Dewpoint Instrument |
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The Dewpoint Instrument uses air flow from the dryer to detect
the dewpoint of the air leaving the drying system. A reading
of -40 is typically considered optimum.
Over time the sensor in the dewpoint instrument may become
contaminated or connections may loosen. Operation should be checked
against another instrument to confirm actual dewpoint
If the instrument is faulty you should test to determine the
cause: faulty mechanical connection, faulty or contaminated sensor,
faulty cable or faulty dewpoint board. All of these tests are
simple to perform.
To perform dewpoint instrument test:
1. Check sample cell for positive air flow. If no positive
air flow check the lines going to the instrument.
2. Test sensor by placing in ambient and view readings - should
climb to 0 degrees or higher.
3. Test cable by unplugging from sensor and view reading - should
drop to -40 or lower.
4. Test dewpoint board by removing cable from board and view
reading - should drop to -40 or lower.
Repair or replace components are required.
Air Leaks | Back to Selection Chart
Leaks must be detected and repaired or hose replaced as these
leaks allow ambient (wet) air into the drying system, having
a significant impact on drying. Some of the problems associated
with air leaks are High Dewpoints, Low Air Flow through the drying
system and Low Process Temperatures detected at the hopper. Some
systems can be hard piped to eliminate the chance of flexible
hose leakage.
Over time flexible dryer hose may develop pin hole air leaks.
Also mechanical connections may loosen with vibration over time.
Check mechanical fasteners. Tighten as required and then check
hose for physical leaks. If leaks are detected the hose should
be replaced.
Valves | Back to Selection Chart
Four-way valves channel the process and reactivation air flows
to the appropriate desiccant beds. If the air flow is not directed
to the appropriate bed the drying system can be adversely affected.
Some of the problems associated with misaligned valves are:
- High Dewpoints as moist regeneration air enters the process
air system.
- Low Air Flow through the system as the process air fights against
the regeneration air.
- High Process Temperatures at the hopper as regeneration air
at 600 degrees F. is misdirected into the process air stream
Wiper blades should cover the duct ports inside the valve
housing and position themselves on the valve seats at the end
of the valve motor stroke. The two valves are controlled by the
single valve actuator motor which simultaneously positions the
wipers in positions parallel to one another.
To perform DHD valve leakage test.
1. Set dryer control to 32 degrees F.
2. Note position of valve. Approximate position of wiper blades
on the shafts is indicated by notches in one end of each valve
shaft.
3. Cycle the dryer to point where the Regeneration Blower is
off. Check at the regeneration outlet for either positive air
flow or vacuum. Either indicates leakage past the valve wipers.
4. If you still think leaking valves are causing system degradation
proceed with the leakage test by blocking the Process Outlet
and checking for leakage past the valve wipers at the regeneration
outlet.
5. Use the controller to cycle the dryer to changeover and repeat
the test.
6. Excessive leakage is considered to be present when 1 percent
or more of rated CFM for the Process Blower passes the wipers.
7. If leakage is detected adjust linkage and wipers so that seating
is complete on both sides of travel, or inspect wipers for damage.
High Return Temperature
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When the temperature of the air returning from the hopper
exceeds 150 degrees F. (66 C.) desiccant cannot adsorb as much
moisture. This gives you higher dewpoints. The return air temperature
must be lowered. Typically this is not a problem using UnaDyn's
patented Pulse Cool Technology (PCT) but if you encounter a return
air temperature problem the following may help.
Check the temperature of the air returning to the dryer from
the hopper. If you cannot lower the process air temperature going
into the hopper you must lower the temperature of the air returning
from the hopper.
The use of a Return Air Cooler (Install in-line between the
hopper and dryer on the return line) may be required to lower
the return air temperature.
The flow of water through the coil may be either continuous
or regulated by a temperature control valve. If you are using
a cooling coil and suspect it is not cooling the air in the system
you can determine if the water is adsorbing heat energy by noting
the relative temperature of the inlet and outlet water lines.
The return air temperature to the dryer should be regulated
to approximately 150 degrees F. 66 C.) or less for optimum performance.
Regeneration Heater |
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A faulty Regeneration Heater can cause incomplete desiccant
regeneration and thus High Dewpoints. The heater amperage should
be checked on each leg of the heater.
