Newbie Piping Stuart S-50

[Korben]

Hello, all. I am brand new to live steam (like about 3-weeks new). I have a beautiful little Stuart S-50 mill engine that was assembled in the 1960's from a factory-machined kit. I'm looking toward piping it to run, first on air, then on steam.

So far, I haven't been able to determine the size of the pipe fittings that attach to the intake and exhaust steam ports. I'll have to order the fittings online but I have no idea what size and/or thread to ask for.

Any help would be appreciated.

Korben

 

[Jasonb]

1/4" x 32 ME

Best to make a threaded union to fit into these tapped holes and then use 3/16" pipework

 

[Korben]

Thank you, that helps a lot. Is regular pipe joint compound or teflon tape good for making a steam-tight joint or do you recommend something else?

(I know these are pretty basic questions but it's all new to me and I want to do things right.)

Korben

 

[Mechanicboy]

Steam pipe in the steam engine 3/16" and exhaust pipe 5/16" for a Stuart S-50. Teflon tape no problem.

 

[Korben]

Thank you for the above information, it's very helpful.

When running my S-50 on compressed air, would it be advisable to include a displacement lubricator in the supply line? It seems logical, to me, that an engine running on air should have the same lubrication as one running on steam.

Korben

 

[Jasonb]

A displacement lubricator works by the water from the condensed steam displacing the oil in the lubricator so it won't work on air.

For short runs a drop of oil in the inlet before you connect up the hose will do fine, for longer runs look at the inline oilers that are sold for use with air tools which will add a small amount of oil to the air.

Also don't use "steam oil" when running on air as its too thick at the lower temperatures.

 

[Korben]

Thanks. I appreciate the caution about using steam oil. I'm hoping to avoid pitfalls like that, so the information is valuable.

Korben

 

[Mechanicboy]

Or you can use the mechanical lubricator instead displacement lubricator. It will works both with air or steam. Here is the drawings of mechanical lubricator. Use brass overall, fastening screws, crankshaft and spring in steel and ratchetwheel in hardened silversteel.

 

[Korben]

Interesting idea. As I said, I'm very new to all of this and I've learned a lot in a short time. I envision a system that would run on steam but that could easily be connected to a compressor and run on air. Right now, I'm trying to figure out what the pieces are and how to connect them together.

Korben

 

[Korben]

Watching YouTube videos, I notice the supply steam is often connected with what looks like rubber or clear plastic (silicone ?) tubing. The tubing is fit to barbed brass fittings or pressed onto copper tubing without any sort of clamp. Is this safe and reliable, given the heat and pressure involved when running on steam?

Thanks,
Korben

 

[tomol409]

I think Mechanicboy is wrong with his size of 5/16th. I have a Stuart made S50 and the thread is only 1/4 x 40tpi. although on the drawing it shows 1/4 x 32tpi, but I think either would do. The smaller exhaust 3/16th exhaust thread is 40tpi.

 

[Mechanicboy]

I think Mechanicboy is wrong with his size of 5/16th. I have a Stuart made S50 and the thread is only 1/4 x 40tpi. although on the drawing it shows 1/4 x 32tpi, but I think either would do. The smaller exhaust 3/16th exhaust thread is 40tpi.

I had no access to the drawing by Stuart S50. As a rule exhaust pipe greater than steam pipe from the table of this book wrote by Tubal Cain as I have taken photo.

 

[Korben]

No worries. Mechanicboy's post makes theoretical sense and the info in his attached image gave me a better understanding of how model steam pipes are sized. It's all good.

For whatever reason, both the intake and exhaust ports on my engine are the same size. They both have barbed fittings to receive tubing but the threads aren't quite right. The bulk of the information I've found on the internet says the ports are tapped for 1/4" x 32 ME threads. I'm guessing the existing fittings are 1/4" x 40 (they go in about a turn and a half then bind). I've ordered a sample 1/4" x 32 fitting to confirm the port size.

I'm inclined to follow jasonb's original suggestion (adapt the existing threads to 3/16" and use more readily available material for the rest of the piping). For starters, I may hook it up with flexible tubing, if that's acceptable practice when running the engine on steam.

Korben

 

[Jasonb]

At low pressures the flexi tube should be fine, just take care that the hose cannot blow off and give you a jet of steam. Infact some of the small steam plants available use this same "feature" as a safety valve where the hose will blow off if the engine is not running and the steam pressure builds up too much in the boiler.

For just running the engines as display items you can get away with quite a bit regarding pipe sizes its only if you want them to work efficiently that it starts to have more of an effect. Also if using a blast nozzel to introduce draft up a chimney the exhaust can be restricted down a lot, for example my 2" traction engine is 1.375" bore x 2" stroke yet the exhaust port in the cylinder is 1/4" dia into a short length of 5/16" bore pipe before it exits through teh blast nozzel at only 5/32" dia. So a much bigger capacity engine yet not much more exhaust size than your little S50 yet still able to pull two adults along without being strangled.

J

 

[Mechanicboy]

The reason we have a larger diameter exhaust pipe: Steam continues to expand under the blowout from the cylinder and shall not provide resistance against the piston during the blowout.

So you know why we have compound steam engine: Utilizing steam expansion without wasting energy of steam.

 

[mcostello]

If the speed of exhausted steam is around 100-150 fps, is the speed comparable for infernal combustion engines? Pun intended!

 

[Korben]

Jasonb, The nozzle idea is interesting, I know they were used in 12" scale steam locomotives. I may experiment with that, later on.

Mechanicboy, My guess is that Stuart made the ports the same size for the sake of simplicity. The exhaust port size probably governs the engine's maximum output and the intake is just oversized. Without enlarging the exhaust port (which could effect valve timing), would there be any percentage in immediately adapting to a larger exhaust stack? That way, once the steam passed through the valve and the port, it could expand in the larger diameter stack.

Another idea I've toyed with is to pass the exhaust steam through a heat exchanger that is cooled with water on its way to the boiler. This feedwater heater (another 12" scale steam locomotive device) could be built above a chuff pot. If it worked efficiently, it would condense all the exhaust steam into water in the pot and produce lots of hot water for the boiler. Perhaps this system could be enhanced further with the addition of an exhaust steam nozzle.

Interesting to think about but, for now, I want to just get the engine hooked up and running the regular way.

Regards,
Korben