Pistons

[robcas631]

For a small stationary steam engine. In order to create the piston "rings" should I use leather? or Cast Iron? If I use leather? Which leather is best and how do you cut it to fit?? Thanks

 

[picclock]

I think you may be able to use Viton oring which would be a sort of half way house, good for up to 200c. For longevity Cast Iron rings are hard to beat but can be awkward to make. lots of info on the forum though.

Best Regards

picclock

 

[gbritnell]

I would use an 0 ring or just a graphite string packing. I would be afraid that the leather would hold moisture along with the tanning acids might corrode a ring around the cylinder when not used for awhile.
gbritnell

 

[Swede]

I agree that graphite string would be a good way to go. More durable than viton, slipperier too.

Or... skived teflon wound into a cord and packed in the piston groove. You can take common irrigation thread tape, and wind it into the groove until it stands proud of the piston OD. Then, tear off the excess.

 

[steamer]

Teflon rings in smooth bores work pretty well for saturated steam....

Dave

 

[Steve_Withnell]

Hi Rob,

You don't say what size, but some of the designs I've looked at with 3/8 inch diameter pistons and smaller don't bother with a ring at all, but they do have a groove cut in the piston anyway. A stationary engine I built with a 1 inch diameter piston I packed with graphite yarn, it absorbs oil so that's good. As a display model it runs without load and it runs the same with or without the yarn!

If the bore is well made and the piston is a good fit, not sure it's necessary for little engines.

Steve

 

[robcas631]

Thank you all for your replies.

Steve asked a very important question regarding piston size. I thank him for that. I will be sure to add the correct dimensions and action of my engine in the future. My error.

Main piston:

The diameter I have is 0.856" x 1.5" stroke. I managed to allow just enough room when boring out the brass to allow for a 0.10" thick stainless steel tube to be press fit. I triple checked for any warping but found none. Then drilled my intake/exhaust holes then bored 0.005" to remove any burs. My stationary steam engine is double actioning. Can that he term full action be used?

Today I finished a composite piston made of two 0.10" x 0.845" dia. brass disks with a leather interior. I used a strong steel bar that was chromed for the piston rod. Everything worked out rather well. about 4 days ago I made the cylinder ends. One was closed....the other I created with a piston pack ( correct terminology?) just in case there might be leakage around the rod in the future. The entire design is made to come apart should I choose not to use leather.

Sorry if I was lengthy regarding my status quot. My question is what is graphite yarn and where can I get it?? Or since you know what I have are there other suggestions?

 

[Rocket Man]

I wish I could remember the name of these grooves. Some small engines use tiny grooves as rings it produces pressure changes along the side of the piston and it works like rings. The grooves are about .030" wide and .030" deep .125" apart the full length of the piston. My physics professor told me about this many years ago, I looked it up and sure enough it says the groove produce pressure changes along the piston that act like piston rings, used on very sensitive equipment were ring friction can not be tolorated. I tried it on one of my stirling engines and it does seem to run better.

 

[robcas631]

OK so graphite rope will stand up to steam?

 

[ShedBoy]

I wish I could remember the name of these grooves. Some small engines use tiny grooves as rings it produces pressure changes along the side of the piston and it works like rings. The grooves are about .030" wide and .030" deep .125" apart the full length of the piston. My physics professor told me about this many years ago, I looked it up and sure enough it says the groove produce pressure changes along the piston that act like piston rings, used on very sensitive equipment were ring friction can not be tolorated. I tried it on one of my stirling engines and it does seem to run better.

Most of Elmers engines have these grooves on them. I may need to remake some oiston for an air/steam engine and was wondering if they would work on a 18mm bore? They worked on my wobbler.

Brock

 

[Steve_Withnell]

Hi Rob,

Yep the graphited yarn is fine for steam. I have the parts of a steam engine my Great Grandfather built, sadly no where near enough to build the engine, but I do have the cylinder (5inch stroke x 2inch bore) and the cylinder end plate where the piston rod goes through (forgotten the technical term) was packed with - graphite yarn.

eMail me at [email protected] and if I can find a length, I'll stick in in the post for you.

Steve

 

[hammers-n-nails]

coles power models has cast iron rings for $5-10.