Thanks for your advice Bob, my instrument is a 1927 model and is of a more
conventional design stack rather than the pouch pneumatics for which Schulz
were (in)famous. It has pouch blocks that lift round valves on wobbly valve
stems, the bottom seats are metal and the top fiber washers. All the
reference material I have found or been given on the late model Schulz stack
refer to square valves on wobbly stems, I have even got photos of this. As
my instrument does not appear to have been subjected to any repair work, and
the condition of the valves is consistent with original parts, I believe
these are the original design. Perhaps Schulz tried different valve shapes
when they changed to a conventional stack. The biggest problem I have
detected so far is that the lead weights in the base of the valve stems have
oxidized, I either need to replace the lead or the whole stems. The valve
facings and bottom seats are in very good condition but the fiber top seats
will need to be replaced. Terry Smythe has helped me enormously with Schulz
info, but I need to locate a parts supplier as in Australia most suppliers
only carry parts for Australian built instruments.

Rgds, Harry Couchman