Emerson Vission 20/20, Руководство по эксплуатации и обслуживанию

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Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
Section 6 • Compressor Control
This feature can be enabled or disabled from this page,
see Figure 6-8. If Pulldown is enabled, this feature will
only function when the compressor is running in local
Auto, Auto Sequencing mode and the Control mode is
Suction Pressure 1.
The Pulldown feature provides a method to slowly pull
the suction pressure down to operating conditions. The
pulldown method used is to step the suction pressure
down over a de
fi ned time interval.
Example:
Assume the suction pressure is at 85 psig and the set-
point we want to get to is 20 psig. The operator wants to
allow 48 hours of pulldown time. Pick a reasonable step
pressure of 5 psig for every step. This de
fi nes a change of
(80 – 20 = 60) psig.
1. Note: First step is applied immediately. So fi rst step
starts at (85 – 5 = 80) psig
2. Number of steps = delta 60 psig change * 1 step/5
psig = 12 steps.
3. Delay per Step = 48 hours / 12 steps = 4 hours/step.
4. So for the
fi rst 4 hours, the compressor runs at 80
psig.
5. Next 4 hours @ 75 psig
6. Next 4 hours @ 70 psig
7. And so forth.
After the 12th step (running at 25 psig), 48 hours will
have elapsed, and the new setpoint becomes 20 psig,
achieving the 20 psig setpoint after 48 hours. After the
pulldown setpoint is equal to or is less than the control
setpoint, the pulldown feature will disable itself.
Pulldown:
• This checkbox enables the Pulldown feature. If this
box is unchecked, Pulldown setpoints are ignored
Figure 6-8. Compressor Control Screen - Pumpdown/Pulldown Control