A.O. Smith ST1302 User manual

APPLICATION
A.O.Smith
Motor
Master y
University
INCLUDES:
SWIMMING POOLS
SPA & JETTED TUB
JET PUMPS
INSTALLATION TIPS
REPAIR
TROUBLESHOOTING
OTHER MODULES INCLUDE:
HEATING, VENTILATION,
AIR CONDITIONING &
REFRIGERATION MOTORS
GENERAL PURPOSE MOTORS
SPECIAL PURPOSE MOTORS
PUMP
MOTORS
A.O. SMITH
A.O. SMITHA.O. SMITHA.O. SMITHA.O. SMITH
http://waterheatertimer.org/Color-codewire.html#motor

Contents
Pump Motors
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Motor Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Swimming Pool, Spa and Jetted Tub Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Service Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Jet Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Motor Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Recommended Wire Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Failure to Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Overheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Noisy Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Electrical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Protect Against Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Protect Against Dirt & Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Conventional Multimeter or Ohmmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Digital Ohmmeter/Multimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Ammeter and Voltmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Voltage Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Amperage Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Start Switch Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Start Switch Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Motor Component Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Ground Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Winding Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Protector (Thermal Overload) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Pump Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Single Speed Motor — Typical Schematic Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Motor Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
How To Replace Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Bearing Information Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Recommended Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Motor Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
2-Speed Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Start Switch Replacement and Adjustment — 2-Speed Motors. . . . . . . . . . . . . . . . . . . .41
Switch Connections High Speed Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Switch Connections Low Speed Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
2-Speed Motors High Speed Schematic Diagram (Remote Switch Operation) . . . . . . . . .44
2-Speed Motors Hi-Low Switch Reconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
2-Speed Motors Hi-Low Switch Reconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
© 2001 A.O. Smith Corporation
The information contained in this booklet is general in nature and is drawn from sources believed to
be reliable. It is intended for general information purposes only. The descriptions in this booklet
may not apply to a particular motor or a particular application. No warranties are intended to be
created by this information.
NOTICE:

Introduction
The motors discussed in this application mod-
ule are those commonly found on swimming
pools, spas, jetted tubs, home water systems and
other centrifugal pumps. The motors are 48 and
56 frame used to pump water.
MOTOR TYPES
There are five distinct electrical designs which
may be found on some or all of the pumps being
discussed.
1. Split Phase
This type is used extensively in spa, jetted
tub and above ground pool pump applica-
tions. Some are used on the lower end of in
ground pool and jet pumps. This design has a
start winding and start switch, but no capaci-
tors.
2. Capacitor Start
This is the most common single phase motor
found on in ground pool and jet pump appli-
cations. The starting torque is higher (150-
175% of full load) and starting current lower
than the split phase equivalent. The opera-
tion is similar to the split phase in that there
is a start switch to take the start winding
and capacitor out of the circuit once the
motor reaches 2/3 to 3/4 of full speed.
3. Permanent Split Capacitor (PSC)
This design does not have a start switch, but
uses a run capacitor that remains in the cir-
cuit at all times. However, the run capacitor
is more expensive than a start capacitor, and
the PSC design has only approximately 40%
of the starting torque of a capacitor start
design.
Pump Motors 1
Level 2 A.O.Smith

2Pump Motors
Level 2 A.O.Smith
4. Capacitor Start/Capacitor Run
This design is used to increase efficiency in
the run mode. Both start and run capacitors
are used.
5. Polyphase (3 Phase)
This is the simplest, most efficient design.
Its use is limited to commercial and industri-
al applications since three phase power is not
available in residential areas.
These same motors may sometimes be applied
to pumps used in other applications where the
selection and troubleshooting procedures are sim-
ilar, but the application has specific considera-
tions due to the fluid being pumped or the oper-
ating environment.
Underwriter’s Laboratories has established
safety standards for many pump motors.
Standard 1081 applies to swimming pool motors
and Standard 778 applies to jet pump motors.
The motors are two pole (3450 RPM) designs or
two pole/four pole (1725 RPM) designs. The two
pole design is used because it runs cooler and
moves more water.
Typical pump motors discussed here use ball
bearings at each end of the shaft, one of which is
locked to take any thrust loading. Some pump
motors have had ball/sleeve bearing construction.
Jet pump motors typically have double shielded
bearings and pool pump motors typically have
double sealed bearings. Both types are perma-
nently lubricated and neither type is waterproof.
Some pumps utilize a partial motor where the
pump provides the shaft extension bearing bore.
This type of construction is not popular, and
replacement usage has fallen dramatically. Some
replacement motors are still available. Two basic
types were used in the past. The difference is the
length of the shaft extension.
ST1302
CAP START/RUN
PT1072
PARTIAL MOTOR

