Question

when designing pressure relief valve, at what circumstances should I use spring or ruptured disc? And what is operating pressure of a tank (for instance) that needs pressure relief valve as safety guard?

Answer 1

Spring valves act as safety valve  for releving overpressure in normal mode of operation and reclose after relieving overpressure in the vessel.Spring relief system generally acts as primary relief control system and spring adjust varying overpressure  while rupture disc burst and reileves very high overpressure.  Rupture disc one time use device and acts in a non-reclosing mode and can used parallely to other relief devices. Whenever vessel overpressure beyond any relief devices or runaway reaction condition then rupture disc acts as last relief system to avoid catastrophic failure of vessel.

when vessel pressure operates 10% above the set pressure we need pressure relief valve as safety guard.