Classification of Mechanical Seals

Classification by pusher vs. non-pusher and balanced vs. non-balanced

Pusher vs. Non-pusher

Pusher seals utilize a dynamic secondary seal which moves axially with the major seal face. Non-pusher seals have a static secondary seal which stays stationary against the shaft or sleeve.

Pusher and Non-pusher types of mechanical seals

Defined by the secondary seal type: o-ring or polymer wedge versus bellow, rubber or metal.

Application fields of each type overlap.

Most apparent distinction is the pressure limit.

Acquisition cost can vary widely.

Balanced vs. Unbalanced

Balanced seal

Reduced closing forces

Reduced power consumption

For pressure up to 3000 psig

Always recommended for volatile liquids

Unbalanced seal

High closing forces

Low leakage

For pressure up to 200 psig

Not recommended for volatile liquids

Next: Classification by face patterns

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