[Jeffrafa]

The only real way to keep it from 'crashing down' is by using flow controls to regulate the speed of your pneumatics (as mentioned by Roger).

None of the valves in the kit will function under ~25 PSI, as you've found. (an exception being a solenoid valve that has an additional air supply line exclusively to function the solenoid, but none of these are included in the kit and they still wouldn't work if you didn't have pressure in your accumulators.) In order to make the arm come down you'd want to have the valve spring return to the lowering direction, then even without incoming pressure the arm's cylinder will be open to exhaust and able to lower just by the weight of the arm on the cylinder.

In order to use multi-positioning in addition to allowing your arm to lower you'd need to use two valves, one to control direction (set to spring return to lowering the arm) and another to regulate the exhaust of the first (set to spring return to relieving the exhaust from the first).

If you were only interested in multi-positioning and not having your arm lower gradually when your tanks run out then I'd reccomend a three position valve instead for ease-of-use. It is simmilar to the dual solenoid valves included in the kit, only the valve is spring return to a third 'center' position, which can be either all ports blocked (what you want for multi-positioning) or all ports open (if you wanted to relieve the cylinder when its not being actuated). This makes it easiest because it only uses one spike, one solenoid valve, and is also easier from a programming standpoint. There are a number of threads that have discussed this if you are interested in it further, just search.

Jeff