I don't have enough experience rebuilding to comment on the reliability
of Craig Brougher technique for setting the gap on Duo-Art valves.
Using my orifice measuring device I have however measured the flow
through stack valves and plotted the results against valve gap.  The
throttling effect " that Craig mentioned is very real and measurable
and seems to occur at a valve gap of about 0.035".

I am slightly concerned about such a subjective test.  With a fairly
simple metering orifice or with Craig's own throttled supply approach
(as described in his book) you could measure or at least compare flow
through the valves.  Although Craig didn't mention it, I assume all the
measurements were made with vacuum on the stack so as to compress the
valve seats.

Phil Dayson