The process pressure was also varied between {HEAD ~ a pressure} of 750 psi at the lower packing temperature to {TAIL ~ a pressure} of 450 psi at the upper packing temperature of 450° F.  
to
The process pressure was also varied between { HEAD ~ a pressure } of 750 psi at the lower packing temperature to { TAIL ~ a pressure } of 450 psi at the upper packing temperature of 450 ° F.
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH