The Negative Impact Of Cavitation On Control Valves And Elimination Methods

The Negative Impact of Cavitation on control valves and Elimination methods

Negative Impact of Cavitation on control valves

Noise has a negative impact on the human body, and certain frequencies can also cause damage to industrial equipment. Most damage is caused by vibration noise energy, accelerated corrosion and process contamination.

The high noise level associated with cavitation reflects the large-amplitude vibration due to the formation and rupture of steam bubbles near and downstream of the valve seat.

High noise levels usually cause vibrations, which can damage pipes, instruments and other equipment. If the control valve is not selected correctly, the risk of cavitation will increase, which can lead to higher noise and vibration levels, which can lead to rapid damage to the valve interior and/or downstream pipelines.

Although cavitation usually occurs in the valve body of stop valves and plug valves, it may also occur in the pipeline downstream of short and high recovery valves, such as (V) ball valves, large ball valves, and especially butterfly valves. When these valves are incorrectly installed in locations prone to cavitation, leakage will usually occur, so this part of the pipeline needs to be replaced frequently to prevent its failure.

Regardless of the place where cavitation occurred, equipment downstream of the cavitation zone may suffer severe damage. Large-amplitude vibrations can cause vibration failures in thin diaphragms, springs, small cross-sections, or cantilever structures. Therefore, the use of anti-cavitation control valves is very beneficial for equipment maintenance and energy saving.

Cavitation Elimination methods for control valves

Choosing a suitable anti-cavitation valve style and modifying the valve process can effectively eliminate cavitation damage. The special valve design that eliminates cavitation uses shunting and pressure reduction, sometimes used alone, sometimes used together. By designing the several flow paths in the valve, "flow distribution" divides a large flow into multiple smaller flows, so that the flow passes through multiple small parallel openings. This is effective because the size of the cavitation bubbles depends in part on the size of the opening through which the fluid flows. Smaller openings will produce smaller bubbles, thereby reducing noise and damage during bursting.

Pressure drop grading means that the valve is designed to have two or more throttling points in series. Therefore, it does not perform the entire pressure drop in steps, but in several steps. A small single pressure drop can prevent the pressure at the cavity contraction (the point where the velocity is the highest and the local pressure is the lowest) from falling to the vapor pressure of the liquid, thereby eliminating cavitation. By combining flow splitting and pressure drop classification in the same valve, cavitation resistance can be improved.

The modification process can position the control valve at a higher pressure position at the valve inlet (for example, farther upstream or lower height) and can sometimes eliminate cavitation problems. In addition, setting the control valve at a location where the liquid temperature and therefore the vapor pressure is low (for example, the low temperature side of the heat exchanger) can help eliminate cavitation problems.