Page 411 - Centrifugal Pumps 2E

376 Centrifugal Pumps: Design and Application

Figure 17-15. Package opposed double seals.

Figure 17-16. Tandem seal installation.

• Unbalanced or balanced
• Rotating or stationary seal head
• Single spring or multiple spring construction
• Pusher or non-pusher secondary seal design

The selection of an unbalanced or balanced seal is determined by the
pressure in the pump stuffing box and the type of liquid to be sealed.
Balance is a way of controlling the contact pressure between the seal
faces and power loss at the seal. When the percentage of balance b (ratio
of hydraulic closing area to seal face area) is 100 or greater, the seal is
referred to as unbalanced. When the percentage of balance for a seal is