Piston Seals

[LCT]

What is normally used to seal the pistons? My design will actually allow the piston to rotate as well as move up and down. I'm worried about premature wear as much as I am about sealing the piston. Just to make matters worse, I'm hoping to not use oil because I wanna reuse my water.

 

[Bogstandard]

Not using lubrication just might be your stumbling block.

The materials you are going to use then have to have their own built in lubrication, or use the condensing water as the lubricant.

Maybe you could get away with cast iron for the cylinder and the same for the piston ring and piston. Or maybe you could use graphited yarn for the ring, but I wouldn't know how long that would last.

A very difficult proposition as I can see premature wear raising it's ugly head very quickly.

John

 

[LCT]

Hmmmm
How about a PTFE o-ring? Mcmaster Carr says it's excelent for steam, and is self lubricating.... Might be just the ticket.

 

[Bogstandard]

The piston ring is the least of your worries.

It is the metal to metal contact, without lubrication and using live steam that will be the stumbling block. A slight mismatch of materials, surface finish and clearances and you will end up with a solid immovable lump of metal.

John

 

[Dhow Nunda wallah]

Before I open my mouth too wide here, please let me make it quite clear, that the following was over 30 years ago.
Memory has not improved

I did work on (full size) steam donkeys, boiler feed pumps in an oil refinery.
These used a unit called a colgraf lubricator (a quick google yields nothing)
They were a quite simple metering pump which injected colloidal graphite into the steam chest.
Colloidal graphite being, simply powdered graphite suspended in water.

Hope this will help, or perhaps give you another angle of attack.
Rgds, Lin

 

[Maryak]

LCT,

Up until 12 months ago I was running a 1000hp steam tug. the engine is a 3 cylinder triple expansion reciprocating steam engine. The engine uses the water contained in the steam for piston and cylinder, (Cast iron), lubrication and has done for the last 60 years, of course flat out is 140rpm so piston speeds are not huge. After exit from the condenser the water enters what is called a hot well. In the hot well over the feed pump suctions are removable hessian filters which trap any stray lube oil or fuel oil, (coming from auxiliary machinery such as feed pumps fuel pumps and heaters). When you reckon the filter has trapped as much oil as it can you quickly change it for a spare and wash the dirty one in soap and water.

In non condensing engines and engines using superheated steam, it is normal to use a cylinder oil, (pretty thick and made from brightstock), in the piston and ring area. The easiest one to fit is a displacement lubricator.

You can see one hanging off the front of the steam chest on my 1st model, a mill engine.

Here is a sketch and explanation of the beasty

Hope this helps if you use superheat you would be well advised to use lubrication.

 

[Mcgyver]

'm hoping to not use oil because I wanna reuse my water.

Lin's idea is interesting, didn't know about that - i bet having worked on full size 'real' equipment there's lots of tidbits us modellers don't know

you can reuse your water with oil, what do the marine engines call it.....hot tank? you just need a hot tank to separate the water and oil - I'd not want to run machinery, especially something I'd put a lot of time into, without a really good lubrication system.

ooops, hot tank!

 

[majorm]

I know this is an OLD post but can you describe how the "hot tank" works? I cant find any real info or pictures so far with a search on yahoo. I have a similar issue with a engine I want to make.

 

[aonemarine]

look for the centrifugal oil seperator used on the barrett steam car....