API Standard 682 PLAN53A,B,C 说明 PLAN 53 或布置 3 有压双端面密封系统用于不允许泄漏液到大气的装置中，PLAN 53A 系统由具有隔离液的双端面密封组成， 隔离液包含在密封罐中， 密封罐中增压到高于密封腔 压力大约 1.5bar(23psi),内密封泄漏将隔离液泄漏到介质中，那里总有一些泄漏。 PLAN 53B 也是有压双端面密封系统，区别
于 PLAN 53A 系统的是，通过在密封循环回路 中使用囊式蓄能器来维持压力。 PLAN 53C 同样是有压双端面密封系统，但是利用一个活塞式蓄能器以维持系统压力高 于密封腔压力。 PLAN 53 通常是超出 PLAN 52 应用范围时选用，当输送赃物，磨料或易结晶介质时，使 用 PLAN 52 能对密封面造成危害，引起缓冲液系统出现问题。PLAN 53 有两个缺点必须考虑， 总有一些隔离液泄漏到介质中，通常，这种泄漏是微细的，泄漏率通过监控密封罐液位来监 控，然而，介质必须适应隔离液的微量污染。第二，PLAN 53 系统依据密封罐压力维持在正 常水平，若密封罐压力下降时，系统将向 PLAN 52 那样开始运行，或无压双端面密封，其不 能提供同一密封完整性的水平。 特别内密封泄漏液方向将反向和隔离液将发生问题的流程介 质污染，包括密封失效。 Plan 53 or Arrangement 3 pressurized dual seal systems are used in services where no leakage to atmosphere can be tolerated .A Plan 53a system consists of dual mechanical seals with a barrier fluid between them .The barrier fluid is contained in a seal pot which is pressurized to a pressure of approximately 1,5 bar(23psi)greater than the pump seal chamber .Inner seal leakage will be barrier fluid leakage into the product. There will always be some leakage .If seal chamber pressures vary significantly, or are above 500psig, the outer seal stresses can be reduced by the application of a controlled differential pressure regulator set 20 to 25 psi higher than the pump seal chamber pressure. Plan 53b is also a pressurized dual seal and differs from Plan 53a in that pressure is maintained in the seal circuit through the use of a bladder type accumulator. Plan 53c is a pressurized dual seal as well but utilizes a piston type accumulator to maintain pressure above seal chamber pressure. Plan 53 is usually chosen over Plan 52 for dirty, abrasive, or polymerizing products which would either damage the seal faces or cause problems with the buffer fluid system if Plan 52 were used. There are two disadvantages to Plan 53 which shall be considered. There will always be some leakage of barrier fluid into the product. The leakage rate can be monitored by monitoring the seal pot level. However, the product must be able to accommodate a small amount of contamination from the barrier fluid. Second, a Plan 53 system is dependent on having the seal pot pressure maintained at the proper lever. If the seal pot pressure drops, the system will begin to operate like a Plan 52, or unpressurized dual seal, which does not offer the same level of sealing integrity. Specifically, the inner seal leakage direction will be reversed and the barrier fluid will, over time, become contaminated with the process fluid with the problem that result, including possible seal failure.