How it works and the troubleshooting steps for the return splitter. Think I read here that Volvo has the same but draw tee and splitter are enclosed in a Volvo box. Tanks the original sizes and locations? Or were they changed?
It is because they use a simple normally closed solenoid bank.
Latching solenoids (or bi-stable, whatever you want to call it) for trucks weren't invented till KW forced them to become invented a few years ago. You can go to a KW dealer and buy a latching start, end cap, and harness layer. Then plug off your solenoid for air suspension, unpin the corresponding terminals, and run an air line and the unpinned wire over to the KW one. It'll then work independent of the key. They are pretty skookum solenoids and latching takes a double unit so it won't be cheap. I can get part #'s if interested.
Or option #2 you can leave your solenoid bank as-is. Get a double check valve and install that in your dump airline (the one from your solenoid to the leveling valve). Port A comes from your current air line & solenoid, Port C goes to leveling valve. Port B comes from an added normally open solenoid hooked to key switched power. Airline to this solenoid would be tee'd from the supply line to the original solenoid bank (or alternately it could be a pressure protected line from tank). Upside to option 2 is it'll hold dump when keyed off like you want. Downside is that it'll dump every time you key off no matter your dash switch position. Use a real good solenoid and do the best wiring you can as any solenoid or wiring failure and you are going to have a dumped suspension whenever and wherever it happens, which isn't really the failure mode you want.
Recommend Clippard double check:
Recommend GT, errr IMI, solenoid:
Or option #3 is to replace leveling valve with a Hadley SmartValve kit. I think it would ignore a dump signal at key off but I'm not 100% sure. I don't really encounter the problem in my world.
You should have some type of crossover hose system that equalizes your tanks as fuel is used. If one tank is draining faster than the other, then something is likely wrong with your crossover hoses somewhere and should be fixed. I am not as familiar with the Volvos, but on my Kenworth the hoses are easy to see and access. I'd start pulling hoses and see if the one from the slow draining tank is clogged up.