.jpg)
In Piping Plan 54, there is a pressurized external barrier fluid system supplying clean liquid to the barrier fluid seal chamber. Piping Plan 54 is used with Arrangement 3 liquid seals and the barrier liquid is maintained at a pressure greater than seal chamber pressure. Barrier liquid is circulated by an external pump or pressure system. The design of the system including instrumentation, coolers, filters, and other components is outside the scope of this standard.
Piping Plan 54 systems are also pressurized dual-seal systems with inner seal leakage into the pumped product. In a Piping Plan 54, a cool clean product from an external source is supplied to the seal as a barrier liquid. The supply pressure of this product is at least 0.14 MPa (1.4 bar) (20 psi) greater than the pressure the inner seal is sealing against. This results in a small leakage of barrier fluid into the process.
This plan with an Arrangement 3 seal should never be used where the barrier liquid pressure is less than the sealed pressure. If it were, the failure of one inner seal could contaminate the entire barrier liquid system and cause additional seal failures.
Piping Plan 54 is often used in services where the pumped fluid is hot, contaminated with solids, or the internal flow inducer is unable to supply a sufficient flow rate. If Piping Plan 54 is specified, carefully consider the reliability of the barrier liquid source. If the source is interrupted or contaminated, the resulting seal failures are very expensive to rectify. A properly engineered barrier liquid system is typically complex and often expensive. Where these systems are properly engineered, they provide among the most reliable systems.