minimax

There was some minor problem with the sphere I had drilled. The pressure shot up but pulling a vacuum on the sphere didn't pull the diaphragm back. Aeons of sitting on a shelf quietly corroding had clearly gummed up the rebound damper valve. Pumped the sphere to 100 PSI and there was a clinking noise and the pressure fell to 40 PSI and stayed stable so I reckoned that was the reason. Rinse and repeat. The valve is still too sticky and the diaphragm keeps returning to the top of the sphere once the pressure is removed, despite a full 760mmHg vacuum. Time to try something. I drilled the sphere out to 9mm having put the drill tip on the linisher to blunt it. Once the hole was drilled, I removed the swarf with a small magnet and used an 8mm drift to roll around the inside of the hole to deburr it. Time to fit the rivnut so clean up the top of the sphere and give the insert a good drop of Loctite 648 all around. Pull the tool up tight, then tighter. The first test to 120PSI held and I depressurised the sphere to give the Loctite time to harden.


One down, three to go. Tomorrow I shall put a small quantity of silicone oil in the lower half of the sphere and pump it up to 10 bar two or three times to clean up the damper valve. If it works, I'll do a pressure test at 10 bar. I suspect that with a bit of exercise, the sphere will come back to life. It will be interesting to see what the next one behaves like. The two front spheres I bought arrived in very good condition with readable numbers and plastic plugs in the filler hole so I hope they will work better.