Cast Iron Valve to PVC Pipe

[p6g2p6]

Hi, I need to connect a 4" cast iron valve to PVC pipe. The cast iron valve has ASME class 125 flanges at both ends. I was thinking of using a PVC NPT TOE nipple and PVC coupling to connect the PVC pipe to the cast iron flange (C.I. flange > PVC nipple > PVC coupling > PVC pipe). Is it okay to thread PVC into cast iron?

 

[TBP]

Class 125 flanges have a flat face. PVC flanges I've worked with also have a flat face. I'd just go with a 4" 150 PVC flange (which will match up) and a full-face gasket. Do not use a ring gasket - it will leave a gap between the flange faces, and the PVC flange will be prone to cracking when tightening the bolts.

And yes, you can screw PVC into metal fittings. Avoid screwing a metal nipple into a female PVC fitting, as - again - you can crack the PVC fitting quite easily.

 

[Compositepro]

There is a very large difference in thermal expansion between plastics and metals. Threaded fittings tend to leak if there is any temperature cycling.

 

[LittleInch]

No it's not Ok.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TBP]

I've seen it done in the HVAC world of low pressure/low temperature water all over North America for 45 years particularly on cooling tower piping.

 

[TiCl4]

Just get a matching PVC flange and bolt directly to the 125 flange. Flat-face gasket, as said by others, to match the flange face and avoid cracking. Simpler and easier to install. Easier to get off later, too, for when (not if!) your PVC line fails. I hope this is something innocuous like plant tap water.

 

[fel3]

Another option would be to use a flanged coupling adapter (e.g.

https://romac.com/fca501)

or an MJxFLG coupling. This would be more forgiving of differential settlement and the resulting stress on the PVC pipe than would using a PVC flange.

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