Gaskets

[Deckel]

Hi all, I'm new here and to steam engines too

I did 2 "steam" engines earlier that I never tried out on real steam, but that runs nice on compressed air ( I'll try to take some pics and videos)
I use to work with some rubber seals but now I am working on a new project (double acting, double expansion steam engine) and I was wondering what do you use as seal for the con. rod of the piston ? ( to seal the chamber under the piston on double acting engines ) or you simply don't seal this part. If so, than the fit must be pretty accurate so there is no pressure lost, and to perfectly align the con. rod guides with this tight hole must be pretty tricky.

Thanks, Deckel

 

[shred]

Traditionally sealing the piston rod in a double-action cylinder is done with a stuffing-box or gland nut and packing material-- think a small cavity in the outside of the cylinder head where the rod passes through-- fill that with graphited asbestos (hard to come by nowdays) or teflon string and pop a nut over the end to hold it all in. I'm pretty sure there are some posts on the subject or close to it hereabouts.

 

[rake60]

This would be a typical model steam engine cylinder head and packing nut.

The through hole in the head has .003 to .004" clearance to the connecting rod.
The packing I use is very low tech. It is a few strands of cotton from an old rag
mop soaked with light machine oil.

I have never tried it with live steam.

Rick

 

[steamer]

Rick

That will work fine for steam. There are several suppliers of packing for steam out there, but for small models, it's less finicky......String impregnated with graphite works well. So does a simple piece of teflon bushing with a hole in it that gets compressed by the packing nut.....just a little, don't reef the nut down or it will lock up!.


Dave

 

[georgeseal]

In the plumbing dept. of big box stores you can get graphite string in various diameters

 

[GailInNM]

In the past I have used the traditional graphite asbestos/string and Teflon packing as drawn by Rick. For the last number of years I have used nothing but O-Rings for piston rods from 3/32 to 3/16 inch diameter. When installed in a properly sized recess the have low friction and low leakage.

The correct size recess is not what is shown in the o-ring charts for static sealing. There are guides for sliding seals, but most of those are for higher pressures than the less than 50 psi steam that most hobby engines use. For reference: I use a 0.254 diameter x .085 deep recess for a nominal 1/4 OD X 1/8 ID o-ring to seal a 1/8 diameter piston rod. The extra depth is very important as it keeps the o-ring from being compressed by the seal retainer.

If you are using saturated steam, Nitrile (BunaN) is completely satisfactory for material. It is the most common material for o-rings. Don't get scared that it is not recommended for steam. That recommendation is because it will deteriorate with high pressure dry or superheated steam.

Gail in NM,USA