Page 237 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

3. Vaporizing Liquids Certain liquids vaporize with heat (think of
steam), and other liquids vaporize with a drop in pressure (think of
liquid propane or freon). To control vaporizing liquids so they
don’t change phase in the seal chamber.

CAUSE OF VAPORIZATION SOLUTION
1. Too much heat Cool the seal chamber. See Crystallization.
2. Drop in Pressure Double seal with pressurized barrier fluid

4. Film or Skin Formation Some liquids form a skin (like hot milk)
with heat. Others form a film (like paints) on contact with air:

CAUSE OF FILM SOLUTION
1. Temperature Control it See Crystallization
2. Contact with air Quench and Drain or Double Seal

5. Very High Temperature Remove the heat with cooling. See
Crystallization.
6. Non-Lubricating Liquids No lubrication or heat dissipation.
Remove the heat with a double seal and a barrier tank with forced
convection flow.
7. Dry Running Pump Again, no lubrication or dissipation of heat.
Remove the heat with a double seal and barrier tank with forced
convective flow.
8. Dangerous Liquids Use a dual seal with a pressurized barrier tank.
9. Gases and Liquids Tending to Gas Gases cannot lubricate the
seal faces. No dissipation of heat. Use a dual seal with forced
convective flow.
10. Slurries and Suspended Solids Should be purged or flushed with:
w Water

w The filtered or cleaned product
A compatible liquid
w A posterior additive in the system
11. Cryogenics Cryogenic liquids are too cold for most seals. Use a
metal bellows mechanical seal with no elastomer parts.
12. Corrosive Liquids Vary with the temperature. Use seal
components resistant to corrosion. You should take into
consideration the: