English (GB)
29
9.1.3 Pressure in the pump
Fig. 24
Pressure in the LS pump
Maximum outlet pressure
Minimum inlet pressure
The minimum inlet pressure must correspond to the
NPSH curve for the pump + a safety margin of
minimum 0.5 metres head.
NPSH appears from the data booklet and Grundfos
Product Center.
Maximum inlet pressure
The inlet pr pump pressure must be lower
than the maximum pressure (p) of the pump. This is
stated on the nameplate. See fig.
, 7.
9.1.4 Flow rate
Minimum flow rate
The pump must not run against a closed outlet valve
as this will cause an increase in the temperature or
formation of steam in the pump. This may cause
shaft damage, impeller erosion, short life of
bearings, damage to stuffing boxes or mechanical
shaft seals due to stress or vibration.
The continuous flow rate must be at least 25 % of the
flow rate in the best efficiency point.
Maximum flow rate
The maximum flow rate must not exceed the value
stated on the nameplate. If the maximum flow rate is
exceeded, cavitation and overload may occur.
Operating at reduced flow and/or head
Do not operate the pump at a flow rate below 10 % of
the maximum flow rate stated on the nameplate or
with the outlet isolating or throttle valve closed.
Operating the pump under such conditions may
involve the risk of the pump being overheated. To
prevent possible damage, use protective devices
such as liquid temperature relay, bearing
temperature relay, inlet pressure monitoring, etc.
If a pump is operated at reduced head, the flow rate
will increase and the motor will consume more
current than normal. This will result in overheating of
the motor. In such situations, throttle the valve on the
outlet side instead. If an automatic throttle valve is
installed, this can be done automatically.
9.1.5 Frequency of starts and stops
The recommended maximum number of starts per
hour below apply to complete pumps with a motor
supplied by Grundfos. The values are
recommendations only.
0 to 50 kW
15 starts per hour. The motor must be stopped for at
least 3 minutes before restart.
51 to 100 kW
10 starts per hour. The motor must be stopped for at
least 5 minutes before restart.
101 to 315 kW
5 starts per hour. The motor must be stopped for at
least 10 minutes before restart.
Greater than 315 kW
2 starts per hour.
T
M
04
0
0
6
2
49
07
The maximum outlet pressure is the
pressure (p) stated on the pump
nameplate.
Inlet pressure
Pump pressure
Pressure p stated on the pump
(pressure above atmospheric
pressure)
