Moving the topic slightly, there's an article in this month's EIM about Walschaerts valve gear. hear the author mentions a 0.010 inch lead. My question is this: Would such a small lead make that much difference even though it is a non negligible portion of the valve travel? Is it fair to consider steam as totally fluid on such a macro scale, and wouldn't turbulent effects etc mitigate against small differences just as 12 inch to the foot steam, small orifices gave 'wire drawing' effects akin to increasing supoerheat? Peter Chadwick Swindon 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.