The lower end of the stem is designed with an integral collar to be stem blowout proof.
It also functions as the back seat to minimize the external leakage from the stem area, if
the gland packing is deteriorated by a plant fire.
The metal-to-metal body seat as the secondary body seat minimize the external leakage, if
the non-metallic gasket is deteriorated by a plant fire.
The integral seats on the body and body cap minimize the internal leakage, if the
non-metallic ball seats are deteriorated by a plant fire