MIL-HDBK-1005/7A
5.4.4
Specific Speed . Centrifugal pump selection is
strongly influenced by efficiency and cavitation considerations.
The specific speed of a particular pump at the discharge head
and suction lift conditions should not exceed that prescribed
for pumps of this type in HI standards, unless the application
is of sufficient importance for military representatives to
witness satisfactory operation - in-shop tests at higher specific
speeds.
5.4.5
Net Positive Suction Head (NPSH) . For centrifugal
pumps, design of the intake system should ensure that the
available NPSH exceeds the required NPSH, to prevent boiling
under reduced pressure conditions and cavitation of the
impeller. A reasonable margin of safety should be provided, at
least 2 or 3 ft. Required NPSH can be obtained from the pump
manufacturers, and available NPSH can be calculated using
formulas in Hydraulic Institute Standards.
5.4.6
Lubrication. The choice (oil, grease, or water) and
treatment should be consistent with the bearings used, as
follows:
a)
Oil for sleeve bearings.
b)
Grease for antifriction bearings.
c)
Water where the heat generated is excessive.
d) Lubrication to be applied in accordance with the
manufacturer's instructions.
e) The system must prevent entry of oil or grease
into a potable water supply.
f) For vertical pump line shafts, use rubber bearings
and water lubrication.
5.4.7
Seals. Mechanical seals should be used where
corrosive or volatile liquids are handled. Stuffing boxes
should be properly packed and sealed by a sealing liquid in
accordance with the manufacturer's instructions.
54
Previous Page
