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.