Front of the bubble [DotD 10.4.2020]

[whole diary]

[Fourbee]

I think this link was originally posted on this forum somewhere. The DMU^▸ (Diesel Multiple Unit) in the video is not identical to the images posted, but some of it might help with the gaps if you search in it:
https://www.youtube.com/watch?v=2VgB3Uwx6oI

If you've got 18 minutes to burn, you could watch the whole thing of course!

[Western Pathfinder]

This may also prove to be of interest
https://m.youtube.com/watch?v=bS5xiM0LYtA.

[Fourbee]

This may also prove to be of interest
https://m.youtube.com/watch?v=bS5xiM0LYtA.

That was the link I meant to post! 

[eightonedee]

Brought back happy memories of a footex gift from my mother in law, taking a DMU^▸ (Diesel Multiple Unit) up and down the Wensleydale from Leeming Bar to Castle Bolton. There is something satisfying when you (think?) have got the hang of balancing the throttle, gears and brake. Recommend it to anyone,

[Trowres]

Many useful bits of information and reminders there.  Looking to correlate that ...

A Engine power controller - idle and 4 power positions; incorporates deadman's device
B AWS^▸ (Automatic Warning System) Cancel button
C Gear Change - 1,2,3,4,neutral. There is also a slot under the circular part of the handle into which a brass forward/reverse lever is placed when the cab is in use. This lever is mechanically interlocked with the gear change handle.
D Vacuum Brake
E Manual Brake
F Rack for vacuum brake handle and forward/reverse handle
G AWS - most recent status indicator
H Speed indication
I Engine Revs
J Vacuum - "duplex" gauge - two indicators; brake pipe and release pipe
K Control air pressure
L Brake cylinder reservoir vacuum - only "bubble cars" had these. Due to having only 2 brake cylinders on the train if a single-car, it was especially important to know if the vacuum above the brake piston was being maintained correctly.

Switches are a problem as the layout varied between DMU^▸ (Diesel Multiple Unit) types. Here's my attempt:-

M Communication buzzer and either demister blower or cab heater
N Control circuit key and did these things have a screenwash?
O Route indicator light switch; two switches for marker lights - each with red/off/white
P Switch to select whether the tachometer is looking at engine 1 or engine 2. Red light to indicate control circuit is energised (i.e. a key is inserted in one or other cab and no fuses have blown); other switch is either demister blower or cab heater fan.


On the indicator panel to the side of the cab, the outer lights indicate engine running; the central light is "air and axle" - it was illuminated only if both final drives on a power car were in the correct direction for running as indicated by one of a pair of air pressure switches (one for forward, one for reverse).

The three black buttons were LH engine start / all engine stop / RH engine start (the red test button was a feature on re-engneered panels).

The drivers cab had a heater fed by engine coolant. A switch was provided to control an air circulating fan fitted to the heater. The demister, however, was fed (if I recall correctly) by air from the Smiths heater warming the passenger saloon. It wasn't terribly effective.

The Smiths heater burnt atomised diesel fuel. A glow-plug provided initial ignition. The start-up sequence was originally a clockwork timer but this was eventually replaced by an electronic unit (as in the bubble car photo) that included a 741 op-amp. Another 741  op-amp was used in an interlock circuit that de-energised the starter motor circuits when an engine reached sufficient rpm to run.

Remember that vacuum brake gauge with the twin indications? Releasing the brake required sucking air out of the train pipe until 21" Hg registered on the train pipe gauge. As the mechanical exhauster wasn't very rapid at doing that sucking, a large tank (about the size of an oil drum) was provided on each car, linked by a "release pipe" with about 30" vacuum. Into this went the air from the train pipe in order to release the brake quickly.

In fact, as the vacuum exhauster was belt-driven off the gearbox input, as soon as the driver put the unit into 1st gear to start from a station, the exhauster stopped. If there wasn't sufficient vacuum in the release reservoirs, the brake would never be released!

The compressed air supply was used for horn, wipers... and engine and gearbox control. The throttle and gearbox controls were just big rotary switches energising a selection of wires down the train. These linked (via relays) to electro-pneumatic valves that operated an air-motor for controlling the engine governors and more pistons to select gears and forward/reverse.

