Blast pipe jimmy

[theflyingscotsman]

Good evening all,
So ive been flicking through some model engineering magazines from 1979 and i came across a brief comment about a Rob Roy that had been fitted with a blast pipe jimmy and that these were a bit naughty. Anyway a bit of googling and as i understand it, its basically a bar that is sat on top of the blast nozzle to change the blast. I wondered if anyone had used or seen one and if there were any pictures? also why were they viewed as naughty?

regards lee

[don9f]

I haven't seen any pictures of one myself and I think they were frowned upon by officialdom in the earlier times, when engines weren't very powerful, due to increasing coal consumption and putting greater strain on things in general.

Cheers Don

[oldnorton]

Yes, as Don says.

Repeating that which I read in an article some time ago: The bar, or lump of metal, would be crudely strapped over part of the blast pipe outlet by the driver before he started his duty. It was done because the engine would have been a known poor steamer and would have struggled to finish its run. With the increased blast steam could now be generated, but at the price of much increased coal consumption - hence the naughtiness or illegality.

How many actually did this, and how effective it was, is maybe questionable. It is perhaps a good tea room yarn that was repeated.

But I do like the idea of modelling it on a scale engine! That is real enthusiasm for authenticity. Ought to be a prototypical engine though.

Norm

[Gary L]

Mar 10, 2022 9:33:23 GMT oldnorton said:

Yes, as Don says.

Repeating that which I read in an article some time ago: The bar, or lump of metal, would be crudely strapped over part of the blast pipe outlet by the driver before he started his duty. It was done because the engine would have been a known poor steamer and would have struggled to finish its run. With the increased blast steam could now be generated, but at the price of much increased coal consumption - hence the naughtiness or illegality.

How many actually did this, and how effective it was, is maybe questionable. It is perhaps a good tea room yarn that was repeated.

But I do like the idea of modelling it on a scale engine! That is real enthusiasm for authenticity. Ought to be a prototypical engine though.

Norm

The story goes that blacksmiths in the Works would make these in their spare time and sell them to drivers. The ones I’ve seen (I seem to recall it was at Steam Swindon) could not be called crude exactly; frowned on by management for sure, but they sometimes looked the other way when applied to known bad steamers. I think it was a lot more than a yarn, though by its nature, first-hand accounts are increasingly hard to find.

We more or less do the same thing on models when we fit narrower blast nozzles to improve steaming, when really the whole geometry needs to be reviewed.

Gary

[lesstoneuk]

I do believe that some Great Western locos had a variable blast pipe. Basically it was a loose top to the blast pipe, restrained of course, that lifted when moving off "enthusiastically". It lifted with the vast amount of steam thus softening the draught through the fire. Ideally, it lessenened pulling the fire through the tubes but I'm doubtful if it was that effective having witnessed a Castle launch burning coal into orbit.

[ettingtonliam]

Yes, it was called the Jumper Top, and was supposed to be quite effective, though I think it could be secretly bolted down on a poor steamer.

'Jimmy's ranged from the quite sophisticated to the downright crude. I've heard that they could be as simple as a long bolt laid across the blastpipe top, with a wagon coupling link weighting it down, hanging down inside the nozzle. I've also heard the story of an old driver who had a collection of Jimmys to fit any loco he was likely to drive, and when he'd booked on and found what loco he'd got that day, would send home for the appropriate Jimmy.

[yorkshireman]

The aim when using a "Jimmy" was to split the cone of the Exhaust into TWO cones, thus to indcrease the
interface area between the fast moving Exhaust-Steam and the slower Combustion-Gases.
Only at an INTERFACE between the two media the impulse of the exhaust can be transferred.
A Jimmy was a crude, but simple thing.

There is a smarter approach: Kiesel-Exhaust-Nozzle (KEN)

Use Google to find pics of a Kiesel-Exhaust-Nozzle, Austrian design...
enginemanwook.files.wordpress.com/2010/07/steam-locomotive-kiesel-star-type-nozzle-from-johnson-p-38.jpg
Unfortunately blurred ...

I've seen pics of such nozzles, where someone created the NEGATIVE of a KEN from Aluminium,
placed a thick layer of Copper around the AL, machined the part and then desolved the AL in the inside.

Johannes

[yorkshireman]

http://instagram.com/p/CbCidVcgtXe

[theflyingscotsman]

thankyou all for the replies, makes sense of the working of it and also made me chuckle how something so simple can have a good effect.

regards Lee