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Discussion Starter #1
I read in the plumbing and FDA codes that water tanks are required to have vent strainers to keep out bugs, and that they be angled down to keep out dust. But I've seen many boats where neither is fitted.

I've seen some where a strainer is incorporated into the through-hull, but more where the vent is a simple mushroom fitting. Are internal strainers ever fitted? I'm sure external strainers are often omitted because the vent is also the overflow, and if they were clogged from the inside, these cannot be cleaned. But I'm not sure that is a sufficient reason for no strainer at all.

I wonder because I occasionally find a bug in the tank, and that seems, well, stupid (my boat has no strainer).
 

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baDumbumbum
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It is probably a good idea -- tho bugs are not gonna hurt you.;) W drink & cook with rainwater here, and more than a few crawlies get past the screen. Dead mice, those get kinda rancid. We try to avoid those. :eek:

Your tank vent terminates inside the boat? An easy solution is a scrap of fiberglass screen wrapped over the end of the tube. Might need a barbed fitting inside the hose if it is flexible. Also, people recommend terminating the vent where spillage wont drip onto electronics, etc. We're contemplating a tank whistle, too -- but I'd like to know if those wheeze like a calliope when the tank contents slosh back & forth. Can anyone give a yea or nay on that?
 

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My "vent" is inside the boat i guess a determined bug could make the trip :)

Pretty much every pump should have and intake screen to keep stuff from fouling the works of the pump.

My wash down and freshwater pumps have one with a clear cover that is easy to remove ,heck the strainers all have quick release fittings
 

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Discussion Starter #4
A good many boats--mine included--have the vent outside, so that an overfill is harmless (I saw a small boat nearly sink when the owner was distractd by dock talk).

Just sayin', folks worry about water filtration and chlorine and microns.... A couple of stink bugs top that.
 

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There is no reason not to have a water tank vent inside the boat. For one thing salt water will not have a chance to get into the tank. The S&S Swans had the vent going into the galley sink. A friend has his vent going to just below the overhead in his Spencer 35 at the main bulkhead - as long as there is a manual pump in the system the water will go into the sink before it gets to the vent top.
 

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"Finished" water, water for food, etc. production stored in vented 'tanks' usually has at least a <3µM filter on the vent - principally to block mold/fungus spores from being aspirated during drawdown of the tank.
Since most 'filters' in this µM size range have poor permeability and poor hydrophobicity .... and 0,2µM hydrophobic PTFE membrane (Goretex !) filters have excellent permeability / air flow, its the 'usual' filter media found there.

BTW - that 'black schitt' typically found growing well down into and inside of your boat water tank vent line is usually fungal. Some of the 'black molds/mildews' are very toxic to human respiratory etc. tissue and damn near impossible to 'cure'. Do websearch: "Stachybotrys Atra"
Botulism (clostridium) is a very rare but still possible airborne 'very very nasty' ... kills lots of ducks and other waterfowl in estuaries/rivers during the height of summer. With some species you only need ONE or two bacteria to pass your lips to kill you. Clostridium toxins are among the 'most fatal' on the planet.
 

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Discussion Starter #7
Rich: I understand the food requirements, though I doubt such a filter exists on any boat. As I mentioned, the code calls for a screen on drinking water storage tanks. Obviously that line cannot be both overflow and vent if there is a fine filter. How would you treat the over flow? Do we simply figure it will back out the fill pipe? I think that is what Mitiempo was suggesting. Clearly, with anything more than a strainer, the vent can no longer serve as overflow.

As for salt water coming in a vent, that doesn't require it to be inside the cabin, it just requires using a routing such as would be used for a fuel tank vent. Cabin air is probably better than outside air, but it's got bugs too. In fact, bringing it to the galley sink, where food is being prepared, dishes washed, and water splashing at the same time the vent is drawing is not perfect. Not at all.

I'm not at all paranoid about what I drink, but the more you dig the more you're reminded of the complexity of the trade offs.

What you did not answer is whether your boats have a screen on the vent line. My assumption from your answers is that they do not. Does the swan? Interesting.
 

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pdq - filling of boat tankage usually is not done 'at pressure' but is discharged into atmospheric pressure and with the tank vent outlet 2-3ft. static height above the tank inlet fill pipe. Nevertheless, such hydrophobic membrane systems will typically have a filter pleat 'burst pressure' of 60 psi in the 'forward' direction and 15 psi in the 'reverse' direction.

Youll now find increasingly that most 'commercial transportation' water tankage vent filters (buses, trains, aircraft, etc.) now being applied per CDC, etc. recommendations are of this hydrophobic genre.

BTW - 'dust' in atmospheric air typically runs at 30,000 particles @ ~0,1µM per cubic foot.

;-)
 

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I agree the vent routed into the sink may not be the best idea. The vent that is at the top of the bulkhead only emits air though and is not an overflow. Any overflow exits through the manual pump into the sink(s).

Here is a pic showing the Swan 44 vents at the right corner of the sink.

 

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baDumbumbum
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We'll be putting a screen on ours. Save a cockroach! ;) Here's a thought to prevent overfilling, for those with internal vents: what about a ball-float check valve in the vent line? Air goes around the ball, but when water reaches it, the ball floats up & closes the vent. When dock hose starts spraying all over your Topsiders, the tank is full. Downside is it leaves the fill pipe with standing water in it. I'm still thinking a whistle might work better, but even then, you only have a few seconds to shut off the fill line.
 

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Discussion Starter #11
Original question; who has a water tank vent strainer or filter? I'm beginning to suspect they are rare.

Yes, I understand most water tanks are filled at atmospheric pressure. That is obvious.

I won't accept a system where I have to stay and watch. Fuel, yes, water, no way.

I'm not certain I believe that a membrane filter buys the bus folks any actual safety; I suspect it is about liabilty. On boats, unless we were to adopt true sanitarty practices--neither pratical by design nor practice--we wouldn't gain either. In the food packaging business the issues are very different.
 
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