Hydractive Spheres, Recharging?

[combwork]

Hi,

The pump rate on my XM Estate seems very variable, sometimes every few seconds, other time it can't be heard for 30 seconds or more. It had new suspension spheres about 18 months ago. From the diagram, it looks as if as well as the normal acumalator sphere there are two others concerned with the hydractive suspension. From reading Peter Russek's XM book it seems that if the hydractive spheres lose pressure, the suspension stays in hard, or Sport mode. Is this correct? Either way, it might not be a bad idea to test/replace them. Any ideas people? I know Norrie has a recharging settup, but is there any way I can test them on the car?

Regards, Jim aka combwork.

[noz]

Jim,

There's no way that I know of to test the residual gas pressure in the spheres whils the spheres are still fitted to the car.

If you think about it the specification for the gas pressure is defined as being when the sphere is off the car and hence the fluid pressure can be guaranteed as being zero.

Next there's the measurement method. The standard plugs are not fitted with any device which would allow the testing of the gas pressure. This would entail, by definition, a direct link through to the gas chamber which could be opened and closed. This is particularly difficult at the kind of pressures we are dealing with. It would need a pretty specialised valve on the end of the sphere. This increases cost so therefore the facility is not fitted as standard.

Why measure the pressure on the gas side when you can use some basic physics principles and measure it on the fluid side? The inconvenience is that the sphere has to be removed form the car to do it. Once removed however the principle is quite simple. Push fluid into the sphere by the normal connection and measure the fluid pressure. Once the pressure has peaked and doesn't rise any more, as you pump fluid into the sphere, the fluid pressure must have reached the same pressure as the gas and the diaphragm is now floating compared to being flattened against the sphere inner wall.

OK, I realise you need to borrow or make some kit to do this but it's the only way I know of.

Alternatively you can remove the spheres and gas to a known pressure with a regassing rig or replace the spheres with those obtained from a reliable source with a guarantee of the correct pressure.

Alternatively, send me a pm and we can arrange to meet. You can use my kit free of charge to check the pressure and re-gas if necessary.

Cheers

noz