API Plan 22

API Plan 22

Recirculation from pump discharge through a strainer, a flow control orifice and a cooler into the seal chamber.

A  Strainer
B  Flow control orifice
C  Cooler
D  Temperature indicator

Seal chamber details

1  From high pressure region of pump (pump discharge or pump discharge piping)
3  Flush (F)
4  Quench
5  Drain (D)
6  Seal chamber

Example seal: EagleBurgmann LY9TC single metal bellows mechanical seal.

P&ID according to API


2  Strainer
TI  Temperature indicator



  • Similar to Plan 21 but with the addition of a strainer to remove occasional solid particles.
  • Acts as a flushing as well as a self-venting plan for horizontal pumps.
  • Uses a flow control orifice to restrict the flow of flush fluid going to the mechanical seal.
  • Improves the product temperature margin thus avoiding vapor formation.


  • Slightly contaminated (fluids with suspended solids), non-polymerizing fluids with high temperatures.

Remarks, checkpoints

  • Strainer to be installed before the orifice.
  • Strainers often have a tendency to choke and thus lead to starvation and, eventually, failure of the mechanical seal.
  • Minimum size of the orifice should be 3 mm (1/8").
  • Cooler duty is high, leading to fouling and plugging on the water side.
  • This plan does not function reliably enough to achieve a three-year operating life and is therefore not generally recommended. Plan 32 or a dual pressurized seal is a recommended option for such duties.

Pump media characteristics

  • High temperature with some suspended solids.
  • Close to vaporization point.

Location, function

  • Process side
  • Flushing and cooling



3CW-BB*, 3CW-FF*, 3NC-FB*, 3NC-BB*, 3NC-FF*

* Remark: The configurations listed for each individual piping plan are to be understood as recommendations including possible utilizations which may also be applied.