API Plan 52
Non pressurized buffer fluid circulation in outboard
seal of a dual seal configuration through a seal
Neither process contamination occure Nor direct
process leakage to atmosphere if used Plan 52 seal
In Piping Plan 52 there is an external reservoir
providing buffer liquid for the outer seal of an
Arrangement 2 seal. The buffer liquid shall be
maintained at a pressure less than seal chamber
pressure and less than 0.28 MPa (2.8 bar) (40 psi).
Buffer liquid is circulated to and from the
reservoir by means of an internal circulating
device. To maximize buffer liquid circulation, the
piping losses should be minimized through the proper
selection of pipe size, elimination of fittings, use
of large radius bends, and reduction in the length
of piping runs.
Piping Plan 52 works best with clean,
nonpolymerizing, pure products that have a vapor
pressure higher than the buffer system pressure.
Leakage of higher vapor pressure process liquids
into the buffer system will flash in the seal
reservoir and the vapor can escape to the collection