Water, Sewage & Effluent January February 2019 | Page 7

High rpm
“The requirement for a flow of 380 cubic
metres of water per hour, at differential
Local pump manufacturer KSB Pumps
and Valves was called upon to develop
a unique flywheel water pump system
able to continue pumping long enough
to mitigate the possible effects of water
hammer in the event of power failures.
Ruan Nel, KSB Pumps and Valves
project engineer, explains that the
pump was developed for the rural
Tsomo District Municipality, where it
is required for critical high-lift pumping
of potable water to supply water
transfer requirements. Due to unstable
electricity supply, the municipality,
however, required a solution to prevent
the potentially catastrophic backward
rush of water in the event of a power
failure, which could lead to water
hammer and the destruction of its
water infrastructure.
This required the technical team to
develop a reliable and failsafe method
of maintaining water pressure long
enough to reconnect power, or in
the event of no availability of power,
to (gradually) slow down and arrest
the flow without air bubble-causing
cavitation. Due to the rural location of
the pump station, the team also needed
to develop a reliable solution with
minimal maintenance requirements.
Flywheel pump
prevents damage
to infrastructure
A unique flywheel water pump system that is able to continue pumping long enough
to mitigate the possible effects of water hammer in the event of power failures, was
developed by KSB Pumps and Valves.
height of 261m with an efficiency of
80.8%, called for a powerful pump and
motor combination with the addition of
a heavy flywheel.
“Weighing in at 681kg each, the
flywheels spin up to 3 000rpm and
provide enough momentum to pump
water for at least four minutes after
power is interrupted. With a flywheel
central to the design chosen, the
pump selection was based on our
high-efficiency Multitec multistage
pumps, which we configured in an
inline orientation with the suction side
on the left front side of the pump and
discharge on the right front side to
make room for the flywheels.
“Considering the critical application
in which the pump is to be used,
we also elected to manufacture all
internals in bronze for corrosion
resistance and low maintenance as
well as added durability. In the end, this
is one of the only times worldwide that
a flywheel pump of this size and such
high revolution has been undertaken
and paves the way to apply a smart
solution to an old problem,” says Nel.
Well balanced
Ruan Nel, KSB Pumps and Valves project
engineer.
www.waterafrica.co.za
Incorporating the flywheel was a
particularly challenging undertaking,
requiring them to be specially designed
and manufactured to high standards
with balancing to G2.5 at 3 000rpm,
which is a particularly close tolerance
to ensure near-perfect balance. Mating
to the pump also required careful
engineering requiring self-centring
ball bearings able to withstand high
pressure, as well as special grease
to allow for the high rpm. Operational
bearing temperatures were tested to
remain at 19–21°C during extended
operation.
The system also uses a variable
speed drive (VSD) to synchronise the
motor, pump, and flywheel speeds and
makes use of specialised couplings
to ensure that the transfer of energy
between the motor and the flywheel
remains seamless at all times, including
start-up, power outages, and restart
while the flywheels are still turning.
The system required a heavy-duty
base plate made from channel-type
steel and reinforced around the
flywheel plumber block pedestal
similar to large industrial baseplates
and ensures that the system remains
perfectly balanced at all times.
“Our flywheel solution now ensures
that the inertia of the flywheel keeps
turning the pump and eliminates air
pockets and water hammer if power
is interrupted. It is just the kind of
reliable, mechanical solution that is
required in this isolated rural area,”
concludes Nel. 
Water Sewage & Effluent January/February 2019
7