A Hattersley valve is a type of valve that is used to control the flow of fluids, gases, and other materials. It is designed to be robust and reliable, and is often used in applications where high-pressure and high-temperature conditions are present. The valve is composed of two main parts: a body and a bonnet. The body contains the internal parts of the valve, such as the seat, disc, and stem, while the bonnet is the outer casing that houses the internal parts. The valve is opened and closed by a stem, which is connected to a handle. The handle is used to turn the stem, which in turn opens or closes the valve. The Hattersley valve is a popular choice for many applications, due to its durability and reliability. It is often used in applications such as oil and gas production, water treatment, and chemical processing.