Minimum Inlet Pressure; Maximum Inlet Pressure; Minimum Flow Rate; Maximum Starts And Stops - Grundfos Hydro Multi-E Series Installation And Operating Instructions Manual

27.5 Minimum inlet pressure

Hf
Hf
H
H
pb
Pb
Fig. 56 Parameters for the calculation of minimum inlet
pressure
The minimum inlet pressure "H" in feet of head required to avoid
cavitation in the pumps can be calculated as follows:
H = pb x 2.31 - NPSH - Hf - Hv - Hs
pb = Barometric pressure in psi. Barometric pressure can be
set to 14.5 psi.
In closed systems, p
b
psi.
NPSH = Net Positive Suction Head in feet of head
The NPSH value can be read from the NPSH curve at
the highest flow which the individual pump will be
delivering.
Hf = Friction loss in inlet manifold in feet of head at the
highest flow the individual pump will be delivering.
Note: If a check valve is installed on the inlet side of
the pump, the friction loss in the valve must be added.
See the manufacturer's data.
Hv = Vapor pressure in ft
Hs = Safety margin of minimum 2 feet of head.
In some regions, the pump system is available with a
low inlet manifold which makes it more suitable for
suction lift operation. Contact Grundfos for further
information.
Example
pb
Pump type
Flow rate
NPSH
(from Grundfos Product Center)
Hf
Liquid temperature
Hv
H
H
This means that each pump can operate at a suction lift of
maximum 3.9 psi (2.8 meters head).
Pressure calculated in psi (bar): 2.8 x 0.0981 = 0.27
Pressure calculated in kPa: 2.8 x 9.81 = 27.4
NPSH
NPSH
Hv
Hv
indicates the system pressure in
= 14.5 (1 bar).
= CRE 15, 50 Hz.
3
= 15 m /h
= 1.7 psi (1.2 meters head).
= 4.26 psi (3.0 meters head).
= 180 °F (82 °C).
= 3 psi (2.1 meters head).
= pb x 10.2 - NPSH - Hf - Hv - Hs
[14.50 psi (meters head)].
= 1 x 10.2 - 1.2 - 3.0 - 2.1 - 0.5
equal to 3.9 psi (2.8 meters
head).

27.6 Maximum inlet pressure

The maximum inlet pressure must not exceed 116 psi (8 bar).
However, the actual inlet pressure plus the pressure when the
pump is operating against a closed valve must always be lower
than the maximum operating pressure.

27.7 Minimum flow rate

Due to the risk of overheating, the pumps must not be used at
flow rates below 10 % of the rated flow rate of one pump.
The pumps must not run against a closed outlet
valve.

27.8 Maximum starts and stops

The system must not be started and stopped via the power supply
more than four times per hour.
When the system is switched on via the power supply, it will start
after approximately 5 seconds.
If a higher number of starts and stops is desired, use the input for
external start-stop when starting or stopping the system.
When started via an external on/off switch, the system starts
immediately.

27.9 Diaphragm tank

The diaphragm tank precharge pressure must be set to 70 % of
the setpoint.
If the setpoint is changed, the diaphragm tank precharge
pressure must be changed accordingly to ensure optimal
operation.
Measure the precharge pressure while the system is
pressureless.
We recommend that you use nitrogen gas for precharging.

28. Inputs and outputs

Ground reference (GND)
All voltages refer to GND.
All currents return to GND.
Absolute maximum voltage and current limits
Exceeding the following electrical limits may result in severely
reduced operating reliability and motor life.
Relay 1:
Maximum contact load: 250 VAC, 2 A or 30 VDC, 2 A.
Relay 2:
Maximum contact load: 30 VDC, 2 A.
GENI terminals: -5.5 to 9.0 VDC or less than 25 mADC.
Other input/output terminals: -0.5 to 26 VDC or less than 15
mADC.
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