Plan 32 is usually called an “external flush”.  It is used in services containing solids or contaminants such that the process stream is difficult to condition in a way that will provide adequate cooling and lubrication to the mechanical seal. Plan 32 is also used when a process stream includes components which may either result in abrasive wear or will impede free movement of critical seal components. In Plan 32, the flush stream is brought in from an external source. This plan should be used in conjunction with a close clearance throat bushing. The bushing can function as a throttling device to maintain an elevated pressure in the stuffing box and as a barrier to isolate the pumped product from the seal chamber.  The design of a Plan 32 flush system involves application of hardware and logic that will provide the seal with an environment conducive to long term service, while not compromising the operation and profitability of the process stream.

Sometimes the external source for Plan 32 is more valuable than the service into which it is injected.  In such cases, the external source fluid is downgraded.  The cost of using Plan 32 can then be quite high.  For this reason, flush rates for Plan 32 are usually controlled to be at a minimum rate.