I just tried it again with two 6" exts and no go. Now the valve sometimes works with the 3" ext and sometimes doesn't. I noticed that the green LED light on the valve is dimmer than another valve plugged in right beside it with no ext. seems to be a voltage problem. I've got the Powerbox set to 5.9 volts. I've tried multiple valves and they all do the same thing. The Powerbox screen says 8.0 volts on batt1 and 2 regulated down to 6.3 volts.