Service manual

B - 4

Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0

Appendix B • Vission 20/20 Application Procedures

SETPOINT SELECTION EXAMPLE

The following example is to illustrate the selection of setpoints for the Pulldown feature. The values picked are NOT

representative of actual ﬁ eld applications.

Assumptions and Variables:

• Current suction pressure is at 80 psig

• Target suction pressure is 20 psig. (This deﬁ nes a change of 60 psig).

• Time duration allowed to get to setpoint is 10 days (240 hours) of Pulldown time.

• Suction pressure change allowed for each step is 5 psig.

Figure B-1. Pulldown Setpoints

So, for the ﬁ rst 20 hours the compressor runs at 75 psig, then for the next 20 hours at 70 psig, then for the next 20

hours at 65 psig, and so forth.

After the 12th step (running at 25 psig), 240 hours will have elapsed, and the new setpoint changes to 20 psig. After

the Pulldown setpoint equals or is less than the control setpoint, the Pulldown feature disables itself.

To calculate the Delay Per Step setpoint:

Number of Pulldown Steps = Delta 60 psig change * 1 step/5 psig = 12 steps

Delay per step = 240 hours / 12 steps = 20 hours/step