MOTIVE-POWER ENGINES
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by Alexander Morton Strathern at tho
Office of the Commissioners of Patents on the 12th April 1877.
ALEXANDER MORTON STRATHERN, Manager to the Firm of "A. F. Craig & Co.,”
"IMPROVEMENTS IN
Engineers, Paisley, in the County of Renfrew, North Britain.
MOTIVE-POWER ENGINES."
This Invention consists essentially in the arrangement of valvos and valve gear
for the economical working of steam, air, gas, or other fluid engines.
Under one modification it is proposed to use the ordinary slide valve with the
three-ported face and the cut-off plate on the back, wrought from the crank shaft
by mitre wheels, and a short shaft parallel to the centre line of the cylinder, on tho
end of which is fixed or formed a Z crank, having two arms and straps distinct
from each other, from one arm of which is worked the inner or main slide, and from
the other the outer or cut-off plate. The arm for working the cut-off is hung in a
frame, and attached to the lifting link of the governor, so that when the engine
varies in speed the frame is either lifted or depressed, thus changing the angle of
motion of the Z crank lever, and consequently the point of cut-off. This motion:
can also be applied for reversing by using a single armi on the Z crank, and moving
it by hand gear round part of a circle until the valve leads at the opposite side of
the piston; and for a pair of engines, with cylinders close together, one Z crank is
made to reverse both, but when they are some distance apart two Z cranks are
required, with a lever on each. For a quick cut-off it is preferred to use gridiron
valves, and in some cases make the motion of the cut-off across the main valves, also
using a main valve and cut-off at each end of the cylinder.
Another improvement consists in using cam motions for working gridiron, valves,
in one modification of which the valves are placed across the cylinders' centre line,
and are worked from the crank shaft by mitre wheels, and a cam shaft running
parallel to the engine's centre line.
The two steam valves are placed preferably on the top of the exhaust valves
below the cylinder, but their positions may be reversed, or they may be placed
vertically, two and two on either side, or all on one side. In the case of the steam
valves being placed two above and two below in horizontal engines the two steam
valves are worked by four cams, the opening cams being fixed on the shaft, the
closing or cut-off cams being movable either by hand or by the governor; if by the

page_text: governor it is preferred to put the cut-off cams on a tube, with an angular groove
connected to the governor, either direct or by links, or by means of a screw and
gearing, in either case combined with an air or oil cylinder to steady the strain of
the cut-off. This steadying cylinder may either be placed in the centre of the
governor on the bed plate of the engine, or mounted on the movable tube, which is
preferred to be made as short as possible, the cams on which work the valves
through levers and shafts having pillow blocks and adjustable bearings. The outer
ends of the levers are preferably forked, with a roller bearing on either side of the
cam, the projections on the cam being made tangential to the small diameter, and
the cover or lap and lead of the valves are made so that the valve is at the quickest
part of its stroke in opening and in closing by the cut-off cam. The eduction cams
are fixed on the cam shaft, the position of which is determined by the amount of
cushion required, and are formed so that the rollers may retain the valve full open
as long as may be desired.
In another modification the cams may be fixed on an upright shaft (in the case of
horizontal engines) worked by two pairs of mitre or bevel wheels, said upright shaft
being also the governor spindle. The projections for working the valves may either be
in the sides of the cams or on the periphery. In the case of the projections being
on the sides of the cams three cams are sufficient for the four valves, namely, one
for both steam valves, one for cut-off valves, and one for the two exhaust valves, the
valves being actuated by rocking shafts and levers, as before.
In another modification the cross gridiron valves may be worked by an eccentric
or other reciprocating motion, the valves to be actuated by projections on the sides
of the reciprocating bar or eccentric rod, another bar moving parallel in an opposite
direction, closing the valves by its projections, and connected to the governor so
that the projecting parts of the opening bar miss sooner, and the projecting parts of
the closing bar catch and closo the valves sooner as the load varies, this arrange-
anent being also fitted with oil or air cylinder for taking up the strain of and
steadying the action in closing the valves, the exhaust valves being also worked
from the same bar as the steam valves, but to be so arranged that they may remain
open during the whole stroke.
In another modification or arrangement the valves are worked by a revolving
shaft and cam, the steam cams having a taper longitudinally on the closing side,
and parallel on the opening side. The valve spindles are made of large diameter,
sufficient to close the valves, and are prolonged and worked into a dash pot cylinder.
The action will then be that the valves open with the steam pressure against the
large diameter of spindle so soon as the taper side of the cam leaves the roller; the
steam pressure acting on the large spindle will close the valve, the dash pot will
cushion the valve, the taper cam will be moved longitudinally by the governor, thus
changing the cut-off, the eduction being worked in the same way as in the other
modifications.
In another modification the end of the levers engaging the cams have single ends,
and all the cams are fixed on two parallel shafts geared together by spur wheels of
equal size. The shaft on which the cut-off cams are fixed moves in the opposite
direction to the steam opening cams. Immediately, the opening cam leaves the
roller the other comes in contact with it, and cuts off the steam, the position of the
cams or shaft being varied by the governor moving either of them on an angled
keyway, or the closing side of the cam may be angled, also using the fluid cylinder
for reducing the steam of cut-off.
In forming horizontal engines for cross gridiron valves it is preferred to form the
cylinder cover on the sole plate, and support the, cylinder by a central stool open
through the centre, and bolted on the eduction valve faces, connecting the two chests
by a pipe, thus making them so that they may be easily removed for repair without
disturbing any of the other joints.
For starting the engine the steam cam lever is disengaged from the valve lever,
and the valve lever either prolonged, or a boss formed on rocking shafts.
For the hand starting levers it is preferred to use for disengaging a loose cam

page_text: lever, with two steel points wide at the outer edge, and a starting collar driven by
one or more feathers sunk in cam shaft, such collar being formed either wholly of
steel, or having steel driver fitting into the two projections on the loose cam
lever.
Instead of making bow or forked arms for encompassing the cams for working
the valves, a frame with the antifriction pulleys on it encompassing the cams may
be used, this frame being either formed in ono with or fixed or jointed on the lever
for communicating motion to the valve spindle direct, or through other intermediate
levers.