The re-manufacture of valves is often left out when an instrument is overhauled.
The difficulty is that if the instrument is over 15 years old, there's a good chance the valves leak. Once the valve block and pistons have been cleaned there is a gap of 0.002-0.004" between them. It doesn't seem much but when we've finished the re-manufacturing process we start hand lapping with a gap of ).0003" so the gap of 0.002" is 7 to 14 times bigger and would definitely leak.
We start by honing the pistons. The piston on the right has been finished and checked to be within 0.0005" of being parallel and round!
We hone the piston smaller than it needs to be so it can have a thick layer of Nickel plating on it.
Then once the valve block is re-honed the pistons will be fitted by hand and made to run really smoothly.
When we've finished the valves will be to a higher tolerance than when they came from the factory!
They'll be good for another 40 years.
Re-manufacturing from £100.00 per valve.