Tuesday, 10 January 2012

Railway Signalling: Tipton (Part 2)

In the post Railway Signalling: Tipton I first wrote about my visits to this box.

There are track and signalling diagrams of the Stour Valley line in the 1950s in the excellent series of publications from the Signalling Record Society 'British Railways Layout Plans of the 1950's' taken from the John Swift Collection. The West Midland lines are included in 'Volume 11: LNW Lines in the West Midlands' (ISBN: 1 873228 13 9).

For details of what remained of this route in 2005, refer to 'Railway Track Diagrams' Book 4: Midlands & North West', Second Edition, published by Trackmaps (ISBN: 0-9549866-0-1). The First Edition of this book was published by Quail in 1988.

Below are some more of my recollections.

1. Tipton Station Signal Box Diagram

The best way to orient yourself in any signal box is to study the box diagram. The diagram below (from my earlier post) is rather simplified, omitting important information such as gradients (see 2 below), distances to distant signals (see 3 below), lists of spare levers and any special levers such as the level crossing gate lock (see 5 below) and details of any Block Control (see 6 below).

The diagram displayed in the box was large enough to be readily visible and hand tinted so that, for instance, stop signal arms were tinted red and distant signal arms yellow. The diagram was mounted, behind glass, in a substantial wooden frame and suspended from the roof above the block shelf. There's a simplified sketch of the block shelf showing the diagram hanging from the roof above the block instruments:-

Of course, the 'regular' signalmen would rarely give the diagram a glance since they became very familiar with every aspect of the layout. 'Relief' signalmen, who might only intermittently work the box, were more likely to look at the diagram but they often preferred to consult the 'Pull Plates', the 'badges' fixed to the front of each lever showing what other levers were first required to release a lever. But, for other visitors, the diagram was an invaluable source of information.

2. Gradient Diagrams

It's important that the signalman has a clear idea of prevailing gradients. If a train becomes divided, particularly a 'loose coupled' freight without continuous brakes, it's important that the signalman understands what may happen to any vehicles running away. Gradient profile information is included on each signal box diagram, from where this information was taken. Main and Branch lines are common between the box and the actual junction - I don't know why the two gradient diagrams show different profiles.

A sketch of the main line profile is given below.

A sketch of the branch line profile is given below, extending to Wednesbury and showing the long-gone King Street Crossing on the Tipton side of Princes End.

3. Distances to Distant Signals

Down: 759 yards and 350 yards from Home.
Up Main 35B: 876 yards from Home.
Tipton Curve: 623 yards from Home.

4. The Lever Frame and Interlocking

Tipton Station box was fitted with the a 36-lever frame. It was the earlier pattern of Webb lever frame - the L & NWR 5.5 inch centres Tumbler Interlocking Frame. For more information about L & NWR signal boxes and the fitted at Tipton Station, refer to the excellent book 'A Pictorial Record of L.N.W.R. Signalling' by Richard D. Foster, published by Oxford Publishing Company in 1982 (SBN: 86093 147 1).

I've always preferred the 'loop' catch handle used by Webb. In the 'Tumbler' design, the catch handles were not interlocked, it was the movement of the lever which moved the Hook Rack associated with the lever within the vertical Guide Rack. Actuators ('L' shaped bell cranks) transferred this movement to U-section Locking Bars moving horizontally in a Guide Rack. Full or Half Locks were attached to each Locking Bar to allow or prevent movement of the Hook Racks attached to other levers as required by the desired interlocks. The whole Locking Rack was held together by a series of vertical Backbones which held the Locking Bars and Hook Racks in position.

5. Spare and Special Levers

The box diagram listed the following Spare Levers:-
1, 8, 9, 10, 11, 12, 16, 17, 23, 24, 25, 26, 27, 28, 29, 36.

Because of the level crossing gates, there were also two brown-painted special levers. Lever 31 was the Gate Lock and Lever 32 the Gate Stops. There were no pedestrian wicket gates - a subway was provided used by both passengers to get between the Up and Down platforms and pedestrians using the public road.

Finally, there was a Ground Frame released from an Annett's Key, described in section 9 below.

