101 DMU question.
 

When I was at Dereham (Mid Norfolk Railway) yesterday, I overheard a conversation from the driver of their 101 DMU set.

He was saying that if the air pressure dropped below a certain level he could not start the engine from his cab, and had to lay on the platform to start it.

Do they not have electric starters ?

They do have electric starters but certainly first start of the day has to be done trackside and then the air has to be built up before the brakes will work. I am fairly certain that if the air pressure falls off you have to start trackside.

I will check this out.

Best wishes,

John H-T.

After a discussion with our DMU expert at Wirksworth I can confirm that there needs to be about 80 psi of air in the system before the engines can be started from the cab, even though they do have electric starters.

Best wishes,

John H-T.

I've resurrected this 11 year old old thread as I've recently been reading the Class 101 traction manual and thought you might be interested to hear the full reasons.

So in fact it's not a case of could not start the engines from the cab, but rather MUST not.

Firstly - yes the the engines have electric starter motors.

The thing is that although the 101s are vacuum braked, they use compressed air to operate some of the mechanical systems, such as throttle, gear change, and the final drive (which is used to change direction).

When the train has been standing with the engines shut down, some of the air will inevitably leak off. If the pressure on the air gauge (see pic below) is around ~80 psi or above, then you can start the engines by using the buttons in the cab - but if isn't then you must use the starter buttons located next to the engines. This is a very common occurance.

Why ?

Well, if you want to start the engines from the cab, you need to liven up the driver's desk. This also activates the air systems. If the air pressure is below 75 psi then the sliding dog inside the Final Drive which moves the cogs into forwards or reverse mesh may not engage fully. This can cause serious damage when the drive train starts to rotate.

Once the engines have been locally started you will build up sufficient air pressure eventually to be able to safely energise the driver's desk.

Incidentally - One of the cab checks is that the 'air and axle' lamp is lit (see pic below). This confirms that the final drive has engaged fully. If it doesn't illuminate you're not going anywhere!

Hope this makes sense ;-)

(Source: Craven Traction Manual)