34
Dry running
When this function is selected, lack of inlet pressure or water
shortage can be detected. This requires the use of an accessory,
such as:
•
a Grundfos Liqtec
®
dry-running switch
•
a pressure switch installed on the suction side of a pump
•
a float switch installed on the suction side of a pump.
When lack of inlet pressure or water shortage (
Dry running)
is
detected, the pump will be stopped. The pump cannot restart as
long as the input is activated.
Restarts may be delayed by up to 30 minutes, depending on the
pump family.
Accumulated flow
When this function is set for digital input 4 and a pulse sensor is
connected to terminal 33, the accumulated flow can be
measured.
17.7.9 Digital flow input (3.12)
This display appears only if a flowmeter has been configured in
display 3.11.
The display is used for setting the volume for every pulse for the
function
Accumulated flow
with a pulse sensor connected to
terminal 33.
Setting range:
•
0-265 gal/pulse (0-1000 litre/pulse).
The volume can be set in the unit selected in the start-up guide.
17.7.10 Constant pressure with stop function (3.13)
Settings
The stop function can be set to these values:
•
Active
•
Not active
.
The on/off band can be set to these values:
•
Δ
H is factory-set to
10 % of actual setpoint
.
•
Δ
H can be set within the range from 5 % to 30 % of the actual
setpoint.
Operating conditions for the stop function
It is only possible to use the stop function if the system
incorporates a pressure sensor, a check valve and a diaphragm
tank.
Descriptions
The stop function is used for changing between on/off operation
at low flow and continuous operation at high flow.
Fig. 50
Constant pressure with stop function. Difference
between start and stop pressures (
Δ
H)
Low flow can be detected in two different ways:
1. A built-in "low-flow detection function" which functions if the
digital input is not set up for flow switch.
2. A flow switch connected to the digital input.
1. Low-flow detection function
The pump will check the flow regularly by reducing the speed for
a short time. If there is no or only a small change in pressure, this
means that there is low flow.
The speed will be increased until the stop pressure (actual
se 0.5 x
Δ
H) is reached and the pump will stop after a few
seconds. The pump will restart at the latest when the pressure
has fallen to the start pressure (actual setpoint – 0.5 x
Δ
H).
If the flow in the off period is higher than the low-flow limit, the
pump will restart before the pressure has fallen to the start
pressure.
When restarting, the pump will react in the following way:
1. If the flow is higher than the low-flow limit, the pump will return
to continuous operation at constant pressure.
2. If the flow is lower than the low-flow limit, the pump will
continue in start/stop operation. It will continue in start/stop
operation until the flow is higher than the low-flow limit. When
the flow is higher than the low-flow limit, the pump will return to
continuous operation.
2. Low-flow detection with flow switch
When the digital input is activated because there is low-flow, the
speed will be increased until the stop pressure (actual setpoint
+ 0.5 x
Δ
H) is reached, and the pump will stop. When the
pressure has fallen to start pressure, the pump will start again.
If there is still no flow, the pump will reach the stop pressure and
stop. If there is flow, the pump will continue operating according
to the setpoint.
T
M
03 8477 1607
Caution
The check valve must always be installed before
the pressure sensor. See figs 51 and 52.
If a flow switch is used to detect low flow, the
switch must be installed on the system side after
the diaphragm tank.
Stop pressure
Δ
H
Start pressure
Continuous operation
On/off operation
Grundfos.bk Page 34 Friday, July 30, 2010 10:10 PM
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