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The Practical Pumping Handbook

.1.5 Diaphragm pump
One of the original diaphragm pump designs actuates a single large
diaphragm in a horizontal casing by means of a spring or a linkage
mechanism. Many of these are still in service in the Municipal markets
and are used to pump heavy sludges and debris laden waste from
manholes and catch basins.

The newer designs include the Air Operated Double Diaphragm
(AODD) pump that has become an industrial standby in spite of the
fact that is limited to low pressure applications and provides a pulsating
flow.

8.1.6 Progressive cavity pump
The Progressive Cavity pump has recently developed a place in the
slurry market for delivering smooth, non-pulsating flows. These pumps
are particularly effective when pumping thicker sludges with limited
amounts of small solid particles. They usually operate at less than :300
rpm to minimize wear. See Chapter 9.4.5 for further details on this
pump style.

8.1.7 Solids and slurries- useful formulae
The formula for specific gravity of a solids-liquids mixture or slurry is as
follows"

Ss x Si
Sm ~-"
Ss = c,,,, (s,- Sin)

where Sm = specific gravity of mixture or slurry
Si = specific gravity of liquid phase
Ss = specific gravity of solids phase
Cw = concentration of solids by weight
Cv = concentration of solids by volume
Example" If the liquid has a specific gravity of 1.2, and the
concentration of solids by weight is 35%, with the solids having a
specific gravity of 2.2, then the following formula will apply.

2.2 x 1.2
Sm = = 1.427
2.2 + 0.35 (1.2- 2.2)

Where pumps arc to be applied to mixtures which arc both corrosive
and abrasive, the predominant factor causing wear should be identified
and the materials of construction selected accordingly. This often
results in a compromise and in many cases can only be decided as a
result of test or operational experience.

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