Exhauster speed up

[bigphill2]

Hi all
What does this little button do? It appears on the 421(electric) and the class 33 ( diesel). I've no idea at all about this and any help would be great.

Regards.....Phill

[davejc64]

At a guess I would imagine it's something to do with the braking system, whether it's actually functional in RW I don't know.

[bdy26]

There's some detail here:

http://www.railway-technical.com/vacuum.shtml

I'm not an expert in this, but the following is my thinking in principle - In most cases, the creation of vacuum in the system (or compression of air) is managed by a governer i.e. when brakes are applied, the vacuum in the system "drops" and the exhauster then starts up to restore the level. Under prolonged / repeated braking it may be necessary to increase the speed of vacuum production to ensure that the brakes are kept off (sounds wrong, but you need to understand triple valves) - when steam pressure drops on a steam loco, eventually there will be insufficient pressure to create a vacuum so the train brakes will apply automatically.

The same theory (at a conceptual level anyway) applies to air brakes - there is a "compressor speed up" function on certain locos / units e.g. the sprinter family.

I don't think these are modelled in RW, but it may well be possible though probably not of much use / interest.

I may well have got some of the above wrong, those who know more feel free to explain it better!

B

[holzroller]

It basically does what it says, speeds up the exhauster to give a quicker release. Especially neccesary sometimes on a big train. The vacuum brake is slower to apply and release than the air brake, this helped on the release side. The braking technique for vacuum is different to air, I remember a colleague trained on the air brake having great difficulty adapting to vacuum braking. Don't quite know why it would be on a 421 though, as far as I know these were air only.

[bigphill2]

Hi
Thank's for the quick response all. That certainly makes a lot of sense. Its nice to know what the buttons and levers are for.

Thanks ...Phill

[Kromaatikse]

On MU trains, the exhauster/compresser speedup button is used when starting up the train after a period of inactivity. There are large reservoirs which need to be charged before the braking system can be tested, which must be done before passengers are allowed to board. The speedup allows this to happen more quickly.

On modern DMUs, the compressor is usually attached mechanically to the engine, so this will rev the engine for the duration. On older DMUs, there was no button, so one simply put the transmission out of gear and applied a little throttle.

[Kariban]

It basically does what it says, speeds up the exhauster to give a quicker release. Especially neccesary sometimes on a big train. The vacuum brake is slower to apply and release than the air brake, this helped on the release side. The braking technique for vacuum is different to air, I remember a colleague trained on the air brake having great difficulty adapting to vacuum braking. Don't quite know why it would be on a 421 though, as far as I know these were air only.

EP/air ( with triple valves! ) - I have a lovely little booklet from the 30s describing the Westinghouse EP/air brake, so I'd think it's on practically everything since then. Maybe it's just mislabled "compressor speedup" on the CIG? the 33 would have had dual brakes so maybe one button for both, I have no idea.

[firetrap1]

You learn something every day. Thanks guys!

[mbtech22]

EP/air ( with triple valves! ) - I have a lovely little booklet from the 30s describing the Westinghouse EP/air brake, so I'd think it's on practically everything since then. Maybe it's just mislabled "compressor speedup" on the CIG? the 33 would have had dual brakes so maybe one button for both, I have no idea.

The existence of the "Exhauster Speed-up" Button on the 4CIG is fictional, RSC must have used a 4TC Driving Trailer for the Cab Model as this does have an additional button for Exhauster Speed-up. TC units were designed to have the capability of leading a train, followed by an SR Loco (Class 33/1 or 73/74), followed by vacuum braked vehicles (coaching stock). The button enabled the driver (in the TC cab) to speed-up the exhauster on the remote loco so as to get a quicker brake release on the vacuum braked vehicles. The loco acted as a "converter" between the air brakes on the TC unit and loco and the vacuum brakes on the trailing stock. This type of operation was not used very often as it was not popular with the operators.
4 CIG units did not have a compressor speed-up facility. The two compressors ran at constant speed when required.

Mark Brinton