Control Valve Parts and Function

Major Components of a Control Valve & Its Working Principle

  • Body
    It is a type of a pressure vessel containing an orifice or an opening. The controlled liquid is allowed to flow through the body of the valve. It helps to monitor the flow regulation behaviour.
  • Trim
    Besides the body, trim is one such part of the valve that comes directly in contact with the fluid. It consists of the seat, disc, plug, and stem.
  • Actuator
    It consists of electric or pneumatic mediums to provide the force required to operate  the control valve.
  • Bonnet
    Bonnet: The portion of the valve that contains the packing box and stem seal and can provide guiding for the valve stem. It provides the principal opening to the body cavity for assembly of internal parts or it can be an integral part of the valve body. It can also provide for the attachment of the actuator to the valve body. Typical bonnets are bolted, threaded, welded, pressure sealed, or integral with the body. This term is often used in referring to the bonnet and its included packing parts. More properly, this group of component parts should be called the bonnet assembly.
  • Piston: A rigid movable pressure responsive element that transmits force to the piston actuator stem.
  • Packing Box (Assembly): The part of the bonnet assembly used to seal against leakage around the closure member stem. Included in the complete packing box assembly are various combinations of some or all of the following component parts: packing,

 Spring: A spring, or group of springs, enclosed in the yoke or actuator casing or piston cylinder that moves the actuator stem in a direction opposite to that created by loading pressure.

Actuator Stem: The part that connects the actuator to the valve stem and transmits motion (force) from the actuator to the valve.

Bellows:-  Seal Bonnet: A bonnet that uses a bellows for sealing against leakage around the closure member stem.

Bonnet Assembly :- (Commonly Bonnet, more properly Bonnet Assembly): An assembly including the part through which a valve stem moves and a means for sealing against leakage along the stem. It usually provides a means for mounting the actuator and loading the packing assembly, and maintains proper alignment of the plug to the rest of the control valve assembly.

Bottom Flange: A part that closes a valve body opening opposite the bonnet opening. It can include a guide bushing and/or serve to allow reversal of the valve action.

Bushing: A device that supports and/or guides moving parts such as valve stems and plugs.

Extension Bonnet:  A bonnet with greater dimension between the packing box and bonnet flange for hot or cold service.

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