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Thread: Butterfly control valves on DCW

  1. #1
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    Butterfly control valves on DCW

    I have an interesting project where the consultant has a drain flushing system for a special area of the facility. Each zone is specified to have a 2" butterfly valve on a DCW line that feeds the drain piping to flush out the drains/plumbing for each section regularly. This is sort of similar to a typical trap primer system, but this is more to flush out all the piping not just prime traps.

    Has anyone seen butterfly valves used in this way to open/close a 75psi DCW line?

    We would be using the Belimo valves, and while I know they are rated for it, instinctively I feel more comfortable using ball valves. I feel they would last longer without leaking.

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  2. #2
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    Pressure rating is one thing, more importantly is material rating, be sure whatever you use is potable rated.

  3. #3
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    Quote Originally Posted by amigo View Post
    be sure whatever you use is potable rated.
    That was my first thought. The ENTIRE system needs to be potable rated. Copper pipe and fittings, no cast iron. Brass or bronze valves, pumps.... everything.
    What the heck are you doing that needs a flush like that?
    As for the valves, as long as they are potable rated they should be fine. They suck for control often, but you do not need control. Also they (likely???) Do not stroke too much as you are not flushing more than once per day (???). So wear shouldn't be horrible.
    Hmmmm....smells like numbatwo to me.

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    The biggest problem with throttling with BFV'S is they do 90% of the throttling within the first 10% open. Your application looks to be OK.
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    I don’t know that belimo has brass butterfly valves? Possibly stainless.


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  6. #6
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    Belimo has 2" balls now and maybe even bigger. Can't beat the close off pressure and I assume its two position duty so flow curves are not an issue.

    I also got notice in the last few weeks they have potable water rated valve line now. Didn't look at what they offer yet. Would look online or call them, they are new.
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  7. #7
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    Quote Originally Posted by WAYNE3298 View Post
    The biggest problem with throttling with BFV'S is they do 90% of the throttling within the first 10% open. Your application looks to be OK.
    Appears to be a common misconception of butterfly valve flow rate. Most butterfly valve vendors make a 0-60% butterfly valves for modulating control.

    https://youtu.be/wwFKn0EwvRQ

    They need to be sized right.

    kontrol out
    Last edited by kontrolphreak; 04-18-2021 at 10:50 PM.
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  8. #8
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    Thread Starter
    Thanks for the responses.

    It will be one stroke daily, no modulation required. They did not request potable water valves as they're being installed on a seperate DCW feed from the building potable water that has a backflow preventor upstream.

    My biggest concern about butterfly vs ball was the close off pressure. They are both rated for it, I was just curious if anyone had any long term experience with butterfly valves remaining able to tightly close off with something like 75psi on it. If it was a ball valve I wouldn't be concerned.

    If you're wondering what the use case is, this is an animal shelter and this will flush out the drain piping from all the floor drains for all the animal kennels. It's something like 4 kennels per valve.

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  9. #9
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    Ball valves would me more tolerant of debris or particles in the piping than butterfly valves, but 75 psi is not a big deal for the belimo butterfly valves. If there is a lot of crap buildup inside the piping than eventually the butterflys won't seal very well and will start leaking.

  10. #10
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    Quote Originally Posted by zzip7 View Post
    Thanks for the responses.

    It will be one stroke daily, no modulation required. They did not request potable water valves as they're being installed on a seperate DCW feed from the building potable water that has a backflow preventor upstream.

    My biggest concern about butterfly vs ball was the close off pressure. They are both rated for it, I was just curious if anyone had any long term experience with butterfly valves remaining able to tightly close off with something like 75psi on it. If it was a ball valve I wouldn't be concerned.

    If you're wondering what the use case is, this is an animal shelter and this will flush out the drain piping from all the floor drains for all the animal kennels. It's something like 4 kennels per valve.

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    I would be concerned, and I would be curious as to why butterflies were spec’d . I would ask the engineer his reasoning, then discuss ball valves with him.

  11. #11
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    zzip7,
    A ball valve will probably be better suited however I would be concerned with the size of the Drain Line !

    A 2" Belimo ball valve can deliver anywhere from 49 to 190+Cv (Cv= GPM at 1 PSI Delta P). I see a huge potential to flood some kennels here.

    If I had to SWAG this my guess would be that a 1" Valve will be better suited. Pose (RFI) this question (Drain Size and capicity) to the CE before this gets finalized.
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  12. #12
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    How many GPM can the drain handle? I would also opt for a ball valve. As part of a Cooling Tower replacement about 6 years ago we had the mechanical contractor replace a 4" butterfly valve on the DCW supply into the building that was Circa 1978. The butterfly had about 2" of turquoise colored calcium growth on it and wouldn't close off.
    To think that all of that had been going into the kitchen and the water fountains for decades really made you raise an eyebrow. This was in a facility that probably had over 500 employees. I would also put a PRV in and drop that PSI down to something more manageable.
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  13. #13
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    Quote Originally Posted by Cagey57 View Post
    I would be concerned with the size of the Drain Line !
    Kennel with this setup? Betting they have planed on flushing large amounts of junk without issue if they want 2" flush valves. Drains prob 2x this valve or more with special attention paid into the design.

    Would consult with Belimo on using any of their valves when closing off to atmosphere on the back side. Some are not suited for this.
    Last edited by orion242; 04-29-2021 at 09:13 PM.
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