Moen's single-handle kitchen faucet assembly uses a ball faucet, whereby a metal ball within the faucet assembly controls the flow and temperature of the faucet's water. The ball rests upon three rubber valve seats. The seats allow the ball to rotate with the faucet's handle. It is these valve seats where the leaks from Moen's faucets are typically found. Replacing the seats is fairly simple, and Moen produces repair kits. Not all Moen repair kits are the same, however, so be sure to note the model of the faucet before visiting the hardware store.
Turn the water supply pipes in a clockwise direction to turn the water off. There are two valves underneath the sink. Both valves are located in the center of the two water lines. Each valve features a single handle, which is used to open or close the sink's water supply.
Remove the handle. A single handle screw secures the handle to the top of the faucet assembly. Tip back the handle to access the screw, then remove the screw with a hex wrench and lift the handle off of the assembly.
Remove the cam nut and the spout to access the ball assembly. The cam nut is the metal cone which sits on top of the faucet assembly and below the faucet's handle. Twist the nut in a counterclockwise direction with a pair of adjustable pliers to remove it. Then lift the spout off of the faucet assembly.
Lift the circular plastic cam off of the faucet assembly, followed by the metal ball. Then remove the valve seats and springs. There are three rubber valve seats at the bottom of the faucet assembly. Pry each valve seat out of the assembly with a hex wrench. Note that a metal spring slides onto the back of each valve seat. Remove the springs with each valve seat.
Press each replacement valve spring onto its replacement valve seat. Then insert the seats into the bottom of the faucet assembly. Lower the metal ball into the faucet assembly, followed by the plastic cam.
Lower the faucet's spout over the assembly, followed by the cam nut. Tighten the cam nut with the adjustable pliers.
Place the faucet's handle onto the top of the cam nut, then install and tighten the handle's screw with a hex wrench. Turn each water valve in a counterclockwise direction to restore the water supply and to complete the repair.