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post #2 of Old 09-10-2008 Thread Starter
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Here is an account of my experience with a new Air Head during a trip this summer:

The device was used continuously for 35 days, plus 6 days intermittently in the month prior to the trip, by a 160-pound man and a 110-pound woman. The voyage was to Nova Scotia (cool and damp weather). The device worked well. The problems with the unit we encountered were minor, particularly in comparison to the release of quarts of raw sewage that sometimes happens with a conventional system. The Air Head represents a real paradigm shift in marine sanitation devices. Its simplicity and reliability eliminated a number of potential nightmares from the list of things one worries about on a long trip. Its installation also freed up two complete lockers (one locker that contained the conventional head's holding tank and flush water thru-hull, and an additional locker that contained the Y-valve, overboard dump pump, and a web of associated sanitation hose and fittings). And in the future I plan to remove at least one now-unnecessary thru-hull. This is a great product.

To get specific, we encountered two problems:

1. Spring clip failure: The trap door is held fully open or fully closed by what might be called a spring-powered over-center mechanism. The spring is held in place on one end by a screw and on the other end by a clip that is inserted through an actuating rod. This clip fell out, releasing the spring. I retrieved the clip (yuch!) and reinstalled it (hopefully correctly), finishing up by bending the clip cotter-pin-style to retain it. Perhaps a step like this was missed during assembly, or perhaps a different type of clip such as a true cotter pin or a cotter ring is called for.

2. Sewage leak: On the very last day of the trip about a quarter cup of dilute sewage leaked through the bushing for the stirring mechanism on the end of the mechanism opposite the crank handle (the handle is on the right side of my unit when the unit is viewed from the front). We noticed the leak first thing in the morning. We cranked the stirring mechanism a few turns, cleaned up the mess, and experienced no further leakage. The cause of this failure was probably operator error:

- Failure to empty the unit after 60 person-days of use (e.g., 30 days of use by a couple) as called for in the instructions. We pushed the unit to see what happens when it is overstuffed (a total of 82 person-days of use), and we found out. The unit should be emptied "by the clock" as specified in the instructions.

- Failure to use coffee filters during continuous use as specified in the instructions. The instructions don't really say why filters should be used in such operation. However, they seem to serve the same absorptive purpose as peat, and perhaps they compartmentalize the mass, permitting better aeration and drying.

- Failure to add additional peat. The biomass had the consistency of bread dough. It was not crumbly, but it was also not sufficiently liquid that it flowed by gravity. Apparently, this consistency is too dilute, and peat should have been added to make it crumbly. However, additional peat might not have been necessary if coffee filters had been used.

Sundry thoughts:
The thumbscrews in the urine container bracket (the thumbscrews that must be undone to remove the urine jug) desperately want to cross-thread when reinstalling the jug. My wife and I have kicked around ideas for a design improvement. Perhaps the simplest is the best: The current configuration of the bracket is such that it is in an unstressed, relaxed state when the jug is installed and the thumbscrews are seated. By necessity, therefore, the bracket must be deformed to get the jug in place and start the thumbscrews, and the bracket fights the operator during this maneuver. The bracket could be modified such that its unstressed configuration results in the thumbscrews just barely clearing the jug, all lined up for threading. Judicious use of vice grips on the current unit might accomplish the same purpose, but I have not yet been moved to try that.

The urine container should be emptied on a daily basis. After 24 hours of use by a non-beer-swilling couple it is not quite half full. Dealing with it when filled to that extent is infinitely easier than when it is overflowing (voice of experience here) or even 3/4 full.

I can't help but consider the implications from public health and regulatory points of view of dumping urine. Composting heads seem to be something of a regulatory step-child - regulations for neither conventional heads nor porta-potties are really appropriate (witness Ontario's regulations). So what is the real public health and environmental impact of dumping urine? It is true that fresh, unadulterated urine is primarily a chemical entity (a solution of salts), not a biohazard. However, in the Air Head, some slight fecal contamination of the urine is inevitable. Without looking into the matter deeply, perhaps this is a potential solution: Each time the urine jug is installed, a small, specified amount of bleach or one of those 1-inch diameter tablets that are used for purification of dish water at camp sites could be added. Such treatment would seem to eliminate the reasonable possibility of human pathogens surviving during storage, while not rendering the solution unfit for release into the marine environment. Or perhaps such an intervention is not necessary, at least in a marine environment, because trace quantities of naked pathogens can't survive long enough to threaten anybody or anything. I wonder.
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