basic metallurgy - valves

[Anatol]

What would be the best choice of metals for making piston valves from stock (not castings)?
What metals work together for best seals, minimum wear etc? . I've seen talk of the way cast iron gets a mirror finish, and that (some kinds of) stainless work harden. I've also seen warnings against silver steel.
Should I regard a piston valve as a shaft and bearing? In which case bronze would be good for the housing/mainfold ?
thx!

 

[stevehuckss396]

I use Silver steel/Drill rod for all my valves. I have engines that have been running for over 8 years and no trouble. 303 stainless might be a good option also. Bronze is a good option for valve guides but brass works well when valves are tiny.

 

[Cogsy]

I use silver steel/drill rod for IC valves but I have heard it's prone to rusting on steam engines.

 

[Anatol]

thanks guys
yes, I'm talking Steam here and heat and water vapor will make rust quick.

 

[Charles Lamont]

thanks guys
yes, I'm talking Steam here and heat and water vapor will make rust quick.

But full size steam engine cylinders, and piston valves, are invariably cast iron. They would not be if rust were a problem. Slide valves are iron or gunmetal.

 

[Blogwitch]

"They would not be if rust were a problem"

Charles, I used to fix a lot of broken steam and i/c engines, and about 75% of them was rust related. When I asked the builder what the parts were made of, because not all of them knew, most would reply silver steel.

Maybe the reason for cast iron not going rusty is because it is contact with steam oil, where most silver steel rods were usually external in con rods, valve operating rods and crankshafts.

Becasue of noticing all these faults, I now use ground stainless rods instead of silver steel, even if it is on tooling I use in the shop.

BTW, silver steel sort of changes it's properties when hardened, I have found it is more corrosion resistant.

John

 

[fcheslop]

For my own toy boats I like good grade cast iron for cylinders and valves or bronze /gun metal
An old adage Piston valves wear out when Slide valves wear in
After building many toy boats the humble wobbler is always my first choice as its just more reliable and doesn't suffer from the dreaded wear in the valve gear that sooner or later makes wet feet a certainty.
If built correctly despite the common myth the simple oscillator is a good performer and they even used them early on in full size applications
I know there is a time and a place for piston valves but other than been easily reversible for models I dont see any advantage
I recently made some slide valves from PTFS (teflon) and it has given a good boost to the engines power up by nearly 10 percent when brake tested
Just my two bobs worth and good luck

 

[Anatol]

But full size steam engine cylinders, and piston valves, are invariably cast iron. They would not be if rust were a problem. Slide valves are iron or gunmetal.

Yeah but, the archetypal steam engine attendant always has an oil can in on hand.

 

[Anatol]

"An old adage Piston valves wear out when Slide valves wear in"

I know

"I like good grade cast iron for cylinders and valves or bronze /gun metal"

here on the west coat of Amurikey, I think few know hat cast iron is, let alone what a good grade is. How do you know good grade of cast-iron ?

Is it wise to combine ie cast iron for valve and bronze for body (for reduces friction) or is it better to use like metals ? (for wear issues).


"If built correctly despite the common myth the simple oscillator is a good performer and they even used them early on in full size applications"
"
You're not the first to tell me this. OTOH, some rail against the wobbler. I think its a high pressure/low pressure issue. Personally I like the wobbler for the reduction of moving parts and intense to build one.

It's off topic but is there a simple formula for correct positioning of ports?
And how do you calculate port size?


"I recently made some slide valves from PTFS (teflon) and it has given a good boost to the engines power up by nearly 10 percent when brake tested"

very interesting. I worried that creep could be an issue with teflon. I'd like to hear further updates.

 

[fcheslop]

The engine is a 2inch bore and stroke twin with balanced valves in a medium sized steam launch that has now ran two years with no ill effect
Not my boat I hasten to add as I found out some time ago the great joy of boat owning is when you first buy/build them and then when you sell them the time in between is just expensive
For porting on oscillators I prefer to drill them from a jig . Just a simple strip of metal drilled as per the cylinders porting and pivot that extends to the crank pin
virtually copying the upright or stand.
On a wobbler the size of the ports will be determined by the cylinders throw as in you need to space the three holes as close to each other without overlapping although if you dont mind wasting a bit of steam a little overlap on the exhaust canbe beneficial or maybe I was just kidding myself
Thats the two ports in the upright and the drilling in the cylinder
K N Harris has some relevant info in his book Stationary Steam thats available on the net he also has some nice guide ideas based a bit like the little loco Crackers cylinder again the drawings are on the net
Iv no idea as to what use if any this engine you intend building is going to power so if its low pressure a wobbler if its higher pressure a slide valve higher still piston valve again I maybe incorrect just my thoughts on the matter. Im sure the more knowledgeable will chime in.
Iv attached a pic of a simple wobbler I built recently for a little loco with a trunk guide for Ellie and you can see the drilling jig used for the ports
Im a bit dyslexic so struggle to answer fluently
best wishes

 

[Anatol]

Thanks for you note and pics.

Iv attached a pic of a simple wobbler I built recently for a little loco with a trunk guide for Ellie and you can see the drilling jig used for the ports

Is it double acting or single acting?
Are the extensions of the cylinder a kind of cross -slide?

"K N Harris has some relevant info in his book Stationary Steam "

thanks, I had downloaded that already but read it again - lots of good tips there.

"Im a bit dyslexic so struggle to answer fluently"

me too, no problem

best wishes

 

[fcheslop]

Yes its single acting and the extension acts like a cross head
cheers