Burgerman wrote:Its a diaphram pump. No flow without power. 2 valves in the way.
Mildly beg to differ, at least in theory... On a low cost pump, both valves are ONE WAY valves, (hydraulic diodes) and both flow from the input side to the output side.... Fancy pumps might have some sort of mechanically actuated valve, but for a basic pump, not really worth it...
(on suction stroke, piston pulls in from supply side, on compression it pushes out pressure side - but the flow is always in the same direction)
A one-way valve will have some sort of spring or equivalent holding it shut, so there will be some amount of pressure needed to get flow through it, but usually the designers try to keep that pressure as low as possible to minimize resistance....
No idea how much pressure it would take to get liquid to flow through a cheap pump, but I would be surprised if it took very much - it might not drip if the bag is just sitting with atmospheric pressure on it, but if something happened to apply pressure to the bag, I wouldn't be surprised to see a puddle....
If I were designing such a setup, I'd want either a solenoid or a 'pop-off' type valve that would resist any pressure less than what would damage the bag anyway....
ex-Gooserider