To perform heater test:
1. In control cabinet locate the regeneration heater contactor.
2. Use the controller to cycle to the dryer so that the heater
is on.
3. Use an amp probe to check each wire coming from the contactor
and record your findings.
If readings vary from leg to leg by more than 10 percent you
may have a faulty regeneration element. Repair or replace as
needed.
Process Heater Amps |
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A faulty Process Air Heater can cause Under Temperature if
an element has failed in the open condition or Over Temperatures
if an element has failed in the closed condition. Amperage should
be checked on each leg to begin your diagnostics.
To perform heater test:
1. In control cabinet locate the regeneration heater contactor.
2. Set the process temperature to 32 degrees F.
3. Use an amp probe to check each wire coming from the contactor
and record your findings.
If you detect amperage on any leg one of the elements has failed
"closed" and over temperatures may result. Repair or
replace as needed.
3. Raise the process temperature to a setting that is safe for
your drying conditions but that will enable the heater to cycle
on for testing.
4. Use an amp probe to check each wire coming from the contactor
and record your findings.
If readings vary from leg to leg by more than 10 percent you
may have a faulty regeneration element. Repair or replace as
needed.
Regeneration Air Flow |
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The regeneration blower supplies air to the regeneration beds.
Air must flow freely and correctly past the regeneration heater,
past the valves and through the desiccant bed or the system will
be adversely affected.
Problems associated with restricted, leaking or misdirected
Regeneration Air Flow include:
High dewpoints develop as moisture laden air enters the process
air stream. High Process Temperatures in the system as regeneration
air at 600 degrees F. is misdirected into the process air stream.
Some of the causes of restricted air flow are:
Improper rotation of the blower wheel. Even if the wheel is rotating
the wrong way it will deliver air to the system BUT not enough.
Physically check rotation of the blower wheel.
A clogged blower wheel will severely restrict air flow. Check
the blower wheel for build and clean or replace as needed. Clogged
regeneration filter; this filter removes air borne particles
from the return air stream entering the regeneration beds and
should be checked and cleaned or replaced as required.
Misaligned wiper valves allow process air to enter the regeneration
air flow. Valves should be adjusted as required. Leaks in the
system allow air to escape which also degrades the system. They
must be repaired as soon as possible
Regeneration Filter |
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A regeneration filter that is contaminated may restrict air
flow and allow dirt to build up on the blower wheel. This causes
incomplete desiccant regeneration and thus raising dewpoints.
To Check and Clean or Replace the Regeneration Filter:
1. Turn the dryer off.
2. Remove the scalloped knob holding the cover on over the filter.
3. Remove filter and check for contamination. Replace or Clean
as needed.
4. Filter can be cleaned with solvent (if metal filter) then
using compressed air from the inside out.
5. After complete drying (if solvent was used) return the filter
to the housing. Replace cover and resume operation.
Regeneration Blower Amps
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Chart
Air must flow freely past the regeneration filter, past the
regeneration heater and through the desiccant bed. If it does
not the desiccant cannot release its trapped moisture and high
dewpoints develop.
The regeneration motor has been appropriately sized to produce
enough velocity to move this moisture laden air to its exit through
the regeneration air outlet. If the blower is not moving air
at an appropriate rate you should test the blower for proper
amperage draw. Look for appropriate nameplate readings at each
leg of the heater.
To perform blower motor test:
1. In control cabinet locate the regeneration motor contactor.
2. Use the controller to cycle to the dryer so that the blower
motor is on.
3. Use an amp probe to check each wire coming from the contactor
and record your findings.
4. If readings vary from leg to leg by more than 10 percent you
may have a faulty regeneration blower motor.
5. Faulty motors should be repaired or replaced immediately to
avoid adverse affect to the drying systems.
Desiccant Maintenance and Testing
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Chart
In DHD style dryers, air from the dehumidifier is heated by
the process heater and circulated through the hopper of material,
which gradually gives off some of its moisture to the surrounding
air.
The moisture removed from the material is carried back to the
dehumidifier, where it is adsorbed by the molecular sieve type
desiccant and held there. If the desiccant is contaminated or
degraded its ability to adsorb moisture is affected. Return air
temperature must also be 150 degrees F or less for effective
desiccant operation.
