Gasoline and Fuel Tank Vent Filters

Rev. 11-24-2012. First posted Spring 2012 as part of a longer blog entry. For my fellow PDQ sailors, Dog House and Shoal Survivor have been testing these since spring with no problems. I re-posted it here with a few revisions because it was buried in a longer post and because the LONG version will be published next month.

Rev. 5-3-2021. A few more updates. 

So what do the new vent filters look like?

This filter housing survived 7 years of testing before the boat was sold.   It is mounted to a FRP mounting plate, which was screwed and epoxy to a cored bulkhead. It was installed in the vent line, between the Raycor Lifeguard air/fuel separator and the through-hull. This is a modified Vetus No-Smell housing. Holding 500 ml of adsorbent, it is the correct EPA-rated size for a 27 gallon tank,  is fuel rated, easy to switch adsorbents, and I had it.

I tested pelletized carbon, silica gel, alumina, and mixed beds. The winner, in terms of water absorption and evaporation was silica gel. Conventional wisdom suggests carbon should work better for vapor control, but because carbon cannot function in high humidity environments, and because much of the vapor is ethanol (which is more water-like) and not gasoline, silica gel performed better in all parameters. It is also easily regeneratable, which carbon is not.

Installed. The vent leads up from the fuel tank, through the Raycor Life Guard, through the Vetus No-Smell (several adsorbant types tested) and down to the existing through-hull. I had to manufacture a new perforated metal retaining plate for the Vetus unit; this allowed testing with a variety of adsorbents.

The H2OUT filter is even simpler. Refilling is a simple matter of loosening a band.

A factory installation, in a 2012 pontoon boat.  Instead of mounting the canister in a high loop, they protect it with a filling cut-off valve and sensor in the fill line (so that auto-stop filling pumps will work), an anti-surge valve on the tank, and a p-trap on the through-hull. These canisters are intended to last the life of the boat. All Attwood equipment.


This may seem a bit over engineered. I don't think so, not if maintenance becomes less, fuel related problems go away, starting is easier, and a material amount of gasoline is conserved (reduced evaporation losses) to pay for the project. Green, cheap, and lazy, over the longer term. That's just smart.

Try this link, if you would like a better summary of both the new rules and the safety rational behind gasoline fuels system requirements.

The full article is in the January 2013 Practical Sailor Magazine.

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Notes, 11-24-2012: We tested granular carbon in Vetus housing in the spring of 2012, but changed to a silica gel/alumina blend after a few months. The carbon was a complete failure, became saturated with water to the point of condensation and dripping.Perhaps carbon will work better in other climates, but not on the Chesapeake in the spring.

We have had 2 test units (H2OUT and Vetus) in service on 27 gallon gasoline tanks since spring 2010; they are both doing well and have not saturated. Humidity readings inside the tank are well below saturation and the color indicators have not changed at all, suggesting that several years of service can be expected.


4-15-2013: After 1-year of service the silica gel has saturated no further, humidity levels on the tank side remain stable (35-45%), and condensation is a thing of the past. A service life for the silica gel of  > 5 years seems certain.

12-14-2013:  Still going strong. 

8-10-2016: Gel finally changed color and had to be regenerated by heating. 15 minutes on low on the propane grill in a pan did the job.

3-10-2018: Still going strong.