Name that tune...

[jimini]

Well, not actually a tune but anyhow... My question is this:

I've noticed a certain noise on C stock trains, usually (but not always) just before the train pulls away. Now how to describe it...? It sounds like a pneumatic noise, coming from underneath. Some might even describe it as a "chugging" sound?

Well, it was a pretty rubbish description, but I'm sure one of the regulars will be able to suss out what I'm wittering on about?! Many thanks all ~ Jim.

[Deleted]

It's probably the compressor, which provides compressed air for train brakes, doors etc.

[Deleted]

Compressors for providing compressed air to brakes and doors etc. ?

[Deleted]

Simultaneous posting ;D ahh - small world

[jimini]

Evening gents - It's not that I think? It carries on for a little while after the train's departed the station, it also occurs sometimes when stationary between stations? Or maybe it is??!! It just seems to happen at really random times, would compressors kick in at random times? I did warn you it was a pretty rubbish description, but as far as I can tell it's a fairly regular occurence. My profuse apologies for being so vague!

[Deleted]

Yes, compressors come in at random times, whenever the air pressure is getting low. Some C stocks seem to leak like the proverbial sieve and so the compressors work more often.

Compressors are only in the trailer cars (the ones without cabs) so if the sound you seek is louder in the trailer cars then that would confirm it.

[jimini]

It certainly is! Been meaning to post that question for ages, many thanks all for satisfying my curiosity once again!

[Deleted]

The sound you hear is the PCM camshaft ticking and clunking as the resistances are switched out of the traction circuit.

Errmm...........Not quite, we have solved the question as being compressor's (see above) ;D ;D
Colin.