Xylem HV 1.1 - 1.2 - Manual (Page 37)

37
Generally a slight pressure drop is allowed on the first pump before the next is started. This
allows for brief systems fluctuations without pump cycling. Once the
next pump starts, however, you will want the system to resume its normal set
pressure.
For example, if the pressure drop allow 0,35 bar before the next pump starts, and
the increased pressure needed to compensate for system losses is 0,2 bar, you would
enter 0,35 + 0,20 = 0,55 bar (= calculated value of the parameter ACTUAL VALUE
INCREASE) to compensate for both system pressure drop and compensation
requirements.
Application example:
1) Pump 1 reaches the speed of ENABLE SEQ: CONTROL
2) Pressure falls and reaches the start-value of the 2
nd pump
(= REQUIRED VALUE – ACTUAL VALUE DECREASE)
3) Pump 2 is switched on automatically
4) The required value is calculated new, after the start of the 2
nd pump in the
following way!
New required value = REQUIRED VALUE – ACTUAL VALUE DECREASE + ACTUAL
VALUE INCREASE
Generally:
k ... Number of active pumps (k >1)
P = P
set
+ (k-1)*[lift value – fall value]
• Lift value = Fall value ⇒ Pressure constant when pumps switch on
• Lift value > Fall value ⇒ Pressure rises when lag-pump switches on
• Lift value < Fall value ⇒ Pressure falls when lag-pump switches on
Note:
This value is cumulative. An extra 0,2 bar will be added to the total system pressure with
each additional pump which turns on. For example, if the initial system pressure was 3,5
bar, pump two would create 3,7 bar, pump three would create 3,9 bar, and pump four
would create 4,1 bar system pressure.
To do this, enter the amount of pressure drop
you will allow before the next pump starts
(=value of parameter ACTUAL VALUE
DECREASE). The diagram shows the pressure
drop and increase.
To increase the pressure even more to
compensate for system loss at higher flows,
enter the total of the system drop allowed
before next pump starts and the increased
pressure (ACTUAL VALUE INCREASE) desired.