Venting the fresh water tank

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Venting the fresh water tank

Postby dh » Sat Apr 30, 2011 11:00 am

I just assumed that the fresh water tank vented through the fill tube, but I got my gravity fill inlet today and it has 3/8'' barb for a vent. Do I need a seperate vent if the fill tube goes to the top of the holding tank?
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Postby S. Heisley » Sat Apr 30, 2011 12:06 pm

I would. The instructions that came with mine said to. It will definitely make the water flow easier, for filling, draining, and sink usage. Here's a picture of how I did mine. (Because I am using such a small space and the hose tended to crimp, I used CPVC elbow connections at the bends, glued with CPVC pipe glue. I used screw connectors on all but the air vent. It has the round black squeeze ring on it. The drain tube is mounted on the back end of the tank but you can't see it in this picture. There is a picture of that in my album.)

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Postby 48Rob » Sat Apr 30, 2011 12:23 pm

Yes, you need to connect a separate tube from a port near the top of your tank, and connect it to the barbed fitting on the gravity fill.

Without a separate vent, the water pump can collapse your tank.

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Postby dh » Sun May 01, 2011 10:55 am

Rob, no offence, but I would love to see a diaphram pump collaps a 6'' schedual 80 PVC pipe. All jokes aside, the tank won't pull in air through the fill tube?
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Postby 48Rob » Sun May 01, 2011 12:12 pm

DH,

None taken! :lol:

I don't know about a schedule 80 PVC tank, but in another camper I built, I once forgot to open the vent tube (I had a shutoff on it for travel and storage) the pump sounded like it was laboring, so I checked the RV fresh water tank, and found it quite distorted!..
I did have a sealed fresh water fill port, which contributed to the collapse...

When you fill your fresh water tank, the fill tube will be full of water.
The air in the tank will have no where to go.
Having a separate vent will allow the tank to fill much faster without burping and spitting water back out the fill tube.
You can fill without a vent, but it must be done very slowly.
It may be overkill, but I prefer to have fresher air from inside the trailer be drawn into the tank to replace the water, than whatever might be in the air outside the trailer (dust, bug spray, smoke, etc.)

It is possible over time, for your fill tube to be crushed or deteriorate allowing the pump to pull it completely closed, again threatening the tank.

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Postby dh » Sun May 01, 2011 3:00 pm

That makes sence. I always had a problem with how open the fill ports on the holding tanks were on the older campers, I don't know if venting inside the camper would work in my build, but what about usind a fuel filter in line to filter out whatever gets drawn into the vent from the outside?
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Postby Larwyn » Sun May 01, 2011 3:24 pm

A filter of some sort (a bit of sponge or scotchbright pad) might help keep bugs and such out of the tank. I guess if you wanted to get carried away with the idea you could use a respirator filter to clean the air that must enter the tank as the water level drops. I have never used one though.

If the filler neck is short and straight enough that you can get the end of the hose down to the tank itself a separate vent would not be necessary for filling the tank but there will have to be some way for air (or water) to enter the tank as the water level falls, or exit as the water level rises. A separate protected vent and a secure sealed water inlet seems like a big step toward keeping the water in the tank fresh and clean. :thumbsup:
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Postby slowcowboy » Sun May 01, 2011 3:55 pm

just listening in folks would the vent line be bettor if it was connected to the fill port with a tee?


I have used mine and have poured water in with the one vent port closed.

I have a cap shoved into a treaded fitting hole on the the top of my tank.

some times I have opened it and some times I forgot and just left the cap in place.

would it be best to connect it to the fill line. or just some place on the outside of the camper? maybee like a breather line on a tranny or atv or something like.

might be a way to run the vent line to a drain valve under the frame of the trailer and just leave the drain line open just enough to let air to escape and to keep most bugs out.

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Postby slowcowboy » Sun May 01, 2011 4:05 pm

also for the tread. my gravity fill port has no vent opening and has just one main large 1 inch and a 14 drain pipe.

also I don't think a manaul hand pump would collaspe a abs black plastic tank that is a lot stoughter and not as flexalble as the white plastic tanks other rvs are carrying them things bend in and bulge when you put water in them the plastic is quite thin on them.

