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I just completed laying irrigation piping (black poly) and by and large it seems solid. I do however have issues with the take-offs from my house's hose bibs, where I have metal risers going into the ground to meet the poly underneath. The "risers" at the start of the system at the sides of the house are stainless steel nipples.

But no matter how much I tighten (with a pipe wrench) and use plumber's tape, the NTP threaded connections between stainless steel nipples and brass reducers (hose-bib end) seems to want to leak. This raises the question, is it a known problem when coupling SS and brass? That their NTP threading isn't exact enough of a match to maintain a dry connection?

I used SS nipples because they were half the price of brass. Was that a mistake?

Paul W
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Stainless steel is a harder metal than brass. The pro is that it's hardness makes it more corrosion resistant and durable. The con is that it doesn't give like brass when tightening threads. I found some info on the Boshart and TerryLove blogs. I'm still working on setting up my water system, but saved this picture of stainless steel grade teflon tape. So far I'm thinking people are using a sealant compound and teflon tape and something for anti-seize protection. enter image description here

cjc
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I put Teflon tape on the threads then “pipe dope” over that and don’t over tighten.

Damon
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Pic would help, but if you are trying to attach NPT to a hose bib the threads are not the same.

Additionally there should be some type of back flow prevention such as an Anti-syphon valve where the irrigation connects to the home water supply. There are NHT and NPT adapters, but to be safe backflow should be added and is mandated in almost all areas of the country.

Have a look at some youtube videos about irrigation systems such as DIY irrigation here.

RMDman
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