Sizing Of Vacuum Valve On Storage Tank

Does anyone know how to size a Vacuum/Relief valve on a storage tank?. API RP 520/521 only deal about Pressure Relief Valves.

I know the spreadsheet of Art Montemayor "Tank Pressure and Vacuum protection" [URL="http://www.cheresources.com/invision/topic/573-sizing-of-vacuumrelief-valve-on-storage-tank/page-3"]http://www.cheresources.com/invision/topic/573-sizing-of-vacuumrelief-valve-on-storage-tank/page-3[/URL], but it's a "logical calculation", not a "legal calculation".

It's based on API std 2000 which is accepted by all industries. You can develop your own spreadsheet if you follow API std 2000, it's very easy/straightforward calcs.

Thank you