LOL! I'm not surprised several people came to the same resulting idea...:p

Btw, if one wants to build passive valve, why not use just float type one, only thing it must be mounted like in pic to ensure floating ball close the barb in case of counterflow...

Oh, and the rattling of the ball hitting the inner walls while operating would be one more thing to solve...;)

Dunno...

Did'nt think of floating!, do you know of anywhere that sells valves like these?, I hav'nt looked yet but thought of RS, I'm sure there are some low restriction jobbies out there, even if it means getting an oversized one and stretching the tube over :) ...

The ball is quite steady in middle of the flow, actually. No boucing around. Those ball + spring valves are quite common in oil pumps, medical systems, and hazardous chemical processing systems. I've seen a lot of em made out of plastic. The ball is made of rubber and provides a good seal against backflow. They come with or withoug spring, that depends on the desired response time.
Without spring the ball 'sticks' to the other side which has openings all around to enable flow (when it's in the good direction)

Im sorry, but I dunno where one can get them...Maybe somebody else can help here...

It's good to know that ball won't rattle in the valve. I've never seen one of those, but it might be worth looking around...

Update!
 

The valve setup works perfectly:cool:, unfortunally my dodgy prototype valve box won't hold together long enough to take any action pics (pressure keeps popping the lid) so "dry" pics will have to suffice.

The completed prototype;
http://users.bigpond.net.au/volenti/VB_1.jpg

closer shot without lid;
http://users.bigpond.net.au/volenti/VB_2.jpg

other angle;
http://users.bigpond.net.au/volenti/VB_3.jpg

The flaps are made of ordinary vinyl, seem to be doing the job nicely.

This is a simulation of what I saw with the valve box in action, pumping in "full bore" mode, no restrictions;
http://users.bigpond.net.au/volenti/VB_00.jpg

what happens after I start to introduce restriction or start to block pump inlet;
http://users.bigpond.net.au/volenti/VB_10.jpg

I didn't record any flow rate or max head readings, all this was for was to see if the valve setup would actually work as predicted/assumed, which it does, now to make a smaller, streamlined version.

W00T!!, wrap a bungie cord round the lid and give us some action shots! :D . a dividor pokeing out an inch between them might be a good idea, stop the good flow lifting the closed flap.

What did you use for the flaps?, car puncture repair patches might be a good idea...

PS, I see they passed the 'poke with a BIC test'! :p, always an encouraging sign!! :D...

Plain, simple and effective!

Congrat's!!!!!:)

I'm going to replace that outlet barb with a larger version and glue the lid on, that'll learn it :D

the material is ordinary vinyl, in the limited testing I did the rather chaiotic flow in the box didn't seem to stop the vlave closing when it needed to.

Ahh good call, actually some rubber from a bicycle tyre tube would work well too, nice and plyable.

You'd have to flatten it though?, a motorbike or pushbike would work better depending on the size of inlet& patch used, they do those square & oblong ones as well as the round ones...

If they were countersunk or surounded with a lip, it'd help focus the backpressure onto the flap would'nt it?...

I don't know weather we'd need to go to that much trouble, I have a couple of simple in-line options I want to try too, they may prove to more cost effective (mainly labour wise) than my flap valve setup.

When you say inline, do you mean one for each tube?, cause you might as well combine them, you're gonna have to with a Y later anyway...

PS. can't wait for some testing!!...

Well for my inital testing I'll have one in each tube (when I said that my idea was simple I meant it:D) plus I already have a pretty good custom made copper Y that I'll use for testing, I'll worry about a nice combined valve/Y when I see the test results.