Like all equipment valves are subject to problems in operation, quick and accurate identification and troubleshooting of the problem is necessary to ensure that the problem doesn’t impede the process or result in equipment failure.
The valve body is prone to cavitation, this occurs when the fluid within occupies 2 phases, vapour and liquid, essentially when the fluid flow gives rise to bubbles and vice versa. This is as a result of pressure differences across the valve resulting in a drop below vapour pressure. These bubbles eventually collapse downstream.
Typically the sever drop in pressure across the valve can bring across this, and it results in the valve vibrating and being noisy. The expansion of bubble out of the liquid phase release energy that causes the erosion and damage of the valve components. By simply listening to the valve we can detemine if cavitation is occuring.
Upon its onset the noise generated in inteermittent, if unattended the noise will become continuous, however the intensity of the sound may be difficult to detect above the background. This specifically is not a problem but beyond this point it can become an issue. Beyond this point cavitation will begin to do damage and destroy the valve, with the potential for material loss. It represents the upper limt of operation for any valve, and can be identified by loud and heavy vibration. If the cavitation progresses further it will result in damage to both the valve and the surrounding piping.
Using two valves in series or orifice plates can help to alleviate the problem. the 2 valve solution helps with high pressure differentials but may be more expensive. The orifice solution, creates back pressure and is used downstream. They are cheap but limited to a small flow range and can reduce the flow capacity of the system. These can also create cavitation at the plate istself and damage the piping so care must be tken when using it.
One can use valving and trim that is designed for the problem or to alleviate the issue. This would involve using an anti-cavitation valve, this solution would address cavitation locally or specifically to the valve.
Argueably the best method would be to go back to first principles and design a system that eliminates or reduces the problem altogether. In this instance the equipment to be used is sized and selected according to the process and the expected parameters of the process. This ensures that instances of cavitation and, other fluid flow issues, are addressed before and influence the selection of equipment.
It would involve modeling of the process fluid flow so as to be able to see and predict the the circumstances of the flow and how best to address it. It would also allow for the iteration of other scenarios that could lead to cavitation or show how it can develop and as such lead to a better design overall.
