Home | Seal Support Systems | API 682 plan 52 | Technical specifications api 682 Plan 52

Technical Specification 
API 682 – Plan 52

The range of Flopac® SPA seal support systems include plan 52 seal flushing units that are typically used with arrangement 2 contacting wet seals (2CW-CW).


Plan 52 – Description


Plan 52 seal support systems provide a buffer fluid to cool and lubricate the (in- and) outboard seal, whilst controlling product leakage.


Plan 52 seal support systems are closed loop systems that use an external reservoir to provide buffer fluid for the outer seal of an unpressurized dual seal arrangement. The process, or inner seal, of the dual unpressurized arrangement usually has its own piping plan. For example, the piping plans for a dual unpressurized seal arrangement might be written as Plan 11/52.

During normal operation, circulation between reservoir and seals is maintained by an internal pumping ring. Operated with an open vent the pressure is kept near to atmospheric, below the process/seal chamber pressure. As a result the normal product leakage will enter the closed loop of the plan 52 piping system. This product leakage is absorbed by the buffer liquid and then channelled to the external reservoir where it is collected for disposal in an orderly way; Usually vented to a flare or vapour recovery system for volatile products, or, periodically drained for non-volatile products.

Maintenance associated with seal repairs, filling, draining, and flushing of a contaminated buffer system can be considerable. Refer to notes/recommendations below.

Heat exchangers

In order to provide cool buffer fluid plan 52 seal support systems are often equipped with a cooler. The cooling capacity must be designed to cope with the seals heat generation and the heat soak.

Although natural air draught cooling is preferred, most plan 52 seal support systems are equipped with an internal liquid (water) cooler. The size of natural air draught cooling sections will often proof impractical.

For the higher heat loads external water cooler or forced air blast cooler may be considered. Flopac can provide all. Please have a look at our cooler section to check our standard availability. Tailored solutions are available as well.


A plan 52 should be equipped with a pressure indicating transmitter, a level transmitter and a level gauge to monitor the systems pressure and level. A temperature instrument could be considered if relevant.   

Provided the unit is equipped with an internal cooling coil one may also consider a cooling water sight flow indicator. 


Flopac provides a complete API 682 compliant package, including all the necessary appendages.

The operating principle of this seal plan accepts a certain product leakage. So inevitably, the inboard seals will pass pump product – mind the seal faces – and may transform the buffer fluid into (hazardous) chemical waste.
A higher cost for maintenance, seal repairs, filling, draining, and flushing of the contaminated buffer system must be contemplated.

Also, contrary to expectations, the low operating pressure of a plan 52 will not buy an inexpensive low pressure design. It is common practice – and API 682 specified – to have the plan 52 seal support systems designed for the same pressure and temperature ratings as the pump. So the non-pressurised dual seal plan 52 solution will not safe (much) compared to the pressurised plan 53 solutions. That is why for dual seal applications we would generally recommend the pressurised plan 53(B) solution as it has quite some advantages – explained elsewhere.

The non-pressurised plan 52 solution should be considered though, for high purity applications where the pumped product accepts no contamination or when high sealing pressures would result in excessive heat loads.

Non-pressurised dual seal plan 52 solutions work best for clean, solids-free and non-polymerizing products with a vapour pressure that is higher than 1.1 bar-a at lowest ambient. It is better not used for products with a low(er) vapour pressure, nor products that are highly dangerous or lethal, like H2S gas.

The unit may see some overpressure and contain product. A safe refill of buffer fluid requires specific equipment, usually referred to as topping-up / make up or refill units. Please refer to our section Make up units for further details. The use of filling funnels is strongly discouraged!

Please contact Flopac for a more detailed advise on all topics related to Flopac® seal support system plan 52. We will gladly assist.

Plan 52 – Features

Plan 52 – main features


(Near) atmospheric operating pressure.


Leakage disposed of in orderly way.


Lubricates and cools the seals.


Lower heat load.


Circulation device needed.


Benefits of the Flopac Plan 52


Wetted parts all SS316.


Flexible designs all properly engineered.


Reliable performance.


(API 682/ISO 21049) compliant.


Compact and lightweight configuration.

Directly from the manufacturer.



Alternative material selections for specific services.


Flexible designs to fit a specific location or available space.


High pressure designs (ANSI 600# / 1500#) for static designs up to 200 barg.

Additional temperature- or flow instruments to enhance monitoring facilities.

Addition of a buffer liquid circulation unit; to ensure circulation and to enhance cooling capacity.


Addition of an all stainless steel 5 ltr refill unit with 75cc/str handpump. (Other refill options available. Note: filling funnels should not be used!) 

Plan 52 – Solutions

Plan 52 Series


Low budget Flopac standard

Plan 52 Series


API 682 compliant package for shaft diameters ≤ 60mm

Plan 52 Series


API 682 compliant package for shaft diameters > 60mm

Contact us


Westelijke Havendijk 15

4703 RA Roosendaal

The Netherlands