Improvements in Trip Expansion Gear of Steam or other Fluid Pressure Engines.
Year: 1889

page_text: Date of Application, 23rd Apr., 1889
Specification Accepted, 8th June, 1889
Improvements in Trip Expansion Gear of Steam or other Fluid
Pressure Engines.
We, JOHN COCHRANE Engineer Grahamstone Foundry Banhead by Glasgow and
WILLIAM CAMERON, Mechanical Engineer, Maryport, Cumberland, do hereby declare
the nature of this invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement :-
This invention relates to improvements in the means of releasing or disengaging the
parts which transmit the movements of the eccentric to the induction valves.
This gear was shown in its original form in the Industrial Exhibition held at
Glasgow in 1888.
The results did not prove entirely satisfactory.
The object of the present invention is to rectify the defects of that gear.
The gear consists essentially of a double box lever or its equivalent, a muff with a
suitable projection, a latch and a trip lever which are hung on the box lever. The
double box lever is hung on prolongations of the muff and is caused to oscillate by an
eccentric through suitable connection. On the upper part of the box lever the latch is
hung which engages with a suitable projection on the muff. The muff is securely fixed
to the valve spindle or trunion and lies between the cheeks of the box lever. When
the latch is in gear with the muff it receives from the box lever through the latch the
motion derived from the eccentric which opens the valve. When the latch is dis-
engaged from the muff the box lever finishes its outward & inward stroke without
moving the valve. On the completion of its inward stroke the latch falls into gear
with the projection on the muff and is again ready to open the valve. On the latch
being released from the muff the valve is instantly closed and brought to rest in the
usual way by springs or weights and a dashpot.
In order to liberate the latch from its mut we hang on a pin fixed in the box lever
at a suitable distance from the free end of the latch a lever hereafter called the trip
lever. This lever has two arms one of which formed in a suitable manner bears on the
latch at its free end the other arm is connected by a swinging link to a lever coupled
to the governor in the usual way, so that any movement of the governor balls caused
by variation of load or fluid pressure is transmitted to the trip lever.

page_text: CRITICT O OCT
stroke as the case may be.
It is to be understood that one box lever or its equivalent with its latch muff and
trip lever is required for each induction valve which are preferedly of that class known
as Corliss valves.
In order that our invention may be better understood we proceed to describe the
annexed drawings.
Fig. 1 Sheet I shows the arrangement of the original gear exhibited in the Glasgow
exhibition in the year 1888.
Fig. 2 Sheet 1 is a side elevation of the trip gear one of the cheeks of the box
lever E is removed showing the latch A muff B with its projection C and the trip
lever D. Fig. 3 Sheet 1 is an end elevation in section showing the box lever hung
on prolongations 21, 2¹ of the muff B which is securely fixed to the valve spindle or
trunion F.
As shown in Fig. 1 Sheet 1 the box lever were coupled directly together by a
connecting link G. We found with this arrangement that equal movements of the
governor balls from their normal position these equal movements being transmitted to
the trip levers did not liberate the muff from its latch at equal periods of the stroke
also when the governor balls were running in their normal position the liberation of
the muff occured at an unsuitably early period of the stroke the range also was
insufficient. For example we would predetermine the normal cut off to take place at
of the stroke and the range of expansion to be from zero to g of the stroke.
With the exhibition gear as shown in Fig. 1 Sheet 1 we found the normal cut off
to that place at something between & of the stroke. It is to be understood that
when we speak of an normal cut off we mean that portion of the stroke moved
through by the piston until the latch is release from its muff when the governor
balls are running in their normal plane of revolution. In order to get a normal
say at of the stroke and that equal movements of the governor balls shall produce
equal points of cut off or approximately so we make use of the following com-
binations.
Fig. 4 Sheet 1 shows a combination in which we use the exhibition gear but
instead of coupling the box levers E E directly together by a connecting link we
interpose a wrist plate and by suitably fixing the position of the pins 1. and 2 in
the wrist plate H to which the box levers are coupled by the connecting links 1a,
2 a we get the desired result.
Figs. 1, 2. Sheet 2. show a rearrangement of parts used in the exhibition gear.
Fig. 1 Sheet 2 is a front elevation of the modified gear one of the boxlever
cheeks being removed. The latch A and the trip lever B are hung on the same
side of a line which passes through the centre on which the box lever is hung and
the coupling pin 2. The arm 3 of the trip lever D is turned upward (the latch A
being slotted to admit of this) and is connected by a swinging link to a lever
coupled to the governor in the usual way. The latch A is shown is gear with the
projection of the muff B. The valve would be open an amount equal to the
lead when the parts lie in a similar position to that shown in Fig. 1 Sheet 2.
The box lever cheeks are hung freely on prolongations 2, 2 of the muff B
shown in Fig. 3 Sheet 2. With this combination wo get very approximately the
desired equality of liberation with the box levers coupled directly together. When
we interpose a wrist plate the result is slightly improved.
Figs. 4 & 5 Sheet 2 illustrate another combination by which we get the desired
equality of liberation.
Fig. 4 Sheet 2 is a side elevation of the modified gear having the cheek of the
box levers removed to show more clearly the various parts. The latch is modified
from that shown in the beforementioned combinations. In this combination we
hang the latch A sufficiently from the vertical to enable it to engage with the
muff by the action of its weight.
The latch A consists of two arms 1 & 2 as shown in Figs. 4 and 6 Sheet 2
these make with each other an angle which may be a right angle but not necessarily

page_text: so. The arm 2 engages with the projection C of the muff B while the arm 1 is
acted on by the trip lever D which is connected by a swinging link coupled to
the governor in the usual manner. A suitable spring 3 may be placed under
arm 1 to cause the latch A to engage with the projection C of the muff B. By
coupling the box levers directly together we get very approximately the desired
equality of liberation. When we interpose a wrist plate the result is improved.
Having now described our invention and shown how the same is to be performed
we declare that what we claim is
1st. The combination of a trip expansion gear consisting of a box lever or its
equivalent a latch and trip lever both hung on the box lever and a muff with a wrist
plate substantially as shown and described for the purpose set forth in relation to
figs. 2, 3 & 4 Sheet 1 of the annexed drawings.
2nd. The combination and arrangement of parts in a trip expansion gear consisting
of a box lever or its equivalent a latch and trip lever both hung on the box lever with
and without a wrist plate, substantially as shown and described in relation to
figs. 1. 2 & 3 Sheet 2 of the annexed drawings.
3rd. The combination and arrangement of parts in a trip expansion gear consisting
of a box lever or its equivalent a latch with two arms and trip lever both hung on the
box lever and a muff with and without a wrist plate substantially as shown and
described in relation to Figs. 3 4, 5 and 6. Sheet 2 of the annexed drawings.
Dated this 22nd day of April 1889.