3/4" Coventry D30 Loco - Exhaust Passages

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Comstock-Friend
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3/4" Coventry D30 Loco - Exhaust Passages

Post by Comstock-Friend »

On the Coventry/Friends Models 3/4" D30 0-6-0, there are very nice cored steam chest exhaust passages. The left and right half passages meet in the middle. For fixturing purposes to drill the mating bolts, Coventry has the passages counterbored where the left and right halves meet. There is a right and left hand port to be drilled to the exhaust stand/nozzle. Should a disc be placed in the counterbores to block free flow from left to right? Or is it OK for the exhaust passages to be common with the exhausting valve putting back pressure on the non exhausting valve?

John
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by FKreider »

Exhaust passages are combined and exit through one nozzle on most locomotives.
-Frank K.
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Bill Shields
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Bill Shields »

However a diverter to influence flow can be helpful
Too many things going on to bother listing them.
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NP317
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by NP317 »

I made a diverter at the exhaust junction under the nozzle of my Mikado.
I silver brazed a plug into the bottom of the exhaust T, then machined the deflector shapes with a ball end mill.
It works nicely, actually producing some vacuum in the opposite cylinder exhaust.
Hopefully the photos will post correctly.
RussN
2-8-2 Exhaust Deflector.jpg
2-8-2 Exhaust T.jpg
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Comstock-Friend »

Here a crude sketch. The "counterbore for tooling purposes" location would allow an easy insertion of a 'plug nickel'!
D30 Steam Chest_Cylinder.jpg
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by FKreider »

Yes I think that is a good idea.
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kcameron
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by kcameron »

For the picky people, cut and thread two plugs with the 45 on the end so you don't get turbulence in the exhaust flow on the way to the combiner. Just make sure it is aligned right and staked or something to stay put. Yes a simple plug of something at the middle face is simpler and likely a high percentage of similar performance I'd guess.

If making where the streams meet gains from being carefully aligned, making the path to that smoother might be worth a little effort too.
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Comstock-Friend »

So it seems the consensus is to keep them separate until they exit at the nozzle...
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Rwilliams »

Several years ago I was tasked with machine work on a new old stock Baldwin blast nozzle casting. Had been in storage in the steam warehouse from well before the end of steam in 1955. The nozzle casting kept the exhaust steam bores separate all the way up to the nozzle where it looked like a double barrel shotgun on steroids. A separate air line came in from the left side for the blower.

Interesting was when the new old stock casting was being milled to fit on the cylinder casting, there was evidence of steel wire to hold the sand cores in place at the foundry. The old damaged blast nozzle casting had the same diameter core wire in the same place.

Corrosion and sand erosion from sanding of the flues over many years had eaten away most of the ears where the nozzle casting bolted to the cylinder casting. The studs which secured the casting had most of the threads down to almost nothing. The hex nuts had almost no hex left and the ears for the bolts to secure the nozzle casting were 3/8 thick where new was over 3/4 inch thick. We made sure to cover the new studs and nuts with a steel shield to prevent the same problem in the future.
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Bill Shields »

It all depends on how much real estate you have to work with.

There are many 3/4" locos built with just the T that run just fine. I have several.
Too many things going on to bother listing them.
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by FKreider »

Bill Shields wrote: Sat Mar 06, 2021 5:59 pm
There are many 3/4" locos built with just the T that run just fine. I have several.
Same here - next time I'm in the shop I'll snap some pictures.
-Frank K.
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Re: 3/4" Coventry D30 Loco - Exhaust Passages

Post by Comstock-Friend »

Thanks guys. I have no experience on this.
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