A. Delta's RP4993 seats and springs function quite simply, really. Not all Delta valves use them, but those that do have two inset holes within the valve (one for the hot water and one for the cold water), and that's where each seat and spring is placed. The spring goes into the hole first; it's wider on the bottom than it is at its top, and is inserted into the hole wide-end-first. The rubber seat is placed on top of the spring, like a cup. The spring presses the rubber cup against the bottom of either the control ball (the RP70 or the RP212) or the operating stem (RP1740), depending upon the type of faucet you have; the rubber cup creates a seal which prevents the water from flowing through (and out of) the faucet unless the faucet handle is used to position the control ball or cartridge in such a way to allow the water to exit.