What kind of valve is this and how do I disconnect it?
I have had good luck getting these fittings to release with an open end wrench. Slide a wrench the same size as the outside diameter of the tubing over the tubing. Then use it to push in the release collar. It works well in tight areas or where the fittings are close together. If you have to replace any tubing a clean cut is required to get a good seal.