not having much luck with slow drip on 3/4 copper/brass compression union

[Mr Blint]

Although the alignment of the pipes is good, my 3/4 copper + brass compression unions are leaking. A single drip every five minutes or so. Three of them have this issue. There's no visible damage on any of them. I've loosened and retightened the threads on all of them and one eventually stopped dripping. This is on a whole-house water-filtration system. Can a dab of teflon paste be placed on the concave surface of the brass fitting?

 

[Sylvan]

A lot of imported fittings are crap and they do leak.

A lot of "old timers" used joint compound on the male flair of a gas connector. You have nothing to lose by trying it

By the way why filter water that is being used for the toilets? Some places use a dedicated like for sprinklers /toilets etc.

 

[Sponsor]

 

[Jeff H Young]

Supposedly dope isnt needed but ill put dope in a case like that . normally I put nothing

 

[Mr Blint]

A lot of imported fittings are crap and they do leak.

A lot of "old timers" used joint compound on the male flair of a gas connector. You have nothing to lose by trying it

By the way why filter water that is being used for the toilets? Some places use a dedicated like for sprinklers /toilets etc.

I had in mind mainly to protect the valves for the clothes washer and dishwasher, and keeping the water-hammer arresters from failing because of limescale buildup, and keeping the air release valve on the boiler from getting clogged with it. But we also have a lot of iron in the water and the toilets do get stained with that, so even they could benefit. These whole-house filtration systems aren't expensive, under $100, with maybe another $75 per year in filter costs.

 

[John Gayewski]

The ferrules on compression fittings leak less with dope on them. It mainly helps them slide into a seated position. None on the threads or the pipe, just the ferrule.

 

[Reach4]

I think you think the leaking occurs at the mating surface of the union, and you are probably right. But also check to see if there is leakage between the copper pipe and the compresion fittings. If there is leakage at the pipes, tighten the leaking compression fitting maybe 1/8 turn... Two wrenches. Longer wrenches are better to a point.