AquaCure Fill Cap Duckbill Valve Kit

These are the parts needed to put a duckbill valve in the Water Fill Cap.
Here is the installation video:

The duckbill check valve in the water fill cap is used / needed whenever you are not using the Tower Cap (which has a built in duckbill).  For example, when using the AquaCure Torch.

The vacuum that forms, as hot gasses cool, and sucks the water back into the electrolyzer (from the humidifier or bubblers) is normal, all electrolyzers form a vacuum when their hot gasses cool.
Backfilling causes the electrolyzer to over-fill, so that the next time gas is produced, lye solution is ejected out with the gas.

Most electrolyzers solve this backfilling issue by adding a check valve to only allow gas/liquid to flow OUT of the electrolyzer but not IN.

But check valves can (and often do) FAIL (for many reasons) allowing the backfilling anyway.

Those check valves ALSO cause a vacuum to be formed (and be held) in the electrolyzer.

They also cause a pressure drop of (usually) 0.5 psi, which means that the electrolyzer needs to be operated at 2.5 psi to have an output of 2 psi (lower pressure is safer).

So all considered, I chose a BETTER option, the duckbill.  This is what a duckbill valve looks like
https://www.zoro.com/aro-replacement-duckbill-neoprene-93114-1/i/G2549942/feature-product

The duckbill allows air to flow into the electrolyzer as it cools and prevents HydrOxy from flowing out, solving all the above issues.

In early versions of the AquaCure I put the duckbill on the reservoir chamber, inside the machine.  But this made maintenance of the duckbill difficult.  So I moved it to the fill cap and it’s now easily serviced if needed.