I think I must be missing something here.
Doesn't the ARB Locker only use a small amount of air to activate the locker via a solenoid? Once activated, the air supply can be removed and the locker will stay locked because it is traped by the solenoid (ie a constant supply of air is not required to keep the locker activated).
To deactivate the locker, the solenoid is opened and the air is released. At least that is how it sounds from their web site.
If that is the case, the small amount of air drawn from the tank to activate the locker could be replaced in seconds.

Richard