Emerson Vission 20/20 Operation And Service Manual Download

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25 – 3

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

Section 25

•

Cool Compression Control

• Auto load will be disengaged when one of the follow-

ing conditions occur;

• Pressure ratio reaches a value of 2.0 or
greater.
• Compressor has been running for 10 minutes
(de

ned by Auto Load Timer).

• Suction pressure setpoint has been reached.

Suction Oil Injection Setting
• In order to maintain adequate lubrication during low

pressure ratio conditions, the Suction Oil Injection
(SOI) solenoid is turned ON and the capacity of the
compressor is reduced.

• The SOI solenoid will cycle ON and OFF based on the

pressure ratio across the compressor.

• SOI Solenoid ON

• De

nes the Pressure ratio value at which

SOI is turned ON (default 2.00) (Digital Output
Board #1:2).

• SOI Solenoid OFF

• De

nes the Pressure ratio value at which SOI

is turned OFF (default 2.04) (Digital Output
Board #1:2).

• SOI Load Limit

• De

nes the capacity slide position at which

the compressor capacity slide will unload to if
pressure ratio falls below “SOI Solenoid ON” set-
point. This setpoint is not active until Auto Load
disengages.

• The SOI solenoid will also cycle on if the discharge

temperature superheat reaches a value of 5°F (this
value is not settable). Generally, anytime the SOI
solenoid cycles on, the capacity is limited to the SOI
Load Limit setpoint. However, this is not true if the
SOI solenoid cycles on based on the discharge tem-
perature superheat 5°F rule. If discharge temperature
superheat continues to climb and reaches a value of
6°F, the compressor will be inhibited from loading. If
discharge temperature superheat still continues to
climb and reaches a value of 8°F or more, then the
compressor will be unloaded until the superheat
drops below 8°F or the capacity has reached the SOI
Load Limit setting.

Using a Positioning Valve for Liquid Ammonia Level
Control
• A level probe inserted in the oil separator detects

liquid ammonia level. Based on the level of the am-
monia (0-100%), the level probe sends a directly pro-
portional 4-20 mA signal to the Vission 20/20 panel.
The positioning valve is then positioned based on
the Positioning Valve settings graph shown in Figure
25-2.

• Looking at the graph, when the compressor starts,

the positioning valve placement (Vertical Axis) is de-
termined based on the liquid ammonia level that is
sensed in the oil separator (Horizontal Axis). It can
be seen that as the liquid ammonia level increases
(corresponding to a larger mA value), the positioning
valve moves towards a closed position.

• The Positioning Valve position (0-100% limits) is de-

ned at three distinct levels:

• Start Level (lowest liquid ammonia level - po-
sitioning valve at maximum open position).
• Leakage (normal operating position and am-
monia level).
• Over

ll Leakage (highest liquid ammo-

nia level–positioning valve at minimum open
position).

• Liquid ammonia levels are de

ned at four distinct lev-

els (4-20ma limits);

• Start SP (minimum liquid ammonia level in
separator – the positioning valve is maximum
open).
• Linear SP (minimum level of liquid ammonia
for normal operating position).
• Upper SP (maximum level of liquid ammonia
for normal operating position).
• Max SP (maximum liquid ammonia level – po-
sitioning valve is minimum open position, main-
taining some leakage).

• On Alarms and Trips screen, Low Oil Separator Start

Temperature, High Filter Diff Start Pressure settings
are disabled.

• On Timers screen Oil Level #1 Safety Trip Delay, Oil

Level #2 Safety Trip Delay settings are disabled.