In a low-pressure system, rupture disk opens at which psig?

• A. 10 psig
• B. 18 psig
• C. 15 psig
• D. 12 psig

Answer: (C)

Rupture disks relieve pressure by bursting at a specified cracking pressure. In a low‑pressure system you want the disk to stay closed during normal operation but open before the pressure reaches a level that could damage equipment, meaning the cracking pressure should be just above typical operating pressure and well below the maximum allowable pressure. The 15 psig setting achieves that balance: it remains intact under normal conditions, yet it will vent when an overpressure occurs, preventing damage. Setting it much lower (like 10 or 12 psig) risks venting during normal fluctuations, while setting it higher (like 18 psig) could allow a dangerous overpressure before relief occurs.