Question
I have a drip system that is fed by a 1500 gal water tank in a remote area.  
I've tried a couple of battery powered valves to automatically open and shut
the system.  I have very low pressure from the water tank - possibly less than
5 psi.  Is there a valve that will work with pressure this low?  The valves I've
tried need at least 10 psi to open.
Rocky

Answer
The only valve that I know for sure will open under very low pressure is a mechanically actuated valve. It is a ball valve with a small motor and gearbox that turns the valve stem. Problem is it require electricity and they are expensive.
Have you tried a Rainbird DV-100? It might be worth an $20.00 investment to try one. They've always amazed me how well they work in strange situations. The can also be used on a battery controller.

Matt