Hi All...Tsk,tsk,here I go again!

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just at the sussing out stage at the mo'......Thinking about putting bags on my latest vehicle. I only have knowledge of valves that I had from Rayvern which were combined lift /dump ,and the expelled air exhausting through the same valve. What other types are there? One for lift,one for dump per corner?
All I want to do is park and drop ,or poss drive it whilst dropped . (I know there are clearance issues with the suspension set up on full drop and I will have to reposition the front shocks) I was thinking of running a valve on the front pair of bags and another valve on the rear pair,to allow a bit of levelling out. Maybe have a lock off valve in the 2 systems to stop body roll? If I run the system from a scuba bottle (ie no comps) do I have to have a holding tank for the air ? Or can I just run it direct from the bottle? The valve on the bottle can be tweaked to allow low pressure to exit ,rather than the full 3500 psi.
What about the bag type? I used firestones on my Merc,are they ok for the t25? or will I need slimmer bags? Whats the best (cheapest) place to get reasonable bags and valves from please?
Thanks in advance for any info .
Regards
Rod
ps Just had a thought! ..what about using manually operated valves to cut down costs? ..**runs for cover**