Separate purge and buffer gas in reciprocating compressors

[Sabergg1981]

Hi all.
I want to know can we use separate purge gas and buffer gas in type in distance piece of reciprocating compressors? In the other word we want sweet fuel gas as a purge gas and nitrogen as a buffer gas. Is this choice true? I doubt.
API 618 use " should " and not "shall" for preference of inert gas as a buffer gas and no comments on purge gas. What"s point of view of manufacturers?

 

[BNiessing]

I've always used the two terms interchangeably and sweet natural gas is typically an acceptable buffer/purging gas. Why do you want to use two different gasses?

 

[CaracasEC]

Why still used two different type of gas. On the distance piece, usually purge gas is nitrogen even on the piston packing. I assume that your purge gas will be in the distance piece? How about the sweet gas? What part of the compressor you are using the buffer gas? We have 4 Boil Off Gas reciprocating compressor and we used nitrogen on the distance piece and piston rod packing.