Railway Signalling in Burma - Part 4: Manual Control of Points and Interlocking

In the previous article on railway signalling in Burma Part 3 - Control of Trains, I reviewed my understanding of the origins of the systems in use. But I started to work out the methods in use much earlier, from observations I made from the cab of a diesel locomotive described in the post Cab Ride from Katha (and the associated posts and links to pictures).

Single Line Passing Loops

At passing loops, the only signals are normally a splitting home signal at each end of the station, situated at the toe of the points, allowing movements onto either Main or Loop line. The signal arms may be arranged as upper-quadrant or lower quadrant but both types are operated by push rods from the ground, interlocked with the loop points. Normally, a single lever ground frame operates the signal with the appropriate arm 'selected' by an interlock with the points. There are also various 'EIC' lock boxes in between the rails at points and mounted near the base of the signals. Apparently, some areas have elevated, multi-lever ground frames by MacKenzie and Holland but stations and junctions I've seen to date use a single-lever ground frame adjacent to the points, provided with a (usually rather derelict) point indicator.

'Trapped Key' Interlocking

The 1930s article refers to 'Simplex' interlocking which I haven't traced but I assume refers to the 'EIC' equipment. I haven't identified 'EIC' either so if anyone has any information it would be appreciated. By studying my photographs, I'd largely decided how the interlocking was intended to work but then I found a Paper by R. C. Rose titled 'A Survey of Indian Signalling' in the 1924 Proceedings of the Institution of Railway Signal Engineers (available online here) which seemed to confirm the philosophy. 'Trapped Key' Interlocking is still widespread in industrial safety as Castell Interlocks (introduced by James Harry Castell in 1922 adapting ideas first used on the railways).

Consider the simplest form of the railway passing loop. A single line splits into two through the station and then the two lines re-converge into the ongoing single line. There are just two sets of points. To reduce cost, both sets of points are operated local to the switch by hand. In Burma, a Single Lever Ground Frame is provided adjacent to the toe of the points and a Point Indicator may be fitted.

Ywa Taung: Single Lever Ground Frame which operates the points via the 'L' crank and Drive Rod on the right. Note that the long arm of the 'L' crank is adjustable, allowing the 'throw' to be adjusted. The Point Indicator on the left is operated directly from the points via a separate delector rod.

The Station Master has two Pointsmen who can be despatched to the handpoints to set them as required. But if the pointsmen make errors, trains can arrive on the wrong track, departing trains can 'trail' incorrectly set points or points can be changed as a train is passing over them.

So, various forms of key-locking apparatus were produced with the aim of giving the Station Master confidence that his instructions had been correctly carried out. The EIC Locking Box is one method of establishing this confidence, using the 'Trapped Key' method.

Detail of EIC Locking Box fitted between the rails on the Loop Points at the south end of Naba station. The Loop Handles on the two lock slides are at opposite ends of the box. The interlocking key is clearly visible on the left of the box. (In addition, the points have been clipped in the normal position - the point clip is on the left hand stock rail).

View of another Point Locking Box fitted between the rails (this one at Ywa Taung). Note the slot on the right of box for the interlocking key. There are two lock slides with loop handles. Each switch rail appears to have a separate detector blade.

What I've called the 'Lock Slides', manually moved in and out using the loop handles, serve the function of locking the points normal or reverse. In normal British Practice, there is one 'Lock' which can pass through either of two notches in the Point Stretcher. But in the EIC Locking Box, there is one notch, allowing one 'Lock Slide' to pass through the notch when the points are set to 'Main' and the other 'Lock Slide' to pass through the notch when the points are set to 'Loop'. As a further refinement, on some designs, each switch rail has its own notched detector blade so that both switch rails are separately detected.

If the 'Main' 'Lock Slide' can be pushed in, the 'Main' Key in the side of the Lock Box can be extracted. Once the Key is removed, the 'Lock Slide' cannot be pulled out and the points are held in the 'Main' position until the 'Main' Key is re-inserted. In a similar way, the 'Loop' Key can only be removed if the points are proved in the 'Loop' position.

Ignoring the complication of signals, if two Pointsmen each present 'Main' Keys to the Station Master, he may be confident that the points are set for the 'Main' at both ends of the loop.

In India, a further development allowed splitting home signals to be worked from a ground frame on the platform. In Burma I've not (yet) seen such an arrangement but at many passing loops splitting home signals are provided but worked locally.

Interlocking between Loop Points and Push Rods for selecting the signal arms of the Down Inner Home at Naba. Note the two 'EIC' lock boxes.

My Pictures

Burma: Control of Points and Interlocking.

The above set of pictures is part of a Collection Railways in Burma.

Railway Signalling in Burma - Part 5: Signal Boxes with Interlocking Frames

The British built the extensive metre gauge railway network in Burma. 

Around Yangon and on main lines there's double track which is being extended but much of the network is single track with passing loops.

  Whilst the majority of the railway has fairly simple arrangements for the control of trains (see Railway Signalling in Burma: Part 3 - Control of Trains there are some signal boxes with conventional interlocked mechanical lever frames. I've seen two at Bago and two at Kyee Myin Daing on the Circle Line in Yangon.

Bago

Bago is on the double-track main line from Yangon to Mandalay and has two mechanical signal boxes - Bago South at the Yangon end of the station and Bago North, controlling the junction with the single line to Mawlamyine at the other end. The area has mechanical operation of points and semaphore signals.

Signal Box at south end of Bago Station.

Signal Box at north end of Bago Station.

I've only seen these boxes from a passing train or, in the case of Bago South, from a roadbridge but more details of both can be found on the International Steam Pages site here ("The Old Order Changeth" by Rob and Yuehong Dickinson) and here (Melvin Haigh's photographs on Rob Daniel's interesting 'Flickr' site).

Kyee Myin Daing

Kyee Myin Daing (called 'Kemmendine' by the British) is an important station on the Circle Line to the West of Yangon Central and retains two mechanical signal boxes. This is rather odd because in January 1946, an order was placed with Westinghouse Brake and Signal Company for a Style 'L' miniature lever frame for Kemmendine (see my post here). I've not been able to find out what happened to this frame although a hunch is that it might have been deployed instead a few stations up the line at Insein. The area has mechanical operation of points and retains some semaphore signals but the main line signals have been converted to colour light signals (the rest of the Circle Line has colour light signals), necessitating electrical detection of facing points in the main line. Whilst the rest of the Circle Line is track circuited, the facing points at Kyee Myin Daing retain locking bars on the facing points and track circuits do not seem to be provided in the area. The box at the north end has a gabled roof and spartan appearance, as shown in the picture below.

Mechanical signal box, north end of Kyee Myin Daing. The building next to the track in the foreground is probably a relay/equipment room since the main running lines have colour light signals.

The box at the south end is adjacent to the clockwise Circle Line and has a hipped roof. I don't yet have a picture.

Mechanical Operation of Points

Points are operated mechanically using steel tubes (as some British practice), as shown below.

Point rodding, showing tube couplers and vertical roller frames at Kyee Myin Daing.

Mechanically operated facing points at Kyee Myin Daing, with separate facing point bolt and locking bar (on left rail). The grey box on the left is electric point detection to control the 2-aspect colour light signal with two line-of-lights route indicators in the background.

Photographs

  Bago Station.
By Train to Maymyo.
The Circle Line, Yangon (2013).

The above sets of pictures form part of the Collection Railways in Burma.