Some of the problems associated with faulty desiccant are:
High Dewpoints as moist air reenters the process air system.
Low Air Flow through the system as the process air fights against
compacted, shifted or contaminated desiccant.
To check the Desiccant:
1. Remove the tower lid. The desiccant may have shifted during
transit. It should sit level across the width of the tower. Simply
level out the desiccant if it has shifted.
2. Perform a desiccant test if you feel the desiccant is faulty
or has become contaminated.
a. Fill a 150 ml glass beaker with 45 ml (approximately 1.36
oz.) of water.
b. Measure water temperature and record. The water temperature
should not be below 60 or above 85 degrees Fahrenheit.
c. Fill a 150 ml glass beaker with 45 ml (approximately 1.36
oz.) of regenerated type 4A molecular sieve (desiccant may be
regenerated using the dryer or an oven - when using an oven.
d. Bake the desiccant at 400 degrees F. (220 degrees C.) for
2 hours, place in a sealed container and allow to cool to ambient
temperatures before proceeding with the desiccant test.
e. Place a temperature probe in the beaker with the molecular
sieve. Quickly pour the water into the beaker containing the
molecular sieve, as you stir.
f. Never add the molecular sieve to water, since the resulting
peak temperature can be as much as 10 degrees F. below what it
should be.
g. Record the peak temperature which should be reached in 10-20
seconds.
h. Subtract the starting water temperature from the peak temperature
of the mixture to get the resulting temperature rise.
i. A 40 degree F. temperature rise is considered an adequate
reading and indicates that your desiccant is not contaminated.
If your desiccant is contaminated do not replace and begin
operation without a thorough understanding of what could have
contaminated the desiccant.
Volatiles may be passing the filter; a Plasticizer Coil may be
needed. Simple housekeeping could be the problem; is the filter
being check, changed or cleaned regularly. Make sure you know
WHY the desiccant failed.
Process Blower Amps |
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Air must flow at the correct rate through the system. If it
does not the system will experience High Air Flow or Low Air
Flow depending on the problem with the blower. These seriously
affect system performance.
Excess air flow may actually convey material from the hopper
to the return air line. This clogs the line and degrades the
system causing Under Temperature conditions at the hopper.
Low air flow does not allow the dry air from the dehumidifier
to enter the hopper at enough velocity to remove moisture from
the material effectively and may also contribute to Over Temperature
at the hopper.
The process blower motor has been sized to produce enough velocity
to move the air through the dehumidifying system. If the blower
is not moving air at an appropriate rate you should test the
blower for proper amperage draw.
To perform blower motor test:
1. Look for appropriate nameplate readings at each leg.
2. In control cabinet locate the process blower motor contactor.
3. Use an amp probe to check each wire coming from the contactor
and record your findings.
4. If readings vary from leg to leg by more than 10 percent you
may have a faulty regeneration blower motor.
5. Faulty motors should be repaired or replaced immediately to
avoid adverse affect to the drying systems.
Blower Rotation |
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Air must flow at the correct rate through the system. If the
blower is rotating in the wrong direction it cannot deliver the
correct amount of air. This seriously affects dryer performance.
If the wheel is turning in the wrong direction it will deliver
air BUT not enough for correct operation and the rotation should
be corrected immediately.
Two of the problems associated with incorrect blower rotation
are Low Air Flow and Over Temperature conditions at the hopper.
To check the blower rotation remove the filter from the housing
so you clearly see the blower wheel.
Open the control box and locate the blower motor contactor
for the blower to be checked. Momentarily engage the contactor
so the motor turns on.
Observe blower wheel rotation. It should rotate so that air
is delivered to the desired components: Regeneration or Process.
There is a directional arrow on the blower wheel housing that
indicates the correct direction.
Cooling Coil | Back to Selection Chart
There are three cooling coils that can be used with these
dryers: Plasticizer Cooler, Process Cooler and Return Air Cooler
The Plasticizer Cooler is used to condense volatiles from
the return air stream before they enter the system and contaminate
the desiccant and filters.
The Process Cooler is used when drying at temperatures below
120 degrees F. It lowers the temperature of the air leaving the
dryer (which can typically reach 150 degrees F. because of residual
heat from the desiccant beds) before it reaches the process heater
and hopper.
