Topic

bryan young wrote:

I understand that the Nitrogen pressure in the top part of the Sphere is 150 psi ( 15 bar) The fluid pressure below this is 400 psi BUT this is static, i dont know how the bounce will affect these figures.

150 psi is just over 10 bar, Bryan.

1 bar is 14.7psi, or atmospheric pressure at sea level. 🌊

My two pedant's worth: at 15 degrees Celsius and an air density of 1035 g/ cubic Metre.

bryan young wrote:

I understand that the Nitrogen pressure in the top part of the Sphere is 150 psi ( 15 bar) The fluid pressure below this is 400 psi BUT this is static, i dont know how the bounce will affect these figures.

The nitrogen pressure will not stay at 150psi!

It will increase to the fluid pressure at 400psi. 400psi will be the resulting static nitrogen pressure.

Now add some dynamic pressure due to suspension compressing and you will easily get to 600-800psi nitrogen pressure.

Additionally the four spheres will act as accumulators, which store hydraulic energy.

Curiosity was getting the better of me so I decided to thread the top of the sphere I had pilot drilled and fitted one of Mike's adaptors in order to find out if the diaphragm was sound. I had intended to pump it up to 30 PSI but the pump whizzed up to 70 in seconds (rather like the MGF,) and it held until I depressurised it so the sphere will serve. I have to drill out larger and deburr for the Rivnut to be fitted but at least if it doesn't seal, I will know where the fault lies.

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.

Nope. Failed at 100 PSI. Need to try one of the fronts next, Don't trust my other rear unit any more than the bloke who sold it to me soI have to hope that those on the car are still serviceable.

So in the end I bought four spheres and had Kevin Wright regas and recrimp them. This he did both quickly and at a very reasonable price. I have a set of four regassed spheres and four new dampers. I have a pump and fluid. A decent weekend's weather and I should be well under way. I can experiment with the ones from the car later.