INSTALLATION, START-UP & MAINTENANCE MANUAL
MODEL NO.: SD-220 TO SD-600- DDS OPTION
REV 0 – May 24,,.2001
18
SECTION 3
3.3 SPECIAL EQUIPMENT
3.3.1 DDS Controls
The DDS control option is a dewpoint demand switching system that monitors the
dryer dewpoint performance and manages the requirement for regeneration of the
dryer. The DDS controls major components are a digital dewpoint display
hygrometer and a humidity sensor.
The
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type SD Air dryer is designed to provide a specific pressure dewpoint
performance (generally –40 F (-40 C)) at the most severe operating conditions
specified. (Maximum flow at lowest pressure and highest inlet temperature). The
regeneration purge flow rate required for the dryer is calculated and adjusted to
achieve this dewpoint and is based on these conditions.
For example, for dryers operating at 100 PSIG (690 kPa) and 100 F (38 C) the
purge flow rate is approximately 15% of the specified maximum inlet flow. Dryers
operating under less severe inlet conditions will introduce a reduced humidity load.
The DDS controls have been factory programmed to monitor the dryer outlet
dewpoint performance and prevent initiation of a regeneration cycle under these
conditions.
The DDS controls system has the following standard features, refer to the enclosed
technical bulletin for a complete overview of the digital hygrometer display.
Digital display can be toggled to degrees F, C, and PPM.
Detection for cable fault between hygrometer and moisture probe.
Stainless steel humidity probe sampling cell with service valves.
3.3.2 DDS Controls – Start up and operation
The DDS controls system when supplied should be disabled for the initial 8 hours
of dryer operation. A dryer fitted with the DDS control will have a 3-position selector
switch on the electrical control panel. The 3 positions of this switch will perform the
following actions:
Position 1: POWER OFF
Position 2: POWER ON
Position 3: DDS ON
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