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Signalling trainstop Photos

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Signalling and Trainstop Photos

Fig. 1: Automatic Signal with Trainstop

Ruislip Manor st.JPG (49145 bytes)

Typical London Underground automatic signal (on the left) with its trainstop in the raised position, placed at the right hand side of the track.  The trainstop is lowered when the signal shows a clear (green) aspect.  Compressed air is used to lower the trainstop against the spring pressure used to raise it.  This provides an element of fail safe, should the air supply be lost.  The air is compressed in the traction sub-stations and is distributed alongside the track in an air main.  This can be seen as the silver pipe in the photo above supported on posts at the track side, together with the signalling and power cables.  Photo taken at Ruislip Manor (Metropolitan).

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Fig. 2: Block Joints and Trainstop

Block joints.JPG (41157 bytes)

This photo shows the insulated block joints in the running rails at the end of a block section.  Note the raised trainstop on the right hand side of the track acting with a red signal (not seen here) to protect the entrance to the next block.

Track circuits were first introduced to the UK in 1903 on the Ealing and South Harrow Railway, now part of the Piccadilly Line branch to Rayners Lane.  This is where this photo was taken.

A problem with block joints is that the surface of the rail spreads over time with the intensive use, forming "scaling" over the block joint.  This causes the two adjacent sections to become electrically connected and results in the "track circuit failure" so often heard about.

The plate on the track shown in the photo above is a stopping mark provided for train drivers indicating this is the place where 8-car trains should stop.

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Fig. 3: Tripcock Tester

Tripcock tester.jpg (63311 bytes)

This photo shows a tripcock tester (Acton Town, Piccadilly Line) with the names of parts.  The tripcock tester is provided to check that the tripcocks of passing trains are in operative condition and within the correct gauge to strike a raised trainstop.

As the train passes over the tester, the tripcock arm should pass through the two vertical gauge posts at the entrance to the tester.  If it does not, and the tripcock hits one of the posts, the train will be tripped and will come to a stand.

If the tripcock arm passes through the gauge successfully, the arm will depress a lightly sprung ramp.  As the ramp depresses, a circuit is completed to indicate the test was successful.  The indication consists of a small light (either white, blue or purple, depending on location) mounted near the starting signal.  The light is switched on automatically as the train approaches the tester and the light will go out if the ramp is depressed correctly.

If the train passes through the ramp too fast, it is likely to get tripped anyway.  For this reason, tripcock testers are invariably located in station platforms.


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