Valves are used to stop and regulate the flow of water, and each type of valve has its pros and cons and applications for which it is best suited. Most valves in a residential plumbing system are part of the water supply system and are used to control the flow of pressurized water from the water utility or a private well. Depending on the design of the valve, they may be best suited for simple ON-OFF control of the water flow, or they may be designed instead for adjusting the volume of the water flow.
Most valves are available in different materials, including bronze, brass, and PVC plastic. Make sure to choose materials appropriate to the type of pipe used in the plumbing system.
Gate valves are among the most commonly used valves in plumbing applications. Gate valves control water flow by raising or lowering an internal gate by use of a twist-type handle or knob located at the top of the valve. Gate valves should never be used to control the volume of flow—they are designed to be fully open (allowing full flow) or fully closed (stopping the flow entirely). Using them to adjust water flow can wear out these valves. Gate valves are very reliable for closing off the water supply, and they are commonly used as shutoff valves on main and branch water supply lines, although ball valves are gradually becoming more popular in these applications. Because internal metal parts may corrode, it is not uncommon for a gate valve to get stuck in an ON or OFF position. They are most commonly used in applications where the water needs to be shut off only infrequently.
Ball valves are perhaps the most reliable type of valve and are commonly used for main water shutoffs and for branch line shutoffs. Like gate valves, a ball valve is designed as an all-or-nothing valve—they should be either fully open to allow full flow, or fully closed to stop all water flow. Internally, these valves have a ball with a hole in the middle, which is connected to a lever-type outer handle. When the handle is parallel to the water supply pipe, the valve is open; when it is perpendicular, the valve is closed. This handle serves as a handy visual aid so you know at a glance whether the water is ON or OFF.
Globe valves are used to regulate or throttle the flow of water in plumbing applications. This type of valve gets its name from the bulge in the body of the valve, a shape not found in other valve types. The handle on a globe valve is usually a twist knob.
Globe valves are usually installed when the flow of water needs to be regulated or when it needs to be adjusted regularly. The internal design features contain a stopper on the end of a valve stem, which is raised and lowered by the valve's twist knob. When the stem forces the stopper down against the interior valve seat, water flow is halted entirely. The stem can be raised incrementally away from the valve seat to precisely control the volume of water flowing through the valve.
Because globe valves are good for regulating flow, they are often used for outdoor faucets (hose bibs) and similar utility faucets.
Externally, butterfly valves resemble ball valves, since they have a lever-type handle that opens and closes the valve. Internally, the design uses a metal disc that rotates to regulate the flow of water. Because the water flows around the disc, which is at the center of the valve, the water flow is reduced somewhat, even when the valve is fully open. Unlike a ball valve, which is intended as an ON-OFF valve, a butterfly valves can precisely adjust the volume of flow. One notable drawback of a butterfly valve is that the gasket inside the valve can present maintenance issues after a few years.
Butterfly valves are used primarily in industrial applications and are not commonly found in household plumbing systems
Fixture Shutoff Valve (Stop Valve)
Fixture shutoff valves are small valves with small twist handles or knobs, used to control water flow to individual plumbing fixtures, such as faucets and toilets. There are straight versions and 90-degree-angle versions (also known as angle valves or angle stops). Shutoff valves allow you to work on a faucet or other fixture without having to shut off the water to the whole house at the main shutoff valve.
Externally, fixture shutoff valves resemble small gate valves, since they usually have a small knob or wheel that turns to open and close the valve. Internally, fixture shutoff valves can use one of several different designs. Some types use a simple compression washer that opens and closes against a valve seat operated by the valve handle. Others use a diaphragm design, in which the valve stem controls a flexible diaphragm that presses down against a valve seat opening to stop the flow of water.
Water pressure-reducing valves are installed to reduce the overall water pressure in a plumbing system to the desired or accepted limits. They normally have a spring and diaphragm that is adjusted to a specific limit, depending on the pressure of the water supply. Pressure-reducing valves are not used to open or close the water flow, but rather to throttle it down to reduce overall water pressure. They are commonly used in homes that receive relatively high-pressure water from the municipal water supply, where the pressure might be sufficient to damage house plumbing systems and appliances.
A check valve is a specialty valve used to keep water flowing in one direction only and prevent flow in the opposite direction. Most types are not operational, and therefore do not have control handles. A back-flow preventer, of the type often found on outdoor faucets (hose bibbs) and on lawn sprinkler systems, is one example of a check valve. Check valves can use different types of inner mechanisms, include ball-check designs and diaphragm check designs.
An operational type of check valve, known as a stop-check, can be used to completely stop all water flow in both directions.