API Plan 32

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API Plan 32 Seal Flush Plan

API Plan 32

Overview:

API Plan 32 utilizes fluid from an external source to provide cooling and lubrication for the mechanical seal. The external fluid is routed through a flow controlling device (e.g. needle valve) before being injected into the mechanical seal. Optionally, a flow indicator and temperature indicator can be included in the piping arrangement. Additionally, a y-strainer can be included in this piping plan to remove occasional large particles.

Advantages:

Increased reliability – The external fluid that is injected into the mechanical seal provides an improved environment for the seal to operate. The external fluid is often a lower temperature and particulate-free fluid. In many opinions, this is one of the best piping plans for both single and dual seals.

Disadvantages:

Cost – Often, the external fluid that is used for plan 32 is costly due to the relatively higher quality of the fluid. Additionally, the volume of external fluid required for plan 32 is typically serval thousand gallons per year, amounting to a substantial annual expense. 

Compatibility – The external fluid must be compatible with the pumped fluid, as the two fluids will mix within the seal chamber and pump. 

Best For:

  • Single and dual mechanical seals. When utilized with dual seals, the plan 32 will be the flush plan for the seal faces that are sealing against the pumped fluid.
  • Dirty (i.e. containing particulates) process fluids
  • Process fluids susceptible to polymerization or “setting-up” at ambient or lower temperatures

Best Practices:

  • The plan 32 flush pressure should be set no less than 15 psi above the seal chamber pressure. This will ensure that the seal is continuously wetted by the external fluid and not the pumped fluid.
  • The plan 32 flush pressure should be maintained at all times, both when the pump is operating and in standby. This will ensure that the seal does not get contaminated by the pumped fluid.
  • The plan 32 fluid supply should be reliable and consistent at all times, even during transient conditions (i.e. startup and shutdown).
  • The recommended flowrate of the plan 32 flush is approximately 1 gpm per inch of pump shaft (e.g. 2.5 gpm for a 2.500 in. pump shaft).
  • A close-clearance throat bushing should be installed in the seal chamber to hold backpressure at the seal and to limit consumption of the external fluid. 
  • Routine Maintenance:
    • Check the flush pressure of the external fluid to ensure it is at least 15 psi over the pump seal chamber pressure.
    • Check the fluid temperature and flowrate, if included in the piping arrangement.