WKT
15
General
The power absorbed by the pump does not decrease
proportionately with decreasing rate of flow, but on the
contrary still amounts to more than 50% of the power
absorbed at the design duty point at zero flow (pump shut
off point). In order to carry off this energy which is
converted into heat inside the pump, it is necessary to
maintain a minimum rate of low through the pump.
In the case of pumps with discharge nozzles of nominal
sizes between 40 and 150 this minimum rate of flow
normally amounts to 0,15 Qopt, taking the heat conditions
and the pattern of the characteristic curve into account.
In the case of pumps with larger sizes of discharge
nozzle, this minimum rate of flow amounts to 0,2 Qopt.
Qopt = Rate of flow at maximum efficiency of the pump.
The pump should only be operated at
rates of flow below the minimum rate of
flow during the switching on and switching off process.
Excessive wear and damage to the pump cannot be
excluded under these circumstances.
Minimum flow circulation via a permanent bypass
The permanent bypass recirculation is selected for plants
with relatively low pressures and low minimum flow rates.
This system is very attractive from the point of view of low
first cost, but is uneconomic in operation because the
minimum flow (or bypass flow) has to be circulated over
the entire operating range of the pump. When sizing the
pump, the bypass rate of flow must be added to the pump
capacity.
In order to ensure the minimum flow, an orifice plate is
fitted in the bypass line between the pump and the
suction vessel.
Minimum flow circulation via an automatic
recirculation valve
The automatic recirculation valve ensures the minimum
flow protection requirement simply and reliably. It is
mounted vertically in the discharge line between the
pump discharge nozzle and the isolating valve, in such a
way that the fluid flow through it from bottom to top.
As soon as the rate of flow of the pump falls below a
given minimum value, the bypass outlet on the automatic
recirculation valve opens sufficiently wide for a
predetermined minimum flow quantity to pass through
and be maintained even when the rate of flow through the
main discharge line is reduced to zero.
6.3 Shutdown
Close the shut-off valve in the discharge line.
If the discharge line is equipped with a non-return or
check valve, the shut-off valve may remain open. If shut-
off is not possible, the pump will run in reverse direction.
This may cause damage to mechanical
seals which are not bi-directional!
The reverse runaway speed must be lower than the rated
speed.
Switch off the drive, making sure that the unit runs down
smoothly to a standstill.
Close the auxiliary lines but do not turn off the cooling
liquid supply, if any, until the pump has cooled down.
Please refer to section 6.1.5.2.
In the event of frost and / or prolonged shutdowns, the
pump – and the cooling chambers, if any – must be
drained or otherwise protected against freezing.
6.4 Operating limits
The pump´s / unit´s application limits regarding
pressure, temperature and speed are stated on
the data sheet and must be strictly adhered to!
If a data sheet is not available, contact KSB!
6.4.1 Temperature of the fluid handled, ambient
temperature, bearing temperature
Do not operate the pump at temperatures
exceeding those specified on the data
sheet or the name plate unless the written consent of
the manufacturer has been obtained. Damage resulting
from disregarding this warning will not be covered by the
KSB warranty.
Bearing bracket temperature see 7.2.1.
The safety instructions set forth in section 2.9 must
be complied with.
6.4.2 Switching frequency
To prevent high temperature increases in the motor and
excessive loads on the pump, coupling, motor, seals and
bearings, the switching frequency shall not exceed the
following number of start-ups per hour (S).
Motor rating (kW) max. S (start –ups / h)
up to 12 15
up to 100 10
more than 100 5
If the above switching frequencies are exceeded, please
contact the motor manufacturer or KSB.
6.4.3 Density or fluid pumped
The power input of the pump will increase in proportion to
the density of the fluid pumped. To avoid overloading of
the motor, pump and coupling, the density of the fluid
must comply with the data specified on the purchase
order.
6.4.4 Abrasive fluids
When the pump handles liquids containing abrasive
substances, increased wear of the hydraulic system and
the shaft seal are to be expected. The intervals
recommended for servicing and maintenance shall be
shortened.
6.4.5 Minimum / Maximum flow
Recommended operation flow range is Q = 0,5 up to
1,15 Q
opt.
Q
opt
= optimum efficiency
For minimum flow in short periods of operation see 6.2.1.
The data refer to water and water-like liquids. 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
Caution
Caution
Caution
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