I can see the value of a vent line though and I am thinking running it to something on the frame for a filter as my fresh water tank is mounted under the flour of my teardrop and is like a gas tank mouted underneath the frame.

I am going to see what I can dream up for a filter.

I would have no problem with a bug if it did get my tank as I don' t drink the water out of my fresh water tank and only wash dishes and cook with it.

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Postby slowcowboy » Sun May 01, 2011 4:07 pm

aslo one other dumb piece of information but if bugs and dirt are going up your vent line into your water tank they do make a non expenseve in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.

the rv catallogs carry them. slowcowboy.
Plans. there was supposed to be plans to be followed when I built this thing. Opps! AH, gee, tum,tee tum. I think I forgot about the plans 2 years ago. ------Tow vehicles, 1995 ford explore, 1994 ford ranger, 1993 ford F-150, 2009 4x9 Off road teardrop, on harbor freight greatly modified frame.
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Postby slowcowboy » Sun May 01, 2011 4:07 pm

aslo one other dumb piece of information but if bugs and dirt are going up your vent line into your water tank they do make a non expenseve in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.

the rv catallogs carry them. slowcowboy.
Plans. there was supposed to be plans to be followed when I built this thing. Opps! AH, gee, tum,tee tum. I think I forgot about the plans 2 years ago. ------Tow vehicles, 1995 ford explore, 1994 ford ranger, 1993 ford F-150, 2009 4x9 Off road teardrop, on harbor freight greatly modified frame.
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Postby slowcowboy » Sun May 01, 2011 4:07 pm

aslo one other dumb piece of information but if bugs and dirt are going up your vent line into your water tank they do make a non expenseve in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.

the rv catallogs carry them. slowcowboy.
Plans. there was supposed to be plans to be followed when I built this thing. Opps! AH, gee, tum,tee tum. I think I forgot about the plans 2 years ago. ------Tow vehicles, 1995 ford explore, 1994 ford ranger, 1993 ford F-150, 2009 4x9 Off road teardrop, on harbor freight greatly modified frame.
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Postby Corwin C » Sun May 01, 2011 4:15 pm

A vent is a definite must. I watched a 2500 gallon steel diesel tank crush itself because the vent didn't get opened and it was simply gravity feeding into an underground tank through a 4" hose about 6' long. Air pressure has a funny way of being a whole lot of force. At 14 psi (sea level air pressure) a 12" x 12" side of a water tank would have to withstand over a ton of crushing force. A 40 psi water pump has the capability of producing almost 3 times that much force.

An extreme example...
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Postby 48Rob » Sun May 01, 2011 5:21 pm

Corwin,

That is a cool video! :thumbsup:

Though I know different, the tanker looks no stronger than an aluminum can...

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Postby 48Rob » Sun May 01, 2011 5:40 pm

I can see the value of a vent line though and I am thinking running it to something on the frame for a filter as my fresh water tank is mounted under the flour of my teardrop and is like a gas tank mounted underneath the frame.


if bugs and dirt are going up your vent line into your water tank they do make a non expensive in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.


Mr. Cowboy,

A vent terminating just above your tank will help, but you will likely be much better off to have it a couple feet above the top of the tank.
A vent lower than that will allow water to slosh out.
A vent opening under the trailer would also invite road spray during a rainstorm, and anything else that is kicked up on a dusty road to make its way into your tank.

A filter is a good idea, but it is generally much preferred, and safer, to be sure only safe water gets into your tank to start with, via the fill port or vent, as once contaminants enter the tank, the tank itself is no longer "safe" for water storage, and bugs and junk can foul the pump and faucets/aerators.
Yes you can sanitize the tank, and no, a few bugs won't hurt you, but most folks would rather have clear clean water...
A filter on the incoming end of the air vent would be the easiest way to avoid problems.
I have a double layer of copper screen wire, and a piece of cotton cloth on mine, which is inside the trailer, to prevent bugs and dust from entering.
I guess I could get more serious and hook up some super filter, but bugs and dust are my only concerns.

Rob
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