View Full Version : How to attach 3/4" shut off valve to cast iron

12-19-2008, 04:00 PM

I am replacing a leaky main shut off valve to my house. I duplicating the exact set up that was there before except I am using brass valves / nipples instead of cast iron. The problem I am having is attaching the 3/4" brass shut off valve to the main water line coming from the city's shut off valve. A small amount of the cast iron (male) threads broke off when I removed the existing shut off valve. Now, I can't get the brass valve to thread onto the cast iron. It almost seems as if the 3/4" brass is too small, but I know a 1" valve would be way too big. Any suggestions for attaching the valve would be great. Also, I can email a picture if need be, but I cant seem to get them to upload to the forum. Thanks in advance.


12-19-2008, 04:03 PM
The nipple needs to be replaced or, rethreaded. Pipe threads are tapered.

12-19-2008, 04:08 PM
Okay, Thanks.

What is involved in rethreading the pipe? Replacing the nipple is going to involve a fair amount of digging.

12-19-2008, 04:37 PM
You would need the proper size threading die. getting it started straight on the remaining threads and haveing the pipe in good enough condition where it can be threaded.

12-19-2008, 05:16 PM
By the way, the existing pipe is most likely steel, not cast iron. :)

12-19-2008, 09:18 PM
Can you use a pipe wrench to unscrew that piece of galvanized pipe and bring it to a hardware store? My local hardware store will cut a new length of pipe to size and thread it for free.

master plumber mark
12-20-2008, 05:34 AM
How old is that pipe that pipe you are messing with???

Trying to re-tap a corroded 1935-50 steel pipe comming out of a concrete wall is a daunting task....

you might get lucky, then again it might be so brittle that it will crumble....

if you actually attempt this,
I suggest you somehow try to stabelize the pipe with a wrench or something at the wall so you dont twist or
disturb the line out in the dirt...
and use plenty of oil and lubrication on that dye.as you are threading it on that
old pipe.

What you are attempting is sort of like doing by-pass surgery.....

get just a little too rough and the patient dies..

12-20-2008, 10:07 AM
get just a little too rough and the patient dies..

And sometimes even if you do it all right the patient still dies.

12-20-2008, 10:38 AM
I'm not exactly clear on where you are working on your line - but. From the city's water meter there is usually a union fitting w/ an attached nipple. From there you attach your water line after that point. If that connection fell apart you may need to call your department of water and power and get a new union to attach to your meter. From there you can attach a valve after that point.

That is what it sounds like you are having a problem with. The union threads on the meter won't match up properly w/ a 1" or a 3/4" female fitting.

PS - water lines are usually run in galvanized steel or copper. Cast iron only gets used by the city water lines and is not like the cast iron materials used for water drains and vents.

master plumber mark
12-20-2008, 10:38 AM
Yes, you are right.....
sometimes no matter what you do ,
the patient still dies.....

but just like the Doctor,

I still hand them the bill..

without pictures you cant really say
what this fellow is working with...

I jsut know he is in it up to his eybrows....