Plan 55 is a new piping plan that was developed in 4th edition of API 682. Plan 55 uses an external source to provide a clean unpressurized (actually low pressure) buffer fluid to a dual unpressurized (tandem) seal. Plan 55 is similar to Plan 54 except the buffer fluid is unpressurized or maintained at a pressure not to exceed 40 psi (2.8 bar), but is always at a pressure less than the seal chamber pressure. Like Plan 54, Plan 55 fluid is circulated by either an external pump or from a process stream. There is no pumping ring in the containment seal chamber.