OK, for once a fun question.
Got fed up with air and ordered my new Arnott conversion kit. Anyone ever kept the compressor for onboard air? I know a regular portable is more logical, but was wondering how hard it would be to just throw an air hose on the old compressor/tank assembly. Anyone with enough idle time to ever try it?

 

Interesting question! My initial suspicion is no, based on 1) the high operating pressure of the pump & small reservoir size, 2) the strain relief needed for any permanent/QD fittings attached to the solenoid block, and 3) the lack of a controller built in to activate the compressor. If I'm wrong on any of these points - I'd love to know!

1) Operating pressure: I believe filling a tire with 200+ psi supply air would be unsafe and potentially damaging to the tire or valve stem. Additionally, the reservoir capacity is only 4.5 lites (1.25 gal) and the pump takes multiple minutes to fill this small reservoir.
"The Nominal pressure developed by the compressor is 15 bar / 218 psi. The safety pressure-relief valve is set to relieve pressure above 17.5 bar / 254 psi...."

"The reservoir has a capacity of 4.5 liters with a maximum design pressure of 15 bar / 217 psi."
​​​​​​
"an algorithm programmed into the ASM limits the compressor motor to no more than 120 seconds of continuous operation before imposing a mandatory cool-down period of 45 seconds"

2) The aluminum valve block is mounted low in the truck and transverse to the vehicle. If attaching a 15+ ft air hose, you would want a Quick Detach fitting + lots of strain relief on the fitting.

3) The air pump is driven based on ride height input, so you'd need a method to tell the compressor to re-pump. The Arnott shocks come with an inductor to mimic ride height voltage output (nominal 5V = satisfactory ride height), so your system would always find ride height satisfactory unless you built a controller to re-energize the pump.


All this info & more can be found this this pinned post!
Air Suspension & ECATS System Summary: Components & Operation

 

 

That's exactly right, beware the dangerous oranges lurking adjacent to the reservoir

 

This is lime-colored, but might be more useful.

Realistically, it's not too expensive, has an automatic pressure gauge, etc etc.
Besides, you go to all that trouble replacing air suspension, and the compressor is the most likely thing to pack up, if it hasn't already.

 

Hi Dave,

That is a very fun question, and maybe not worth the effort, but fun to think through.

Once the Arnott coilovers and the Electronic Bypass Module are installed, the compressor will never run. So you'd need to wire a switch to power the compressor directly. Easy enough to do that at the compressor relay socket. Wire the switch so it jumps terminals 3 and 5.

With control of the valve block disabled, valves to the air spring lines may be open, which would prevent the reservoir from pressurizing, so you would want to bypass the valve block entirely and connect a valve on the reservoir outlet line.

I don't think the high pressure capacity of the compressor would be a problem. Air is so highly compressible that even if the reservoir were fully pressurized, adding air to tires would probably be a manageable process. But if you were concerned about overpressure you could easily add a pressure regulator at the reservoir outlet.

But as you already noted, a regular portable is more logical.

Cheers!

Don

 

That may be true - but the small overpressure I used popping a brake piston clear of the caliper was frightening! I agree, air is highly compressible. And, feeding the air into a tire may not pose a risk, especially with a pressure regulator. However, air can be quite powerful, too!

 

Been there, done that!

Not much resistance on a caliper piston compared to compressing air in an enclosed volume, since the piston can easily relieve the pressure, as we've all discovered the hard way!

Typical compressors used in professional shops can supply 150-175 psi at very high flow rates (many cubic feet per minute). The compressor in the X350 can eventually work up to 250 psi or so of pressure, but it does so in tiny little puffs, which you can feel and resist if you hold your thumb over the end of its output. It's flow rate is very low, which is unsurprising given the small volume displacement of its cylinder. The volume of the reservoir is also very small, which would also serve to limit how long the system could supply high pressure to a lower pressure/larger volume receptacle such as a tire.

One other issue is that because the compressor does not have a temperature sensor in the Jaguar implementation, the Air Supsension Control Module limits its run time to a maximum of 120 seconds, with a minimum cool-down period of 45 seconds between runs. So you would want to take care not to run the compressor too long at a time or risk overheating it. The Audis that use the same compressor have temperature sensors, so if you really wanted to get crazy, you could add an Audi sensor and a temperature gauge or shut-off circuit.

Cheers,

Don

 

You guys with V8's could stick tire adapters in the spark plug holes of TWO cylinders and you would still have more power than me. Garrumph
4.2L /8 *6 = 3.15L. XJ6=3.0L

 

Easy now, you're assuming we all have running, driving cars