Panel on left of driver on classic DMUs

[Ken H]

Following on from https://www.railforums.co.uk/thread...-ever-in-regular-service.231560/#post-5653555

On the wall between the windscreen and the drivers door on the left there was a panel of lights
3 across, 8 or 9 down (cant remember)
Originally with blue lenses but then blanked off with metal except with a small hole which the light shone through.
I think these were engine running indicators but I dont really know.
Can anyone explain their purpose.

 

[matchmaker]

From memory, I'm pretty sure they were engine running indicators.

 

[Bletchleyite]

From memory, I'm pretty sure they were engine running indicators.

They were, yes.

 

[Ken H]

They were, yes.

someone said on the long DMU thread that classic DMUs were limited to 9 power cars.
I think there were 9 rows of lights. Which fits
2 engines in some power cars so 18 lights needed. What are the other 9 for?
And when making up a train from 2 or more units, would someone (driver? Shunter?) check the panel simulated reality?

 

[LowLevel]

They show two bits of information. The outer lights show that the relevant engines are running. The middle air and axle light shows that the transmission is in the correct position for the direction selected (crucially important because if you change ends and one gearbox doesn't throw over properly there's every chance you'll be on fire in fairly short order).

 

[trainmania100]

Yes I think they're the engine lights if I recall some of my past Train simulator world experiences lol

 

[Ken H]

They show two bits of information. The outer lights show that the relevant engines are running. The middle air and axle light shows that the transmission is in the correct position for the direction selected (crucially important because if you change ends and one gearbox doesn't throw over properly there's every chance you'll be on fire in fairly short order).

Please bear with me because I observed this as a kid!
The driver came to the cab with a key, a big handle for the brake valve, and a small brass handle that I think was for the reverser. It fitted under the gear change handle. i think without that you could not put the unit in gear
so when he selected forward from his cab, that message would go down train wires to the gearboxes.
but you are saying that sometimes one gearbox would select the wrong location???

 

[jupiter]

Oil pressure good on the outside pair, and the middle one, as quoted is a little more complicated. It lights when both final drives on the car have fully engaged in the correct direction corresponding to the reversing (direction control) lever and the control air pressure is over a set value eg 60psi

 

[MadMac]

Oil pressure good on the outside pair, and the middle one, as quoted is a little more complicated. It lights when both final drives on the car have fully engaged in the correct direction corresponding to the reversing (direction control) lever and the control air pressure is over a set value eg 60psi

I think they were labelled "Air & Axle".

 

[Ash Bridge]

Cravens 105 driving cab below,

 

[Ken H]

Cravens 105 driving cab below,

only 7 rows. was that usual?

 

[MadMac]

only 7 rows. was that usual?

Only six. I think this panel was “standard” across the various classes.

 

[hexagon789]

Only six. I think this panel was “standard” across the various classes.

Yes, six was the standard.

 

[Western 52]

6 rows due to 6 power cars maximum in one formation.

 

[Grumpy Git]

6 rows due to 6 power cars maximum in one formation.

What was the limiting factor (notwithstanding platform lengths)? Was it purely down to the number of indicator lamps, or something else like permissable volt-drop on the (long) control cables?

Edit; having written this, I assume it was the latter which then dictated the maximum number of indicator lamps required?

 

[MadMac]

What was the limiting factor (notwithstanding platform lengths)? Was it purely down to the number if indicator lamps, or something else like permissable volt-drop on the (long) control cables?

There was some mention up-thread about voltage drop. Presumably some sort of calculation was done in the early days. I’ll pose the question to the owner of the Railcar site.

 

[Taunton]

Allerton depot used to turn out 8-car formations for summer excursions to Blackpool. However, their Derby Lightweight 2-car units were divided about 50-50 between sets with the normal one car powered, and "power twin" sets with both powered (despite which they seemed to be normally assigned quite randomly). However, on these big lash-ups they had to be careful that at least half the sets were the lower powered ones, otherwise they exceeded the limitation.

 

[jupiter]

Cravens 105 driving cab below,

Good looking cab.

There are four 19-way jumpers between each car. The interconnections that carry the oil pressure and air/axle indications are complex so the correct engine (or axle) appears in the correct place on the panel. It’s not as straight forward as you might imagine, but a very interesting problem to think about!

 

[MadMac]

Good looking cab.

There are four 19-way jumpers between each car. The interconnections that carry the oil pressure and air/axle indications are complex so the correct engine (or axle) appears in the correct place on the panel. It’s not as straight forward as you might imagine, but a very interesting problem to think about!

That leads nicely into “Why only six sets of engine indications?”. From discussion with the owner of Railcar, his thinking is that six power cars was the maximum number that could reasonably be expected and as such, the expense and complexity of wiring to support any more simply wasn’t considered worthwhile.

 

[jupiter]

This is my understanding of how the oil pressure indicator wires “move about” as they cross the junction between driving end to driving end and non-driving end to non-driving end.

 

[Ken H]

This is my understanding of how the oil pressure indicator wires “move about” as they cross the junction between driving end to driving end and non-driving end to non-driving end.

View attachment 114581

Ah. But what happens when the take a 2 car, and put a driving motor on one end to make a 3 car. Or replace a driving car on a set with a bubble car?

 

[Taunton]

I understand the Modernisation Plan mu control system was devised by Walker Brothers of Wigan, who did various other rail engineering items in the 1950s (including the County Donegal narrow gauge railcars). The initial Yellow Diamond system pretty much got it right, but some design issues came to light with experience, particularly with engine starting on a multiple formation, so the Blue Square system is just a variation on that. Presumably it wasn't worth rewiring the Yellow Diamond cars.

One of the very few journeys I made on Yellow Diamond cars was on the rare Derby-built 4-car sets, of which I believe there were only five, allocated all their life to Gosforth, but running a service one afternoon from Leeds to York. Two units were lashed up into an 8-car formation, which is probably as lengthy a train as was got for these pioneer units.

If you try to think out the logic of this system, the cars can be assembled in any order, any way round. They may approach the coupling-up from the same or opposite directions. When the driver engages gears to move the whole formation off, they all have to respond in the same direction. You have to admire the engineer who came up with the approach, which stood things in good stead for the lifetime of the type. I believe that when multiple coupling was first attempted on the first two Class 20 locos, possibly when testing at the factory, they set off in opposite directions.

 

[6Gman]

I believe that when multiple coupling was first attempted on the first two Class 20 locos, possibly when testing at the factory, they set off in opposite directions.

I've heard the same story about Class 33s.

Which makes me think it may be apocryphal . . .

 

[jupiter]

Ah. But what happens when the take a 2 car, and put a driving motor on one end to make a 3 car. Or replace a driving car on a set with a bubble car?

On the second question I’ll tell you in a couple of weeks when we’ve tried it. If a bubble car is connected onto a 3-car set it depends which end is connected. From memory if the B end is coupled all is good. If the A end is coupled the indicators still work but don’t necessarily appear in order correctly on the panel.