Pump Motors 3
Level 2 A.O.Smith
The overloads or protectors used on pump
motors are tested on an eighteen day locked cycle
test. The eighteen days simulates a two week
vacation plus weekends and a couple of extra
days. During the test, the motor shaft is locked
and power is applied to the motor. Since the
motor cannot start, it will heat up rapidly and
the overload will take it off line. After the over-
load resets, the cycle is repeated. The motor
must operate at the end of the test.
If a motor does not operate because the over-
load has failed you should look for other prob-
lems. Its failure is often a symptom of another
problem.
The pumps are designated centrifugal since the
motor spins an impeller which moves the water
by centrifugal action.
Pumps used in these applications are classified
as centrifugal pumps. A centrifugal pump
derives its name from the principal known as
centrifugal force.
A centrifugal swimming pool pump, in its sim-
plified form, consists of two components. One
component is stationary and serves as the hous-
ing. It is known as the volute. Inside the volute
is the rotating component known as the impeller
which is driven by a motor. The motor is the
“work horse” of the pump while the impeller is
the “cartwheel” that moves the water.

4Pump Motors
A.O.Smith
The principle of operation can be demonstrated
by a whirling bucket of water. As the bucket is
rotated (figure 1), the water is held in the bucket
by centrifugal force. If we were to punch a hole
in the bottom of the bucket, the water would be
forced out, again by centrifugal force (figure 2).
Speeding up the rotation of the bucket, the water
would exit with greater force (figure 3).
This same principle is performed by the
impeller of the pump. As the motor turns the
impeller, the water is forced through the impeller
vanes toward the outside edge (figure 4). The
spinning action of these vanes generates cen-
trigual force (figure 5). This action imparts
kinetic or velocity energy into the water. As the
water is propelled to the outer edge of the
impeller, there is a reduction in pressure at the
eye of the impeller, creating a “vacuum” (figure
6).
The combination of atmospheric pressure on
the surface of the water and vacuum at the eye of
the impeller, causes the water to flow in the “suc-
tion pipe” to the pump.
The amount of pressure imparted into the
water by the impeller is determined in part by
the size and design of the impeller which also
effects forces placed on the motor. There are
basically two types of impellers used on these
applications; the semi-open has vanes exposed on
the front or receiving side. The back side is
closed by a shroud (figure 7). A closed impeller is
designed to have two shrouds completely enclos-
ing the vane area of the impeller (figure 8).
IMPELLER
ROTATION OF
IMPELLER
FLOW
UNDER
PRESSURE
VOLUTE
5
6

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An open impeller puts a great deal more force
on the motor bearings than does the closed
impeller. A 203 bearing is often used with closed
impeller pumps while open impeller may require
a larger 304 bearing on shaft end. Closed
impeller pumps are used extensively today.
The performance of the pump and motor is
affected by another major factor, the speed at
which the impeller is driven. The capacity of an
impeller varies in proportion to the change in its
speed.
EXAMPLE:
The capacity of an impeller is 50 gallons per
minute at a motor speed of 3450 RPM. Its
capacity will drop to 25 GPM if the motor
speed is reduced to 1725 RPM.
The above example is what takes place when
using a 2-speed motor (3450/1725) for energy sav-
ings during low traffic periods on pool or spa
motors. The load on the motor is reduced drasti-
cally but you also do not get the turn-over rate of
the high speed.
In the original applications, each motor is test-
ed with a specific pump,under a range of operat-
ing conditions. Each impeller requires a specific
amount of horsepower to turn at a given speed.
If a weaker replacement motor is selected the
pump’s output will not just be reduced, the motor
will be overloaded. The motor is trying to run at
its normal speed around 3450 RPM, and the
impeller needs more power to be driven at that
speed. If a stronger motor is selected, there will
not be a significant increase in the pump’s out-
put. The stronger motor may run a little faster,
but the impeller does not need the added horse-
power to run around 3450 RPM. In summary,
the motor and impeller should be considered a
matched set.
7
8

