93
Step 5.
On the Flo-Trex Performance Curve
with Valve in Full Open Position locate the
differential pressure obtained in Step 3 and
project line horizontally across to intercept
with Valve Performance Curve. Drop a line
vertically down to read the flow rate at the
bottom of the chart.
Step 6.
Calculate the flow rate of the valve in
the throttled position by multiplying the flow
rate (Step 5) by the percentage of maximum
flow rate (Step 4).
Example:
Valve size: 4 in.
Differential pressure is 5.4 ft
Number of open rings is 3.
From the table, the number of rings for the
4in valve fully open is 6.
Divide open rings by total, 3/6 = 50%
throttled.
From the Flo-Trex performance curve, a 4in.
valve with 5.4 ft of pressure drop represents
a flow of 400 USgpm
From the flow characteristic curve, a 4in
valve at 50% open represents 34% of
maximum flow.
The approximate flow of a 4in 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.
Safety glasses should be worn.
CAUTION
Summary of Contents for LZ Series
Page 2: ......
Page 27: ...27 Figure 6 Concrete Pad Mounting with Dimensions Figure 7 LZ Base ...
Page 36: ...36 Figure 17 Typical Flue Vent Piping ...
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Page 95: ...95 Flo Trex Cross Section ...
