THE MACPHERSON SWITCH
AND MOVABLE FROG;
CANADIAN PACIFIC RY.
Engineering NewsFebruary 21, 1895
When the stub switch was in general use in this country various
modifications were devised which were styled safety switches,
and were intended to prevent derailment caused by a misplaced
switch leaving the running rails discontinuous, so that the wheels
would inevitably drop onto the roadbed. With the introduction
and general adoption of the split switch, however, these devices
became practically obsolete, and where the stub switch is now
retained it is generally in the simple unprotected form, while
the use of the safety spring in the switchrod or switchstand has
greatly increased the efficiency of the split switch in trailing
operations. In Canada, however, the stub switch is still generally
used, and several safety arrangements have been introduced. On
the Canadian Pacific Ry., for instance, there is used a half-Cooke
switch, so arranged as to prevent derailment from the main track,
as noted in: our issue of Nov. 8.
One of the latest and most satisfactory of these safety switches,
and one which appears to present certain important points of superiority
over the split switch, is that invented by Mr. Duncan MacPherson,
Division Engineer of the Canadian Pacific Ry., and tried with
successful results on that road, being used in connection with
a movable frog also designed by Mr. MacPherson. If set for the
side track, a train on the main track may safely trail through
the switch; but if set for the main track, a train coming down
on the side track would be stopped at the frog. It is thought
that a car blown along the side track by the wind would be more
likely to be seen if stopped at the frog than if blown out along
the main line for several miles. It is for this reason that the
Cooke switch, used on the Canadian Pacific Ry., is made in half
sets, as above noted, so as to protect the main track and to stop
or derail a car moving along the side track. With the ordinary
stub switch the main track and side track rails are both broken
at the switch, while with the split switch one rail of the main
track and one of the side track are left unbroken. With the MacPherson
switch the main track rails are not broken, either at switch or
frog. This is a most important feature, as the switch and frog
are only touched by trains using the side track, and, therefore,
other things being equal, this device should be more durable than
other forms of switches.
IllustrationThe
MacPherson Switch and Moveable Frog; Canadian Pacific Railway
The switch consists of two moving rails, connected by heavy
switch rods, and the moving rail inside the main tail having a
guard rail attached to it and also moved by the rods. A short
guard rail is spiked to the ties on the inside of the other main
rail. The switch rails are slightly higher than the main rails
and have the ends beveled. The connection between the switch rod
and the connecting rod from the switch stand is effected through
a coil spring, as shown. When the switch is set for the main track
the main rails are entirely unobstructed, as on any part of the
open line. When set for the sidetrack, the ends of the switch
rails are in contact with the main rails, while the head of the
inner switch rail overlaps that of the main rail. The switch rails,
therefore, engage the wheel treads and carry the wheels up, so
that the flanges clear the heads of the main rails. A main line
train trailing through the switch, when thus set, will force both
switch rails back, the coil spring allowing of such movement without
affecting the switch stand or moving the frog.
At the frog the main rail is unbroken, and when the switch
is set far the main track the track is no different from that
at any part of the open line. The turnout rail is raised, as already
noted, and is, therefore, cut at the intersection with the main
rail, connection being effected when the switch is set for the
side track by means of a pivoted frog point, the toe of which
rests upon the main rail. This frog point is operated by pipe
connections from the switchstand, working in conjunction with
the switch, the arrangement being very similar to that of the
Price movable frog, shown in our issue of April 6, 1889; but,
while the latter has three hinged and movable parts, the MacPherson
frog has only one moving part, which slides positively and surely
into place, guided by the bar projecting under the main rail.
Should a main line train trail through the frog when set for the
side track, the wheel flanges would mount the incline of the beveled
toe of the frog, the wheel running along the frog and down another
incline upon the rail, a guard rail at the opposite main rail
holding the wheels so that they cannot get on the wrong side of
the main rail. The ends of these inclines are made of the right
elevation to engage a wheel flange without giving it a blow. When
the head of such a train reached the switch each wheel would open
the switch, but without moving the frog, as the bell-crank connection
from switch rod to frog rod joins the switch connecting-rod between
the coiled spring and the switchstand, so that there would be
no danger of derailment of the train or injury to the switch and
connections by the moving of the frog point. The frog cannot move
unless the switch lever is unlocked and thrown. It has been tested
by trailing through it a train of 20 cars, at a speed of 20 miles
an hour.
One of these switches has been in use in the Montreal yard
for over a year. It was used from 25 to 50 times daily and gave
entire satisfaction, the same switch being afterwards put in main
line service. Another has been in use at Hochelaga for more than
three years, during which time the spring in the connecting rod
(which was of special design, admitting of adjustment) has not
once required to be adjusted. Several other switches have been
made and their service has been favorably reported upon. All parts
are made of steel rails or steel forgings, and it is said that
the switch and frog can be made as cheaply as the Cooke switch
and frog, and will last much longer. The switch can be used with
a common frog, if desired, and the frog can be used with a split
switch, while the switch connections can be applied to any form
of switch stand and used with or without the spring. There being
no gap in the main rails, expansion and contraction do not cause
any trouble, and in winter the switch has given no more trouble
in snow than a stub switch. The device has been very favorably
reported upon by Mr. C. W. Spencer, General Superintendent of
the Eastern Division of the Canadian Pacific, and experience with
it has been so favorable that several of the switches have been
ordered for use on different parts of the line.
Track Page
| Contents Page
|