API Plan 32

API Plan 32 is essentially the injection of clean and/or cool fluid, from external source, into the seal chamber, to cool the mechanical seal faces to help improve seal longevity.

The injection of the external fluid is typically done through the FLUSH seal gland orifice port, or FLUSH orifice in the seal chamber of the pump.


Plan 32 comprises of an external fluid supplied from an external source.

The simplest type of Plan 32 is cold water piped from the water ring main of a plant.

Where the water ring main pressure is insufficient, the Plan 32 external fluid can be pumped from a water reservoir and delivered at the desired pressure to the seal chamber. The same applies when the external fluid is oil, or other types of liquid. This arrangement clearly requires one or more "additional" external pumps in the system, which consumes energy and can, itself, be prone to failure.

The external fluid then goes through a strainer to help eliminate debris. Debris in the external fluid will act to "shot blast" the mechanical seal faces if left in-situ.

After the strainer, a flow meter shows the external fluid flow rate entering the seal chamber. Hence the volumetric amount of fluid delivered into the process fluid over a set period of time, can be calculated.  

A needle valve helps to adjust the external fluid flow rate and increase/decrease pressure to the seal. A pressure gauge confirms the pressure of the external fluid entering the seal flush orifice.

IMPORTANT - If the flush orifice in the mechanical seal is smaller than the pipework, the pressure of the external fluid at the seal faces will likely be greater than what the pressure gauge is showing. Checking the actual size of the flush orifice in the mechanical seal, is a best practice tip.

Lastly, a Non-Return Valve (NRV) or Check Valve, helps to eliminate process fluid entering the external fluid ring main, in situations when the external fluid ring main pressure is interrupted/lost.


Plan 32 helps to reduces flashing and/or seal face dry running from entrapped air, by providing a positive flush.

Plan 32 helps to maintains vapour pressure margin at the seal faces, as the external fluid pressure can be precisely delivered.

If maintained properly, from a seal face cooling perspective, Plan 32 is technically one of the best single seal plans, assuming process fluid contamination is acceptable.

However, from an holistic pumping system efficiency perspective, Plan 32 has many technical, commercial and environmental drawbacks. Rotating equipment engineers need to be aware of these drawbacks and only apply Plan 32 systems wisely and with caution.


In applications were dilution of the process fluid with an externally supplied fluid is not acceptable, Plan 32 cannot be employed.

Plan 32 uses high energy. In hot applications, injecting a cool external fluid into the seal chamber (and suction end of the pump) will ultimately reduce the process fluid temperature. In consideration of the "whole system", this can be very inefficient and costly as it takes energy and heat input to get the process fluid to the desired temperature upstream of the pump. That heat and energy input is wasted if further downstream the process fluid is cooled just to help the single mechanical seal last longer. Other API plans can achieve the same benefit for the seal faces WITHOUT compromising the holistic pump system efficiency.

In pumps with temperature sensitive process fluids, controlling the fluid to an absolute temperature is difficult with the Plan 32 injection of an external fluid, specifically given in some parts of the world, the ambient temperature of externally piped fluids can range by 20-30+ Deg C depending on the time of year (Winter/Summer).  

Plan 32 should not be used upstream of an evaporator. By adding "additional" external fluid to the process fluid, it will dilute it and if there is an evaporator downstream of the Plan 32 application, that evaporators job is to essentially remove the fluid. Plants can therefore waste enormous amounts of the energy dealing with the effects of Plan 32.


Plan 32 is almost always used with single mechanical seals. Single mechanical seals rely on the process fluid to create the fluid film between the counter rotational seal faces.

Plan 32 is typically used in applications where the process media contain solids, debris and/or contaminants. These contaminants can affect the fluid film condition at the seal face, therefore reduce seal life. As such, the flush injection of a clean external fluid will improve the single seal fluid film and hence seal life.

Plan 32 is also used in polymerizing and oxidizing process fluids, or where the process fluid has poor lubrication properties.It is also found in some high temperature process fluid applications, but, as detailed in the drawbacks section, Plan 32 is often misapplied to high temperature applications.

Plan 32 must always use an external fluid at a higher pressure than seal chamber pressure. Pressure of the external flush should always be at least 2 barg (30 psig) above the seal chamber pressure to ensure a position flush flow.

Throat bushing is required to maintain an elevated pressure in the seal chamber and help to isolate it from the pumped media at the suction side of the pump. The throat bush will help reduce external flush fluid consumption.

The external flushed fluid must be compatible with the process fluid, given process fluid dilution will occur.

Warning Notes

1. The Plan 32 external flush source must be reliable and deliver a continuous flow of fluid to the mechanical seal at all times, especially during equipment start up and shut down. Failure of the external system, even just for a few seconds can irreversibly change the seal face condition and lead to seal face wear and failure.

2. Careful selection of external flush fluid is required to ensure that it does not vaporize on entering the seal chamber, as this will cause the seal faces to dry run, rapidly wear and fail.

3. Flush fluid must be compatible with process fluid due to product contamination.

4. Process fluid degradation can occur.

5. Without a close clearance throat bushing in the seal chamber, Plan 32 can be very ineffective and inefficient.

6. The cost of the external fluid, the external ring main and associated pumps, and/or the dilution of the process media and subsequent re-heating or evaporation can make Plan 32 systems VERY costs and commercially unattractive.

7. Should be used with a multi-port flush ring/design, for even distribution of the clean external fluid around the mechanical seal faces.

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