16
Determine average outlet flow available by subtracting Aver-
age Purge Flow (APF) found in 3.6.1.2 from the inlet flow to the
dryer.
NOTE
Average outlet flow may be used to determine available down-
stream air supply if a storage vessel (e.g. receiver tank) of sufficient
volume is available between dryer and point of air usage. Otherwise
use minimum outlet flow to determine downstream air available.
EXAMPLE
Find maximum inlet flow, maximum and average purge flows,
and minimum and average outlet flows for a 60 scfm unit with a MWP
of 150 psig operated at 120 psig on a 10 minute cycle. Dryer will
operate with an inlet air flow of 46 scfm.
Step 1: Find Maximum Inlet Flow @120 psig by multiplying
Maximum Inlet Flow at Rated Conditions from
Table 3E by Inlet
Pressure Correction Factor for 120 psig from
Table 3F : 60 x 1.08 =
64.8 scfm.
Step 2: Find Maximum Purge Flow by multiplying Maximum
Inlet Flow at Rated Conditions from
Table 3E by Maximum Purge
Flow Factor from
Table 3G : 60 x .162 = 9.7 scfm.
Step 3: Find Average Purge Flow by multiplying Maximum
Inlet Flow at rated conditions from
Table 3E by Average Purge/
Repressurization Flow Factor from
Table 3H: 60 x 0.097 = 5.8 scfm.
NOTE
At 46 scfm inlet flow, dryer is operating at 70% of maximum flow
found in Step 1: (46/64.8 = 70%.) Average purge flow is based on
Economizer Switch setting of 70%.
Step 4: Find Minimum Outlet Flow available by subtracting
Maximum Purge Flow (Step 2) from inlet flow: 46 - 9.7 = 36.3 scfm.
Step 5: Find Average Outlet Flow available by subtracting
Average Purge Flow (Step 3) from inlet flow: 46 - 5.8 = 40.2 scfm.
3.7 Determining outlet pressure dew point at
various inlet compressed air temperatures:
The outlet pressure dew point is determined by the compressed
air temperature at the inlet to the dryer and cycle time selected ( 4
or 10 minutes). Use
Table 3I to determine outlet dew points at var-
ious inlet compressed air temperatures and cycle times.
3.5 Verify that dryer is operating within design
parameters
3.5.1 Maximum working pressure:
Refer to Serial Number Tag to determine maximum working
pressure of dryer.
WARNING
Do not operate dryer at pressures above the maximum pres-
sure shown on the tag.
3.5.2 Minimum working pressures:
150 psig, 10.5 kgf/cm
2
MWP models -
60 psig (4.2 kgf/cm
2
) for dryers operated on a 10 minute cycle
80 psig (5.6 kgf/cm
2
) for dryers operated on a 4 minute cycle
250 psig, 17.6 kgf/cm
2
MWP models
125 psig (8.8 kgf/cm
2
) for dryers operated on a 10 minute cycle
150 psig (10.5 kgf/cm
2
) for dryers operated on a 4 minute cycle.
If lower inlet pressures are encountered, consult factory.
3.5.3 Maximum operating temperature: 120
°
F (49
°
C).
3.5.4 Maximum Inlet Flow Capacity
3.5.4.1 At 100 psig ( 7.0 kgf/cm
2
): For maximum inlet flow at 100
psig (7.0 kgf/cm
2
) refer to
Table 3E.
3.5.4.2 At pressures other than 100 psig (7.0 kgf/cm
2
) : Multiply
inlet flow from
Table 3E by multiplier from Table 3F that corresponds
to system pressure at inlet to dryer.
3.6 Determining Purge and Outlet Flows:
3.6.1 Purge Flows
3.6.1.1 Maximum Purge Flow.- Maximum Purge Flow (MFP) is
the amount of purge air flowing through the off-stream tower when
the purge/repressurization valve is open. After the purge/
repressurization valve closes, the purge flow will gradually decrease
as the off-stream tower repressurizes to line pressure.
For maximum purge flow multiply inlet flow at rated conditions
from
Table 3E by Maximum Purge Flow Factor from Table 3G that
corresponds to the dryer MWP, Cycle Time Setting, and air pressure
at inlet to dryer. For dryers supplied with the optional Automatic
Purge Saving System operating in the Demand Cycle Mode, use 10
minutes as the cycle time.
3.6.1.2 Average Purge Flow - For dryers with the standard
control board and dryers with the Automatic Purge Saving System
operating in the fixed cycle mode:
The Average Purge Flow (APF) is the actual amount of flow
used during the entire purge/repressurization cycle. It includes the
maximum purge flow (MFP) for a portion of the purge/repressurization
time and the volume of air used for repressurization, averaged over
the cycle time.
To determine average purge flow, multiply maximum inlet flow
at rated conditions from
Table 3E by Average Purge/Repressurization
Flow Factor from
Table 3H that corresponds to the dryer Maximum
Working Pressure, Inlet Pressure, Cycle Time Setting, and Econo-
mizer Switch Setting.
3.6.2 Outlet Air Flow
3.6.2.1 Minimum Outlet Flow
Determine minimum outlet flow available from dryer by sub-
tracting Maximum Purge Flow (MFP) found in 3.6.1.1 from inlet flow
to the dryer.
3.6.2.2 Average Outlet Flow - For dryers with the standard
control board and dryers with the Automatic Purge Saving System
operating in the fixed cycle mode: