Fresh water tank vent location options - Page 2 - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 10-18-2010
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Quote:
Originally Posted by Sabreman View Post
All the descriptions make sense, but now I'm confused. Like josrulz, my vent is in the anchor well which definitely gets wet. While quite a bit higher than the tanks and faucets, I now wonder why I don't receive any contamination. Perhaps the vent is a one-way valve. That's the only explanation that makes sense to me.
Hi Sabreman, if your set up is like mine (good chance it is), the vent is like a holding tank vent high on the bulkhead of the anchor locker. Although the locker gets wet inside, the vent is aimed down, so to get sea water in it, the anchor locker would have to literally fill up.

I don't know if I'm going to re-run it, but if I do, I like the sink location idea.
-J
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Old 10-18-2010
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Jos,

My two tanks each have their own vent. The vent hoses are led to a thru-hull vent located just below the toerail. Port to port and starboard to starboard, naturally, and positioned roughly below the fresh water deck fill. The same for the holding tank, a vent of its own located just under the toerail on the port side.

Works great.
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Old 10-18-2010
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In most 'sanitary' systems the vent discharges to the HIGHEST part of the system ..... and is protected by a 'bio-blocking' filter. This is to protect the entire system from aspiration of biological spores, spores that are bacterial, or fungal. Mildew (fungal) spores are the most prevalent contamination to a boat's water tankage, many of these are very toxic or dangerous especially to one with a weakened immune system.

The vent filter can be a commercial/industrial 'capsule' filter made from hydrophobic/teflonic membrane @ 0,2µM (100% - absolute) retention and approx. 1-2 sq. ft. surface area and mwith 3/8 or 1/2" hose barb connectors. These are available from those filter suppliers/distributors who serve the bio-pharm industry. Approx. $75-100 ea.
If thats too much $$$ then take a fist sized 'wad' of bandage cotton placed over the terminal end of the vent tube, cover with bandage gauze, and tape in place. Keep dry and change every 6-12 months. The vent filter is always at the 'highest' elevation in the entire system.

Suggest you inspect and visualize the vent line 'all-the-way-to-the-tank'. 99% of the time such an unprotected vent line will contain massive colonies of bacteria/mold/mildew, etc. .... and 99% of the time this is why your tank eventually become totally fouled with biological growth. Typically if the vent hasnt been protected it usually needs replacement if not 'totally' free of discoloration/growth. To a microbiologist, most boat water tank 'vent systems are cause for projectile vomiting.
;-)

Last edited by RichH; 10-18-2010 at 07:22 PM.
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Old 10-21-2010
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Quote:
Suggest you inspect and visualize the vent line 'all-the-way-to-the-tank'. 99% of the time such an unprotected vent line will contain massive colonies of bacteria/mold/mildew, etc.
Excellent idea.

I like the sink location too.
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Old 10-21-2010
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Quote:
Originally Posted by Sabreman View Post
I like the sink location too.
Not a good idea, too close to 'food, etc. contamination' and the bacteria, etc. then enter the tankage by 'retrograde' movement from the 'sink' area TO the tank.

If you had a portable drinking water container, would you leave the lid off or keep it in/near your 'sink'? Dont think so once you saw or realized the quickly growing bacteria colonies (slime) that form on the inside walls of the container.
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Old 03-26-2011
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Rich,

I was reading forums on how to keep water tanks clean and came across your suggestion here to put a hydrophobic vent filter on the tank vent line. That makes a lot of sense.

I've searched extensively for this product and it's hard to find. There's a whole class of vent filters for the lab market (Pall Acro 50, Millipore Aervent), but their filter size is way below the 1-2 ft^2 you recommended (20 cm^2). One claims 27L/min air flow, which seems marginal assuming say, a ~5 gpm fill if I've done my math right.

The only filters I've found larger seem to be aimed at massive tanks for the beverage industry and cost in the thousands. I'd consider up to about $100. Any suggestions for brand / model / where to buy?

Thanks!
- Craig
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Old 03-26-2011
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What you want is slightly larger than the 50mm. Pall, Millipore, Parker Advanced, Meissner, Whatman, etc. all make 'capsules' of 1 sq. ft. of membrane surface area ... abut "fist" sized and come with hose barb connectors. Suggest you contact a 'distributor' not 'direct w/ mfgr' and sweet talk them into omitting the minimum charges / minimum qty, etc. that usually apply. Also you dont need a 'sterile' system filter, just a 'log reduction' value (LRV) @ 0,2µM, hydrophobic teflon or equivalent membrane. an example: Single-Use Capsule Filters - Meissner Filtration Products

Failing to obtain one from an ethical mfg., just take a fist sized wad of loose bandage cotton held in place with bandage gauze and a minimum of bandage tape to hold in place on a hose end; keep dry and change-out at least every 12 months. That will keep all the 'spores' out of the tank ... but tank, vent and distribution lines, etc. still needs to be 'shock sanitized' yearly with clorox, etc . at ~40 oz. clorox per 100 gallons for 1-2 hours.
When you open the tank's inspection port, reach in and feel 'slimey stuff' (bacteria, etc.) on the tank walls, then you need to 'scrub out' the tank, etc. before sanitizing.
;-)

Last edited by RichH; 03-26-2011 at 10:54 AM.
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Old 07-05-2014
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Re: Fresh water tank vent location options

Is there any reason one could not use say a 1 micron 10" standard sediment water filter instead of these "capsule filters"? The same kind of filter used in under the sink filters for water consumption? Yes one would have to add some adapters to the filter housing but the advantage is standard filter, reasonable cost and available at big box stores.
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Last edited by Captainmeme; 07-05-2014 at 08:38 PM.
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Old 07-06-2014
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Re: Fresh water tank vent location options

My Tartan 27's fresh water tank vents inside the anchor locker, FWIW.

SKywalker
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Old 07-06-2014
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Re: Fresh water tank vent location options

I know that the original thread is from 2010, but since it was warmed up I came across it and don't think I saw in any of the replies a mention of a bend to allow venting overboard. Granted, venting inboard is best, but if I have a bend that brings the hose up as high as possible under the deck, I would think that should suffice. I never thought about a bio filter on that line. How is that different from air that gets into the system from other sources (e.g., while repairing stuff)? I always though it would be enough to add chlorine to the tank while filling after an initial shock treatment.
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