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Butterfly Valve to Cast Iron Strainer Inlet

Butterfly Valve to Cast Iron Strainer Inlet

Butterfly Valve to Cast Iron Strainer Inlet

I've attached a photo a Butterfly Valve being bolted to a Cast Iron Strainer - 8" Class 125 installation.

My concerns:

1. Turbulence - the butterfly valve is only rotated off by one bolt, so the load balance under flow as it feeds into the strainer won't be greatly affected. However, it is feeding directly into the inlet of a Y-strainer, basically a 45 degree elbow. What will this do to the strainer screen and butterfly disc loads?

2. Cracking Flange - flat face gaskets and A307 studs are recommended for cast iron flanges per ASME B16.1: With the ductile iron flange and ductile iron butterfly valve, plus the offset between bolts and point of contact with the butterfly valve face - how likely is this to damage the cast iron Y-strainer? I've seen butterfly valves bolted to cast iron flanges before, but I've also seen steel and cast iron flanges bolted together crack the cast iron flange.

Any comments are appreciated.

RE: Butterfly Valve to Cast Iron Strainer Inlet

1) I can't see much wroong with this, but it would be better not to have such a close coupling of the valve - can the BF disc fully rotate?

2) Cast iron will need a FF to FF set of sealing on the BF valve to avoid racking and also on the upstream flange so that the sealing force goes through the BF valve body.

The fact that two nuts are not connected looks odd and one nut looks half the thickness of the others??

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RE: Butterfly Valve to Cast Iron Strainer Inlet

With respect to the fasteners, I believe that these are SAE and the head of the bolt is thinner than the nut at the other end. With the way the strainer & valve bodies are manufactured, you won't be able to feed all the bolts in from the same side of the flanges.

RE: Butterfly Valve to Cast Iron Strainer Inlet

Is there a reason two studs don't have nuts?

RE: Butterfly Valve to Cast Iron Strainer Inlet

They were in the middle of trying to install and found out they can't get around the belly of the strainer with the studs projecting.
Needed to pull the assembly apart to get them in place, and thread it all back together.
Neither strainer nor butterfly valve literature recommends this configuration, but....

RE: Butterfly Valve to Cast Iron Strainer Inlet

also, one may verify the proper installation to have the bolting with fully engagement of all the thread of the nuts.

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