Most valves use a pressure fitting which connects by pushing the water line into the end of the fitting until it stops. A tug on the line will verify it has been captured and is locked in place. To remove these fittings, you must press in on the line while applying pressure to the outer ring where the line enters the fitting. Then the line can be pulled free. If you need further assistance, please provide a model number so we can better understand what you are working on.