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A plumbing valve is a device used to control the flow of liquid or gas through a plumbing pipe. Some of these valves may be hidden from view, while others are located in easy-to-access areas. Each type of plumbing valve features some form of control system, which allows a plumber or repair person to operate the valve and control the contents of the pipe. Plumbing valves play an important role in everyday safety and operation of basic water and sewage systems, as well as emergency repairs or modifications.
Depending on the application, a plumbing valve may be made of metal or thermoplastic. Common materials for these valves include PVC, steel, or copper. The plumber must choose the size of each valve to fit the adjacent pipes, and some valves require special connectors that allow them to fit pipes of a larger or smaller diameter. The size, features, and materials of a plumbing valve are typically regulated by local building codes in most areas.
Plumbers join pipes and valves using a variety of different techniques. Many of these plumbing supplies feature threaded ends that allow them to be screwed together to form a tight bond. Some valves subject to high pressure or force may be designed with flanges at the ends that allow the user to add screws or bolts for a more secure connection. Others may require welding to ensure a water-tight seal.
The gate or stop valve represents one of the most common types of plumbing valves. It consists of a thin metal flap roughly the same diameter as the pipe. Using a wheel located outside the pipe, users can spin the flap to cover the entire inside of the pipe to block the flow of water. By rotating the control wheel the opposite way, users can open the flap and allow water or gas to flow freely.
Globe or ball valves are also commonly used in basic plumbing systems. These units include a handle or similar operating device on the outside of the pipe. When the handle is turned, it forces a metal ball into position within the pipe to either block or unblock the flow of water or gas. This type of device is often referred to as a quarter-turn plumbing valve.
Many valves contain additional devices that perform special functions to control and regulate flow. For example, a check valve not only controls how much liquid flows through a pipe, but also keeps the liquid flowing in only one direction. This type of valve is commonly used in sewage systems to prevent raw sewage from re-entering a building. Other specialty valves include devices to reduce pressure in pipes that carry steam or volatile materials.