends of the
cylinders. The air pumps, one on each side, are set in an inclined position in
the base plate; they are inclined in the reverse direction to the steam cylin-
ders, that is to say, their upper ends are directed towards each other; their
pistons are worked by rods fast by their upper ends in the steam pistons.
These rods, one to each piston, work through stuffing boxes in the lower ends
of the steam cylinders, the air pump pistons being on the lower ends of the
rods. Thus the starboard piston works the port air pump, and the port
piston works the starboard air pump; or instead of this plan two piston rods
may be used for one pump, and one for the other, so that the rods may clear
easily.
The bilge and feed pumps are placed one on each side of the air pump,
and are worked by means of a cross head carried by the air pump rod. The
valve gear is arranged so that the valves of both cylinders are worked from a
single eccentric. Engines of this class are peculiarly suited for screw pro-
pulsion, as they are compact, and can be entirely disposed below the water
line; but they are also applicable for any situations where the peculiar
qualities sought for in their construction are at all desirable.