Did you know to exclude the exit pipe fitting in your PSV outlet pressure drop calculations if your PSV discharges to atmosphere?
If you have performed an outlet pressure drop calculation for a PSV relieving to the atmosphere, you may have noticed that often a significant portion of the pressure drop is contributed by the exit pipe fitting. This is because the equivalent resistance of the fitting is high relative to a typical length of pipe. However, did you know that current industry guidelines recommend excluding the exit pipe fitting in your PSV outlet pressure drop calculations if your PSV discharges to the atmosphere?This is because, according to research and fluid dynamic principles such as Bernoulli’s equation, there is no appreciable resistance once the flow exits to free air. Removing the exit fitting from backpressure calculations may lead to more accurate and slightly lower predicted backpressure on the valve, which aligns with current best practices within the industry.
