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Old 10-09-2015, 09:21 AM   #1
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Suction line from fresh water tank

What is the purpose of the poly line that is teed into the suction line from the fresh water tank to the water pump?

I replaced a leaking screen filter and all fresh water hoses and now the pump will not pump a normal water stream. The faucets start out okay and over a minute or two turn to mostly air. I pulled out the pump and primed it and it discharged. A steady stream of water into a bucket. After reinstalling the pump, the same sucking air problem occurs.

Can I block off the poly line as I think that is how air is getting onto the suction line?

Thanks for any help as we are stumped.

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Old 10-09-2015, 09:37 AM   #2
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It's for putting in antifreeze. It should have a valve to close it off.

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Old 10-09-2015, 09:43 AM   #3
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Originally Posted by nrgtrakr View Post
It's for putting in antifreeze. It should have a valve to close it off.
And it was added by a previous owner, not original from Airstream. So it is hard to say where it goes and where the shut off valve might be.
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Old 10-09-2015, 11:10 AM   #4
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if it is an anti freeze draw line it most likely will have a cap on the end as apposed to a valve.

You are sucking air if the pump loses flow. Make sure that draw line is sealed at the end and all connection from the tank to the pump are tight. If you have Auto Fill make sure it is turned off. If there is a filter make sure is sealed.

About the only way you can check a suction line is to seal the pick up end and back feed it with pressure. Not easy with the tip in the tank However you could cut the line as close to the tank as you can get and seal it there to run a test from the pump back.

You have already tested the pump for leaks when you drew water from a bucket.
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Old 10-09-2015, 12:08 PM   #5
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If the above tests fail, it is also possible that the tank vent is plugged. If no air can get into the tank as water is being pumped out the pump will stop delivering water. It could also collapse your tank.
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Old 10-10-2015, 11:15 AM   #6
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As a new owner I recently installed a Camco t-valve at the pump inlet adjacent to the filter you described in order to make it easy to pump antifreeze into the system. The poly tube inserts into the 1 gal container of antifreeze and tge valve turned accordingly. You may see such a valve if the previous owner installed a similar system.
"Having differences makes a difference"
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Old 10-11-2015, 12:35 AM   #7
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In my experience and Airstream Service's recommendation I have found that pump by-pass systems reduce water pressure and flow to the outlets because of the added smaller diameter fittings. Also you can not use Shark fittings because they are designed for pressure not vacuum and will suck air when trying to seat. Rather than the by-pass kit, I took a length of polly hose, put a valve in it, then added a pump inlet fitting on one end, then stick the other in anti-freeze and pump away. If access is a problem, add a marine deck plate, and cover, 10" dia., to the floor above your pump. Then you do not have to move a whole shelf or floor of thing to get to the system.
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Old 10-11-2015, 10:40 PM   #8
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Guskmg's comment may explain why I observed sputtering at the faucets while pumping antifreeze ftom the gallon jug, which I attributed to the fact that I had already drained the system and used compressed air to clear the lines.

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