Utilizing the robust primary faces of the 9200 series single seal, the 9200 dual retains the flexible stationary element on both inboard and outboard seal faces. The dual seal is used wherever additional environmental protection is required. For example if media poses a safety hazard, to provide some protection from intermittent dry running and applications with high solids content. The dual seal can also be specified with contacting and non-contacting secondary containment.

• Requires a seal support system such as Plan 52, 53a/b/c, 54,55.
• Can use non-contacting containment faces in specific applications.
• Provides critical environmental protection in the event of a primary seal failure.
• Can be designed for thin cross-section applications.

The Thomson 9000 series pusher seals are all stationary flexible element as standard.

According to API 682 4th Edition 

“Perpendicularity of the mating ring to the shaft axis is important for both stationary and rotating flexible element designs. “

“Perpendicularity for a rotating mating ring mounted on the sleeve (where a stationary flexible element is used) is controlled by the seal sleeve run out and perpendicularity of support surface on the sleeve. It is independent of the seal chamber face run out. An advantage of a stationary flexible element is that it will deflect to a fixed position to align with the rotating face. “

This fundamentally means that whilst the current standard views rotating and flexible element seals as the same. A design using a flexible stationary element has some benefits over flexible rotary designs that can not be dismissed.
Stationary flexible elements are preferred in many oil and gas applications, such as:

• High-temperature pumps
• Multi-stage pumps
• Pump installations with high pipe strain
• High-speed applications
• Shaft diameters above 4.25”

It is important to note that the advantages of the flexible stationary face would apply even in applications that are not as demanding as those noted above. Flexible stationary faces should be considered the preferred option in almost all applications.
API Seals and Suspended Solids

Seals using a stationary flexible element with springs external to the liquid are also a proven design in process fluids with high particulate concentrations.

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