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In Piping Plan 53B, there is an external barrier fluid system pressurized by a bladder accumulator supplying clean liquid to the barrier fluid seal chamber. The accumulator and barrier liquid are 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 53B is used with an Arrangement 3 liquid seal and differs from Piping Plan 53A in that pressure is maintained in the barrier liquid system through the use of a bladder-type accumulator. The use of an accumulator prevents contact between the pressurization gas and the barrier liquid. This prevents gas absorption into the barrier liquid and allows for high-pressure operation. The accumulator is precharged prior to filling the system with barrier liquid and is brought to operating pressure by compressing the bladder in the accumulator as the system is filled with barrier liquid. Leakage past the inner and outer seals results in a decrease in the barrier system pressure. This requires that the barrier system be pressurized to a higher initial pressure and allowed to “leak” down to the minimum allowable system pressure. At this time, the system would be refilled to restore the maximum working barrier liquid volume. Seal performance is therefore monitored by pressure decrease and not by barrier liquid level as in Piping Plan 53A.
Effective flow of the Piping Plan 53B 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.