Major Components of a Control Valve Parts
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 behavior.
Besides the body, trim is one such part of the valve that comes directly in contact with the fluid, and the heart of the control valve is the trim, especially the mating parts that throttle the stream to the demands of the controller. These valve parts are subjected to the most taxing service, and selecting the best type for an application involves many considerations. Because the trim in rotary motion valves is vastly different in design from that in linear motion valves, body choice is also affected.Aside from being the right size, the most important consideration is probably serviceability – will the trim do a proper job for an acceptable length of time? The corrosive and erosive nature of the fluid is important elements in the analysis, as are extremes of temperature or pressure differential.
The risk of cavitation or excessive aerodynamic noise requires an appraisal, as does the importance of flow characteristics on the loop stability. The trim design affects the forces that are demanded of the actuator. Hence, dynamic and actuator costs are involved.
Special considerations for valve trim include a need for tight shutoff and regulatory requirements, such as those governing sanitary service or the desirability of having a quick-change facility for easy cleaning or replacement.
It consists of electric or pneumatic mediums to provide the force required to operate the control valve.
Bonnet: The portion of the valve that contains the packing box and stems seal and can provide guidance 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 it included packing parts. More properly, this group of component parts should be called the bonnet assembly.
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 the 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 a greater dimension between the packing box and bonnet flange for hot or cold service.