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Replacement
Motor
Selection
Thru Bolt Round Flanged Keyed Round Flanged Threaded Square Flange
REPLACEMENT MOTOR SELECTION
The nameplate on the motor being replaced
contains much of the critical information needed
to select a new motor. Some of the nameplate
data detailed in the Replacement Module is
repeated below in order to reemphasize its impor-
tance to the application.
Choosing the right replacement motor is easy
using these 5 steps:
1. Know which end frame you need. Is it:
2. Know the total horse-
power output.
Find it on the motor's name-
plate. Use this equation:
The total horsepower times
(x) the service factor of the
replacement motor must be
equal to or greater than that
of the original motor being
replaced.
3. Is the original motor single or three phase?
The original and replacement motors must be the
same unless the power supply is being changed.
4. What is the correct voltage?
The operating voltage of the replacement motor
must match the voltage of the original motor. A
single voltage motor is an acceptable replacement
for a dual voltage motor and vice versa.
5. What is the motor's cycle or hertz?
As a general rule, 50-cycle motors should not be
substituted for 60-cycle motors and vice versa.

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SWIMMING POOL, SPA
AND JETTED TUB MOTORS
Applications include in-ground pools, above
ground pools and pool cleaners.
There are no efficiency standards for single
phase motors. Motors designated high efficiency
by a motor manufacturer are just more efficient
than their standard motors. Swimming pool
pumps are an excellent application for high effi-
ciency motors since they typically run many
hours a day, even continuously. Compare the
operating costs of two motors with their purchase
price.
All commonly used swimming pool, spa and jet-
ted tub motors also operate on the principle of
centrifugal force.
Pool and spa motors are two pole (3450 RPM)
designs. The two speed versions are 3450/1725.
Four pole windings are used on the low speed.
Theoretically, the loading on these pump motors
drop off at a cubed rate compared to the speed.
Examples of horsepower ratings are one (1) HP
on high speed and one-sixth (1/6) HP on low
speed and 2 HP / 1/2 HP.
Pool and spa motors are required to have a
ground bonding lug. This lug is on the outside of
the motor and when connected offers visual
assurance that the motor is grounded. Before
doing any work on a pool or jet pump motor,
check to see if there is any current leaking to
ground.
Swimming
Pool, Spa and
Jetted Tub
Motor s
JBT2072
JETTED TUB MOTOR
SQ1072
BONDING LUG

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In the past when brass pumps were common,
the use of motors with cast iron instead of alu-
minum end frames was common. The cast iron
has less reaction with the brass. Today, most
pumps are plastic so this is not a concern.
Small above ground pumps have a sealed
motor/pump unit which is not repairable. Motors
on the other applications are easily identified by
the type of end frame and shaft extension.
NEMA 56C face (56C and 56J) and square flange
motors are common on in-ground pool pump
applications. Many above ground pool pumps
and jetted tubs use the motor through bolts to
secure the pump to the motor. The motors have a
“Y” after the frame designation on the nameplate
indicating a non-standard mount. Even though
the mount is not standard per NEMA, it has
become standard among the pump manufactur-
ers. Spas and jetted tubs may sometimes be sim-
ilar in looks and construction with the distinction
that the water is normally drained from a jetted
tub after each use. Spas use NEMA C, square
flange and thru bolt mount motors.
Two speed motors are common on single pump
spas. High speed is used for the invigorating jet
action, and low speed is used to circulate water
when the heater is on. Less common is the use of
two speed motors on swimming pools. The unit is
run on high speed several hours a day for maxi-
mum filtration action and then switched to low
speed and run continuously. Some filtration
action does occur on low speed and a better
chemical balance is maintained. Total electrical
and chemical consumption may be reduced.
SK1072
ST1072
SQ1152
CBS2072

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Pool sweep pumps may use motors with special
flanges and shaft extensions. These are specifi-
cally identified in motor manufacturers’ catalogs.
Running a pump dry does not harm the motor
which is actually operating at a very light load.
However, if the seal is damaged by the dry oper-
ating condition, it will leak and probably allow
moisture into the motor bearing.
It is not recommended that a jet pump motor
be used as a replacement for a pool pump motor
even though horsepower and mountings may be
equivalent. The pool motor will have a ground
bonding lug, different ventilation standards for
safety, possibly larger bearings, and a higher
ambient temperature rating.
Specifics of motor construction, operation,
nameplate information, and servicing are covered
in other modules. Following are points which are
important to reemphasize in relation to pump
motor applications.
SPS1052
POOL SWEEP MOTOR
RPS1052
POOL SWEEPMOTOR
PL1072
POOL SWEEP MOTOR

