In selecting a valve for use plenty of characteristics must be suitable for your desired application. Readers recently asked Béla Lipták some questions regarding control valves and their characteristics. Some of the questions and answers are presented below. The complete list can be found at the link below.
- What are the definitions of wide and small ranges in terms of flow turndown?
A control loop will be stable if its gain does not change with variations in the load. The loop gain is the product of four gains (process, controller, sensor, valve) and, ideally, it should stay constant at about 0.5. If the process gain varies with load and the sensor and controller gains are constant, the ideal valve characteristic is one that will compensate for the variation in process gain, so that if the process gain rises with load, the valve gain drops (equal percentage); if the process gain drops with load, the valve gain rises (quick opening) and if the process gain remains constant, the valve gain should also be constant (linear).
- How would I go about measuring flow of hydrocarbons with 1% sand by mass included?
Either Coriolis or vortex can wear at a rate proportional to the percentage of sand in the flow, and both meters could have a short lives. Sharp-edge orifices are similarly vulnerable. The choice is affected by flow rate and pipe size.
I would worry about any Coriolis flowmeter with a relatively thin metal wall. Magnetic, ultrasonic and flow nozzles have been recommended. With a sufficiently high flow rate, an elbow meter will also work. Any DP meter might need a chemical seal or liquid purge to avoid plugging.
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