The Return Cooler is used for drying at temperatures above
250 degrees F. It lowers the air temperature of the process air
returning to the desiccant beds. If the return air temperature
is not 150 degrees F. or lower the desiccant cannot adsorb moisture
from the air stream.
A cooling coil that is clogged will cause Low Air Flow and
Over Temperatures. Check the coil on a regular basis and clean
as required.
If water is not delivered to the cooling coil at an appropriate
rate it cannot do its job and High Dewpoints and Over Temperature
can also result.
If you are using a cooling coil and suspect it is not cooling
the air in the system you can determine if the water is adsorbing
heat energy by noting the relative temperature of the inlet and
outlet water lines.
The flow of water through the coil may be either continuous
or regulated by a temperature control valve.
Process Filter |
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A process filter that is contaminated may restrict air flow
enough to seriously degrade the drying system because of low
air flow and the resulting Over Temperature conditions at the
hopper.
An improperly positioned filter can allow dust and fines to contaminate
the dryer and desiccant.
To Check and Clean or Replace the Process Filter:
1. Turn the dryer off.
2. Remove filter and check for contamination. Replace or Clean
as needed.
3. Filter can be cleaned by using compressed air blowing from
the inside out.
4. After completion return the filter to the housing. Replace
cover and resume operation.
Process Air Damper |
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If the damper is not set appropriately the drying system cannot
operate effectively.
Some of the problems associated with an incorrect damper setting
are:
Low Air Flow; this restricts the system ability to remove moisture
from the material. Low Air Flow also contributes to Over Temperature
conditions at the hopper.
High Air Flow; this does not give the air enough time in the
hopper to effectively remove the moisture and can also contribute
to Under Temperature conditions at the hopper. Can also cause
material "carryover", plugging filter, and return air
lines.
Adjust the Process Air Damper so that the Process Blower draws
name plate amperage.
Plugged Hopper |
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Over Temperatures result from the Low Air Flow caused if the
hopper, spreader cone or return air line are plugged. Air cannot
move through the system as it is designed to do.
Check the spreader cone and make sure it is properly seated
in the hopper. If it is not, material may have bypassed the cone
and entered the return air line. Clean the line, seat the spreader
cone and begin operation.
If the spreader cone is properly seated check the spreader
cone surface. If the cone is a perforated style the holes in
the cone may have become clogged. After cleaning the cone return
to normal operation.
Vacuum at Hopper Air Inlet
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If you have Vacuum at the Hopper Air Inlet you can experience
Under Temperature or Over Temperature conditions and High Dewpoint.
Vacuum at the hopper inlet can be caused by several things:
1. Valve Leakage caused by misaligned or worn valves. Check
alignment and wear. Leakage here not only causes vacuum at the
hopper inlet but over and under temperature conditions.
2. Desiccant Bed Leakage caused by bad gasketing or desiccant
bed lids that are not seated to the tower or contaminated desiccant
also cause vacuum at the hopper inlet. Check all systems and
components for correct operation, fit and seal.
3. Improper adjustment of the process air damper.
4. The process air filter if allowed to become plugged will also
cause vacuum at the hopper air inlet. Clean or replace the filter.
5. Hopper loaders can also contribute to vacuum at the air inlet.
If the flapper is not sealing properly during loading air is
being drawn from the hopper rather than from the material source.
Check flappers for fit. Repair or replace as needed.
Positive Pressure at Hopper
Air Outlet | Back
to Selection Chart
If you have Positive Pressure at the Hopper Air Outlet you
can experience Under Temperature conditions and High Dewpoint.
Positive Pressure at the hopper inlet can be caused by several
things:
Misaligned or worn valves. Check alignment and wear. Leakage
here not only can cause positive pressure at the hopper inlet
but under temperature conditions.
The process air filter if allowed to become plugged will cause
positive pressure at the hopper air outlet. Clean or replace
the filter.
The regeneration air filter if allowed to become plugged will
also cause positive pressure at the hopper air outlet. Clean
or replace the filter.
A plugged or dirty Cooling Coil can also cause positive pressure.
Inspect the coil and clean an necessary.
Improper adjustment of the process air damper.
Technical Support
telephone: 703-490-7009
fax: 703-490-7008
Email