Pressurized external barrier liquid reservoir supplying clean fluid to the inboard and outboard seal faces.
Description
This plan is used in Arrangement 3 seals and requires the use of a pressurized barrier fluid seal reservoir and forced circulation via a pumping ring.
Application Notes
- Used with Arrangement 3 seals.
- Typically chosen for dirty, abrasive, or polymerizing products not compatible with a Plan 32.
- Barrier liquid is maintained at a pressure greater than the seal chamber pressure. It is recommended that the barrier liquid pressure always exceeds the maximum seal chamber pressure by at least 20 psi [1.4 bar].
- Circulation of barrier liquid to and from the reservoir is dependent on thermal siphoning and/or an internal circulating device (pumping ring) inside the seal.
- Used when no process leakage to the atmosphere can be tolerated.
- Process fluid never leaks to the atmosphere unless reservoir pressure is lost.
- Cooling system is typically built into the reservoir.
- Barrier liquid must be compatible with the process liquid because it will leak into the product.
- Best piping practices must be followed to avoid vapor entrapment and stalled flow in the tubing.
Pros:
- No process fluid leaks
- Integral cooling system
Cons:
- Barrier fluids might undergo gas entrapment
- Requires strict adherence to best piping practices
- Barrier fluid levels must be maintained
- Barrier fluid and process fluids must be compatible due to the possibility of mixing