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Is there a reason why OS&Y would be better on backflow preventers for fire suppression systems over butterfly valves?
One application where we often must use the OS&Y is when the backflow serves a fire pump and we don't want to distort the flow and cause cavitation at the pump - but otherwise the butterfly valves are a major space saver. Just curious if others feel differently or if I'm missing a major benefit to the OS&Y type. Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
6 Comments
Rusty Scott
6/17/2019 10:29:52 am
These are just my thoughts and don't have any real backing but most of the backflow preventers that have been submitted to me that had the butterfly isolation type (our specifications call for OS&Y type) the components appeared to have a lot of plastic components which as an engineer makes me hesitate. The name brands also tend to be of companies I've never heard of and for the main shutoff to the building I would not want it to be plastic component based. As an engineer you are protecting the client and we deal with a large variety of contractors that seem to be more concerned with saving on cost, labor, and easy of install since their contract prices are locked. Let me put it this way, I do specify the butterfly type but have allowed it on low budget projects after expressing the concerns to the owner/architect. Also I think if you have a butterfly type and a fire pump, it is required to be 50 ft from the suction flange of the pump. 10 pipe diameters away if its OS&Y type.
Rusty Scott
6/17/2019 12:09:32 pm
Correct on my poor typing skills, *"I DON'T specify the butterfly type"*
Jevarajan
10/7/2020 12:45:44 pm
Can show which clause stating 10 pipe diameter for OS&Y gate valve.
Paul
6/17/2019 11:18:37 am
Interesting perspective from Rusty's side, being on the design-build side I have heard it is because Consultants/Engineers don't trust them (furthering Rusty's point). He is also correct as far as the 50 ft rule (NFPA 20 ('16): 4.15.5.1).
Cordell Beache
6/17/2019 07:57:43 pm
The OS&Y gate valve on the backflow device should never be used as the OS&Y valve on the suction side of the fire pump. The backflow device must be located a minimum of ten pipe diameters from the suction flange of the fire pump. If a backflow device is required I would recommend using a device with OS&Y valves rather than butterfly valves to reduce any turbulence in the suction pipe.
Anonymous
6/18/2019 10:36:58 am
Good question. Aside from fire pump applications, FWIW, personally, I prefer butterfly valve backflows for savings including in weight, size, and ease of installation, if the assembly has gone through the rigid USC testing. One argument I have heard for OS&Y is that it's easier to swap out or repair an OS&Y tamper switch without taking the system out of service than to repair a backflow butterfly valve. But how often have you seen a butterfly valve that is rarely operated fail? OS&Y tampers on the other hand can get knocked out of adjustment. Butterfly valves, though a special valve that one cannot purchase separately (and should not swap out from a listed assembly anyway) are serviceable/repairable. (Vault locations in areas prone to water infiltration I would still use OS&Y to raise the tamper higher.) So my personal opinion is that for in-building applications, the industry standard has shifted to butterfly valves, and at least in my local area, that is what is commonly stocked. I have colleagues in strong disagreement with this however, and specs are slow to evolve. Leave a Reply. |
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