Rule of thumb re. cylinders and pistons

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

User avatar
Bill Shields
Posts: 10464
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Rule of thumb re. cylinders and pistons

Post by Bill Shields »

But not enough to allow the oring to roll in the groove.
Too many things going on to bother listing them.
jscarmozza
Posts: 599
Joined: Mon Mar 03, 2014 5:09 pm

Re: Rule of thumb re. cylinders and pistons

Post by jscarmozza »

Thanks guys, I didn't know there were different groove dimensions for static and dynamic applications, I have them now.
User avatar
Dick_Morris
Posts: 2841
Joined: Sat Jan 04, 2003 2:09 pm
Location: Anchorage, AK

Re: Rule of thumb re. cylinders and pistons

Post by Dick_Morris »

To ensure long life on the O ring, what's the best way to insure the smoothest cylinder walls? Is pushing a ball bearing through with a slight interference a good choice?
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Rule of thumb re. cylinders and pistons

Post by Harold_V »

In my opinion, that would be an excellent method of producing a superior finish. Instead of cutting, it burnishes.
Interestingly, that's one of the recommended methods of sizing an Oilite bushing.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
jscarmozza
Posts: 599
Joined: Mon Mar 03, 2014 5:09 pm

Re: Rule of thumb re. cylinders and pistons

Post by jscarmozza »

That sounds like something I'm going to have to try, thanks.
jeanluc83
Posts: 118
Joined: Tue Feb 26, 2019 8:02 pm
Location: Connecticut

Re: Rule of thumb re. cylinders and pistons

Post by jeanluc83 »

Look up Model Engineers Handbook by Tubal Cain. There is a section on using o-rings as as piston rings. It gives modified equations for sizing the groove. According to the book standard o-ring grooves result in too much drag.

There is a pdf of the book you can find with a Google search but it doesn't appear that the book is all that expensive to buy.
User avatar
gwrdriver
Posts: 3439
Joined: Mon Jan 06, 2003 10:31 am
Location: Nashville Tennessee

Re: Rule of thumb re. cylinders and pistons

Post by gwrdriver »

I was about to recommend looking for the Parker O-ring Handbook (if such still exists), which at one time was the go-to reference for fitting O-rings, but I would try and trust Tom Walshaw's modifications first.
GWRdriver
Nashville TN
Rich_Carlstedt
Posts: 1754
Joined: Sat Dec 21, 2002 12:16 am
Location: Green Bay Wisconsin USA
Contact:

Re: Rule of thumb re. cylinders and pistons

Post by Rich_Carlstedt »

many years ago, Tom Patton of Kalamazoo Michigan showed me his Pacific cylinder construction (CI) and he used Teflon tape that was rolled into a string and then the string packed into the CI Piston groove and Tom advocated it's construction as superb. The tape was normally used for industrial sealing.
In my employment, we had High temperature seals , and high pressure, that required custom machined rings of Bronze filled Teflon. The material is superb to over 400 degrees. Since I have been out of that Die machinery work for many years, I cannot give current vendors, but found this FYI.

https://www.fluorotec.com/materials/ptf ... lled-ptfe/

Rich
pat1027
Posts: 444
Joined: Sat Oct 09, 2004 3:45 pm
Location: Michigan

Re: Rule of thumb re. cylinders and pistons

Post by pat1027 »

Rich, I'm certain my dad (Tom Patton) used step cut iron rings on both the pistons and piston valves. The cylinders were fabricated with the cylinder bores machined from a continuous cast iron tube and valve cages machined from a bronze bar. The only tape product in the cylinders is a graphite foil tape packing the piston and valve rods.

Pat
User avatar
Bill Shields
Posts: 10464
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Rule of thumb re. cylinders and pistons

Post by Bill Shields »

Dick_Morris wrote: Sun Aug 15, 2021 12:15 am To ensure long life on the O ring, what's the best way to insure the smoothest cylinder walls? Is pushing a ball bearing through with a slight interference a good choice?
I lap with non embedding compound
Too many things going on to bother listing them.
Post Reply