Class 66 loco engine RPM ‘increase’ at idle

[ANTONOV 12BP]

I’ve fumbled onto a characteristic of few 66s during idle where occasionally, the RPM increases and stays that way for a minute or two before idling back down. Does anybody know what triggers this?

My guess is it feeds pressure onto the brakes at the back of the modal.

Here’s references below for query:

go to 18:27

go to 01:50

Credits: The Enthusiast’s Transport Videos

 

[Numbskull100]

I’ve fumbled onto a characteristic of few 66s during idle where occasionally, the RPM increases and stays that way for a minute or two before idling back down. Does anybody know what triggers this?

My guess is it feeds pressure onto the brakes at the back of the modal.

Here’s references below for query:

go to 18:27

go to 01:50

Credits: The Enthusiast’s Transport Videos

It's recharging the brake pipe, the air demand causes the engine governor to increase RPM to put more air through.

 

[The Puddock]

Class 66s follow the American practice of having the compressor directly mechanically driven by the power unit. If you need more air then the engine RPM has to increase to produce it. British built locos use electric compressors, so there is no noticable change to the engine speed when the compressor starts, speeds up or stops.

 

[ExRes]

Great fun when the ground staff started coupling 67s to mail vans, one of them decided my parents weren't married as he was convinced I was taking power while he was in between didn't take that long to get used to but the increased revs were certainly 'interesting'

 

[Deepgreen]

Great fun when the ground staff started coupling 67s to mail vans, one of them decided my parents weren't married as he was convinced I was taking power while he was in between didn't take that long to get used to but the increased revs were certainly 'interesting'

Yes, but you didn't need to give the two tones as well!

 

[hwl]

Class 66s follow the American practice of having the compressor directly mechanically driven by the power unit. If you need more air then the engine RPM has to increase to produce it. British built locos use electric compressors, so there is no noticable change to the engine speed when the compressor starts, speeds up or stops.

The newest US locos in the past few years have gone electric compressor as well as it makes getting through the Tier 4 emissions regulation easier.

 

[ExRes]

Yes, but you didn't need to give the two tones as well!

You have to take your enjoyment where you can

 

[Deepgreen]

You have to take your enjoyment where you can

Yes - I do wonder how much stuff went on with steam - clearing the drain cocks, for example, can be a 'blast' (but with a high risk of scalding). A slight digression but I wonder what these NR guys thought when they were trapped against the wall at Victoria!