AAON LC-054 - Manual (Page 43)

43
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 US gpm;
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 from
accumulating 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.
Step 4. Inspect and clean O ring cavity and
install new O ring and seat. Valve disc stem
should be inspected and replaced if worn.
Valve stem O ring should be replaced at this
time as discussed under Repacking of Flo-
Trex section.
Safety glasses should be worn.
CAUTION