Ball valves are standard on shower faucets manufactured by Delta since the business was a pioneer in the development of ball-valve technology. When the rubber components within a faucet wear out, it may cause the faucet to leak. In the case of a ball-valve faucet, the rubber pieces that wear out are the seals that are placed in the valve seat between the hot and cold input ports. The seals have springs inside of them that press them firmly against the ball in order to keep the water out, but these springs eventually wear out as well. After taking apart the faucet, you will find that the seal and spring for each port may be replaced as a single unit.