I'll adjust the pressure. Here are a few photos of the parallel system. The ARB pump is an old one circa 1999 or 2000. The air solenoids are covered with open cell foam to help exclude debris and they have not clogged in the years since I did that. There is a mesh of nylon stocking under the foam for a bit finer filtering.
The OBA feeds the tank through an oil separator (vaguely seen as a blue cylinder behind the converted A/C pump) then to a cut-off switch sourced from the local hardware. The regulator is a commonly available unit which I believe I have seen at Wal-Mart.
The connecting hose between systems started life as a pre-packaged hose, again from Wal-Mart, to which I simply added appropriate automotive quick disconnects, male on both ends. As built I need to disconnect the ARB system when airing tires because I never got around to building a manifold for the tank. Figured since I don't lock axles to air tires it was no big deal.
The tank is small, somewhere around 1.5 gallons, but will air the lockers for half a day of regular on and off use on the trail. I leave the OBA compressor off once the tank is charged so that the A/C pump I use for air won't run unless I know about it. Since it does not have an oil source, I don't want the A/C pump to cycle excessively and want to keep track, so I turn it off. When the tank runs the pressure down, the ARB pump kicks in letting me know I need to recharge the tank, at which point I re-arm the A/C pump. Letting the ARB pump recharge the tank takes forever and is hard on that pump, so I avoid using it when the systems are crossed.
The cross-plumbing is simple. The ARB came with a multi-port manifold and I just use one of the available ports for a female quick disconnect. Separating the systems requires removing the hose from both ports. Not complicated at all.