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Voltage
VOLTAGE
Most dual voltage (115/230V) motors are con-
nected at the factory for 230 volts for two rea-
sons. First, the highest percentage of motors are
installed on the higher voltage. Second, if a
motor is connected for 230 volts and 115 volts are
applied in the field, the motor will hum and trip
the overload. If connected for 115 volts and 230
volts are applied, it burns out immediately.
Motors are designed to operate at plus or
minus 10% of the nameplate rating. This means
the motor will operate at 103 volts to 126 volts on
the 115 volt connection; and, 207 volts to 253
volts on the 230 volt connection. At 207 volts, the
amps will be higher and the RPM will be approx-
imately 25% lower.
If the system is rated at 208 volts or 200 volts,
a motor specifically designed for these ratings
should be used since the voltage could go as low
as 187 or 180. Specific 208 and 200 volt single
phase motors are not normally stocked for
replacement. The alternative is to use the next
higher horsepower motor. For example, use a 1
horsepower, 230 volt motor when a 3/4 horsepow-
er 208 volt motor is needed. Three phase motors
have some greater ability to operate at 208 volts.
But, the next higher horsepower should be used if
a 200 volt motor is required.
NEMA no longer recognizes 208 volt systems.
The standard is now 200 volts.

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Service
Factor
SERVICE FACTOR
Typical service factors for full rated one horse-
power pool pump motors are 1.65 for square
flange and 1.4 for NEMA C. One horsepower jet
pump motors typically have a 1.4 service factor.
Over the years, various amp ratings have been
used on motor nameplates. Some motors may
have rated amps which are amps at one horse-
power. This number is basically useless since
the impeller loads the motor to the service fac-
tor. This motor would also have a rating for full
load, service factor or max amps. This is the fig-
ure to use when checking a replacement motor
after installation. Some service people make a
temporary connection so that the amps may be
easily checked, or the connections are made so
that a loop in the wire is available for checking
amps.
If total horsepower or horsepower times ser-
vice factor is difficult for service persons to
understand, the concept is practically impossible
to explain to a homeowner. If a one horsepower
motor came off the installation, a one horsepow-
er must go back on. Uprated motors are ones on
which the horsepower is increased and the ser-
vice factor is decreased. The total horsepower
remains the same. To see how this works, make
a copy of a motor manufacturers full rated and
uprated motor listings. Put the two listings side
by side so that the one horsepower uprated
motor lines up with the three quarter horsepow-
er full rated motor. You will see that the charac-
teristics such as amps and weight are the same.
The same comparison may be done with pump
curves.

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The following chart illustrates the important
fact of comparing total or maximum horsepower:
High Service Low Service
Factor Motor Factor Motor
NEMA
F.L. Std. Motor F.L. Up-Rated
HP SF MAX HP HP SF MAX HP
1/3 1.75 .58 1/2 1.16 .58
1/2 1.60 .80 3/4 1.07 .80
3/4 1.50 1.13 1 1.13 1.13
1 1.40 1.40 1-1/2 1.00 1.50
1-1/2 1.30 1.95 2 1.00 2.00
High Service Low Service
Factor Motor Factor Motor
Higher than
F.L. NEMAS.F. F.L. Up-Rated
HP SF MAX HP HP SF MAX HP
1/3 1.95 .65 1/2 1.30 .65
1/2 1.90 .95 3/4 1.27 .95
3/4 1.65 1.25 1 1.25 1.25
1 1.65 1.65 1-1/2 1.10 1.65
1-1/2 1.47 2.20 2 1.10 2.20
2 1.30 2.60 2-1/2 1.04 2.60
Uprated
Uprated
Uprated
Uprated
Uprated
CAPACITORS
It is recommended that replacement capacitors
be of the same MFD and voltage rating as the
original. If the exact replacement is not avail-
able, it is recommended to use one with a MFD
rating not more than 10% greater. Using one
with a larger value could make the motor run hot
and loose torque. The voltage rating should also
vary only on the high side. In some cases, it will
be necessary to go beyond 10%. Example, if a
370 volt unit is not available, the next rating is
440 volt.
Uprated
Uprated
Uprated
Uprated
Uprated
Uprated