6. Track Circuits and Block Control

There was one track circuit - a short 'Berth' track approaching the Up Home. The track circuit was numbered TC10013, dating from a period when track circuits were quite rare and track circuits from a large area shared a common numbering scheme. Later, as track circuits proliferated, each signal box had its own number series, starting with 'T1'. The box diagram recorded that 'TC10013 controls the Up Block Instruments. With Lever 34 (the Up Home) Normal operates the Annunciator (a buzzer reminding the signalman that a train is approaching a 'Stop' signal at 'Danger'). Line Clear Up Main requires Lever 34 Normal.'

7. The 'Fobbing Bar'

Lever 18 was painted Blue and operated a Locking or Clearance Bar. However, it was not associated with a set of facing points but was situated on the track from the Down Main to Tipton Curve Junction. This line became rising once clear of the junction with the Stour Valley and spring-operated Catch Points were provided to prevent runaway vehicles running back and obstructing either the Up Main or Down Main.

Like a normal facing point Locking Bar, the Locking Bar operated from Lever 18 usually lay below the level of the wheel flanges but was raised via point rodding from the signal box. If a train was standing or passing over the locking bar when the signalman attempted to raise it, the wheel flanges would interfere with the raising of the Locking Bar and prevent the lever movement from being completed.

Before the signalman could clear the Down Main or Up Main signals, lever 18 had to be operated both ways - this was called "Fobbing Up". If successful, the signals were released. If you'd 'pulled off' the signals in one direction, you could also clear the signals the other way without "Fobbing Up" again.

Exactly what disaster scenario this special locking was installed to prevent, I'm not quite sure. The most puzzling aspect of the interlocking was that you could "Fob Up" at any time, not just immediately before clearing the main line signals. The universal practice after a train passed on the main lines was to restore the signals to danger, wind the gates open to road traffic and immediately "Fob Up" ready for the next train, even if that train was not expected for some time. I never heard of this curious arrangement being used elsewhere, but I'd be delighted to hear from anybody with more information.

8. Short Section Working

Under normal Absolute Block Regulations, a signalman had to have the line clear for 440 yards (1/4 of a mile) beyond his first Home Signal before accepting a train from the box in the rear. This 'Clearance' was a safety margin so that, if the driver of the approaching train 'missed' the Distant and only saw the 'Red' Home Signal when he was on top of it, he'd still got at least 1/4 of a mile to make an Emergency Stop before reaching an obstruction. At Tipton, the Up Main Home was only about 350 yards before the Starting signal, so the 1/4 of a mile extended into the section of the next signal box, Watery Lane Crossing. Tipton was not allowed to accept an Up train while the Watery Lane block stood at 'Train on Line'. Similarly, Watery Lane could not accept a Down train while the Tipton block stood at 'Train on Line'.

There were old 'Face Discs' in Tipton Station box but they had been out of use for some time. What did remain was a mechanically-operated indicator for the Watery Lane Up Distant weight bar. It was in the form of a cast box fixed to the wall behind the frame with a vertical slide operated from beneath the floor. Tipton was not allowed to clear the Up Distant until the indicator showed that Watery Lane's Distant was 'Off'.

Distant Indicator at Watery Lane, as shown on Tipton Station signal box diagram.

There was a similar arrangement on the Down line and the Tipton box diagram depicted the indicator in Watery Lane box which was operated from Tipton's lever 2.

9. Ground Frame

There was a Ground Frame released from an Annett's Key, pattern 'A'. This was Roberts Siding, leading to sidings behind the Up Platform. When I was visiting Tipton, these sidings were heavily overgrown and I never saw the Ground Frame used.

The sketch above shows Roberts Siding Ground Frame as depicted in the John Swift diagram which shows the five parallel sidings behind the Up platform I remember. But his diagram also shows a second connection to sidings for "Freakley's Stone etc. Sidings" extending towards Tipton Curve. That had gone by the time I took an interest in Tipton.

10. Station Bell

The sketch of the block shelf in section 1 (above) shows a bell push marked 'BOOKING OFFICE'. This worked an electric loud-sounding bell on the adjacent station principally used to alert the station staff to approaching stopping trains. The simple bell code was:-

1 ring: Down Stopping Train approaching.
2 rings: Up Stopping Train approaching.
3 rings: Speak to Signalman on the Box-to-Box telephone circuit.