Mecanical Seal

What is a mechanical seal ?

When sealing a centrifugal pump, the challenge is to allow a rotating shaft to enter the ‘wet’ area of the pump, without allowing large volumes of pressurized fluid to escape.

To address this challenge there needs to be a seal between the shaft and the pump housing that can contain the pressure of the process being pumped and withstand the friction caused by the shaft rotating.

So, a mechanical seal is simply a method of containing fluid within a vessel (typically pumps) where a rotating shaft passes through a stationary housing.

Why we don’t use the traditional method of gland packing anymore ?

Gland packing is a braided, rope like material that is packed around the shaft - physically stuffing the gap between the shaft and the pump housing.

Users are increasingly adopting mechanical seals for the following reasons:

• The friction of the shaft rotating wears away at the packing over time, which leads to increased leakage until the packing is adjusted or re-packed.
• The friction of the shaft also means that packing also needs to be flushed with large volumes of water in order to keep it cool.
• Packing needs to press against the shaft in order to reduce leakage – this means that the pump needs more drive power to turn the shaft, wasting energy.
• Because packing needs to contact the shaft it will eventually wear a groove into it, which can be costly to repair or replace.

Can you name every parts of a mechanical seal and their roles ?

• Spring Retainer
• Spring
• Rotating seal
• O-Ring or Primary seal
• Stationary seal
• O-Ring or Secondary seal

https://www.youtube.com/watch?v=m24uWL6f8K4

There is 3 sealing points on a mechanical seal :

• One rubber seal on the stationary seal, it’s call the O-Ring
• One that is created between the two surface of the stationary seal and the rotating seal and that is lubricated with the pump water or an external source
• One rubber at the end of the rotating seal on the shaft

DO NOT with mechanical seal :

• Do not touch seal face during installation !