Every air suspension system I have ever seen is based on a sealed bladder system, I have serious doubts that a seal designed to hold back fork oil that is not under any pressure would come close to supporting the forces required for an air suspension system.
Yeah, most of what I've seen for air shocks/springs involves bladders, Haven't found a good exploded diagram for air ride forks (I've seen the forks, just not how their internals are designed). An air piston though is an entirely different animal more akin to a steam engine's or a hydraulic piston.
To some extent our fork seals are designed to hold back oil under pressure as there are no vents in our forks to bleed of pressure. The evidence to support this is the fact that with no other modification (aside from adding the valves to the caps) the forks hold pressure. Just like in our engines, as the forks volume decreases during compression, the pressure inside increases. I've no doubts that the sliders and tubes can hold back at least 200PSI without failure, air assist shocks have much thinner shells and add 500 to 1000 lbs. per shock of additional support/lift at around 100PSI for similar surface area (far above our needs). The question falls to the difference in seal design between air pistons not typical air suspension design and our forks. A good example of the force that can be generated with an air piston of similar bore is the actuator piston from the 1969 Roper/White Spot welder at our shop which at 100PSI is capable of 900lbs of compression force according to the builder's plate. The seals on this unit are "O" rings, one on the piston, two on the cylinder. The piston is 1.25".
There's a lot to be researched before I'm ready to make any claims related to ditching the springs entirely, including actually removing them and testing whether it will be reliable. But that's a ways off, at the very least not until I have some spare seals on hand, and have determined that a catastrophic failure will not result in the bike being rendered unrideable (IE> with the forks completely compressed the frame hits the ground) or wrecking. Looking for an elastomeric bumper that will fit inside the fork to at least prevent damage to hard parts and make it capable of limping home if the seals were to fail...might even resort to using valve springs held in place by lengths of hydraulic tubing. I dunno, we'll see where things lead me.
Today marks more than 48 hours of the forks being pressurized (I think. I'll have to double check.). Still at 30 PSI still no leaks after two full tanks of riding on them deliberately choosing rough roads to really give the suspension a workout. Very hard on the rump, even at the lowest preload on the rear the back's ride is to stiff. The front is still awesome. I've discovered riding off a low curb the front makes the transition much more smoothly than stock, the rear still sucks. A tiny bump VS a big thump.
I have pushed the front to 80PSI but wouldn't ride it that way, even putting all of my 260lbs on the front end the forks do not move. This of course leads me to believe it might only take 45 or 50 PSI to support the front end without the springs.....Again much more homework to do before trying it.
More status updates to follow. Any issues will be reported honestly and as accurately as possible. Would be pretty ****ing stupid to claim no problems if it turns out there are, after all if someone else tries it and horrible things happen....Well it wouldn't be good for all involved.