GEA Grasso - Page 57

Grasso
Refri
g
eration Division
GRASSO SYSTEM CONTROL
01.2004/1 638660E_chapter2.doc Chap. 2 - 21
2.7.2.9 High discharge pressure limitation
The discharge pressure limitation is intended to prevent a high discharge pressure alarm.
If the discharge pressure reaches its initial limitation value, the compressor capacity cannot be increased any
further. If the discharge pressure reaches the decrease limit, the compressor capacity is reduced by 1 capacity
step immediately.
The signal dominates compared to the capacity control and is effective until the discharge pressure has become
less than the limit value and the limit timer has expired.
The discharge pressure limitation function is illustrated in the following diagram.
P
dis
Discharge pressure
A.. Time characteristic of the discharge
pressure
V.. Forced reduction of the capacity due
too high discharge pressure
B.. High discharge pressure limitation
active
T.. Limit timer active; After that this timer
has expired the capacity control is
enabled again and the compressor
capacity can be increased.
b.. Limit value for disabling capacity
increase
f.. Limit value for forced reduction of
capacity
W.. Warning limit
Al.. Alarm limit
Figure 2.25, High discharge pressure limitation
Pdis hi alarm 
High limit - 
Decr limit - 
Pdis hi alarm: Alarm limit for maximum discharge pressure in bar (a)
High limit: Begin of the discharge pressure limitation —
enter value as an offset to the alarm limit in bar
<< Limit values 01 >> Decr limit: Begin of the forced capacity reduction —
enter value as an offset to the alarm limit in bar