# hydraulic cylinders for steam?



## Anatol (Sep 16, 2018)

Somewhere (here) recently I read an aside that people have used hydraulic cylinders for steam cylinders  because of their mirror finish. Has anyone has experience with using such cylinders, or cylinders and pistons? It seems like a double acting hydraulic cylinder might be quite adaptable. I see some pistons have nylon wearbands, but others appear to have iron rings.


----------



## john_reese (Sep 22, 2018)

I doubt the mirror finish would last long in that environment.  Some cylinders have aluminum pistons.  They are likely to corrode and seize up..


----------



## Anatol (Sep 22, 2018)

john_reese said:


> I doubt the mirror finish would last long in that environment.  Some cylinders have aluminum pistons.  They are likely to corrode and seize up..



Thanks for your reply. Yeah, it would depend on what the mirroring is. 
I read somewhere they're sometimes chromed. That's pretty tough. 
And one could swap out the piston...


----------



## Entropy455 (Sep 23, 2018)

Steam turbine cases and steam valves are typically made from 12% chrome steel. It's a weldable alloy (just barely), and holds up very well to a steam environment (both strength at elevated temperatures, and corrosion resistance). I've never seen 12% chrome steel offered in bar-stock (only castings) - but that's not to say it doesn't exist in bar-stock form.

Using carbon-steel hydraulic cylinders for stem - unless you can completely dry & oil the cylinder walls after each use - you are going to corrode & pit the surfaces. Unprotected carbon steel is simply not going to last. One thing steam does very well (even low energy steam) is completely strip oil films from metal. For an occasional use model engine, I would recommend 304 or 316 stainless bores - a machinable & weldable alloy, but as you know, not exactly wear resistant. A 400 series martensitic stainless would probably work better, but 400 series stainless is not exactly user friendly (it's heat treatable, and not weldable without accomplishing annealing & re-heat-treat) - and it's quite expensive. . .


----------



## Entropy455 (Sep 23, 2018)

FWIW, steam turbine blades, which endure extreme punishment, are typically made from 420 stainless. Steam valve stems & valve seats, which also endure extreme punishment, are typically made from 440C stainless.


----------



## Anatol (Sep 24, 2018)

Thanks for this very useful summary of stainless, etc!
"One thing steam does very well (even low energy steam) is completely strip oil films from metal."
This would be useful feature in some applications but a disaster for steam engines! Its no wonder that in every picture of a steam engineer they have an oil can in their hand! Sadly, 100 years of materials science doesn't seem to have created a steam/heat resistant, machinable, self-lubricating material.


----------



## johnwm (Sep 26, 2018)

Traditionally steam cylinders have always been cast iron. I suspect that a mirror finish won't retain the (very necessary) oil film. Might be worth looking at cast iron cylinder liners (as fitted to loads of car engines). Cheap replacement liners are readily available.


----------

