Pumping Calculations - Basic Mathematics for Water and Wastewater Operators - page 198

the speed of the water through the pipe—the more water you try to pump through
a pipe, the more pressure it will take to overcome the friction. The resistance can
be expressed in terms of the additional pressure needed to push the water through
the pipe, in either psi or feet of head. Because it is a reduction in pressure, it is often
referred to as friction loss or head loss .
Friction loss increases as

• Flow rate increases.

• Pipe length increases.

• Pipe diameter decreases.

• Pipe is constricted.

• Pipe interior becomes rougher.

• Bends, fittings, and valves are added.

The actual calculation of friction loss is beyond the scope of this text. Many pub-
lished tables give the friction loss in different types and diameters of pipe and stan-
dard fittings. What is more important here is recognition of the loss of pressure or
head due to the friction of water flowing through a pipe. One of the factors in friction
loss is the roughness of the pipe wall. A number called the C factor indicates pipe
wall roughness; the higher the C factor, the smoother the pipe.

Note: The C factor is derived from the variable C in the Hazen-Williams equation
for calculating water flow through a pipe.

Some of the roughness in the pipe will be due to the material; cast iron pipe will
be rougher than plastic, for example. Additionally, the roughness will increase with
corrosion of the pipe material and deposits of sediments in the pipe. New water
pipes should have a C factor of 100 or more; older pipes can have C factors very
much lower than this. To determine the C factor, we usually use published tables. In
addition, when the friction losses for fittings are factored in, other published tables
are available to make the proper determinations. It is standard practice to calculate
the head loss from fittings by substituting the equivalent length of pipe , which is also
available from published tables.

BASIC PUMPING CALCULATIONS
Certain computations used for determining various pumping parameters are impor-
tant to the water/wastewater operator. In this section, we cover important basic
pumping calculations.

p uMping r ates
Note: The rate of flow produced by a pump is expressed as the volume of water
pumped during a given period.

The mathematical problems most often encountered by water/wastewater operators
with regard to determining pumping rates are often solved by using Equations 14.4
a nd 14.5: