In order to ck the bypass valve you need to remove the reservoir and you will see as snap ring about the size of a dime. Pull the snap ring and push down on the piece and let it spring back until it pops out. The piece on top contains the O-ring and the valve and spring are below it. Ck for trash in the valve and bore. You can clean up the valve with some fine emery cloth to make sure it moves freely. You'll need a rebuild kit on hand for the new O-rings.