Valve a device used for controlling the fluid or air passage through a pipe or a duct. Around hundreds of valves are used in a single power station to control almost every aspect of its operation. It is used in power plants to fulfill process gear which can increase power generation efficiency.
There are many valves parts that are used to construct the valves:
The body is the key element. It contains the moving components. They are in contact with the fluid. It has to withstand the pressure that exists in the piping system. The body is manufactured by forging or casting steel in many designs, shapes and material grades. In the oil industry the most common material for bodies is ASTM A105 for forged bodies.
Bonnets are very important components of globe and gate type. By dismantling the bonnet the maintenance staff has access to the internal mechanisms. It can replace components like seat, stem etc.
The trim is the collective name for the internal parts. It can be removed and they are replaced and are called wet. They are in direct contact with the conveyed fluid. The trim includes components as the seat, stem, glands, disk, sleeves, and the bushings. It needed to guide the stem that made up the trim by the type of device. The factors to consider are temperature, pressure and type of fluid.
The disc closes and opens or modulates the flow of the fluid. In the case of the gate valve and gate wedge is the disc of the valve. After the body and the bonnet, the disc is the third most important element for the good performance of the valve. Discs are manufactured of steel and they are mostly reinforced to enhance the properties of the base material.
Seats accommodate the movement of the disc. Globe or the swing check valves are then lifted with one seat. It opens and closes the passageway of the fluid. Gate valves generally have 2 seats, one is on the upper side and the other is on the lower side.
The stem of the valve is used to close and open the fluid as it moves the disc. The stem is linked to the valve actuator or to the manual hand wheel. Stems are made of forged steel and connected to the disc by threading and other means.
Valve material and its packing material is actually installed between the packing box and valve material which helps in preventing the outer leakage. There are many kinds of valve packaging materials such as flexible graphite pickings, vegetable fiber packing, PTFE valve packing, rubber filler, carbon fiber packing, metal and rubber valve packing and many more.
A hand operated is generally equipped with the hand wheel and it rotates clockwise. Ball, plug and butterfly are actuated using a lever. There are many types of valve actuator are also available:
1. Gear actuators
2. Electric actuators
3. Hydraulic actuators
4. Pneumatic actuators
5. Gas over oil actuator.