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View Full Version : joining pvc sch40 to copper or brass


itteitj
04-05-2006, 11:19 AM
I read some time back about a rule of thumb concerning joining copper to plastic and can't remember what it said. My feeling is to only join plastic threads to metal and never visa versa. your thoughts.
Tom:confused:

Dirty Water
04-05-2006, 11:22 AM
Thread male plastic into female metal and never the other way around.

So your PVC piece will be a male adapter, and your copper/brass/galvi piece will be a female adapter, or any other sort of female threaded fitting.

PurpHaze
04-05-2006, 11:29 AM
So your PVC piece will be a male adapter,...

We use SCH 80 nipples (TOE or cut them in half) quite nicely. :dancing:

hect911
04-08-2006, 12:39 PM
Thread male plastic into female metal and never the other way around.

So your PVC piece will be a male adapter, and your copper/brass/galvi piece will be a female adapter, or any other sort of female threaded fitting.

If you use it the other way around, the copper/brass/galvi male adapter will break the female pvc adapter as you are tightening it and you will have a problem.

SprinklerGuy
04-08-2006, 01:21 PM
I have seen many many copper male adapters threaded into pvc that did not crack the pvc and have been installed for many many years.

In fact....sometimes I do it myself. A sch 80 1x3/4 reducer bushing with female threads is very thick and if you don't screw the copper MA in too far and tighten like you are Lou Feriggno...it works fine. Not my preferred method, but I have done it in a pinch and I don't feel guilty about it at all.....

Dirty Water
04-08-2006, 01:31 PM
Tony, I think the expansion rate of copper/brass/galvi is different from plastic, and thats why fittings crack.

Wet_Boots
04-08-2006, 02:14 PM
A sch 80 1x3/4 reducer bushing with female threads is very thick....That reminds me of trying to figure out the best way to fit a boiler drain to PVC manifold of antisyphon control valves, worrying about the brass threaded into the PVC. I sometimes used a 1 x 1/2 bushing for the boiler drain faucet, and those had plenty of thickness.

I always thought it a bit dumb to avoid the spending few extra pennies it would cost to use a CxFPT fitting. Lately, though, those pennies have graduated into dimes and quarters. Still a good investment, I think, if only for peace of mind.

jerryrwm
04-08-2006, 04:42 PM
The main reason it is preferred to use metal female/plastic male is because of the way threaded fittings are manufactured. The threads are tapered so that they can be joined and not leak. So if you strong-arm the fittings when joining, or even using to much teflon tape, you can exert extreme pressure on the fitting. Therefore if using the metal (or even sch 80 nipples) it is very easy to over-torque the fitting, and it will break from hoop stress. It happens using sch 80 fittings and nipples also, and years ago in the oil patch,I saw galvanized fittings crack also. (I told him he didn't need a 48" wrench to tighten that 2" fitting!)

So, yes it is preferrable to join plastic male to metal female, but if you use a little common sense it can be done the other way around and last for many years.

BSME
04-10-2006, 12:35 AM
Happened to me today where the last sprinkler company put a 3/4'' to 1'' pvc bushing (3/4 was female) on a 3/4'' copper.

they installed it in the fall and it is already cracked.

it was eventually going to 1'' poly so I soldered a wyboo (is that how it's spelled) on to hook straight up.

did that makes sense? I need to start carrying the camera in the truck