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AODD Configurator

AODD Configurator

Mechanical Pump Seals

8 February 2019

A mechanical seal is used to separate two environments through which the fluid must not pass.

O-RING

The O-ring is a circular ring used as a mechanical gasket or seal. It is designed to be inserted in specific housings and compressed during the assembly or two or more parts.
The joint between the parts where the O-ring is positioned can be static (if the two parts don’t move in relation to each other) or dynamic (if they move).
The latter requires adequate lubrication due to the friction, and therefore heat, produced.

The unique aspect of O-rings is that they can be made with a vast range of materials, based on the fluid that they will come into contact with.
Usually they are elastomers (elastic material designed to support a deformation and guarantee an adequate seal), but it’s not unusual to find stiffer materials (PTFE, for example).

When designing the housings it is important to create very smooth surfaces, without any crinkles or burrs, and sized according to the detailed reference manuals available.

BELLOWS SEAL

These types of seals are usually used in centrifugal pumps.
They are used to separate the fluid inlet chamber from the mechanical parts, such as motor, shaft, etc.
They are mainly used when the pump works with fluids with suspended solids, whose percentage, even in the case of a centrifugal pump, must be limited.

The figure shows a section of a centrifugal pump with a bellows seal produced by Debem.

The bellows mechanical seal, shown in the red box, consists of the following:

  • Silicon ring (grey), or in another material if requested, complete of with O-ring (fixed part)
  • Ceramic ring (white), or in another material if requested, complete of with O-ring, secured on the bellows
  • Bellows in flexible PTFE
  • AISI 316 steel spring that ensures the extension of the bellows and therefore a pressure between the two seal rings

Bellows, spring and ceramic ring are a single assembly that rotates with the pump shaft, on which the impeller is secured.
The two rings are lubricated directly by the fluid, that creates a microfilm that can reduce rolling friction.

LIP SEAL

These types of seals are usually used in centrifugal pumps.

They are used to separate the fluid inlet chamber from the mechanical parts, such as motor, shaft, etc.

The figure shows a section of a centrifugal pump with a lip seal produced by Debem.

It is used mainly for less demanding applications than the previous seal and can be made in Viton or EPDM (or other materials, according to the manufacturer)

This is a fixed mechanical seal, inside which the pump shaft rotates.
It doesn’t require lubrication, but it requires a certain amount of cooling that must be guaranteed by the pumped fluid.

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