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Old 03-31-2014, 06:24 PM   #1
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Mystery fresh water disappearance

I have an unusual situation and a theory...wanted to see if anyone else had a similar situation. We stayed in a COE campground for two weeks while helping a daughter move homes. Since we were gone every day from early to late, I turned the water off at the pump by dropping the handle, but did not disconnect the hose. One evening it was supposed to get below freezing, so I checked our fresh water tank before dropping the hose. The tank was nearly empty so I filled it 3/4 full, then dropped the hose, reconnecting it the next morning. Our fresh water tank was still nearly 3/4 full at that point. I dropped the handle when we left in the morning but left the hose connected. When we got home that evening the fresh water tank was nearly empty. I checked everywhere for leaks but couldn't find any evidence of one. We were parked on an asphalt pad, so I am pretty sure I would have seen evidence of a 25 gallon leak. No obvious leaks in the belly. I filled it up again and the same thing happened the next day. The third day I filled the tank, but dropped the hose while we were gone. No water loss..tank remained at the same level. No water loss for the remainder of the trip.

So my theory (and I know it is a stretch) is that dropping the handle created a vacuum that pulled water out of the tank. Weak...but it is the only thing that seems to work. Any other ideas?

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Old 03-31-2014, 06:34 PM   #2
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try it one more time, but stick around and watch what happens. Either it's siphoning back into the supply somehow, or it's leaving the tank some other way. If you're around you can discover how.

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Old 03-31-2014, 06:37 PM   #3
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Yes it does create a vacuum.
Those type of lawn/garden hydrants that many use in campgrounds where there are freezing temps are Really 2 valves in one.
What it is is this.
Just like the frost free house spigot. The valve is far away from a the handle.
This one is underground. That is why when you turn them on there is a quite a delay at getting water out.
When you shut one off as you close it it closes the hose to the water supply pipe FIRST then another little valve opens that lets the water in the top of the hydrant drain into the bottom under ground. by leaving the hose hooked up I bet is siphoned the water right out of your tank.
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Old 03-31-2014, 06:40 PM   #4
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If it is a frost free it will do just as you say. They drain under ground below the frost line and will continue to drain until the vacuum is broken, the drain is full or no water left. This is why you want anti siphon blocks on a well. The frost free will drain it back into the well.
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Old 03-31-2014, 07:10 PM   #5
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thanks for the confirmation! My wife was beginning to suspect a "senior moment"
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Old 03-31-2014, 08:13 PM   #6
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If you add a anti siphon valve hose bib that may correct the problem. If you google it you may come up with some pricey stuff, but I know home depot have some inexpensive ones that are on most new homes by code.

I may get one myself, I think I have had similar problem before.

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Old 03-31-2014, 08:40 PM   #7
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You could just get a y connector for your water hose that has shutoff valves attach your hose to one and when you shut off the hydrant just open the valve without a hose letting air into the hydrant. Simple and cheap.
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Old 04-01-2014, 09:07 AM   #8
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Originally Posted by tom2500 View Post
So my theory (and I know it is a stretch) is that dropping the handle created a vacuum that pulled water out of the tank. Weak...but it is the only thing that seems to work. Any other ideas?

Good theory, Bad check valve.

First: the handle you drop the valve is underground, perhaps 3 feet, It is a 2-way valve.. it connects the standpipe and outlet either to the water line (Main) or to open air (Drain) so that the water drains out of the fixture and nothing freezes This is a very common fixture on farms such as I was raised on and yes, we had them.

On your RV there is a check valve it is part of the inlet, and something kept it from closing or.. the vacuum was simply too great.

The solution #1

Install a vacuum breaker (Link below) before your hose

Solution 2: Make sure the check valve is not stuck open as well

Do both please

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Old 04-02-2014, 09:34 AM   #9
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FWIW - Quick fix

Sounds like weak spring or dirt in the check valve at the city hook up on your unit. After closing the park handle, you might be able to just walk inside, open a faucet & flip the pump on for a bit and slowly close the faucet to pressure up the system before you leave. Then turn the pump off. It should seat the check valve if it's just a spring.

(Had this happen on a 5er I once owned)
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Old 04-02-2014, 09:50 AM   #10
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Those hydrants are called a stop amd waste bury hydrant.. When you shut it off the water drains out at the bottom into the ground so it will not freeze. There is no way for the water to backflow into the well.

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