Why two check valves?


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Old 08-15-22, 08:15 PM
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Why two check valves?

I'll be installing a Big Blue whole house sediment filter in my girlfriend's house in the next week or so and noticed that not only is there a check valve on the main feed coming into the house from the well (prior to the pressure tank), but also another check valve (a dual check valve) just prior to the inlet of the acid neutralizer cylinder six feet away. I'm confused as to why a check valve would be needed here. Can I remove it?
 
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Old 08-15-22, 08:19 PM
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The valve before the pressure tank keeps the line down to the pump primed.
I'm wondering if that second valve keeps water from the filter getting back into the piping.
 
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Old 08-15-22, 08:33 PM
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Here's a pic with both CV's circled. Not sure why there would need to be backflow prevention on the acid neutralizer inlet.




A related question, the pressure tank shown is 14 years old. Should I go ahead and replace it or wait until it fails?
 
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Old 08-16-22, 05:09 AM
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I could understand a check valve on the neutralizer to prevent it's contents from backing up into the water supply line. I think the check valve in front of the pressure tank is redundant tooth.

The pressure tank at my house is over 21 years old and still works properly so I wouldn't remove your 12 year old one unless it has failed. Plus, they are rather expensive right now so I'd get as much life out of the old one as possible.
 
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Old 08-16-22, 07:14 AM
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My understanding was that the first check valve prevents the pressure tank from pushing water back into the main line when the well pump is off. Is this not the case? And why would it matter if water from the neutralizer back flowed into the feed line? Same thing would happen without a neutralizer.
 
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Old 08-16-22, 01:18 PM
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M -

I can’t see the pictures (looks like an infinite loading loop) but if you have an upflow Acid Neutralizer then maybe someone thought a check valve would prevent the neutralizer material from ever going back into the pressure tank. I have a downflow Neutralizer (it does a backwash and needs a drain).

I believe that because of the way the upflow works, material can leave the tank. I think that some people put a filter downstream from the upflow filter to catch any loosened material. I guess it makes more sense that you would be more worried about material going into your home and appliances so a filter after the Neutralizer would make sense.

Your setup is puzzling.

(What - now I see the pictures?????)

Are you sure that's a check valve? Could it be a chemical injection fitting? Just wild guesses!
 
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Old 08-16-22, 01:31 PM
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Wells contain a check valve down at the bottom of the well. So, additional check valves are not needed. Some people will install another one above ground like yours so they don't have to pull the well for a proper repair.
 
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Old 08-16-22, 02:44 PM
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Yep. That happened to me. There was a check valve at the tank and sure enough it was masking a leaky service pipe. Until the leak got bad enough so that the pressure tank couldn’t be pumped up to switch cutoff – I never knew there was a problem.

I just noticed there is in fact a valve on the tank. I think that means it’s not an upflow filter. Those don’t need a valve. But I don’t see a drain line from the valve for backwashing. Is it possible it’s not an AN Filter? But still – I guess that wouldn’t be a reason for a check valve. Unless it is in fact really some other device.

(Just noticed the tank has a note "Raw ph= 6 Top Screen" - so I guess it is for treating low ph. )
 

Last edited by zoesdad; 08-16-22 at 04:44 PM. Reason: "Just noticed ...
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Old 08-16-22, 07:17 PM
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"Dual check" is printed on the side:





It's a downflow filter and has a drain line to the outside.

One more question to add into the mix, how do I detach the filter head from the bypass valve? Unscrew the two small screws on either side and pull the head forward/away from the valve?




 
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Old 08-17-22, 10:31 AM
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M -

Itís been years since I installed mine, and I have never taken the bypass valve off of the tank. But if I remember correctly those 2 screws you point to are all that fastens the bypass valve to the filter head. Iím almost 100% sure, because when I installed mine I was worrying if just tightening those 2 screws would make a watertight connection. But they did. So I think you are right.

That double check valve there seems very strange. I looked at whole lot of installation diagrams before I installed mine, and I never saw anyone indicate you need a check valve at the input to the filter.
 
 

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