Page 206 - Know and Understand Centrifugal Pumps

Mechanical Seals

BALANCED SEAL
Fiqure 13-8

Advantages of balance

1. Less heat Generated - Less force between the faces indicates less
heat generated. Heat is the principal reason for premature seal
failure for two reasons:
w It affects the elastomer, which is the seal component most
sensible to temperature.
Heat can cause a phase change in the pumped liquid.
- Some liquids like caustic soda can crystallize with additional
heat.
- Some liquids can solidify with heat (sugars).
- Some liquids can vaporize with heat (water, propane).
- Some liquids lose their lubricating qualities when heated
(water).
- Oils can varnish and carbonize with heat.
- Some liquids can form a skin with heat (milk, paints).
- Plated seal faces can suffer heat check with additional heat.
- Acids become more corrosive when they are heated
2. Balanced seals can seal vacuum - this is common in condensate and
lift pumps.
3. High Pressure - High pressure was the original purpose bringing
about the development of balanced seals.
4. Less energy consumed - Saving energy is more important every day.
5. Less wear - All other conditions being equal, balanced seals wear
less than their unbalanced versions.

6. High Speed Shafts - Shafts at 3,000 rpm or higher causes the seal
faces to generate even more heat. Balanced seals reduce the
pressure and force between the faces, thereby generating less heat.

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