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Thread: Swing Check vs. dual check vs. double check valve

  1. #1
    DIY Junior Member colbymom's Avatar
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    Default Swing Check vs. dual check vs. double check valve

    Hi and thanks in advance for the great info I've already gotten off this forum!

    I recently had a steam shower generator installed. At the rough in inspection, the inspector said that I needed a dual check valve in the line that connects the autoflush drain from the generator, which is gravity fed not pumped, to the DWV. The way the line is plumbed is from the generator with 1/2" copper to the PVC shower drain
    pipe before the shower trap.

    The plumber insists that I don't need a dual check valve, and installed a swing check valve. The plumber also thinks that a dual check valve may cause my steam generator to malfunction. I've called the maker of the steam unit and technical support there was not much help.

    Can somebody please tell me what to do. Who's right - the plumber or the inspector? Can you explain how each of these valves work so that I can weigh in during the next rough-in inspection?

    Thanks for your help!
    Maria

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    First off, what does the manufacturer's printed instructions say with regards to this? Code typically says 'install per manufacturer's instructions'.

    Barring that, the inspector has the final say, and unless you can point out code that says it is not required, he wins.

    Let the pros weigh in based on common practice.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Master Plumber Redwood's Avatar
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    I find it to be a good practice not to butt heads with an inspector!

    I have discussed how to do something and pointed out what my point was and at times he agreed to my point and at times he didn't....

    In the end I installed what he said to install and the job passed...

    Sounds like your plumber might be head strong...
    Good luck on the inspection!

  4. #4
    DIY Junior Member colbymom's Avatar
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    Yes, it's true I'll let the inspector win in the end. However, I'd like to know the correct thing to do.

    The unit does say install according to manufacturers instructions, however it doesn't mention valves in the autoflush line at all. It leaves all the plumbing up to a licensed plumber. I have two licensed plumbers who disagree on the best way to handle this. What is at stake is the operation of the somewhat expensive steam unit. Yes it's covered under warranty, but not if it is installed incorrectly. I'm also not one of those people who says, "oh I'll just sue somebody later if it's done wrong."

    It seems that both these valves will prevent DWV water from backing up into the generator, which is what everyone is worried about. One valve does it with a swinging arm that is forced to close under flow in the wrong direction. No problems with water flowing in the line in the correct direction. As I understand it, the dual check is spring operated, by what looks like a drop in pressure in the autoflush line. However, the autoflush line is not ever under pressure as the potable supply line is. The air pressure in the autoflush is that of whatever vents the line. The water pressure, when water is allowed to drain, is rho*g*h + ambient pressure. What plumber #1 is worried about is that the dual check might close and stay closed causing the unit not to drain or start to drain and then close. Is that even possible?

    Can anybody explain the dual check better or enlighten me on the pressure that causes the dual check to operate or what might cause my steam unit to malfunction? If I'm totally missing the point, I'd appreciate an explanation of the correct thinking.

    Thanks!
    Maria

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default check

    The dual check has an integral air gap which may be why he wants that particular valve. If we saw how the autoflush is plumbed it might make it more logical. It is spring loaded so it will take a certain amount of pressure to open it.

  6. #6
    DIY Junior Member colbymom's Avatar
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    Thanks! I've attached my quick sketch of the plumbing I have seen with my own eyes. I know that pipe size and angles are important to plumbers, but this is just a sketch and doesn't represent that stuff. I you need more info about that stuff I can write it.
    Attached Images Attached Images  
    Maria

  7. #7
    In the Trades SacCity's Avatar
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    Nice sketch!
    As installed you have about 6 feet of head pressure which is about 3 psi
    3 psi should be enough to open both check valves
    Michael

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    In the Trades Tom Sawyer's Avatar
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    You need a dual check with intermediate vent there. The set up presents the possibility of a backflow situation. The inspector is correct and the plumber that says no needs to go back to school.

  9. #9
    Plumber jimbo's Avatar
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    When we are talking about backflow, I don't think a single swing check is ever an approved solution. I would consult a licensed backflow prevention company if you want better info, because hopefully they have attended "Backflow Univ"

  10. #10
    DIY Senior Member Smooky's Avatar
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    You could use something like a Watts #7 dual spring check. They have diagrams on their web site. Another option would be to create an air gap. It might be possible to pipe this auto flush line into the shower just below where the steam line enters the shower.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    The autoflush MAY operate while there is still steam pressure in the unit, in which case it will be adequate to operate a double check valve. The few I have worked on have the drain going outside into a planter area, because you are NOT supposed to discharge "superhot" water directly into the drain system, and DEFINITELY NOT into an open shower drain where hot water under pressure could splash up and burn the user. But a better way, if it can be done depending on what is behind the wall would be an indirect connection using an air gap, similar to a washing machine drain.
    Last edited by hj; 05-07-2011 at 08:05 AM.

  12. #12
    In the Trades Tom Sawyer's Avatar
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    I've seen one piped into the drain upstream of the water closet. Melted the wax ring

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    In the Trades Jerome2877's Avatar
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    You could use something like a Watts #7 dual spring check. They have diagrams on their web site. Another option would be to create an air gap. It might be possible to pipe this auto flush line into the shower just below where the steam line enters the shower.
    A cross connection between potable water and a sewer can not be directly connected. This would require an air gap unless the appliance already has one.

  14. #14
    Moderator & Master Plumber hj's Avatar
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    A steam unit is NOT potable water.

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    In the Trades Tom Sawyer's Avatar
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    where does it get it's supply?

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