There are multiple designs available for the mechanical seal configuration. Understanding how they work will help the readers select the appropriate type for their application.

They are:

  • Conventional

  • Pusher

  • Non-pusher

  • Unbalanced

  • Balanced

  • Cartridge

Pusher seals incorporate secondary seals that move axially along a shaft or sleeve to maintain contact at the seal faces, to accommodate wear and to assist in the absorption of shaft misalignment.

Advantages are that they inexpensive and commercially available in a wide range of sizes and configurations.

The primary disadvantage of this seal type is that it is prone to secondary seal hang-up and fretting of the

shaft or sleeve, especially when the seal is exposed to solids. A pusher seal type should not be selected if the secondary seal is likely to hang-up. Can small deposit of solids form ahead of secondary sealing member?

The non-pusher or bellows seal does not have a secondary seal that must move along the shaft or sleeve

to maintain seal face contact. In a non-pusher seal the secondary seal is in a static state at all times, even

when the pump is in operation. A secondary sealing member is not required to make up the travel as the rotary and stationary seal faces wear. Primary seal face wear is typically accommodated by welded metal or elastomeric bellows which move to assist in the compression of the rotary to stationary seal faces.

The advantages of this seal type are the ability to handle high and low temperature applications (metal bellows), and that it does not require a rotating secondary seal, which means it is not prone to secondary seal hang-up or shaft/sleeve fretting. Elastomeric bellows seals are commonly used for water applications.

The disadvantages are that thin bellows cross sections must be upgraded for use in corrosive environments, plus the higher cost of metal bellows seals.

Cartridge seals have the mechanical seal pre-mounted on a sleeve (including the gland). They fit directly

over the shaft or shaft sleeve, and are available in single, double, and tandem configurations. Best of class pump users give strong consideration to the use of cartridge seals.

The advantages are that this seal configuration eliminates the requirement for seal setting measurements at installation. Cartridge seals lower maintenance costs and reduce seal setting errors.

The primary disadvantage is the higher cost, plus in some cases they will not fit into existing stuffing box/seal housings.