New vented loop squirting water

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kacecar

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Hi
I've just installed a new Jabsco toilet, replacing a non- Jabsco device that became unreliable. The plumbing is all new. Because the loo is below the waterIine, I followed the Jabsco installation instructions that require a vented loop in inlet pipe between the pump and the bowl (the previous loo didn't need/have any vented loops). Freshly launched I've been testing the new system and am dismayed to find that when I pump water into the bowl it seems to work OK but a significant quantity of the wet stuff squirts out of the vented loop on each up-stroke (the "suck" stroke). The little duck valve in the top of the loop looks OK; I'm not aware that direction of flow in the loop is critical; everything that should be tight appears to be tight; there are no apparent blockages or constrictions anywhere in the pipes. The loop is there to prevent syphoning and, I thought, should only let air in and definitely shouldn't let water out. What do you think is wrong and how do I fix it?
 
Does the duck beak point into the loop? It should.
If it is the right way round and still lets anything out then it is dirty, something is topping the duck shutting its beak.
 
The loop can be fitted either way. Pressure from the pump keeps the "bill" part of the valve closed, if water tries to syphon into the toilet the bill will open and break the syphon. I cannot think that it can be anything other than the valve not sealing, either the bill is not closing correctly (try blowing through it) or the whole thing isn't seated properly.
 
Thanks for the input everyone - it's nice to know my understanding of the valve's operation was indeed correct.

The valve and its seating all looked OK when I checked it earlier this week. However, I suppose there's a chance I've overtightened something and/or distorted it - either that or it's a duff unit. I'll have another go at it when I'm next down on the boat (Friday I expect) and will let you know how I get on.
 
As promised, here's what happened - just in case it's useful to someone. The problem turned out to be a combination of unwelcome distortion and a weak unit.

I replaced the first unit and fitted a new one - out of the box so to speak, without making any adjustments at all to the position of the valve (its in a hex casing that can be tightened / loosened with a 17mm spanner). Initially it leaked through the thread on the casing but I found that tightening it (slightly) fixed that. However, over-tightening distorts the valve such that it doesn't close. It was very a fine line between distorting the valve and allowing a leak through the thread but a bit of trial-and-error seems to have fixed the problem.

I looked at the unit I'd taken off. I'd over-tightened it far too much (very easy to do with a 17mm spanner) and the valve had become permanently distorted. I suppose the plastic valve might have recovered with a bit of gentle heat but it was a cheap unit so I threw it away. With hindsight, perhaps I should have paid more.

Again, thanks for your input. Now I'll try to get the engine going!
 
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