Page 193 - Womens Pavilion

“Oil-Less” Scroll Medical Air

3.0 System Operation

3.4 Normal Operation NOTE: For a compressor to be considered
available to the system, its pump must be in the
3.4.1 Controls “Automatic” position.

During normal operation, all pumps should be Table 3.1 System Pressure Factory Settings
in “Automatic” mode to eff ectively control the
system. The controls monitor the system pressure Start Stop
condition (see the table 3-1), starts and stops the System Pressure Settings (Close) (Open)
compressors depending on changing pressure Lead Varies 110 psig
conditions, and automatically alternates the lead Lag 85 psig Varies
position between compressor units. Backup Switch 80 psig 105 psig

In a typical duplex system, one compressor will be NOTE: Factory settings may vary depending on
able to handle the system load. The control will system size and confi guration.
signal the lead compressor to start at 90 psig with
falling system pressure. If the one compressor can For maintenance or other reasons, compressors can
carry the load, then the system pressure will rise to operate in “Manual” position. The compressor(s)
110 psig. At this point, the control will turn off the in the “Manual” mode will start and stop
lead compressor. When the system pressure drops depending on backup pressure switch conditions.
again to 90 psig, the control will automatically
sequence the lead role to the other compressor NOTE: Any compressor in the “Manual” mode
and will start it. This is known as “fi rst on/fi rst off ” will start and stop depending on backup pressure
instead of the more traditional “last on/fi rst off ”. switch condition.
With the “fi rst on/fi rst off ” sequencing technique,
starts and stops on the compressor are minimized. 3.4.2 Dryers
If the lead compressor runs continuously in
lead for more than 17 minutes, the control This fully automatic, heat-less type dryer
will automatically sequence the compressor alternately cycles the compressed process gas
attempting to evenly distribute the run time among fl ow through two desiccant charged vessels where
the gas’ vaporous moisture content is adsorbed.
all available compressors. If during operation, One desiccant vessel is always on-line in a drying
the second compressor is required to come on in
addition to the lead compressor, the control will cycle throughout normal dryer operation. The
turn on the “Lag Alarm” (see Section 3.6). opposite, off -line vessel is in a regeneration cycle
for removal of the previously adsorbed moisture
content, or in a purge saving cycle at line pressure.
In a triplex or quadruplex system, the operation
is very similar to the duplex operation described When the dryer is in the “Manual” mode, the
above with the following diff erences. With a
triplex or a quadruplex system, the lag unit running dryer will shift towers every 30 seconds. At normal
alarm may not necessarily correspond to the third operating conditions, one tower is approximately
or fourth compressor coming on. To determine 100 psig and the other tower is at 0 psig. Any
condition other than this is not normal and will
when the control turns on the lag alarm, it counts cause a high dew point condition. During tower
the number of units in the “Automatic” position
and makes a decision based on the pressure changeover, the online chamber will exhaust,
conditions. For example, in a quadruplex system and the chamber that is regenerating (purging)
with only 2 units in the “Automatic” mode, the lag will come to line pressure. There is a 5 second
repressurization cycle. If the dryer is in the
alarm will turn on when the pressure falls to the “Manual” mode, the dryer will use 15% of the
lag set point on the controller.
system capacity to purge the dryer.

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