If a tank is designed as per API 650 ,then what can be the set pressure of Vacuum Relief valve.
Please suggest or one can mention the maximum limit of vacuum a API650 tank can withstand.

Thank & Regards.

Biswajit.

The maximum limit of vacuum for an API 650 tank is 1" WC. After that there is nothing specific mentioned nor is it covered by API. After 1" WC vacuum, you can specify anything you want (be prepared to pay for it) and you must provide vacuum protection. Unless you have a real good reason to go any lower, I suggest no more than 4" to 6" of vacuum. This will allow adequate protection using pretty standard vacuum relief/conservation breather vents.