Railway Preservation News

Reverse engineering a whistle bowl
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Author:  economyhaze [ Tue Mar 06, 2018 3:45 am ]
Post subject:  Reverse engineering a whistle bowl

Hi all,

I recently discovered the bell of an unknown 3-chime whistle, without its the bowl and languid plate. There are no markings of any kind and the cap and acorn nut are also gone so I have no way to identify it. If I were to make a new bowl and languid plate, how would I determine the ID of the bowl and the gap between it and the languid plate? Will the languid plates chamfer have any effect on the whistle's properties?

Author:  Alexander D. Mitchell IV [ Tue Mar 06, 2018 8:24 am ]
Post subject:  Re: Reverse engineering a whistle bowl

The science involved is a bit trickier than just spouting a bunch of specs.

I strongly recommend that you get yourself a copy of "The Engine's Moan: American Steam Whistles" by Ed Fagen (2002) while Amazon or whoever else you like to patronize still has some copies. As I described it in a review for Railfan & Railroad, it's "part social history, part collector's guide, part shop manual," and it's the latter part you'll need. The $40 or whatever you spend will save you a lot of grief.

It's possible, albeit tricky, to fabricate what you want out of a giant pipe nipple, although you will be better served by learning the fine science behind the precision tuning that makes the difference between a whistle you can hear across the street and one you'll hear across a city.

Author:  Donald Cormack [ Tue Mar 06, 2018 11:33 am ]
Post subject:  Re: Reverse engineering a whistle bowl

First off, welcome to the forum. Whistle building is part engineering part dark arts. You can apply sound engineering principals based on tons of theory but what matters is how it sounds. I’ve seen whistles that look like they were dropped out of a plane from 30,000 ft be the best sounding whistles I’ve heard. On the opposite end of the spectrum, I’ve seen and built whistles that are machined with all the right clearances, angles etc. and have it sound like pure garbage. This is the dark art I speak of. I’ve built a few whistles from scratch including the bowl, languid plate and bell. Here is what I have found:

If you decide to build your own bowl whether it be a weldment or a machine piece of billet, you want to match the OD of the bowl to the OD of the whistle bell; mostly for appearance purposes. In order for the whistle to perform efficiently and avoid squealing at higher pressure, you want to inset the steam slot roughly .125” to .1875” from the ID of the lip of the bell. In other words, you want the jet created by the languid plate to be inboard of the ID of the bell so as the pressure running past the slot increases the jet migrates outward and still catches the lip of the bell in order to maintain proper resonance. Chamfering the languid plate has a mild effect on the direction of the jet but I have found a 1/16” chamfer on say a .1875” thick plate to be adequate. Any more may direct the jet too far outboard and cause over pressure/squealing at higher steam volume.

The steam slot or “gap” you’re referring to is very important as it determines the velocity of the steam jet and the efficiency of the whistle. A good gap to maintain is .015” plus or minus .005”. It is absolutely critical that this gap is consistent throughout its circumference. If it is not, you’ll have difference voicing about three notes. In other words, if you have three people singing a harmony and one of the three decide they’re more important than the rest and sings louder, you’ll hear their voice and it will drown out the others. This leaves a sour sounding chord. It’s worth noting that most 5 or 6 chime locomotive whistles had their bells radially scaled, where the deepest note had the largest opening and it progressively got smaller as the notes got higher. This was done to avoid the natural tendency for a higher pitch notes to usurp the lower notes. For three chime whistles, this usually isn’t the case as the bells were typically made to have equal voicing.

I hope this helps. This is what I found personally has worked for me. As many on this forum like to say when they’re offering advice “your mileage may vary”.

Happy whistling,

Author:  economyhaze [ Wed Mar 07, 2018 8:09 pm ]
Post subject:  Re: Reverse engineering a whistle bowl

Thanks for the help and advice! Looks like I have some fiddling ahead of me.

Author:  HudsonL [ Wed Mar 07, 2018 9:05 pm ]
Post subject:  Re: Reverse engineering a whistle bowl

In another thread I posted a drawing of a Northern Pacific Whistle.



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