Compression joint leak

I've installed 5 compression joints in a system on copper pipe, and after pumping it up with air to 60 psi, three of the joints are leaking slightly and it seems like no matter how tight I make them, they continue to leak, as evidenced by tiny bubbles around the top of the joint when sprayed with soapy water. The system loses about 1 psi every half hour. Should I keep tightening, or will this small of a leak fix itself?

leaks

The larger the size compression fitting, the more important it is that the tubing be "straight" into it. Even a slight misalignment can cause a leak and all additional tighening does is distort the tubing. It is possible that water in contact with the metal will clog the leak, but it is also possible that it will just slow it down, and eventually the joint will be encrusted with the minerals left as the water evaporated.

Is there any kind of rule of thumb for deciding if a leak is "acceptable"? The system is about 300 ft of 3/4" pipe. Over 12 hours, the pressure dropped from 60 psi to 40 psi. However, the temperature also dropped about 15 degrees. Thanks.

Leaks rarely "fix themselves", although it can happen it there is water involved.

If these are compression joints with metal ferrules, there is a certain "touch/feel" involved. Broad rule of thumb is hand tight, then one half to at most one full wrench turn. A 1" fitting feels different than a 3/8" fitting. Unless you were really wimpy on first install, retightening may not help. You could try and additional one quarter turrn. But overtightening is a real problem which damages the tubing.

Pressure will change with temp, but you said the soap test reveals bubbles, and that is not good.
The issue is based on Boyle's law, Charles' Law, and probably Avogadro's number. This is the combined gas law equation:

Combined Gas Law:
Gas Equation: P[SUB]i[/SUB]V[SUB]i[/SUB]/T[SUB]i[/SUB] = P[SUB]f[/SUB]V[SUB]f[/SUB]/T[SUB]f
[/SUB]
where i is the initial numbers, and f are the final numbers. You can see that with volume constant, if the Temp changes, the pressure changes proportionately.


Why so many compression fittings?

The only "acceptable" leak is one YOU are willing to put up with. A plumber's criteria is ZERO leaks.

Thanks for the replies. This is an underground system for watering the garden. The horizontal pipe is all black poly, with the risers for the various hydrants being copper. I used compression fittings to connect the copper risers underground (to a brass tee) to avoid having a buried soldered joint. I plan on having the system under pressure only during use (ie, watering with a hose from only one hydrant at a time) and drained at the end of the season, so I'm tempted to call it "good enough" and begin backfilling.

In that case, all the leak will do is add to the watering in the ground

I finally pressurized the system with water, and to my shock, the joints that had leaked air did not leak any water during the 12 or so hours under pressure. So I guess all is good. Thanks to everyone for their input.

The solder joint is so unreliable people have resorted to using compression joints to avoid them underground. LOL

In this case, I guess it would be difficult to solder or flare the poly pipe. Lack of visual leaks does not mean it is not leaking. Check the joints in 6 months or so to see if they have mineral encrustations from water seeping and evaporating.

Just a thought, but plastic is just that, at least somewhat plastic. Maybe the pipe or fitting was slightly deformed, and after sitting for awhile under tension/pressure, or whatever, it reformed and made a better seal.