The PAK-45 was developed in the early 1970's, and was probably discontinued in the early 2000's.  It uses Nitrogen as the plasma gas and C02 as the shield gas......air plasma cutting had not yet been developed.  Many were equipped with hand torches for up to 400 amp cutting.  It generally was used for cutting stainless and aluminum up to 2" thick.  Steel cutting was drossy and horrible in most cases.  Probably not a good process to use today! 

We had one years ago, purchased new, as Jim Colt stated it needed Nitrogen and CO2 to operate, ours had a holder on the back of the machine for the two compressed gas cylinders.  At the time it was it was the cats meow, we got it dialed in to cut carbon steel reasonably fair for the time. We donated ours to a high school some time in the early 80's.  It went to the scrap heap a few years later when we donated a newer plasma power source to the school.