"...In Funnel no. 124 page 56 Sam Wilkinson is talking about piston (spool) valves and there clearance.
He suggests a clearance of approx 0.005" (0.013 mm) for a simple, and 0.0015" (0.038 mm) for a HP valve on a compound. The latter in order to give a small leakage to ease starting and reversing without the need for a simpling valve...."
Another way is to cycle the gear from astern to ahead and back to astern quickly.
That will move the valves enough to put a puff of steam in the receiver and get the HP of dead center.
Of course...if you've got a big slug of water in your LP....it won't do squat..
I built my valves with .001" clearance on my HP spool and .0007" clearance on my LP spool, so she's pretty tight...maybe too tight...but she runs nice at 160psi!
But that may explain the lock up sometimes. It happens when I am coming into the slip, I have some headway on and I stop the engine and coast, expecting to back to a stop. I think in the 10-15 seconds the engine sits there stopped, I get the LP cool and she condenses, not only the steam in the cylinder, but the steam in the feedwater heater and exhaust pipe as well. If I had a seperate wet air pump running as an independent auxillary, I think this problem would not happen. The condensate would work its way out to the condenser. Having a tight fitting piston valve just makes this worse......I guess I will have to make sure I open the drains on the LP when I am coming into the slip.....and keep the speed down a bit....NO SHOWING OFF!