Hi
I was reviewing a relief system design this week, and it reminded me of an important factor that is used in the sizing of Pressure Safety Valves (PSV), which is the accumulation or overpressure.
When sizing a PSV, it is easy to focus only on the required orifice area and forget the mechanics of how the valve actually opens.
Here is why accumulation pressure (overpressure) is so critical to your design:
- What it is: Accumulation is the maximum pressure that builds up above the PSV set pressure while the valve is opening.
- Why it matters: A PSV relies on this overpressure to push the disk open completely. It must achieve full lift within the accumulation limit.
- The Danger: If your system exceeds this limit, the valve will not open sufficiently. It fails to relieve the required capacity, putting your vessel at risk of rupture.
This is actually one of the important factors affecting the PSV sizing. I broke down accumulation pressure—along with blowdown, piping effects, and multiple relief scenarios—in a detailed guide on our blog.
You can check it out by clicking on the below button:
Are you currently struggling with a tricky relief valve calculation or API 521 scenario? Reply to this email and let me know!
Keep designing safely,
Mohamad
P.S. If you want to go deeper into pressure protection, our PSV Sizing & Relief System Design course walks you through API 520/521 methodologies step-by-step, including fire cases and flare header analysis.
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