The Steamboating Forum

In the Steamboats and Modern steam launches from March-April 1962 there is an article that says that 100 degrees of superheat is in effect saturated steam and up to 250 degrees of superheat you may not need cylinder lubrication. At 90psi we have 330 degrees so less than 580 degrees I may not need lube. My question is if I remove the lubricator and replace it with a temperature gauge and measure something less than 580 degrees , than oil may not be needed? Also , if I measure 580 degrees at the gauge my average steam temp in the cylinder will be lower. Any idea how much lower it will be? My cylinder and rings are cast iron. I don't know if that matters. Does any of this sound reasonable?-
Thanks-Peter

I expect that the 100 degrees mentioned is the amount the the author assumed would be lost in heating the cylinder block, but every engine is going to be different. Without oil, the engine relies on liquid water for lubrication, and any time the engine becomes dry, it's going to groan. So, with superheat and without oil, you are going to be on the hairy edge of having a chronically groaning engine.

That being said, you don't need much oil. My 6 hp compound has a mechanical lubricator that I can dial in to a precise amount of feed (basically turned as low as possible to prevent groaning when throttling back), and it uses about a tea spoon of oil in a full dry of running.

If it were me, I wouldn't remove the lubricator, just turn it off, and see if I can get away without oiling. If concerned about feeding too much oil, leave it turned off until the engine groans, then turn on the lubricator until the groaning stops then turn it off again.

Other than satisfying your curiosity, having a temperature gauge isn't needed, either the engine groans or it doesn't.

The engine will typically groan after running hard for a while and then throttling back... the throttling back superheats the steam (drops the pressure, leaves the temp the same) and the engine is hot, so groaning occurs.

- Bart

"My question is if I remove the lubricator and replace it with a temperature gauge and measure something less than 580 degrees , than oil may not be needed?" The need for cylinder lubrication, as well as valve lubrication, depends on engine details, and in my experience lubrication is generally required even with saturated steam on our launch engines. The lubricating "value" of water is less than about 1% of the lubricating capability of oil, so parameters such as piston ring tension, valve design, etc. strongly influence this result. Kelly's advice is best.


Also , if I measure 580 degrees at the gauge my average steam temp in the cylinder will be lower. Any idea how much lower it will be? Cylinder temperature is generally about half way between saturated steam inlet (main steam saturation) temperature and saturated steam exhaust temperature. Details as to engine valve events, throttling of steam admission, leakage, plus several other variables influence this result.

I guess I will skip the temp gauge and listen for groaning. Is the groaning sound like a squeak or is it more lower pitched.

You will know it when you hear it.

Compared to the quiet yickity yick of a good running engine, when it starts to groan, it hits you like fingernails on a chalkboard.

My 1960s vintage Blackstaffe steeple compound engine is condensate lubed, and I've never heard it groan.
Max operating pressure is close to 100 psi.

I must not be steaming it often enough...
RussN

My 1960s vintage Blackstaff steeple compound engine is condensate lubed, and I've never heard it groan.
Max operating pressure is close to 100 psi.

Otter's safety goes off at 180 psi; I hear the squeak/groan after running for a while at 125+ psi and then throttling down.

- Bart

RNoe wrote: ↑Sat Feb 24, 2024 4:42 pm My 1960s vintage Blackstaff steeple compound engine is condensate lubed, and I've never heard it groan.
Max operating pressure is close to 100 psi.

Looks like your engine is using saturated steam? That and the low pressure could be the reason she doesn't groan. Raise the pressure and add some superheat and I'll bet $0.05 that she will be wanting some oil.

Yes. Higher pressure and super heat would definitely need some lube oil.
But then...
The hot well would need to be enlarged to accommodate oil removal,
and that requires new engine/boiler mounts,
and...
I may as well build a different launch.
I recognize that this steam launch has historic value as originally built.

I plan on resetting the safeties to 125psi from 100 psi, and see what that does for operation with some pressure "overhead."
However, the entire system was designed by Cliff Blackstaffe for 100 psi operation.
RussN