{HEAD ~ The live loading} is optimized to maintain a seal at the upper packing set to less than 500 ppm leakage, minimize packing friction from both the upper and lower packing sets, and seal {TAIL ~ the lower packing set} during fire safety tests 
is optimized to seal
{ HEAD ~ The live loading } is optimized to maintain a seal at the upper packing set to less than 500 ppm leakage , minimize packing friction from both the upper and lower packing sets , and seal { TAIL ~ the lower packing set } during fire safety tests
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH