Test · 2023-06-06

Collapsing one-way valve (balloon → duckbill)

The question

Can a collapsing one-way valve (balloon, then duckbill) manage the engine's excess pressure without drowning it?

The answer

Yes. A balloon, then a large flexible breast-pump duckbill, then the water column, and finally a 6 in pipe rising out of the engine with a small duckbill at its end. The last one replaced everything and is the working solution.

Kind: Test
Status: Retired
Date: 2023-06-06

Video

What it is

Early one-way valve experiments for pressure relief, superseded by the water check valve design.

Results

→Balloon valve: worked as a soft vent; replaced.
→Large breast-pump duckbill: the big flexible bill had give on suction, which the engine needs, but less so than water.
→Water column: the best runner (see the water-tube entry) but it drinks the water on cool-down.
→6 in vent pipe, up and out, with a small duckbill at the end: vents on warm-up, nothing comes back, nothing to drown it. Current design.

Lab notes

Why the pipe matters

The pipe is not just a holder for the valve. Air pushed into it cools, contracts and is drawn back, so the pipe adds the give a dead flap lacks, in a small way the water column did in a big way. The duckbill at the far end only has to pass the warm-up surplus.

Notes from the build videos and the designer's account of the valve sequence.

01Build · 2023BuiltDoes the design still work scaled to 3 feet?Yes. It runs at 3 ft, and it's the channel's most-watched build.See more →07Build · 2023BuiltDoes less air make the engine run faster?Yes. Venting the excess lets the small air volume oscillate faster.See more →10Design · 2024SimulatedCan the clamp itself be the heat sink?In simulation, yes. About 2× the heat rejection in still air. Not yet built.See more →

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