API Plan 53A
API Plan 53 – Pressurized Barrier Fluid System for Dual Seals
API Plan 53 is a pressurized barrier fluid system used with dual mechanical seals to prevent process fluid leakage and enhance seal performance. Unlike API Plan 52 (which operates at lower than process pressure), Plan 53 maintains the barrier fluid at a pressure higher than the process fluid, ensuring that the barrier fluid always flows toward the process side. There are multiple variations of API Plan 53, each with different ways of maintaining barrier pressure:
- API Plan 53A – Uses a regulated gas system to maintain pressure, whereby the gas is contacting the barrier fluid direct
- API Plan 53B – Uses a bladder accumulator to pressurize the barrier fluid, whereby the gas is contained in the bladder, and therefore indirect contact with the barrier fluid. This helps to avoid aeration of the barrier fluid.
- API Plan 53C – Uses a piston accumulator with an external gas source for pressurization, whereby the gas is contained at the other side of the piston, and therefore indirect contact with the barrier fluid. This helps to avoid aeration of the barrier fluid.
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Features
How it Works
- The barrier fluid system is pressurized above the process pressure, typically 2 Barg (30 psig).
- 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.
Benefits
- Bathes the seal face fluid film in cool, clean barrier fluid to optimise mechanical seal longevity.
- Zero process leakage – Ideal for hazardous, toxic, or volatile fluids where leakage is unacceptable.
- Enhanced seal cooling and lubrication – Extends seal life and reliability.
- Prevents process contamination – Ensures process purity, especially in pharmaceutical and food applications.
- Multiple configurations available – Different Plan 53 variations allow for flexibility based on pressure and operational needs.
Drawbacks
- 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.
Applications
API Plan 53 is a high-performance sealing solution designed for zero leakage applications, providing pressurized barrier fluid protection for critical processes. However, it requires careful system design, monitoring, and maintenance to ensure long-term reliability. Applications include;
- For reliability focused plants with high expectations of equipment longevity.
- For dirty, abrasive and/or polymerizing products.
- Applications 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.
Industry Sectors
- Oil & Gas Industry – Used in sealing volatile hydrocarbons, LNG, and crude oil pumps.
- Petrochemical & Chemical Processing – Ideal for toxic, hazardous, or corrosive chemical pumps.
- Power Generation – Used in boiler feed pumps and high-temperature applications.
- Pharmaceutical & Biotechnology – Prevents contamination in sterile processes. Also used for polymerizing products.
- Food & Beverage Processing – Ensures hygienic operation in food-grade applications.
- Mining and Minerals - for slurry, dirty and abrasive processes
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
Applicable Products
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