At first glance, it may seem that a logical way to achieve these goals would be to limit valve trim exit velocity head to a maximum of 480 kilopascals (kPa), and this indeed is how some have addressed the issue. In practical application, however, it is an oversimplified approach that, in many cases, will not produce the desired results. First, it typically requires the use of expensive multi-stage or multi-turn trim designs, which can cost up to 30% more than a simpler solution. More importantly, it also can create a false sense of safety.
This article will explain why the focus should instead be on keeping the valve outlet mach number low. Practical examples will be used to illustrate that:
Even if the trim exit velocity head is kept below 480 kPa, valve noise can be unacceptably high if the valve outlet mach number is high.
Even if the trim exit velocity number is above 480 kPa, valve noise can be kept to acceptable levels — without using costly trim designs — if the valve outlet mach number is kept low.
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