On/off valves, also known as shut-off valves, are a type of flow control valve that are used to start or stop the flow of a fluid through a pipe or system. These valves typically have a handle or lever that can be turned to open or close the valve, allowing or preventing the flow of the fluid. On/off valves are commonly used in a variety of industrial and commercial applications, including plumbing, HVAC systems, and process control systems. They are designed to be durable and reliable, and can be made from a variety of materials, including metal, plastic, and rubber. Some common types of on/off valves include gate valves, globe valves, ball valves, and diaphragm valves.
Control valves are modulating type of valves which can operate at several intermediate positions. The purpose of using control valve is to regulate some parameter. In case of a heat exchanger, control valves are used to control the quantity of heat transferred by modulating the flow of hot fluid.
In case of steam systems, a control valve is used to control the process temperature. Temperature and pressure of steam are directly related to each other. The control valve controls the pressure of steam thus leading to change in temperature. A temperature sensor senses the pressure temperature and sends signal to actuator which modulates the valve output to give correct output.