Abstract: A method for isolating a relief valve, the relief valve being positioned in fluid communication with a pressurized vessel by positioning a gate valve body between and in fluid communication with the relief valve and the pressurized vessel, the gate valve body including a plug and a cap positioned to sealingly close an opening in the gate valve body generally covered by a gate valve bonnet cover and yoke, removing the cap, sealingly positioning a sandwich valve over the opening in the gate valve so that when the pass-through is opened a passageway through the pass-through sandwich valve is generally co-axial with the opening in the gate valve, sealingly positioning a removable yoke over the passageway through the pass-through, the removable yoke including a stem and being adapted to movement of the stem through the removable yoke; opening the pass-through; moving the stem into engagement with the plug and removing the plug from the opening in the gate valve body; and positioning a valve gate on the stem and mo