OS&Y Valves NFPA requirement

[wfjer]

Hi,

According to NFPA 20, section 2-9.5:
"A listed outside screw and yoke (OS&Y) gate valve shall be installed in the suction pipe. No valve other than a listed OS&Y valve shall be installed in the suction pipe within 50 ft (16 m) of the pump suction flange."

I was wondering why there is not a similar requirement for discharge pipes and OS&Y valves in section 2-10, as a manner to instantly know if such pipe is open or closed.

Maybe somebody can clarify me the purpose of this part of the code, and if it´s a good idea to install OS&Y valves in discharge pipes.

Thanks.

 

[TravisMack]

It is my understanding that you do not want anything causing non laminar flow. The other commonly used valve is a butterfly valve which has the vane in the waterway at all times. An OS&Y gate valve does not have anything in the waterway.

You are required to have an indicating valve. A butterfly valve is an indicating valve. You can tell if it is open or closed as soon as you look at it.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[NJ1]

There have being incidents on which a butterfly valve was installed and when th pump activated the flapper on the butterfly did not fully open causing the piping and valve to cavitate. This will not happend with the OS&Y valve.
This requirement has being in the code for quite some time now. I have seen incidents where the spacing in the fire pump room did not allowed for an OS&Y screw yolk type valve and a butterfly was installed. Not a good practice.
You also have the stainer distance requirement 10 times pipe diameter away from suction.

 

[spkreng]

In the discharge piping there is no worry about turbulence in the water flow (which affects the suction side - impeller) so any listed indicating valve will do, same with the bypass, test header, etc.

spkreng, CET

 

[rconner]

Mr. Mack, I have enjoyed your wisdom/experience in these blogs. Just a fine point or question concerning your statement “A butterfly valve is an indicating valve…” in your preceding post (that was of course responding to this thread in which “OS&Y” gate valves had previously been mentioned);

I guess this can be argued as being true (sort of like the clear the visual indication of an OS&Y valve) if the butterfly valve (BFV) were simply a small lever operated flap-type valve, wherein the alignment/position of the normally relatively large lever (like with most ball valves) relative to the axis of the pipeline tells (at least someone with minimal experience) whether the valve is open or closed. I think also “Open/Closed” smaller indicator sort of lever-like dials, that I guess most often extend straight up rigidly from some BFV shafts through to the outside of the operator case, are available for some handwheel operated BFV’s to essentially give a visual indication if one looks close enough.

However, as a blanket statement I do not believe ALL butterfly valves per se (e.g. those with just plain Jane wrench nut or maybe some other operators without a separate/ accessory indicator post) necessarily provide "indicating" feature.