Beam engine piston ?

[MalcParticipant @malc]

Is Nylon a suitable material for the piston in a beam engine? The piston is approx. 30 mm dia. and 6mm thick. PTFE is the reccomended material but not so available locally.

[MalcParticipant @malc]

[Michael GilliganParticipant @michaelgilligan61133]

Unlikely, Malc

Nylon is notoriously hygroscopic.

MichaelG.

[Mick B1Participant @mickb1]

Nylon 66 has a max service temperature of 180 C for short periods, 95 and 80 for 5000 and 20000 hours continuous respectively. I'd guess it *might* be just OK.

Delrin maxes out about 82 C, so I'd think not.

Whereas PTFE is OK up to just over 200 C, so it's clearly better if you can get it.

Why not brass with a greased string packing ring?

[Nick_GParticipant @nick_g]

Posted by Mick B1 on 29/08/2017 10:45:12:

Why not brass with a greased string packing ring?

.

Or even aluminium for a nice light piston that will have less mass and assist the engine to run more smoothly at the lower speeds associated with beam engines.

Nick

[Gordon TarlingParticipant @gordontarling37126]

If you're always going to run it on air, then nylon will probably be OK, just don't put any steam through it.

[JasonBModerator @jasonb]

The PTFE "washer" does act a bit like a piston ring to seal the built up piston to the bore if you opt for some of the other suggestions then rather than sandwich the ring between two brass discs it would be better to make a solid piston with a groove in it to take either graphite yarn packing or an O ring.

If you are just going to run it on air for display then you could leave out the ring and just cut some shallow "V" notches to retain some oil and run like that provided you get a good fit between piston and the steel cylinder.

[MalcParticipant @malc]

Hi all, many thanks for the replies. You have confirmed my suspicions about using Nylon. I only plan to run the engine on air (assuming it runs at all of course)! I rather like the idea of an Aluminium piston. Thanks again.

[Clive HartlandParticipant @clivehartland94829]

If you boil Nylon for while then it will not take up moisture.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Hartland on 29/08/2017 22:18:33:

If you boil Nylon for while then it will not take up moisture.

.

That's interesting, Clive

I know, from bitter experience, that [unboiled] Nylon swells when it absorbs water

The question is: Does 'boiled' Nylon dry out and shrink ?

… or does it remain stable in all ambient conditions ?

MichaelG.

[Chris Evans 6Participant @chrisevans6]

" If you boil nylon for a while it will not take up moisture"

Yes interesting Clive, this was done to some mouldings I worked on the tooling for to speed up the measuring process post mould. I was heavily involved with the tooling for plastic plumbing fittings and these where measured after two or three weeks to stabilise. We would then spark erode things like thread form to final size. I know it is hard for people to believe plastic can absorb moisture.

[Clive HartlandParticipant @clivehartland94829]

This knowledge came to me via an Australian manufacture of the Nylon sliders in Surveying staves. He was having problems that the sliders were sticking tight when wet but worked Ok when it was dry. From this he boiled all the extruded Nylon bits and had no more problems as he was a world exporter.

Clive

[Adrian GilesParticipant @adriangiles39248]

Most manufacturers now recommend keeping your strimmer line in water to keep it flexible and resist hardening and becoming brittle, breaking off at the eyelet and super annoying you! Also those white swinging blades for heads as well.

[Author]

Posts