API Plan 53A

Within the Plan 53A system the pressurised barrier fluid is set a higher pressure than the process fluid pressure, typically 2 barg (30 psig). This optimises seal face longevity as it helps to ensure clean, cool barrier fluid between the counter rotational seal faces.

In summary, Plan 53A is a relatively simple but very effective reliability focused tool for rotating equipment uptime. As such, if you want to adopt best practice techniques at your plant, the start point is nearly always "install a double cartridge mechanical seal and a Plan 53A system".


  • The barrier fluid is directly gas pressurised (inert gas). As there is no bladder (like Plan 53B systems) there is no bladder wear and rupture potential. System simplicity always has a place in the reliability took-kit of solutions.
  • If the barrier fluid pressure is lost, it works as a Plan 52 system.
  • Prevents process fluid leaking to atmosphere.
  • Cool, clean barrier fluid is formed in the fluid-film between the inboard counter-rotational seal faces. This provides seal life longevity.

Related Products

Double Cartridge Seals (Rotary) = RPW516,

Double Cartridge Seals (Stationary) = SPW516,

API682 Double Cartridge Seals = SPW682-53,

Slurry Double Cartridge Seals = SPS610, SPS625

Seal Support Systems (Pressurised) = STAN12, STAN28


  • Improved mechanical seal and rotating equipment longevity as the Plan 53A system creates an idealised fluid film condition between the counter-rotational seal faces.


  • As with all double mechanical seals using a higher barrier fluid pressure compared to the process fluid pressurise, process media quality can deteriorate due to barrier fluid contamination.
  • In process media sensitive applications where barrier fluid contamination is not permitted, dry running sealing technology is employed, where the barrier media is gas.


  • For dirty, abrasive and/or polymerizing products.
  • Application where process media leakage cannot be tolerated.
  • Any fluid which is unsuitable to act as a fluid film in-between the counter-rotational seal faces
  • Hazardous, toxic and inflammable process fluids.

Warning Notes

  • As with any pipework system, always vent the Plan 53A system properly before equipment start up.
  • As with all pressurised double seals, always check the barrier fluid compatibility with process media. There will always be some leakage of barrier fluid into the process media.
  • Significant environmental temperature changes and heat load can cause fluctuations on the system pressure.

Related Technical Papers

For further reading on API Plan 53A seals and systems, please click the following links to related Technical Blogs;

Applicable Products

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