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Old 04-24-2016, 07:59 PM   #1
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water tank check valve question

I recently installed a second fresh water tank and teed the two tanks together together with a common suction line to the pump. I discovered that for some reason the new rear tank drains into the original front tank and flows out the front tank fill port and on to the ground. The new rear tank does have its own fill and vent port. I want to put a SharkBite Pex check valve in each tank outlet line to eliminate this problem. The Sharkbite check valve needs at least 2psi to function. Does anybody know if the water tank pressure combined with the pump suction will overcome the check valve resistance? Thanks.
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Old 04-24-2016, 09:06 PM   #2
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The first problem will be getting the pump to prime. Even if you get it primed, I think you'll lose a good bit of flow through the system due to the spring pressure on the suction side of the pump.

Is the pump above or below the FW tanks?

Have you considered using a check valve with less cracking pressure? They make check valves with as low as 1/3rd psi cracking pressure.
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Old 04-24-2016, 09:12 PM   #3
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Instead of a check valve try a swing check. properly installed, there should be very little resistance for the pump to draw water through them.
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Old 04-24-2016, 09:22 PM   #4
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Thanks for the responses. The pump is above the tanks. I found even though I have lots of water in the front tank the pump won't prime because it is just sucking air through the vent of the empty rear tank. I think you are both correct about looking at a swing check instead of a spring type. I was just looking a Spears brand 1/2" swing check valve that opens at less than .5 psi. I think that is the way to go. Thanks again.
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Old 04-25-2016, 07:27 AM   #5
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Forget the check valves.

You need to bring a suction line from each tank to a 3 way valve so you can select which tank you are drawing from. This will solve both the issue you have sucking air from the empty tank and the siphoning issue from one tank to the other.

The issue I have seen with a two tank setup is too long of a suction line. Most pumps start have a problem pulling a prime after you go beyond 6' to 8'.
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Old 04-25-2016, 08:29 AM   #6
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I agree with Mr Havercamp, a 3-way valve or two 2-way valves will be a much better setup. The only way the connected suction setup would possibly work is if both tanks are at the same level and relatively close together. Apparently yours are not the same level or you would be emptying the one tank out the vent of the other tank.
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Old 04-25-2016, 09:17 AM   #7
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The tanks are at the same level, both are mounted between the frame rails, but the new rear tank holds about 10 gallons more which I believe starts the flow to the smaller front tank. Then a siphon effect is created and out the front fill port it goes. The pump does prime as before as long as there is water in both tanks. I already ordered swing check valves so I will try that first, otherwise I will go with a valve set-up. Ain't nothing ever easy!
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Old 04-25-2016, 09:32 AM   #8
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I think you're still going to have problems. Would go with 3 way valve and be done.
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