duck bill valves

Hi
Just wondering if any1 has tried duck bill valves for a non return system on a hand pump? ive tried lots of different things from rubber flaps to spring check valve and atm have not found anything that works well with out blocking or keeping the valve open. any other suggestions would be great.
cheers

C&C - Does duck-bill mean two (flexible ?) flaps working against each other ?
My basic PVC Yabbie Pump is awkward and I am keen to put some thought into an efficient design. I'm interested to hear that you have tried a few types of valves. The Lake Bolac Caravan Park design uses a steel ball and the unit at the dealer in Ballarat has a single flap valve. I hope some other experienced users/designers will comment here.
Cheers

Ive been using hand pumps , made from a 3inch drain pipe as a base , but all open ended , no valve , no bend, and they work fine , just suck , lift , swing to bucket and expel , the simpler it is the better it goes.

yea im thinking the same, mine is not to bad, its made out of 65mm pvc with the 65mm adjustable rubber check valve. might try some leather thoe, maybe smoother?

Cannot think how big that is but a tennis ball fits the drain pipe I use perfect and makes a bril seal , just put two big washers either side on a threaded rod and squash the ball to fit and adjust as it wears.