AAON BL-600 - Manual (Page 15)

15
See appendix for additional information on
the installation, operation and maintenance
of pumps.
Makeup Water
A city makeup water connection is provided
to replace water that is lost from the system.
Glycol units require a glycol feeder
(optional factory installed or field installed)
to replace fluid that is lost in the system.
Water should not be added to glycol
applications as this would dilute the glycol
concentration and thereby increase the
freezing temperature of the fluid.
The makeup water connection is provided
with a backflow preventer that has isolation
valves on the inlet and outlet for service.
Figure 1 shows the pressure drop versus
flow rate for the backflow preventer.
Figure 1 - Backflow Preventer
There is a pressure-reducing valve after the
backflow preventer. This valve reduces the
city water pressure to maintain the operating
pressure of the system. This valve is
adjustable from 10-35 psig with a factory
setting of 30 psig. The system pressure
varies with the height of the system. The
pressure-reducing valve setting should be set
so that the pressure at the high point in the
system is high enough to vent air from the
system (usually 4 psig). There should be air
vents at all parts in the system where air
could be trapped. If the pressure is not high
enough throughout the system, flashing
could occur in the piping or the pump could
cavitate. There is an isolation valve on the
inlet and outlet of the pressure-reducing
valve for service.
The pressure reducing valve fills the system
at a reduced rate. There is a bypass around
the pressure reducing valve for the initial fill
of the system to increase the initial fill
speed. After the initial system fill, this valve
should be closed.
Compression/Expansion Tank
As the water temperature in the system
increases, the volume that water displaces
increases. In order to compensate for these
expansion
forces, a compression or
expansion tank must be used. The factory
installed tank option includes a pre-
pressurized diaphragm compression 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