IMPROVEMENTS IN STEAM ENGINES OF THE CLASS USUALLY TERMED TRUNK ENGINES
Year: 1854

page_text: PROVISIONAL SPECIFICATION left by William Macnab at the Office of
the Commissioners of Patents, with his Petition, on the 24th February
1854.
I, WILLIAM MACNAB, of Greenock, in the County of Renfrew, North
Britain, Engineer, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN STEAM ENGINES OF THE CLASS USUALLY TERMED TRUNK
ENGINES" to be as follows:-
This Invention relates to the class of steam engines known as "trunk
engines," now ordinarily adopted for marine purposes. In this new arrange-
ment a single front trunk or hollow rod or case is used for the connecting rod
to work through. The piston is solid, that is to say, it has no central passage
through it, and the connecting rod joint is on the front side or on the side next
the crank shaft. A solid piston rod is attached to and projects from the
opposite side of the piston, being screwed or otherwise attached to the piston's
centre.
This rod works through a back or outside stuffing box, and answers
as a guide as well as a means of oiling. To render it available for this latter
purpose, a small hole is bored down through its centre from the outer end,
where a cover cap may be fitted; this hole may then have divergent branches
passing to the working surfaces of the connecting rod joint through the body
of the piston, so that the oil may flow freely through when poured in from the
upper end of the rod. Or instead of making this secondary rod solid, with a
small hole through, it may be in the form of a tube with a solid neck or end at

page_text: the point of connection with the piston. It is proposed to arrange the cylin-
ders of such engines, especially when used for screw propelling purposes, with
their axes in parallel vertical lines standing fore and aft, the connecting rods
working downwards to the cranks. Instead of a single back or secondary rod
two or may be used. The pin of the connecting rod joint is used as the means
of working the air pumps, rods from each pin or joint stud being passed down
through the trunk to the air pump pistons or plungers. By another modifica-
tion the piston is bored directly through its centre, and the back or reverse
tubular rod, working through a back stuffing box in the cylinder, is forged or
shaped in one piece with the clutch or connecting rod joint piece, this piece
being passed through the aperture in the piston from the trunk side; that is to
say, the connecting rod is jointed to its double eye piece on the back rod, and
the latter is then passed up through the hole in the piston, and is secured in
position by a collar nut passed over the back rod on the protruded side. Or
instead of this arrangement, the connecting rod joint piece may have a cylin-
drical neck formed upon it to pass into the hole in the piston, and be secured by
a collar nut on the other side, the back tubular rod being attached to the reverse
side of the piston by an end flange and bolts over the securing collar of the
connecting rod joint piece; and instead of using a loose end cap for the
connecting rod joint at the piston the joint eye in the rod may be solid with a
contrivance for adjusting the brasses from the outside without necessitating an
entry into the trunk. This is effected by boring the connecting rod longi-
tudinally to receive an adjusting bar, one end of which presses upon the front
brass, whilst the other is acted upon by a cutter arrangement in the connecting
rod outside and clear of the trunk. Thus a solid connection is secured, whilst
the engineer can at any time adjust his joint with great facility, and instead
of working the air pumps off the connecting rod joint pin by rods passing
through the trunk, the double eye pieces of this joint may be prolonged to
carry each a separate stud pin for this purpose. In any of these arrangements
the oil for the connecting rod joint may be passed down through holes in the
back rod or intermediate piece, or it may be conveyed by pipes from the reverse
or back rod side. Or instead of these plans the oil may be conveyed into the
trunk from beneath by means of a syphon pipe arrangement.