Control Valve Sizing for Liquid Applications

Define valve authority for a fully open valve and for any operating point, emphasizing sizing with 20–80% openings and comparing valve vs discharge piping pressure drops for stable control.

Explore the difference between inherent and installed valve characteristic curves, understand valve authority and system effects on pump-driven liquid transport, and learn to plot the installed curve.

Compare the installed valve characteristic curve to the inherent curve using pump and system data; compute valve authority at operating points and observe how piping losses shape the installed curve.

Explain how valve authority and inherent versus installed curves respond to system pressure drop, and how equal percentage, linear, and quick opening valves behave across flow rates.

Modify the system head curve for a 20% opening equal percentage valve, convert CV to resistance coefficient, apply opening-specific correction factors, and compare equal percentage, linear, and quick-opening valves.

Explore how elevation shapes the system head curve. See how velocity and frictional head loss, plus valve opening, shift the operating point and flow.

Define valve rangeability as the ratio of maximum to minimum controllable flow and summarize how minimum controllable flow, CV, and hysteresis influence throttling, with geometry, leakage, and actuator considerations.

Explore rangeability for a control valve by calculating maximum controllable flow (44.7 gpm), minimum controllable flow (0.9 gpm), and minimum controllable CV (0.2) for sizing.

Determine the valve turndown ratio as the maximum operational flow divided by the minimum controllable flow, and ensure range ability exceeds turndown to meet the process needs.

Apply rules of thumb for sizing a liquid control valve, using 20% minimum and 60–80% maximum openings, with 50–60% pressure drop guidance and suitable turndown.

Keep valve size between 20% and 80% opening to avoid oversizing or undersizing, ensuring stable control and preventing high velocity, noise, erosion, cavitation, or flashing.

Explore cavitation and flashing in control valves, including how vena contracta causes high velocity and low pressure, vapor bubble formation, and potential damage, and how valve characteristics predict cavitation risk.

Learn to predict cavitation and flashing in control valves using ISA standards, maximum allowable pressure drop, and pressure-recovery factors to assess choke flow and guide valve selection.

Assess cavitation and flashing for the three-inch valve by comparing pressure drops to the maximum allowable; the example shows no severe cavitation or flashing at min and max flow.

Learn key parameters for control valve selection from flow medium and port types to leakage class, pressure ratings, materials, and CV sizing to guide supplier decisions.