SUMP PUMP FAILURES
Charles C. Roberts, Ph.D., P.E.
pump failures lead to substantial water losses and insurance claims that
require the attention of claims representatives. There are a variety of failure
modes associated with sump pumps, some covered by insurance, others not. Before
proceeding to discussing typical failure modes, a brief review of sump pump
system technology may be helpful.
Figure 1A depicts a typical
submersible sump pump system where the pump motor is in a waterproof enclosure and
designed to operate below water level. A float switch is used to control
operation and comes in a variety of designs, including the free floating type
(Figure 1A) as well as internal float or diaphragm designs. A check valve is
typically installed to reduce excessive cycling of the pump from back flow.
Figure 1B shows a pedestal
sump pump where the electric motor must be above the water level, since it is
not in a waterproof enclosure. The float switch is at the motor and is usually
not waterproof. The discharge piping and check valve are the same as that of
the submersible sump pump. The pedestal and submersible sump pumps are the most
Sump pumps fail to operate
for one or more of the following reasons:
Improper or lack
The following is a review of
typical failure modes, taken from actual losses involving sump pumps. Power
failure is probably the most common cause of sump pump failure. Electrical
power outage without a battery or auxiliary generator back up, results in many
flooded basements. Occasionally, even back-up systems fail especially during
long term outages. Batteries loose capacity over time and may not be able to
power a pump for sufficient time during the power outage.
that supplying electricity to
the sump pump. Figure 2 shows a sump pump system that failed as a result of
branch circuit overloading, considered an improper installation. When a power
fluctuation occurs in such an overloaded circuit, the starting current, which
is often much higher than the steady state operating current, from the other
appliances as well as the sump pump will trip the breaker and render the sump
pump system inoperative. A dedicated
circuit for the sump pump is certainly recommended.
Figure 3 is a view of a sump
pump plug that was connected to an extension cord. Rust patterns on the plug
suggest that the connection was occasionally under water which caused the circuit
breaker to trip and sump pump failure, an improper installation. It is not
recommended to attach extension cords to sump pumps. Extension cords offer
increased electrical resistance, which can drop voltage and damage pump motors.
Also the connection (Figure 3) can fall into the sump, an electrical safety
hazard as well as a possible obstruction to normal pump operation.
Interference with mechanical
operation of the pump is another common cause of sump pump failure. Sump pits
with gravel bottoms are susceptible to this. Figure 4 shows a rock jammed in a
sump pump impeller, causing sump pump failure and a water loss. Interference of
the float switch also can cause sump pump failure. These are both maintenance
related causes of sump pump failure.
Internal failure of sump
pumps occur as a result of wear out or manufacturing defect. In Figure 5, a
winding failure in the single phase motor caused non operation of a new sump
pump, which was attributed to a manufacturing defect. There was premature
insulation breakdown on stator windings after a very short usage time, a
manufacturing defect in this case.
Figure 6 is a view of failed
contacts on the pump float switch. This particular case is a wear out failure
that was brought on by improper installation. Drain back of water, as the
result of a lack of a check valve in the system, caused excessive cycling of
the switch and premature failure of the switch. Early contact failure can also
be a result of a manufacturing defect such as improper plating or excessive
current draw by the motor. The expected life of a sump pump is approximately 10
years, but varies depending on operating hours and number of start/stop cycles.
Figure 7 is an example of an
improper wiring job on a pedestal sump pump. What is depicted, is the float
switch wiring with the arrow pointing to chaffed insulation as a result of
interference with the float switch push rod. As the push rod rises to turn on
the switch, the push rod retainer clip chafed against the hot wire, which
shorted out, tripping the circuit breaker. The pump failed to operate during a
vacation period, flooding the finished basement.
Care should be taken in
handling pumps involved in basement water losses. Removal of the pump in order
to send it out for analysis may dislodge a rock (Figure 4) that caused a
malfunction. With the rock dislodged, the pump may operate properly. If the
pump must be removed and sent out for analysis, it is recommended that a
description of the system, along with photographs, accompany the pump to aid
the analyst in determining the probable cause of sump pump failure.