AAON LN-140 - Manual (Page 18)

18
Dual Pumps
When redundant pumping is required,
factory installed dual pumps can be ordered.
A dual pump is a pump with two
independent motors and pumps in a single
casing. This dual pump has a swing split-
flapper valve in the discharge port to prevent
liquid recirculation when only one pump is
operating. Isolation valves in the casing
allow one pump to be isolated and removed
for service while the other pump is still
operating.
The controls package will activate the pump
when the unit is given a run command. If the
controls do not recognize flow in 60
seconds, the second pump will be activated
and an alarm signal will be generated. If the
second pump does not activate, the cooling
will be locked out. See appendix for
additional information.
Pressure Gauges and Thermometers
Pressure gauges and thermometers are
available as a factory installed option.
Thermometers are installed on the inlet and
outlet of the unit. One pressure gauge is
installed at each pump. This pressure gauge
is connected in three places to the water
piping before the suction guide/strainer,
after the suction guide and before the pump,
and after the pump. There is also a needle
valve at each of these points to isolate the
pressure. To measure the pressure at any
given point, open the needle valve at that
point and close the other two needle valves.
One gauge is used so that the calibration of
the pressure gauge is irrelevant in the
calculation of the differential pressure.
Pipe Insulation
The water piping and components on units
with pumping packages are not insulated at
the factory. Insulation should be installed on
the water piping after the system has been
checked for leaks.