E-Mail: aavolyn@bellatlantic.net

The piston rod packing can be the largest single source of compressor cylinder gas leakage.
Quality sealing installations are your best chance to control compressor emissions to
the piston rod from the compressor cylinder into the distance piece and from the distance
piece into the compressor frame and the atmosphere. These mechanical sealing rings by
their design are controlled leakage devices. As the packing wears over time, packing
leakage will occur. To prevent gas from passing back into the distance piece and
or/compressor frame and potentially becoming fugitive emmissions, it is necessary to direct
normal gas leakage into a flare or vapor recovery system. This can be accomplished with a
pressure packing case design, which utilizes a special inert buffer gas sealing ring
arrangement as illustrated above. This packing design uses one or two sets of wedge rings
to seal buffer gas (nitrogen is commonly used) in two directions, which creates an inert buffer
gas barrier. By maintaining the buffer gas pressure 15 PSIG higher than the vent pressure
(as recommended by API 618), cylinder gas packing leakage that may occur is directed into
the packing vent an ultimately into a flare or vapor recovery system. Since the wedge rings
seal the buffer gas in two directions, buffer gas usage is normally low. When the packing
rings and piston rod are in good condition,the usage of packing buffer gas is normally in the
range of one cubic foot per hour. An increase in the buffer gas usage rate indicates packing
ring wear is occurring. This information can be helpful in identifying and scheduling packing
maintenance. If excessive pressure packing wear should occur, additiional protection against
gas migrating from the cylinder through the distance piece into the compressor frame cane
be utilized. A simliar buffer gas sealing arrangement can be incorporated in the oil wiper
packing and/or partition packing.All packing cases in process applications have vent
connections to remove any gases leaking past the pressure packing where strict emissions
control is required.

616 ORANGE ST.

P.O. BOX 1097

MILLVILLE, NJ 08332

Telephone: 856-327-8040

Fax: 856-327-9595

E-Mail: aavolyn@bellatlantic.net