AAON BL-600 - Manual (Page 48)

48
From the Flo-Trex performance curve, a 4
in. valve with 5.4 ft of pressure drop
represents a flow of 400 USgpm
From the flow characteristic curve, a 4 inch
valve at 50% open represents 34% of
maximum flow.
The approximate flow of a 4 inch valve with
a 5.4 ft pressure drop when 50% throttled is:
100
34) x (400
= 136 USgpm
100
34) x (25.2
=8.57 L/s
Note: To prevent premature valve failure
it is not recommended that the valve
operate in the throttled position with
more than 25 ft pressure differential.
Instead the pump impeller should be
trimmed or valves located elsewhere in
the system to partially throttle the flow.
Operation
To assure tight shut-off, the valve must be
closed using a wrench with 25 to 30 ft-lbs of
torque.
To assure trouble free check valve operation
and shut-off operation, the valve should be
periodically opened and closed to keep valve
seat and valve disc guide stem free of
buildup of system contaminants.
Repacking of Flo-Trex valve under full
system pressure
If it is necessary, the stem O ring can be
changed under full system pressure.
Step 1. Record the valve setting.
Step 2. Turn the valve stem
counterclockwise until the valve is fully
open and will not turn any further. Torque
to a maximum of 45 ft-lbs. This will ensure
good metal to metal contact and minimal
leakage.
Step 3. The valve bonnet may now be
removed. There may be a slight leakage, as
the metal to metal backseating does not
provide a drip-tight seal.
Step 4. Clean exposed portion of valve stem
being careful not to leave scratches.
Step 5. Remove and replace the O ring
gasket.
Step 6. Install the valve bonnet.
Step 7. Tightening the valve bonnet is
necessary to stop any leaks.
Step 8. Open valve to balance set point as
recorded in Step 1.
Note: On valve sizes of 2-1/2 inch and 3
inch, the full open position is 5 turns,
though the valve will open to 5-1/2 turns
which is just back of seating of valve.
Seat Replacement
Step 1. Drain the system and remove valve
from piping.
Step 2. Remove the body bolts from the
body using an Allen Key.
Step 3. Remove seat and O Ring. O rings
are not used on valves of 8 inches or larger.
Safety glasses should be worn.
CAUTION