Seal System Plan 53B
In flush Plan 53B barrier fluid circulates to and from a double mechanical seal (Arrangement 3 seal). Pre-pressurized bladder accumulator provides pressure to the circulation system. Flow is maintained by the seal impeller. Heat is removed by either a water cooled or an air cooled (with finned tubes) heat exchanger. A centralized or local auto top up unit is recommended for higher pressures.
Plan 53B vs Plan 53A
- Plan 53B is recommended when barrier fluid pressure is above 10 bar to avoid the problem of nitrogen dissolving into the barrier fluid. In Plan 53B barrier fluid and nitrogen are physically separated by the elastomer bladder.
- A Plan 53B system does not require a nitrogen line near the installed pump unit. Nitrogen is injected into the system only once with the required pressure. During operation only fluid make-up is required (Automated top up is recommended for higher pressures).
- A Plan 53B system is a must for high pressure double seal applications (if Plan 54 is not considered) because it can be easily equipped with an automated top up unit which will allow for maintenance-free operation for the specified period. Fill-ups for a Plan 53A system at high pressure would be too difficult and would be required too often.
Having said that, we would recommend API Plan 53A for lower pressure applications because:
- A Plan 53A system is many times cheaper.
- A Plan 53A system is easily and cheaply made of chemically resistant components. The elastomer bladder can be damaged, e.g. by solvents which the pump is pumping. How? Doesn't the double mode prevents the pumped product from getting into the seal system? Unfortunately, no, not always, at least not for systems with manual top up. If a double seal fails but the pump has to continue operating for some reason, the pressure in the Plan 53B system may go down and become equal to pressure in the seal chamber. Then the pumped product will migrate into the seal system. If solvents are present they will attack the rubber bladder. Soon the system will start leaking solvents and oil outside. The repair will cost a lot.
All in all, a Plan 53B seal system will be a system of choice for many applications, especially for higher pressure applicataions.