The valve stem screws into the body of the faucet. The stem washer, which is held at the bottom of the stem by a brass screw, fits into a valve seat when the stem is all the way down, and thus closes off the opening for the flow of water. When the handle is turned, the coarse thread on the stem lifts the stem and washer off the valve seat, permitting water to flow. The bonnet screws onto the main body of the faucet and prevents you from turning the handle so far that the valve stem comes clear of the faucet body. Packing in the bonnet prevents water from leaking up between the stem and bonnet.
Each time the faucet is closed, the washer is compressed against the valve seat and at the same time rotated against it. This constant rubbing slowly wears away the washer so that eventually it no longer fits tightly against the valve seat. Then the faucet will drip even when the stem is apparently all the way down. This may not be annoying but is a waste of water that can be expensive. Furthermore, it can only get worse.
When a closed faucet drips, you can usually fix it simply by replacing the washer. First, shut off the water running to the faucet, and then remove the handle. The handle is held onto the stem by a screw, but the screw my be covered with a decorative plate. The late may be held on by a knurled collar, which must be twisted off, or by friction, in which case it can be pried off with a small screwdriver. At any rate, unscrew the screw holding the handle and lift off the handle. Now unscrew the bonnet from the body of the faucet, using an adjustable wrench, and slide it off the stem. Now you can unscrew the stem completely from the faucet. You may find it easier to put the handle back on the stem to rotate it out of the faucet. You can now get at the washer on the end of the stem.
Many people have gouged their hands with screwdrivers while tying to remove the screw at the end of the stem. If you hold the stem in one hand and apply a screwdriver with other, there is a tendency to push the hands toward each other as you turn the screw. If for any reason the screwdriver slips, it moves very rapidly toward the hand holding the valve stem. To prevent this, do not use pressure as you turn the screw. Better still; put the stem in a vise instead of holding it in your hand.
After you remove the washer, replace it with a new one of the same size. You can buy an assortment of washers of different sizes very inexpensively, but most of them won’t fit. It’s better to find the size you need and buy some of that size only. Replace the screw holding the new washer, again being careful not to gouge your hand with the screwdriver. Before putting the stem back into the faucet, look at the valve seat and feel it with your finger. It should be smooth. If it has rough edges or if there are particles of grit on it, the new washer will soon be chewed up. You can buy a very inexpensive seat-dressing tool to smooth a rough valve seat. Let the hardware dealer show you how to work it. It will save replacing a lot of washers.
If the faucet leaks at the top of the bonnet either when it is open or shut, the packing in the bonnet is worn. With the faucet apart, dig out the old packing from the bonnet with a screwdriver, and install new packing. Packing material looks like heavy string impregnated with graphite. Wind it around the stem until it fills the bonnet cavity. It is usually held in place with a packing nut. Some faucets use a plastic ring as the packing material and plastic rings may be available as a replacement for the old packing on older faucets. If you need new packing, take the bonnet with you when you visit the hardware dealer and let him tell you what to use. Don’t forget to turn on the water again after the faucet is repaired.
