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Old 10-19-2014, 10:33 PM   #1
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Mantua , Ohio
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New pump and tank questions

I want to change out this old 20 gal Galv. tank for a new 20 to 35gal plastic tank and at the same time put a new pump in.
This might sound stupid, but basically I will just use a compressor to pressurize the tank? The existing pump/compressor appears to be 12 volt, so that I would assume is the ONLY way to go so I can use batteries to have water?
I don't understand how the existing system works as there is only one inlet for water. Or did they just let the tank fill and use that as the pressure?
I think I'd rather put some valves in and just by pass the tank. Would that make any sense, instead of having to fill the tank? How are new units setup?
Thanks for any input!
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Old 10-19-2014, 10:46 PM   #2
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I don't know what Airstream model you have, but the old ones which used a galvanized tank and air compressor system worked like this: The tank was filled with water and caped off. The air compressor added air to about 40 psi and that forced the water out of the tank and to the faucets.

Modern systems using a plastic tank are not pressurized that way, it would explode the tank. When you put a plastic tank in, you will change to a demand pump which draws water from the tank (not under pressure) and pressurizes it. When a faucet is opened, the decrease in pressure starts the pump automatically. When the faucet is shut off, the pump has a pressure switch which shuts the pump off. These pumps cost $75 to $150 and operate on 12 volts.

To use city water on the system, you put an inlet hose connection with a check valve into the line between the pump and the faucets. The pump will not allow water to back up into the tank, as it has a one way valve built into it. The check valve on the new city water inlet keeps the water from flowing out of it.

Does that make any sense to you? Hope so. Ask more if you need to.
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Old 10-20-2014, 09:01 AM   #3
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LOTS of sense!
Except where and why the check valve and hose connections go?
Is there one or two "Hose connections"?
Sorry to sound so stupid on this subject. And THANKS for your help!
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Old 10-20-2014, 10:29 AM   #4
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You will fill your water tank with a connection to the new tank and gravity. The tank connection is usually about 1.5 inches in diameter and the exterior inlet is a plastic part which recesses into the trailer wall and has a cap over the end, and often a little lockable door so it is only accessible by you. They are available at any decent sized RV parts place. They also will have a smaller vent tube nipple which must be connected to the new water tank so it will vent air out as you put the water in. You fill the tank with a hose, but it is not screwed into the new tank inlet, gravity does the job. This is so you don't pressurize the plastic tank, which would break it.

The city water connection usually, but not always, has a check valve built into it. There are several types available, again go to a good sized RV parts place and see which one works best for you. Then look to see that it has a built in check valve. That check valve prevents the new internal pump you install from simply forcing water out the city water inlet. This city water inlet is going to have a 1/2 or 3/4 inch threaded outlet so it can attach directly to the pressurized pipes inside the trailer. It will also have a hose connection on the outside, so a hose can be screwed directly into it running full city water pressure.
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Old 10-21-2014, 05:49 PM   #5
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related question...
can the pump be put in series or in parallel? does it ruin it to have it in series when using shore water?
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Old 10-21-2014, 07:13 PM   #6
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The city water should be connected to the plumbing downstream from the pump. In other words, on the discharge side.
It can be connected virtually anywhere in the cold water line.


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Old 10-21-2014, 09:40 PM   #7
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I see, I see said the slow guy...
A simple google produced this drawing, which now makes PERFECT sense to me...
So this is what you meant... TWO check-valves... I got it now.
Here is the pic that made me understand in seconds.
Water, Water, Everywhere!
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Old 10-22-2014, 11:54 AM   #8
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See how smart you can get quick? Google is almost as fun as asking on the Forums, but we like to post too. Thats how you become a rivet master, just post on and on and on ......

Anyway, glad you are up to speed now. We probably didn't slow you down more than a day or two... LOL.
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Old 03-11-2015, 12:54 AM   #9
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Thanks for the link studioman I have been reading the forum for a few nights looking for this info.
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