If you’re new to the process industries and have responsibilities including a safe, reliable and efficient production process, then you likely need to understand how control valves work. And, one of the best sources for learning is the Control Valve Handbook.
For instance, if you need to learn about globe valves, section 3.1.1 of the handbook includes information on single-port valve bodies, post- and port-guided valve bodies, cage-style valve bodies, double-ported valve bodies, and three-way valve bodies.
The section opens with a hyperlink to a 3-minute video, What are the Components of a Globe Valve? This educational video shares the basic body styles, trim components, and bonnet styles that make up a globe valve. It’s really the best place to begin before exploring the various body styles.
The Emerson Educational Services instructor for control valves opens the video explaining the two main components of a sliding stem globe valve and an angle valve—the body and the bonnet. Inlets and outlets are on the same axis for globe valves and perpendicular axes for angle valves.
Showing a cutaway view of the globe valve enables a look at the internal trim components inside the globe valve. The common assemblies found inside a sliding-stem valve include the plug & stem assembly, cage and seat ring. The only moving component is the plug & stem assembly which slides up and down based up the position sought by the valve actuator.
The available flow area through the cage changes based upon the position of the plug & stem assembly. These plug & stem assemblies can be balanced or unbalanced. Section 18.104.22.168 of the handbook explains these concepts:
In balanced designs, downstream pressure acts on both the top and bottom sides of the valve plug, which nullifies most of the static unbalanced force. Reduced unbalanced force permits operation of the valve with smaller actuators than those necessary for unbalanced valve trim. Interchangeability of trim permits choice of several flow characteristics, noise attenuation, anti-cavitation, or other severe service capability.
Proper alignment is critical for the plug to seat properly into the seat ring. Two ways to properly guide the plug are cage guided and post guided. Section 3.5 describes characterization of cage-guided valve bodies and section 22.214.171.124 describes post- and port-guided valve bodies.
Visit the Training – Valves, Actuators & Regulators section on Emerson.com for more educational opportunities on these final control elements which are critical to safe, reliable and efficient operations.
You can also connect and interact with other valve experts in the Valves, Actuators & Regulators group in the Emerson Exchange 365 community and/or at the September 23-27 Emerson Exchange conference in Nashville.