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In Piping Plan 53C, there is an external barrier fluid system pressurized by a piston accumulator supplying clean liquid to the barrier fluid seal chamber. The barrier liquid is maintained at a pressure greater than seal chamber pressure.
Barrier liquid is circulated through the system by means of an internal circulating device. To maximize barrier 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 53C is used with an Arrangement 3 liquid seal and differs from Piping Plan 53A in that pressure is maintained in the barrier liquid through the use of a piston accumulator. The piston accumulator senses pressure from a reference source (normally a line connected to the seal chamber) and creates a higher pressure through differential areas in the piston. This high pressure creates the required pressure differential necessary for an Arrangement 3 seal. Since the barrier pressure is generated from the seal chamber pressure, the system is self-energizing and reacts to fluctuations in the seal chamber fluid pressure.
To create the reference pressure in the piston transmitter, process fiuid is introduced into the piston. This requires that the materials used in the piston transmitter are compatible with the process fluid. Process fluids that contains solids, tend to plate out on metal surfaces, or solidify under atmospheric temperatures are not suitable for a Piping Plan 53C.
Effective flow of the Piping Plan 53C system is only achieved with proper exclusion of all gas and air bubbles from the seal cooler and piping. Venting of the system during commissioning is critical to proper operation.