openings of the two ports will be the same; and the question is, Will
this maximum effective port area give a sufficient supply of steam?
This diagram is the same as the one actually used in the engine under
consideration, in which it was required to follow a minimum distance of
5 inches in the stroke of 22. Under these conditions it is found that
the actual port opening for that point of cutting off is three-fifths of
that allowed when following full stroke, whereas the speed of the piston
at the time when this maximum opening occurs is less than half its
greatest speed.
This, it would seem, is ample; but we now find the eccentric, K, no
longer in the right position for backing; when the engine is reversed it
ought to be at, P, the angle, POL, being equal to the angle, KOL. By
leaving it free, therefore, to move upon the shaft, by the means above
described, through the angle, KOP, the desired object is accomplished.
The real eccentricity is now reduced in the proportion of OK to OH,
while the lengths of the cut-off valves, and what is equally important,
their travel over the back of the main valve, are reduced in the
proportion of CK to CH, in this instance nearly one-half; a gain quite
sufficient to warrant the adoption of the expedient.
The third, and perhaps the most notable, peculiarity is the manner of
suspending and operating the main link. As before stated, this link is
used only for reversing, and is therefore always in "full gear" in one
direction or the other; and the striking feature of the arrangement here
used is that, whether going ahead or backing, there is _no slipping of
the link upon the link block_.
The link itself is of the simplest form, being merely a curved flat bar,
L, in which are two holes, A and B (Fig. 7), by which the link is hung
upon the pins, which project from the sides of the eccentric rods at
their upper ends.
This is most clearly shown in Fig. 8, which is a top view of the
reversing gear. The link block is a socket, open on the side next to the
eccentric rods, but closed on the side opposite, from which projects the
journal, J, as shown in Fig. 9, which is a vertical section by the
plane, XY. This journal turns freely in the outer end of a lever, M,
which transmits the reciprocating motion to the valve, through the
rock-shaft, O, and another lever, N. Connected with the lever, M, by the
bridge-piece, K, and facing it, is a slotted arm, G, as shown in the end
view, Fig. 10. The center line of this slot lies in the plane which
contains the axes of the journal, J, and of the shaft, O.
A block, E, is fitted to slide in the slotted arm, G; and in this block
is fixed a pin, P. A bridle-rod, R, connects P with the pin, A, of one
of the eccentric-rods, prolonged for that purpose as shown in Fig. 8;
and a suspension-rod, S, connects the same pin, P, with the upper end of
the reversing lever, T, which is operated by the worm and sector. The
distance, JO, in Fig. 10, or in other words the length of the lever, M,
is precisely equal to the distance, AB, in Fig. 7, measured in a right
line; and the rods, R and S, from center to center of the eyes, are also
each of precisely this same length. Further, the axis about which the
reversing lever, T, vibrates is so situated that when that lever, as in
Fig 11, is thrown full to the left, the pin in its upper end is exactly
in line with the rock-shaft, O.
When the parts are in this position, the suspension-rod, S, the arm, G,
and the lever, M, will be as one piece, and their motions will be
identical, consisting simply of vibration about the axis of the
rock-shaft, O. The motion of the lever, M, is then due solely to the
pin, B, which is in this case exactly in line with the journal, J, so
that the result is the same as though this eccentric rod were connected
directly to the lever; and the pin, P, being also in line with B and J,