When a leak occurs in a shut of valve, it is easy to assume it is the valve that is leaking. This may not always be the case. Many times, it is actually the compression fitting that is failing and causing the leak. The compression fitting ensures a tight seal between two tubes or pipes. Replacing the fitting first may save both time and more complicated repairs.
Step 1 - Remove the Old Fitting
First, turn off the water supply at the shut off valve. Disconnect the water supply line from the shut off valve. Remove the old fitting by pulling the O ring out, removing any gaskets, and slipping the compression nut off the supply line. Some lines may be flared at the end. In this case, you will need to cut off the flared section of the tubing.
Step 2 - Install New Fitting
Replace the compression fitting in the reverse order that it was removed. Slip the nut onto the supply line, insert any gaskets, and replace the O ring. Wrap the shut off valve's threads with plumbers tape. Tighten the nut back onto the shut off valve. If the water line needs to be flared, use a flaring tool to do this, after the nut has been slipped onto the line.