Hi Keith,

The material I've used is a bearing grade thermoplastic containing 10%
Carbon Fibre, PTFE, and Graphite, which goes under various names such
as Ketron HPV and PEEK bearing grade. It's a lot harder than ordinary
PTFE and also has a lower expansion rate, although still much higher
than bronze or stainless steel. It will withstand a continuous working
temperature of 250°C, has a very low coefficient of friction and good
machinability.

I am not sure I would go down this route again as the fitting of the
valves is very fiddly and time consuming. I think it is probably much
easier to get a good fitting valve made from stainless or bronze.
By the way PEEK stands for PolyEtherEtherKetone.

John

--- In halfinchlivesteamforum@..., "Keith Taylor"
<iblskeith@...> wrote:
>
> Hello John,
>
> Showing my ignorance, could you please tell me what "PEEK" piston valves
> are?
>
> Is this a material similar to Teflon?
>
> Thanks!
>
> Keith Taylor Jefferson, Maine USA
>
>
>
> _____
>
> From: halfinchlivesteamforum@...
> [mailto:halfinchlivesteamforum@...] On Behalf Of John
Baguley
> Sent: Wednesday, May 02, 2007 5:03 AM
> To: halfinchlivesteamforum@...
> Subject: [Half inch live steam forum] Helen Longish
>
>
>
> Hi all,
>
> Just been steam testing Helen now that the boiler is finished. I used
> the propane torch through the firehole rather than coal as it's more
> controllable!
>
> As suspected, the PEEK piston valves were still too tight at the
> normal running temperature so I had to keep removing them and skimming
> a fraction of the diameter until they were ok. A bit fiddly but
> fortunately not a big job as the valves are easy to remove and
> replace. I tried measuring the cylinder temperatures but my
> thermometer only goes to 150° C and that disappeared off the scale!
> The superheaters are stainless radiant type which extend to the back
> of the firebox so the steam is well and truly hot!
>
> I noticed that the lubricator doesn't seem to be pumping properly so
> the cylinders are probably being starved of oil. I'll look at that
> today. It didn't seem to affect the running though as I ran her for
> about 30 minutes non-stop last night with no problems.
>
> Looks as though I might be struggling to have her running for Stafford
> on the 27th.Depends on how quickly I can knock the tanks and cab up.
> Otherwise it's a big water tank on the driving trolley!
>
> John
>
>
>
>
>
> [Non-text portions of this message have been removed]
>