Consider the control valve
Loops everywhere you look, if you look hard enough
By Robert M. Donnelly
A process plant is a kind of control-loop network, with multitudes of automated, semi-automated and manual control loops embedded within it. Other loops are mostly interpersonal or may be the product of one person’s thought processes, perhaps expressed by means of a spreadsheet.
Control valves regulate flowing fluids, including gas, water, steam or chemical compounds. Within these networked control loops, valves keep some important process variable — pressure, flow, level or temperature — within required operating ranges to ensure end-product quality.
Valves are the most common process industry control element, and ball valves are the most common of valves. Then again, many different type ball valves are available.
For large flow variations there is a concentric-segment ball valve with a V-notch, also used for controlling fluids with slurry or fiber.
Spring-loaded single-seat Trunnion-design valves with a V-port segmented ball are for fast accurate response to signal changes.
Reduced-bore two-piece body-ball valves can be metal-seated, as can three-piece high-pressure full and reduced bore-ball valves.
Butterfly-style valves are available for control applications.
V-type control ball valves offer maximum Cv’s*, substantially larger than that of other throttling globe-type control valves. In many cases, use of short-pattern valves results in savings for both valves and actuators, as well as in maintenance.
Depending upon its application — from simple on-off to the most delicate of control modulations — choosing the right control valve guarantees end-product quality and process longevity.
*Cv = Valve sizing coefficient determined experimentally for each style and size of valve, using water at standard conditions as the test fluid
Robert M. Donnelly is the Vice President of Marketing for Flo-Tite Valves & Controls