Maybe some further explanation of the receiver is in order. Oil-flooded rotary compressor systems utilize air/oil receivers for oil separation and recovery. In most large systems the air/oil receiver is separate from the compressor (connected by pipes, tubes, fittings, etc.). However, in small compressor systems the compressor often is mounted inside the air/oil receiver (encapsulated) to economize space, pipes, fittings, etc. The function of the air/oil receiver is the same in both large and small systems, except that in the smaller systems the compressor and receiver have a common flange. The reciever will be subjected to maximum system pressure as oil is removed from the air and the air is delivered to the customer.
So, is the encapsulated version excluded from code requirements based on the integration of the air/oil receiver and the compressor (U-1(c))? Or can the same argument apply to separate air/oil receivers?