API Plan 21
Product recirculation from discharge through flow control orifice and heat exchanger to seal chamber.
- Improves pressure margin over vapor pressure.
- Improves temperature margin to meet secondary sealing element limits, to reduce coking / polymerizing & improve lubricity.
- Self venting plan.
- Provides sufficient pressure difference to allow proper flow rate.
- For high temperature applications e.g. hot water application (temperature > 80ºC), hot hydrocarbons etc. In hot non-polymerizing fluids.
- Always ensure that cooler is placed after the orifice.
- Check pressure difference between discharge and seal chamber.
- Cooler duty is high leading to fouling on waterside.
- Potential plugging on process side if fluid viscosity gets high quickly.
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