Parts of valve:
Parts of valve are very necessary to understand the working of a valve. Different valves use in an industry for different purposes. Regardless of valve types, the following are the basic parts of the valve. Parts of Valve
Body: Valve body is also known as a shell, which contains and regulate fluid flow. Body is a primary pressure boundary of a valve and holds everything together. Inlet and outlet piping connected with the pump body through bolts, threads, welding or other suitable fasteners. Valve bodies are forged or cast in the different variety of shapes.
Bonnet: Bonnet gives the closure or cover to the valve body. Some bonnets use as a cover of a body while some support valve internals and accessories such as the stem, actuator, and disk. To approach the seat and disc, bonnet removes normally. Bonnet made by casting or forging with the material same as a body material. Bonnets connected with the body through threads or screws bolted flanges or welding. These bolts or weld joints connect to a body are pressure retaining parts.
Bonnet increase the complications of a valve, increase valve size which increases the cost of the valve. Source of leakage also increased due to the bonnet.
Trim: Internal elements of valves collectively called valve trim. The trim includes a disc, stem, seat, and sleeves needed to guide the stem. Basic motions and flow controlled by trim. In rotational motion, the disk slides closely past the seat to produce a change in flow opening. In linear motion, the disk lifts perpendicularly away from the seat so that an annular orifice appears.
Disc: Disc is a flat or cylindrical fluid control element which places across the fluid pathway to block flow. Disc also a pressure retaining the part. Discs made through forging. In some designs, discs are hard-surfaced to provide good wear characteristics.
Seat: In order to prevent downstream leakage when the disc is blocking flow there must be a tight-fitting closure between the disc and valve seat. The seat or seal rings provide the fine finish seating surface for the disc. For this sealing purpose metal to metal seal, resilient seal or metal to metal seal with resilient is use.
Stem: Stem or spindle connect the actuator and disc to slide the disc across the fluid path. The connection of the disc to the stem allows some rotation to ease the positioning of the disc on the seat. The stem is a basic part of valves. Two common types of valve stems are rising stems and non-rising stems.
In a rising stem valve, the stem will rise above the actuator when the valve is open. This occurs because the stem is threaded and mates with the bushing threads of a yoke that is an integral part of, or is mounted to, the bonnet. Rising stem valve is ideal for corrosive or high temperature working fluid.
There is no upward stem movement from outside the valve for a no rising stem design. In the no rising stem design, the valve disc internally threaded and mates with the stem threads.
Valve Actuator: Actuator use to operate the stem and disc assembly. An actuator is manual operator hand wheel, manual lever, solenoid operator, motor operator, pneumatic operator, or hydraulic ram.
Packing: Packing use to prevent leakage from the space between the stem and the bonnet. Packing is usually a fibrous material (flax) or another compound (Teflon). That fibrous material forms a seal between the internal parts of a valve and the area where the stem extends/ exit through the body.
Valve packing appropriately compressed to prevent working fluid loss and damage to the valve stem. If a valve packing is too loose, the valve will leak, which is a safety hazard and also affect the process parameters. If the packing is too tight, it will damage the movement as well as probably damage the stem.