Correct. Whenever the system is depressurized, you should have all tires suspended so that the bellows do not crease. When you crease your bellows, they will wear on the mark and can cause leaking later.

 

In response to
"P.S. what is not clear to me is how to remove all the 's*it' from system before refilling ?"

One answer is pressure and de-pressure the system.

"Overpressure Purging" is used to removed undesired gases from process vessels / piping in industry. The equation for calculating the number of purge cycles required is a function of the desired final desired concentration and the pressures used during the pressure and venting cycles.

Number of volume changes:
i = (ln(ca) – ln(ce)) ⁄ (ln(p1) – ln(p2))

*where "ln" is the natural log.
ca = initial concentration
ce = final concentration
p2 = venting pressure
p1 = pressurization target pressure

Let's say for your example you want to get to 98% (2% remaining) removal of all initial system gas and you plan to pressure to 100psig.

You must use absolute pressures in this calculation not gauge pressure (just add 14.7 to convert psig to psia)

ca = 100 (all air)
ce = 2 (2% of air left)
p2 = 14.7
p1 = 114.7

n = [ln(100)-ln(2)]/[ln(114.7)- ln(14.7)]
n = 1.9

so it takes approx 2 cycles from 0 psig to 100 psig with N2 to remove 98% of the gas that was initially in the system.

Important -- this is all based on perfect mixing of the gases in the system during pressurization and venting. Air suspension does not lend itself to mixing very well -- I'd add at least one cycle to account for non-ideal mixing.

 

From what I understand, shocks and reservoir are all connected to valve block, and are not accessible unless the block valves are opened. Each component is self contained (shocks keep their pressure, so does reservoir, compressor, etc.).

Service manual calls to connect nitro tank regulator via an adapter, to passenger front shock pipe (unscrew from top of shock, and connect to nitro tank via the adapter).
Then, using software diags, valve block is requested to open valve to the reservoir, make the needed pressure check/fill, close the valve. Then open another valve to a shock. Then the next one, etc. until all components are checked. Once that is done, reconnect the line back to passenger front shock.

Some specifics on steps are missing in the service manual, as it refers to PIWIS to follow steps therein.

If someone has done this, please chime in. Very helpful.

 

I am about to replace the compressor. It is not easy to find the PIWIS outside of a Porsche workshop. So my idea is to put a T-connector in the line between compressor and pressure tank. Then add a manual valve at the 3rd port of the connector. This can be used the tank with nitrogen and keep it at 17 bars. Let the car adjust itselve. Then close the manual valve and disconnect the nitrogen bottle. Could this work? The advantage is that not PIWIS needed.

 

Most people here seem to just let the car fill with normal air. You would then leave the T-connector there permanently? Interesting idea! I saw the filling function in my Foxwell NT510 Elite when I replaced the front left air strut, without needing to fill/replace Nitrogen. You can verify with Foxwell it will work as a not very expensive option….

 

Yes, I will leave the T connector and the valve permanently. Then is easy to connect in the future. Foxwell looks interesting. It shows more features than my icarsoft.

 

Brilliant idea! Don't know if I've read anyone do that but I don't see why it won't work. Here the USA at least buying from Amazon seller OBDZON is risk free (minus you pay to ship it back after regular Amazon return policy of 30 days. At just prior to 1 year Foxwell stopped updating my old NT644Pro, and refunded all my money when I shipped it back to them in GA). If they don't have a similar policy in your country better check with Foxwell directly for whatever function(s) you need, before you purchase. (I have Toyota software add on and spent a long time asking them to implement the TPMS sensor registration in Toyota models. They eventually did but it took a long time (6 months) and repeated asking them politely.)

 

There is a service document called "WM 4301IN Bleeding and filling the levelling system". It details what to do in case of system part replacement, for example I replaced the front left strut with no leak in the system. Process (with no leak) is to bleed the strut/shock you want to replace which sends the N2 all over it seems. Then to fill the new strut/shock with PIWIS or equivalent. If someone were to have a leak then filling the system with N2 is prescribed. No mention of filling and vacating cycle to get rid of "crud". As noted 70% atmospheric air is N2 at 1 ATM combined with pressurized N2 5.0 at (7 bar each strut/shock) and (16.5 bar system fill) is very pure already I guess, not knowing the math personally...

 

This is my little pneumatic access gate. I will install it on Tuesday in the line between compressor and pressure tank. I will leave it there permanently. Then it is easy to refill. I think it is not important to have 100% nitrogen in the system. More important is to have a minimum of moisture and oxygen inside. This can cause corrosion or blocks when freezing. So I will use the nitrogen from a bottle to fill up to the 17 bar.

 

nice solution

 

I'm really curious if this worked out? Also what source for nitrogen did you use and the fittings on that unit to attach to your valve? I would like to duplicate this

 

Actually I wonder too, if this was installed, and if yes, did it work (sealed well, no leaks, easy to fill, etc).

As for nitrogen, you can get it from any welding supply store.
Nitrogen II I believe.

 

I'd really like the specific spec for each component used. I want to do this tomorrow if I have the chance. Anyone know the fitting and air line sizes? Also, where is the suspension compressor located. I've seen stuff online when searching that says under the floor if the trunk then others saying it's under the vehicle by the accumulator tank.
. I think this is worth being a sticky if it works.

 

I used quite normal nitrogen. I think the only important thing is that the gas is dry for the initial fill. During the normal operation the system releases and takes air from the environment anyway. It just breathes through a dryer unit which takes the moisture from the intake air and gives back moisture to the air when release it to the environment. I didn't touch it again, because is works until now.

 

Can you confirm if these are 6mm or 1/4in fittings?