Environmental Engineering Reference
In-Depth Information
2.8 hydrauliC MaChines (PuMPs)
Chapter 3 presents a thorough treatment of pumps and pumping
characteristics important to wastewater treatment. In this chapter,
we briefly introduce pumping basics in order to provide a more com-
plete treatment of water hydraulics. Conveying wastewater to and from
process equipment is an integral part of the wastewater industry that
requires energy consumption. The amount of energy required depends
on the height to which the water/wastewater is raised, the length and
diameter of the conveying conduits, the rate of flow, and the physical
properties of the water/wastewater (in particular, viscosity and density).
In some applications, external energy for transferring wastewater is not
required; for example, when water/wastewater flows to a lower elevation
under the influence of gravity, a partial transformation of the poten-
tial energy of the water/wastewater into kinetic energy occurs. However,
when conveying water or wastewater through horizontal conduits, espe-
cially to higher elevations within a system, mechanical devices such as
pumps are employed. Requirements vary from small units used to pump
only a few gallons per minute to large units capable of handling several
hundred cubic feet per second (Cheremisinoff and Cheremisinoff, 1989).
Table 2.2 lists pump applications in wastewater treatment operations.
Note:
When determining the amount of pressure or force a pump must
provide to move the water or wastewater, the term
pump head
is used.
Several methods are available for transporting water, wastewater,
and chemicals for treatment between process equipment:
•
Centrifugal force inducing fluid motion
•
Volumetric displacement of fluids, either mechanically or with
other fluids
•
Transfer of momentum from another fluid•
•
Mechanical impulse
•
Gravity-induced transport
Depending on the facility and unit processes contained within, all
of the methods above may be important to the maintenance operator.
2.8.1 Pumping hydraulics
*
During operation, water enters a pump on the suction side, where
the pressure is lower. Because the function of the pump is to add pres-
sure to the system, discharge pressure will always be higher. An impor-
tant concept to keep in mind is that in pump systems measurements are
taken from the point of reference to the centerline of the pump (horizon-
tal line drawn through the center of the pump).
*
This section is adapted from Arasmith, S.,
Introduction to Small Water Systems
, ACR
Publications, Albany, OR, 1993, pp. 59-61.
