6.4.2 Frequency of starts
DANGER
Excessive surface temperature of the motor
Explosion hazard!
Damage to the motor!
▷
In case of explosion-proof motors, observe the frequency of starts specified in
the manufacturer's product literature.
NOTE
The values indicated for the frequency of starts apply to the pump only.
The frequency of starts is usually determined by the maximum temperature increase of
the motor. This largely depends on the power reserves of the motor in steady-state
operation and on the starting conditions (DOL, star-delta, moments of inertia, etc).
Observe the manufacturer’s instructions. (⇨ Section 9 Page 67)
▪
The permissible number of start-ups per day is 25.
6.4.3 Fluid handled
6.4.3.1 Flow rate
The minimum flow rates indicated refer to water and water-like fluids. Longer
operating periods with these fluids and at the flow rates indicated will not cause an
additional increase in the temperatures on the pump surface. However, if the
physical properties of the fluids handled are different from water, it is essential to
check whether an additional heat build-up may occur and if the minimum flow rate
must therefore be increased. The calculation formula in this manual can be used to
check whether an additional heat build-up may lead to a dangerous temperature
increase at the pump surface.
Unless specified otherwise in the characteristic curves or data sheets, the following
applies:
Q
max.
9)
: See characteristic curves
Q
min.
10)
= 0.15 x Q
opt.
11)
The data refer to water and water-like fluids. Longer operating periods with the
fluids and flow rates indicated will not cause an additional increase in the
temperatures on the pump surface. However, if the physical properties of the fluids
handled are different from water, the calculation formula below must be used to
check if an additional heat build-up may lead to a dangerous temperature increase at
the pump surface. If required, increase the minimum flow rate.
T
o
= T
f
+ Δ
T
Δ
T =
g
x
H
c
x
η
x
(1 -
η
)
Fig. 13: Calculation formula
Table 14: Key
Symbol
Description
Unit
c
Specific heat capacity
J/kg K
g
Gravitational constant
m/s
2
H
Head
m
T
f
Temperature of the fluid handled
°C
9)
Maximum permissible flow rate
10)
Minimum permissible flow rate
11)
Best efficiency point
6 Commissioning/Start-up/Shutdown
WKTR
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