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I just got the call from Great Hobbies telling me that this Sullivan valve will only operate if there is "back pressure" from the line on the outflow side of the valve, to seat the ball. I think they ---well--it doesn't matter what I think. Fact is, I'm out $35 and don't have a solution to the problem. I can try building another one myself, with a smaller ball (My first one had a 3/16" diameter ball) which may have been too heavy for the venturi vacuum to lift of the seat. If anybody knows of a source for a purchased anti backflow valve that doesn't rely on back-pressure in the line to make it work, please tell me.---Brian