TM 5-814-2/AFM 88-11, Vol. 2
required voltage. Motor starters will be designed for
engine mounted adjacent to the pump. A vertical motor
limiting the inrush current where shocks or disruptions to
mounted above, and at a distance from a vertical pump,
the electrical supply are likely to occur as a result of
will be connected to the pump with one or more lengths
pump start-up. Where low starting inrush current is
of flexible shafting. Direct drive offers the most efficient
required for constant speed pumps, such as when using
operation because no power is lost between the drive
engine driven generator sets, wound-rotor motors will be
unit and the pump.
considered as an alternative to squirrel-cage motors.
b Belt drive. Belt drives may be utilized if the
The voltage required for operation of motors and other
pump speed is different from those available with
equipment will be determined in accordance with
standard drive units, or if speed adjustment is required.
Speed adjustment is accomplished by changing pulley
engines.
Internal
or sheave ratios. Belt drives used with horizontal pumps
b Internal
combustion
combustion (I.C.) engines will be used primarily at large
require more floor space than a direct drive unit. There
pumping stations where electric motors are the primary
is power loss through the belt, which results in lower
drive units, and where emergency standby facilities are
efficiency, and belt wear increases maintenance
required. Conditions which dictate the use of fixed,
requirements. Belt drives will be used only when it is
standby power at wastewater pumping stations are
not possible to choose single speed equipment to cover
outlined in paragraph 7-4. I.C. engines will be required
service conditions, or where pump speed adjustments
for small pump stations in remote locations where no
may be required, but variable speed operation is not.
electric power source exists. At large wastewater
c Right angle drive. Right angle drives will be
treatment plants where abundant digester gas is
used on vertical pumps being driven by horizontal
produced, it will generally be more feasible to use I.C.
engines. If the engine serves as emergency standby, a
engines which are fueled by the waste gas. I.C.
combination gear box will be installed on the angle drive
engines may be arranged to drive horizontal pumps by
to allow operation of the pump by the primary drive unit,
direct or belt connections, or they may drive vertical
which is normally an electric motor. A clutch or
pumps through a right angle gear drive with an electric
disconnect coupling disengages the right angle gear
motor as the primary drive unit (dual drive). It is more
when the motor drives the pump. When the engine
common however, and will be the general rule at large
drives the pump, the clutch is engaged and the motor
pump stations, to provide fixed emergency generator
rotates freely. In case of a power failure the engine is
sets powered by I.C. engines. Generators produce
automatically started, and after reaching partial
electric power not only for pumps, but also for auxiliary
operating speed is engaged to drive the pump.
equipment such as heaters, lights, alarms, etc., and for
critical pump control systems. The types of internal
4-4.
Pump speed controls
combustion engines normally used include (1) diesel, (2)
a Mode of operation. Wastewater pumps will be
gasoline, (3) natural gas, primarily digester gas, and (4)
designed to operate in one of the following modes: (1)
dual-fuel diesel. The use of gasoline engines for
constant speed, (2) adjustable speed, or (3) variable
anything except small, remotely located pumping
speed. The type of speed control system will be
stations is not recommended due to the hazards
selected accordingly. As indicated in paragraph 4-2a,
associated with fuel handling and storage. Dual-fuel
the type of speed control required will influence the type
diesel engines fire a mixture of diesel oil and natural
of electric motor to be used.
gas, with a minimum of 10 percent diesel fuel required
(1) Constant speed. Constant speed drive is
to ignite the mixture. Propane is usually provided as a
the simplest, most reliable, and most economical mode
backup fuel for gas and dual-fuel diesel units. The
of operation, and will be suitable for the majority of
selection of I.C. engines will be coordinated with the
wastewater
pumping
applications
at
military
installation's Facility Engineer to insure that adequate
installations. However, where there is a need to match
operation and maintenance can be made available.
pumping rates with the incoming wastewater flowrates, a
variable speed drive will usually be more appropriate.
(2) Adjustable speed. By changing pulley or
4-3.
Drive mechanisms
a Direct drive. Direct drive, with the shaft of the
sprocket ratios on a belt driven pump, the speeds can
drive unit directly connected to the pump shaft, is the
be adjusted to accommodate several constant speed
most common configuration. This connection can be
pumping rates. This type of system will be used mainly
either close-coupled or flexible-coupled. When using a
in sludge pumping, but can be a good alternative
close-coupled connection, the pump is mounted directly
on the drive shaft. This is the normal arrangement for a
vertical pump driven by an electric motor. A horizontal
pump will usually have a flexible connection, with the
4-3
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