A more subtle but equally important concept is the shaft seal and how it is integrated into the process screw for ease of maintenance. With this shaft seal design the normal wear items (namely the seals) are mounted on and removed with the quick release process screw. They can then be easily cleaned, inspected or replaced without tools or additional disassembly. The process screw is designed so that the seals do not turn with the screw, rather the screw has a special adapter mounted on it which acts as a seal gland surface. This adapter rotates with the screw and runs on the inside diameter of the non-rotating seals.
In normal service the seals are the only wear items, however if abnormal screw damage has occurred, the process screw can be disassembled. This feature allows the drive shaft assembly to be removed from a damaged screw and reused on the replacement screw. Also the rotating adapter and drive key can be reused or replaced in the field with a minimum amount of down time.
Seal construction is carbon fiber (graphite) reinforced PTFE with a 302 stainless steel canted-coil energizing spring.
The process screw has a round stub shaft which the adapter slides over prior to inserting into the mating hole in the screw drive shaft. This assembly along with the drive key is pinned together. This design allows for component replacement in the field. If required, the screw can be disassembled from the screw drive shaft assembly by driving the pin out. Once completed the drive shaft assembly and adapter can be withdrawn off the round stub portion of the screw.
If the screw becomes jammed the spring pin will shear and protect the screw, reducer and drive motor.