6
OWNER'S INFORMATION cont.
Expansion tank:
• As the water temperature in the system
increases, the volume that water displaces
increases. In order to compensate for these
expansion forces, an expansion tank must be
used. AAON uses a pre-pressurized diaphragm
expansion tank that is preset for 12 psig.
• The factory pre-charge pressure may need to be
field adjusted. The tank must be pre-charged to
system design fill pressure before placing into
operation. Remove the pipe plug covering the
valve enclosure. Check and adjust the charge
pressure by adding or releasing air.
• If the system has been filled, the tank must be
isolated from the system and the tank emptied
before charging. This ensures that all fluid has
exited the diaphragm area and proper charging
will occur.
• If the pre-charge adjustment is necessary, oil
and water free compressed air or nitrogen gas
may be used. Check the pre-charge using an
accurate pressure gauge at the charging valve and
adjust as required. Check the air valve for
leakage. If evident, replace the Schrader valve
core. Do not depend on the valve cap to seal the
leak. After making sure the air charge is correct,
replace the pipe plug over the charging valve for
protection.
• Purge air from system before placing tank into
operation. All models have system water
contained behind the diaphragm.
• It is recommended that the pre-charge be
checked annually to ensure proper system
protection and long life for the vessel.
Pressure Relief Valve:
AAON installs the required pressure relief valve
in the unit. This valve is set at 125 psig. The
chart below shows inlet pressure versus capacity
for this pressure relief valve. See appendix for
additional information.
Automatic Air Vent:
There is an automatic air vent installed at the
high point of the system inside the pumping
package compartment. The air vent valve must
be in the proper position for operation. Ensure
that the small vent cap is loosened two turns
from the closed position, allowing air to be
vented from the system. It is advisable to leave
the cap on to prevent impurities from entering
the valve. See appendix for additional
information.
Dual Pumps:
• When redundant pumping is required, factory
installed dual pumps or two single 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.
• When redundant pumping is required with high
flow rates, AAON will install two independent
pumps in parallel. Each pump will have its own
suction guide/strainer, combination valve, and
isolation valves.
• The AAON 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
regarding dual pumps.
