Is it typical to later find steam passages need to be bored bigger?

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shild
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Is it typical to later find steam passages need to be bored bigger?

Post by shild »

Working on an impact wrench at the moment, doesn't have good power so trying to drill passages bigger. Makes me wonder Is it typical for live steamers to have this problem with their loco's cylinders?
shild
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by shild »

Probably the exhaust side needs to be much bigger than the inlet side doesn't it?
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Bill Shields
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by Bill Shields »

Boring passages bigger after the loco is built is very difficult.

Best to get it correct from the get go
Too many things going on to bother listing them.
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Builder01
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by Builder01 »

If you are using a proven design, you will get it right the first time if you make the passages as per the drawings. If you are making something up with no prior experience, you might want to run your dimensions by others that have been there before.
David Powell
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by David Powell »

I have played around with steam passage sizes a lot over the years. The writer LBSC got them pretty well right, they need to be big enough to pass exhaust freely, but not so big that excess volume leads to waste.
While every detail matters I have found that most complaints regarding low power( Providing that pistons and valves are fairly steamtight: have their origins in poor valve gear design, construction, or just setting.
Regards David Powell.
Pontiacguy1
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by Pontiacguy1 »

A lot of throttle valves and steam inlet lines are oversized vs. being undersized. If you have one undersized, it will affect the high-speed performance and power. You will still have plenty of low speed power and torque available. If you oversize one, then the locomotive tends to be very touchy and slippery when starting off. I've seen quite a few that had very touchy throttles and were extremely slippery, and would go from barely any steam admission to slipping the wheels with just a slight throttle adjustment. You don't want that either, as it makes the engine a lot more difficult and frustrating to run. As was said above, if you follow a proven design you'll be successful. Some of the proven designs may not be exactly optimal, but they have been shown to work good through the years and so will not give you any undue headaches if done correctly.
David Powell
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by David Powell »

I was taught to drive a full size steam roller at the age of 10 so that the owner and my Dad could go off to the pub for a few and the job would continue. The roller is a single cylinder Marshall 10 tonner, typically with an almost all or nothing regulator. I quickly found that life was MUCH easier if I ran with only about 75 lbs of steam rather than 150 that she carried.
I see many model fellows running with safeties blowing furiously quite un necessarily..
Increasing superheat, or indeed adding some to a wet steamer will do far more for performance than enlargiing reasonable sized steam and exhaust passages,
Regards David Powell.
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baggo
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by baggo »

It's interesting that although LBSC was indeed a big advocate of large ports and steam passages, those on his 2½" Gauge Ayesha are quite small in comparison to those in his later 2½" gauge designs and Ayesha still runs very well.
Ayesha Ports 1.jpg
I can't remember exactly but the passages are only about 3/32" diameter. The cylinder bore is 3/4". The valves are circular and the ports were cut with an endmill at an angle.
Ayesha Ports 2.jpg
He was obviously happy with Ayesha's performance otherwise I am sure that he would have modified the cylinders over the years.

John
Secretary of The National 2½" Gauge Association
Member of North West Liecestershire SME

http://www.modeng.johnbaguley.info
David Powell
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Re: Is it typical to later find steam passages need to be bored bigger?

Post by David Powell »

Ayesha is an anomaly. LBSC did once tell the story. I seem to recall Greenly and Bonds of Euston Road were somehow involved. Possibly the idea was to be able to do most machining on a lathe.
I once owned and ran a 2 1-2inch gauger which had tiny square ports and passages. she ran remarkably well . certainly surprised me.
Regards David Powell.
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