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THE MACPHERSON SWITCH AND MOVABLE FROG;
CANADIAN PACIFIC RY.
Engineering News—February 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.

Illustration—The 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.


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