Hi John, Thanks for this. I have gone ahead and made a pair of slide valves out of "the black stuff". It's very easy to machine but it's fairly abrasive on the cutting tools. I used HSS and they required sharpening a few times although it wasn't very obvious as the stuff imparts a terrific shine on the tool. Anyway, if these high tech valves fail to do the bizzo - you will be held responsible! Of course, if they are a resounding success, you can rest assured that you won't even get a mention! Cheers, Barrie > Hi Barry, > > I've made solid piston valves from PEEK HPV which is a high performance > bearing grade plastic filled with PTFE, Carbon, and Graphite with some > success, apart from the difficulty of getting the correct fit at working > temperature due to the expansion (not a problem with slide valves!). > Using this for slide valves should be no problem as it will stand the > temperatures involved and it's very easy to machine. I've used it for > all sorts of bearings including coupling rod bushes etc. > I made a set of slide valves for my brother's Rob Roy from solid PTFE > which seem to be ok so far although it hasn't run a great distance yet. > I have heard mention of PTFE valves distorting but as mentioned above, > the ones I made haven't. The carbon filled variety would probably be > more rigid and perhaps more suitable. > > John > > Barrie Purslow wrote: >> I am currently refurbishing a 5" gauge Simplex which has non ferrous >> cylinders. The slide valves are rather badly scored so I have skimmed the >> top of the cylinder block no problem but I am reluctant to skim the valve >> itself as it is obviously not made of a material with good rubbing >> characteristics against the cylinder block. >> I have it in mind to make new valves out of carbon filled ptfe which I >> have previously used for a regulator valve with good results but this >> duty is a little more onerous. >> Any thoughts anybody? >> Barrie >> MODEL ENGINEERING DISCUSSION LIST. >> >> To UNSUBSCRIBE from this list, send a blank email to, >> modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject >> line. >> >> >> >> > MODEL ENGINEERING DISCUSSION LIST. > > To UNSUBSCRIBE from this list, send a blank email to, > modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject > line. > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.503 / Virus Database: 269.16.8/1153 - Release Date: > 26/11/2007 21:08 > > MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.