Air Water Separator

We encountered rough weather on our trip from Canada to San Francisco during the fall of 2004. Our main leg was 700 miles and we had 4 people aboard. Because the harbors were closed due to the bars and the weather, my concern was having enough fresh water to keep the crew happy with hot showers. I thought I had it made since we have a 6 GPH watermaker which had worked well all summer. However, I soon discovered the watermaker was not making much water.

The problem was air entering through the seacock. The rough weather was creating foam and the foam was flowing along the hull and being sucked in. Each bit of air destroyed the 600 lbs of pressure needed to make water. So, I spent a considerable amount of time in the engine room jury rigging an air water separator and vowed to make that problem go away evermore.

The photo below shows my contraption, made of PVC. I have not had a need to use the watermaker since installing, but theory and static testing seems to prove out the design.

Basically sea water is pumped into the middle of the 2 inch PVC tube, air flows up and away from the outlet at the bottom that runs to the filter and then to the watermaker pump. Air collects at the top of the tube, creating a mini-pressure tank out of the tube. The 1 GPM pump has an automatic shut off switch, so it cycles as maximum pressure is reached. There is an air bleed near the top to allow air reaching that level to bleed overboard. A small valve controls the rate at which air and water are bled out.

There is extra plumbing involved for fresh water feed to the watermaker, back flushing, etc. But, the basic parts are simple.