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JET PUMPS
The two most popular types of home water sys-
tems have their water delivered and pressure
developed by either a jet pump or submersible
pump.
As the name implies, the submersible
pump/motor unit is located in the water supply
and connected to a waterproof electrical supply.
The jet pump/motor unit may be located in the
home, or outside if there is little risk of freezing.
In freezing areas, the pump may be located out-
side in a pit which is covered and protected from
freezing.
Most jet pumps use open drip proof motors
(ODP). When used in a vertical application out-
doors, a different or additional rain canopy is
required. A separate “dog house” or motor cover
such as the Blue Devil™ unit shown here provide
protection from the elements and improves motor
life. Motor covers must allow free air flow so that
hot air from the motor is not recirculated, short-
ening motor life.
Jet pumps are called single stage if they have
one impeller and multi-stage if there are two or
more impellers.
The motor shaft is parallel to the ground in a
horizontal jet and vertical in a vertical jet.
All jet pump motors are two-pole (3450 RPM)
designs.
Jet Pumps
8200 MC-200
UNIVERSAL MOTOR COVER
(fits 1/3 HP to 2 HP motors)

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Most jet pumps use NEMA C face (56C or 56J)
or square flange motors. Most square flange
motors have 1/2-20 threads but some have 7/16-
20 threads. Many other centrifugal pump appli-
cations such as lawn sprinklers and irrigation
use jet pump type motors.
Jet pump motors typically have shielded bear-
ings while swimming pool pump motors have
sealed bearings. Both types of bearings are per-
manently lubricated and neither is waterproof.
Running a pump dry does not harm the motor
which is actually operating at a very light load.
However, if the seal is damaged by the dry oper-
ating condition, it will leak and probably allow
moisture into the motor bearing.
Jet pumps operate on the principle of centrifu-
gal force. The motor spins the impeller which
does the work.
Jet pumps get their names from the principle of
operation in which a stream of water is pushed
through a nozzle into a diffuser creating an area
of low pressure. This low pressure draws addi-
tional water from the supply (usually a well).
The action of getting water from the well into
the pump system is caused by air pressure. At
sea level, air has enough pressure to lift a column
of water thirty-four (34) feet. Because of differ-
ences in air pressure, elevation and system effi-
ciencies, most jet pumps have an arbitrary lift
rating of twenty-five (25) feet.
T1072
JET PUMP MOTOR

One way of visualizing the action is comparing
it to drinking from a straw. The partial vacuum
created when you suck on the straw causes the
drink to be forced up the straw by air pressure. If
the container from which you were attempting to
drink were sealed, liquid would not be drawn into
and up the straw.
Jet pump systems may be shallow well or deep
well. In shallow well systems the jet assembly is
located on the pump. In deep well systems the
jet assembly is located in the well, normally
below water level. If the water level falls more
than twenty-five below the jet during pumping or
draw down, the pumping action will slow and
eventually stop as the water level in the well con-
tinues to drop.
Convertible jet pumps may be configured for
either shallow or deep well applications.
Shallow well systems use one pipe into the
water source and deep well systems use two
pipes. One pipe provides water to operate the jet
and the second pipe carries water to the surface.
Systems known as packers are deep well systems
which use the well casing itself as one of the two
pipes.
A pitless adapter is a fitting which goes
through the well casing below the frost line. The
part inside the well has two pieces, with an O-
ring seal, which slide apart. A piece of pipe is
threaded into the top of the adapter so that the
movable part and the pipe or pipes extending to
the water may be removed. The use of a pitless
adapter allows the pipe or pipes going to the
pump to be buried below the frost line.
PITLESS ADAPTER
GROUND
LEVEL
FROSTLINE
WATER LEVEL
CHECK (FOOT)
VALVE
PITLESS
ADAPTER
TO HOUSE
LIFTPIPE
Pump Motors 15
Level 2 A.O.Smith