[grahame]

Huge "thank you" to everyone who's helped me fillin what all the nobs, dials and levels do - Trowres, Martyjon, Electric Train, Witham Bobby, Rogerw, Western Pathfinder, Bobm, Fourbee and Eightonedee. 

You correctly identified that the original picture was of the trailing cab during a journey - three vital elements missing to operate the vehicle from this end. Here, from earlier in that day, is a further picture with those three emenents shown:

1. The handle on the vacuum brake (on item D)
2. The forward / reverse level (fitted under the gear change on item C)
3. The driver - physically larger that any of the controls and blocking much of the view in the bottom left of the picture.

[eightf48544]

If I recall correctly the Rev counter acted as a gear change indicator, There being a yellow crescent round the top of the dial as the revs increased the needle moved round when it reached the end of the yelllow band it was time to change gear.

It then crawled round again until after a painfully long time you got to fourth gear and 70mph!

Modified to add round.

[bradshaw]

Especially when the panel located between the door and the left hand window showed one or more engines out!

[Electric train]

The gear box on DMUs^▸ (Diesel Multiple Unit) is a 3 speed epicyclic, fourth gear being direct drive.  The coupling to the engine is a fluid fly wheel.

The original driving technique was in first gear take the train to the speed that the engine tacho showed change up, where the driver would change gear with out dropping the engine revs off.

It was soon found that this cause excessive where to gear box brake bands and over heating of the fluid fly wheel.  The driving technique was changed, the driver when a gear change is needed drops the engine revs off change gear and the apply engine power.

The final drive on the driving axels has a sliding dog to provide reversing .  One of the checks that had to be done on a power car that had a final drive change was to check the axel turned in the right direction, get the pneumatic lines crossed and the dog would engage in the wrong direction 

[Trowres]

Compared with today's mess of incompatible trains, most heritage DMUs^▸ (Diesel Multiple Unit) had a remarkable degree of compatibility (identified by a coupling-code symbol on the cab ends). Most units had the "blue square system" that used four jumper cables connected down the length of the train. No fancy computers or change-end reboots. A clever staggering of connections on the power cars (e.g. pin 1 at one end connects to pin 2 at the other end of the coach) was all that was required to ensure that the leading driving cab could monitor the status of engines on six power cars.

Forward and reverse was managed with similar simplicity. Selecting "forward" in the leading power car was correctly interpreted as backwards by any power car in the train that was pointing in the opposite direction. All done by the way the jumper cables were wired. The only use of relays was to ensure that each power car supplied the current to work its own electro-pneumatic valves, with a relatively small current from the leading power car operating all of the relays down the train.

I came across one class 108 2-car unit in which engine coolant from the power car was used to provide water heating in the toilet in the trailer car (via flexible coupling pipes between the coaches). I have no idea how commonplace this was and have never seen the practice described in any manuals or historical notes.

[Fourbee]

Forward and reverse was managed with similar simplicity. Selecting "forward" in the leading power car was correctly interpreted as backwards by any power car in the train that was pointing in the opposite direction. All done by the way the jumper cables were wired. The only use of relays was to ensure that each power car supplied the current to work its own electro-pneumatic valves, with a relatively small current from the leading power car operating all of the relays down the train.

On class 483s (so not comparing apples with apples) the unit coupling was needed the right way round, observing the letters on the cab ends; presumably you end up with an intra-train tug of war otherwise!

[TonyN]

The central column of lights indicated that the final drive was engaged correctly

These where added after an early incident when one power car in a set did not reverse and tried to fight against the rest of the train. This resulted in overheating and a fire fortunately the car was empty at the time.

[Reading General]

This is an interesting thread, I'm learning a lot from it. These trains took me many places when I was young. I distinctly remember riding on one from Reading to Henley (when the branch train was a through train from Reading) with my Dad where the blinds were up in the drivers cab at the Reading end of the train. We got to see the line view going backwards through Sonning Cutting and then watch the Driver and see out of the front from the reversal at Twyford. A wonderful experience for a small lad.

[Oxonhutch]

A wonderful experience for a small lad.

Indeed. Daring to sneak into an empty First Class for a journey towards St Annes-on-the-Sea just so I could watch out the front.

[CyclingSid]

Used to enjoy going from Reading to Basingstoke in summer and watch the rabbits on the line. They had obviously sussed out these large things that invaded their space and had timed getting out of the way perfectly.