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
The UDC dryer uses a spool valve with high temperature seals
and an actuator motor to direct airflow through the appropriate
beds of the dryer. Proper alignment is crucial for satisfactory
system operation.
Some of the problems associated with improper alignment of
the valves are:
High Dewpoints as moist regeneration air enters the process air
stream. Low Air Flow as process and regeneration air fight against
each other within the system. Over Temperature conditions at
the hopper because the regeneration air during a portion of it
cycle is at a significantly higher temperature than material
is normally exposed to.
How to check for leakage at the valves:
1. Set controller for 32 degrees F.
2. Turn dryer off.
3. Remove two top hoses from spool valve assembly and cover openings
with tape.
4. Turn dryer on.
5. Check exhaust ports on back of machine. There should be no
air coming out of the exhaust ports. If air is detected you have
a sealing problem.
6. Cycle the dryer through changeover and check both valve positions.
If leakage is detected at either position adjust the sealing
disks or replace as required.
High Return Temperature
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Chart
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 cooling
the air in the system you can determine if the water is absorbing
the 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 |
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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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A single blower supplies air to both the regeneration process
sides of this system. Bleed air is used in the regeneration side
while the process side uses the main part of the air stream.
Air must flow freely and correctly through the regeneration heater,
past the valve and through the desiccant bed or the system will
be adversely affected.
Problems associated with restricted or misdirected Regeneration
Air Flow include:
High dewpoints develop as moisture laden air enters the process
air stream.
High Process Temperatures at the hopper as regeneration air at
600 degrees F. is misdirected into the process air stream
Some of the causes of restricted air flow are:
Clogged filter; filter should be checked and cleaned or replaced
as required.
A loop in the return air line from the hopper restrict air flow.
Remove loops.
A return line packed with material will also restrict air flow.
Remove the obstruction.
One of the causes for misdirected air flow is a misaligned
valves allow process air to enter the regeneration air flow.
Valves should be adjusted as required.
Blower Filter |
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A filter that is contaminated may restrict air flow and allow
dirt to build up in the blower housing. This causes incomplete
desiccant regeneration, and over temperature conditions at the
hopper because of the restricted airflow.
To Check and Clean or Replace the Blower 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 by using compressed air from the inside
out.
5. After cleaning return the filter to the housing. Replace cover
and resume operation.
Desiccant Maintenance and Testing
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Chart
In UDC 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 thus 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.
g. 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.
Volatile 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.
Blower Motor Amps |
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Air must flow freely past through the filter, through the
appropriate bed and out of the system. If it does not the desiccant
cannot release its trapped moisture and high dewpoints develop.
The blower motor has been appropriately sized to produce enough
velocity to move air through the system. 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 blower motor contactor or relay.
2. Use an amp probe to check each wire coming from the contactor
and record your findings.
3. If readings vary from leg to leg by more than 10 percent you
may have a faulty regeneration blower motor.
4. Faulty motors should be repaired or replaced immediately to
avoid adverse affect to the drying systems.
Blower Rotation (UDC 100 &
150 only) | Back
to Selection Chart
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 cover from the housing
so you clearly see the blower wheel. 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.
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.
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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Chart
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:
Valve Leakage caused by 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 regeneration air filter if allowed to become plugged will
also cause positive pressure at the hopper air outlet. Clean
or replace the filter.
Technical Support
telephone: 703-490-7009
fax: 703-490-7008
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