Only compression valves have valve seats. When repairing a compression valve, check to see if the valve seats need to be resurfaced. You will need to stick your finger down into the faucet body to feel if the valve seat is rough. If it is rough it will quickly damage a washer. You should either replace it or resurface the valve seat at the same time you are replacing the faucet washer.

Step1: TURN OFF THE WATER SUPPLY AND DISASSEMBLE THE FAUCET VALVE

Lower the sink stopper and cover it with a cloth to prevent loose parts from falling into the drain. Pry off the handle cap with a screwdriver. Remove the valve. Now loosen the compression valve with water-pump pliers and remove it. Make sure you keep any and all washers or O-rings with the valve and set them aside.

Step2: BACK OUT THE SEAT

Use a seat wrench to remove the valve seat. Now select an end that fits snugly into the seat. Insert the end of the wrench into the seat and tap the top to seat if firmly. The valve seat may be stuck, so the first turn should be quick and firm to release it without stripping the threads. When you have it loose, turn the wrench until you can remove the screw and take the seat out. You will need to take the old seat with you when you go to buy a new one. That way you will get the right one.

Step3: REPLACE THE SEAT

Install the new seat into the faucet. Apply pipe dope to the seat threads to seal them; insert the end of the seat wrench into the seat and set the seat in place. Now, screw the valve into place and assemble the compression valve, faucet handle, and handle cap. When you turn the water supply on make sure you go slow and check for leaks.