16 Pump Motors
Level 2 A.O.Smith
A check valve or foot valve is normally located
in the plumbing line before the pump. This “one
way” valve is needed so that the pressure in the
system will not bleed off when the pump stops. If
the valve leaks, the pump will start and stop,
even through water is not being used.
Since for all practical purposes, water is non
compressible, a pressure tank is used in the sys-
tem.
A pressure switch is used to start and stop the
motor. The “cut in” setting is the pressure at
which the motor starts. The “cut out” setting is
the pressure at which the motor stops. The
amount of water (in gallons) that is pumped in
each cycle is called draw down. In a specific sys-
tem, the draw down amount may be varied by
changing the cut in and/or cut out settings.
The low and high pressures of the system are
determined by the cut in and cut out settings, not
by the amount of air pressure in the system.
As water is pumped, air in the tank is com-
pressed until system pressure reaches the cut out
level. The most popular tanks have a bladder or
diaphragm which separates the air and water.
Other systems use an air volume control and put
air into the tank each time the pump is started.
If the water and air were not separated, or air
was not added, the air in the tank would all dis-
solve in the water and the tank would become
“waterlogged”.
If the air charge in a system is reduced, the
pump will still start and stop at the same pres-
sures, but less water will be pumped in each cycle
because there is less air to compress. As the
amount of air is decreased, the tank approaches a
waterlog condition and the system operates as if
there were no pressure tank.
AIR
WATER
AIR
WATER
DIAPHRAGM
TO HOUSE
PUMPSIDE
DIAPHRAGM
PRESSURE TANK
30 PSI CUT IN
50 PSI CUT OUT
HOUSE PUMPSIDE
AIR
WATER
HOUSE PUMPSIDE
BOTH AIR AND WATER
AT 40 PSI
1. FAUCET OPENED
2. AIR PUSHES ON DIAPHRAGM
3. WATER SENT TO SYSTEM
4. AT 30 PSI, PUMPSTARTS
AT 50 PSI,
PUMPSTOPS

Pump Motors 17
Level 2 A.O.Smith
The primary function of the pressure tank is to
protect the pump motor. Without a tank, pres-
sure in the system would drop to zero almost
immediately when a faucet was opened. Then,
almost as quickly, the cut out pressure would be
reached and the pump would shut off. The cycle
would repeat as long as the faucet remained
open. This is the same thing that happens when
a pressure tank becomes waterlogged.
Short or rapid cycling is hard on the pump
motor whose windings are subjected to starting
or in rush current levels on an almost constant
basis. The start capacitor will often fail because
its duty cycle is exceeded. They are rated at
twenty starts of three second duration per hour.
Rapid cycling causes heat to build up which may
cause failure. Premature wear also occurs on the
start switch.
When a pump’s flow decreases, the pressure
increases to a point known as shut off. This pres-
sure may be many times the cut out pressure set-
ting. Water hammer is caused by flowing water
in a system suddenly being stopped. Water ham-
mer can cause sudden pressures as high as 760
PSI with system pressure of only 60 PSI. Since
there is a delay between the time the pressure
switch senses cut out and the time the pump
actually stops, water hammer will occur.
The shut off point may be determined by a
gauge with the pump running against a closed
discharge. This point could also be found by
lengthening a vertical discharge pipe to the point
where the pump is unable to cause water to flow
from the top.

18 Pump Motors
Level 2 A.O.Smith
When running at shut off the energy is convert-
ed to heat. The water in the pump casing can
boil under pressure to the point where a plastic
impeller is melted. Some of the heat goes into
the motor shaft and back to the bearing causing
possible failure.
If a jet pump is used as a centrifugal pump
with the jet assembly removed, the motor may
overload particularly in a flooded suction condi-
tion. Flooded suction means water is available to
the pump without the pump having to create a
suction lift.
Jet pump motors may be either single voltage
(115 or 230 for example) or dual voltage
(115/230). On original equipment, 115 volt 1/3
and 1/2 HP units are common since there is
enough volume to warrant a separate model with
a slightly lower motor cost. Most replacement
motors are dual voltage and factory connected for
high voltage. If 115 volts are applied to a motor
connected for 230 volts, the motor will just hum
and probably not turn. In the reverse condition,
the motor will immediately burn out.
The motor will not run faster or be more effi-
cient on the high voltage,but a smaller wire size
may be used since the amps at 230 volts are one-
half the amps at 115 volts.
A dual voltage motor is sometimes temporarily
run on low voltage at a new home site until the
permanent power supply is available.