Power supplies often have protection from short circuit or overload that could damage the supply or cause a fire. Fuses and circuit breakers are two commonly used mechanisms for overload protection. Overload protection can be automatically enabled in response to high pressure or high temperature situations. Circuit breakers may be manually activated to interrupt the flow of electricity for the purpose of planned equipment maintenance or serviceable repair. A reducer changes the size of a pipe from a larger to a smaller bore (inner diameter). Alternatively, reducer may refer to any fitting which causes a change in pipe diameter. This change may be intended to meet hydraulic flow requirements of the system or adapt to existing piping of a different size. The length of the reduction is usually equal to the average of the larger and smaller pipe diameters.
Although reducers are usually concentric, eccentric reducers are used as needed to maintain the top or bottom of pipe level. Speed reducers are mechanical devices that help drive systems (motors) maintain optimal speed and torque for the application. Also known as gearboxes and gear drives, they lower the speed of rotation of the input shaft by a certain ratio and increase the power transmitted to the output shaft by the same ratio. They are often used in applications where the speed reducer will not be directly attached to the drive mechanism. A vacuum breaker is an attachment commonly placed on a bibcock valve or toilet or urinalflushvalve, that prevents water from being siphoned backward into the public drinking water system. This prevents contamination should the public drinking water system's pressure drop. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. Valves may be operated manually, either by a handle, lever, pedal or wheel. More complex control systems using valves requiring automatic control based on an external input require an actuator. They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water.