Environmental Engineering Reference
In-Depth Information
they must lift liquids more than about 4 feet. Diaphragm pumps are
frequently used for chemical feed pumps. By adjusting the frequency of
the plunger motion and the length of the stroke, extremely accurate flow
rates can be metered. The pump may be driven hydraulically by an elec-
tric motor or by an electronic driver in which the plunger is operated by
a solenoid. Electronically driven metering pumps are extremely reliable
(few moving parts) and inexpensive.
3.4.3 Peristaltic Pumps
Peristaltic pumps (sometimes called tubing pumps ) use a series of
rollers to compress plastic tubing to move the liquid through the tub-
ing. A rotary gear turns the rollers at a constant speed to meter the flow.
Peristaltic pumps are mainly used as chemical feed pumps. The flow
rate is adjusted by changing the speed at which the roller gear rotates
(to push the waves faster) or by changing the size of the tubing (so there
is more liquid in each wave). As long as the appropriate type of tubing
is used, peristaltic pumps can operate at discharge pressures up to 100
psi. Note that the tubing must be resistant to deterioration from the
chemical being pumped. The principle item of maintenance is the peri-
odic replacement of the tubing in the pump head. This type of pump has
no check valves or diaphragms.
3.5 ChaPTer revieW QuesTions
3.1
Applications in which chemicals must be metered under high
pressure require high-powered
pumps.
3.2
materials are materials that resist any flow-produc-
ing force.
3.3
What type of pump is usually used for pumping high-viscosity
materials?
3.4
High-powered positive-displacement pumps are used to pump
chemicals that are under
pressure.
3.5
viscosity materials are thick.
3.6
When the of a pump impeller is above the level of
the pumped fluid, the condition is called suction lift .
3.7
When a pump is not running, the conditions are referred to
as
; when a pump is running, the conditions are
.
3.8
With the , the difference in elevation between the
suction and discharge liquid levels is called static head .
3.9
Velocity head is expressed mathematically as
.
3.10 The sum of total static head, head loss, and dynamic head is
called
.
3.11 What are the three basic types of curves used for centrifugal
pumps?
 
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