Standard Screw Compressor - RWB Series
3-14
M&M
R
EFRIGERATION
I
NC
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Slide Valve Position Ramp Start Limiting
The Slide Valve Position Ramp Start feature has been provided to limit capacity increases
after the compressor starts. The operator can define the minimum positions to start ramp-
ing, the total time to limit capacity increases and the maximum position. Once the com-
pressor is started the capacity ramp timer is started, and the capacity will be allowed to
increase to the minimum position as soon as required. Once at the minimum, capacity
increases will be limited. The maximum allowable position of the slide valve will be gradu-
ally increased from the minimum position to the maximum position over the ramp dura-
tion. When the capacity is limited due to this feature, the screw state will display
“LIMIT:SV”. Unlike other limiting and unloading, the compressor is not considered fully
loaded when in this state. This feature is available in Automatic, Auto-Remote and
Sequenced mode. When in sequenced mode, the capacity ramp is also used to limit
movement of the slide valve when the compressor is a fully loaded machine. If a fully
loaded compressor is forced to unload for any reason, the capacity ramp will engage from
the current slide valve position once capacity control resumes. The capacity ramp start
parameters are set-up on the slide valve position setpoint screen.
High Unload
High Limit
Ramp Unload
Ramp Limit
Compressor
Start
Ramp
Duration
Parameter
Value
Time After Compressor Start
Compressor is Unloaded
Compressor is Limited
Ramp Figure
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