Small leak with new valves

Hi

I'm changing my countertop and other things in the kitchen so wanted to add some shutoff valves under the sink so I could have water in the rest of the house while I did the work.

It seemed like a simple job...unscrew hoses under the sink and screw in new valves. But for some reason, I have a "slow" leak where both valves are screwed in the pipes/hoses. Like a drop of water every couple of minutes.

I was told at hardware store not to put teflon tape because thread is small so it's not needed. Make sense?

What are the possible causes?
Over tight? If yes, new hardware is needed or just untight a little?
Old hoses bad where they screw in the valves?
Anything else?

Thanks for advice.

Before I touched anything...


After with leak...

COmpression fittings do not work well with teflon tape; the threads aren't sealing the fitting, it's the compression ring that is doing it. Which end is leaking? If it is the supply side of the valve, tighten it up an 1/8-th turn or so. You MUST use two wrenches - one to turn the nut and a second one to hold the valve so it doesn't turn.

The faucet side of the valve often has a gasketted seal, and should not need to be overly tight.

Hi

It's the supply side that is leaking.
I tighten a little more this morning and it seems to have solved the problem on one valve. But the other one is still leaking just a little. Like one or two drops per hour or so.

I guess I will try to tighten that one a little more as well. I'm just afraid because I realy tighten both of them alot already. And my landord is not there to turn off the water if anything blows.

I guess that thing can blow in my face if I over tighten it right?
Those reno shows make things look so easy. But it's the not being 100% sure what you are doing that makes it scary. Last thing I want to do is flood my landlords house.

Thanks for answering btw.

The threads of those things are often not nice and clean and can bind a bit, making it seem like it is tighter than you think it is. Give it another 20-30 degrees and see what happens. You must support the fitting while turning the nut, so two wrenches is essential...don't try to hold one with a pair of pliers...it can be done, but isn't a good idea until you've done it awhile.