Cavitation in Control Valves
Fisher anti-cavitation trims for control valves help eliminate or control cavitation damage in clean and dirty service.
Fisher anti-cavitation trims for control valves help eliminate or control cavitation damage in clean and dirty service.
Cavitation is the formation and collapse of vapor bubbles (cavities) in the liquid flowstreams caused by changes in pressure and velocity. There are four primary negative side effects of uncontrolled cavitation in control valves: high noise, excessive vibration, material damage, and deterioration of flow effectiveness. Physical damage to valve trim is usually characterized by a pitted, rough appearance.
Cavitation in control valves occurs only with liquid flows—gases cannot cavitate.
Vapor bubbles form if the liquid’s pressure falls to near the vapor pressure as the liquid passes through the control valve. Bubbles can suddenly collapse or implode as the pressure increases down line, producing cavitation.
Cavitation is one of the results of choked flow. It is the point at which increasing the pressure drop while maintaining a constant inlet pressure yields no further increase in flow rate.
Cavitation damage is characterized by a round, cinder-like appearance of the eroded surface. High-speed, destructive microjets and localized shock waves attack the material surface of the control valve during the vapor-to-liquid phase change.
Cavitation doesn’t always cause damage when it occurs.
The extent of cavitation damage is a function of numerous factors:
Cavitation can cause unacceptable noise and vibration. It is frequently described as sounding like gravel flowing through the control valve.
Although the noise associated with a cavitating liquid can be quite high, it is usually a secondary concern when compared to the material damage that can exist.
Vibration resulting from cavitation may be more prevalent than cavitation damage. It can affect the valve positioner, linkage, tubing, and adjacent pipe.
Damaging cavitation can take place without noise, and the level of noise and vibration from a control valve may not always coincide with the cavitation damage level.
Cavitation in control valves can be treated by several means. The first is to eliminate the cavitation and thus the damage by managing the pressure drop. To eliminate cavitation the total pressure drop across the control valve is split, using multi-stage trims, into smaller portions as shown in the image.
The second method does not eliminate the cavitation but rather minimizes or isolates the damage. The aim is to isolate the cavitation from control valve surfaces and to harden those surfaces that the cavitation does impact.
The third is to change the system in a manner to prevent the cause of the cavitation.
Emerson engineers conduct noise and vibration tests on cavitating applications. Transparent pipe allows visualization of the cavitation field. To arrange a cavitation demonstration, contact a local Emerson sales office.
Come along as we demonstrate the Fisher™ Cavitrol™ Hex Trim, which provides improved performance for severe service applications and maintains the efficiency of a rotary valve.
This video shows the damaging effects of cavitation on a control valve and downstream piping. Then it shows the difference that Fisher Cav Hex trim has on eliminating the effects of cavitation.
Learn more about valve cavitation and some of the technical solutions using Fisher products.
Get a unique look at the effects of cavitation in a pipeline, including turbulent flow and noise, and learn how you can reduce your risk with Fisher solutions.
See the difference valve trim can have on pipeline flow patterns in this side-by-side setup at the Emerson Innovation Center for Fisher technology.
Learn more about reducing flow pressure in stages to avoid the damaging effects of cavitation from sudden pressure drops.
Come along as we demonstrate the Fisher™ Cavitrol™ Hex Trim, which provides improved performance for severe service applications and maintains the efficiency of a rotary valve.
This video shows the damaging effects of cavitation on a control valve and downstream piping. Then it shows the difference that Fisher Cav Hex trim has on eliminating the effects of cavitation.
Learn more about valve cavitation and some of the technical solutions using Fisher products.
Get a unique look at the effects of cavitation in a pipeline, including turbulent flow and noise, and learn how you can reduce your risk with Fisher solutions.
See the difference valve trim can have on pipeline flow patterns in this side-by-side setup at the Emerson Innovation Center for Fisher technology.
Learn more about reducing flow pressure in stages to avoid the damaging effects of cavitation from sudden pressure drops.
Reduce maintenance costs with Fisher control valves and instrumentation that can withstand damaging vibration.
