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AODD Configurator

AODD Configurator

MECHANICAL SEAL PUMP

8 February 2019

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

There are different kinds of pump mechanical seals:

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.

They are usually 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.

TYPES OF MECHANICAL SEAL FOR CENTRIFUGAL PUMPS:

BELLOW MECHANICAL 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.

Section of Centrifugal Pump

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

In the red box, we can see the mechanical bellows seal which is made up as follows:

  • 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.

MECHANICAL LIP SEAL

These types of mechanical 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.

Mechanical Lip Seal

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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