Injection of clean or cool liquid from external source into the seal chamber.
1. Reduces flashing or air intrusion across seal faces by providing a positive flush.
2. Maintains vapour pressure margin.
3. Always provided at a pressure greater than seal chamber pressure.
4. If maintained properly the best of all single seal plans (subject to acceptance of contamination).
1. Dirty or contaminated fluids.
2. High temperature applications.
3. Polymerizing and oxidizing fluids.
4. Media with poor lubrication properties.
1. External source should be continuous and reliable at all times, even during start up and shut down.
2. Flush fluid must be compatible with process fluid due to product contamination.
3. Product degradation can occur.
4. Ensure use with close clearance throat bushing to maintain pressure in stuffing box and control the rate of contamination of pumped media.
5. Careful selection of flush fluid required to ensure that it does not vaporize on entering the seal chamber.
6. Fluid expenditure of Plan 32 may be as expensive as one or more seals per year.