English
18
Wilo AG 09/2005
The example (N) value is given for the preferred
operating flow region (typically this may extend to
70 to 120 % of the pump best efficiency point);
outside the preferred flow region the actual vibra-
tion experienced may be multiplied by up to 2.
These standard values can vary with the rotational
speed and the power absorbed by the pump. For
any special case, do not hesitate to consult us.
5.5.6 Stop/start frequency
Pump sets are normally suitable for the number of
equally spaced stop/starts per hour shown in the
table below. Check actual capability of the driver
and control/starting system before commissio-
ning.
Where duty and standby pumps are installed it is
recommended that they are run alternately every
week.
5.6
Stopping and shutdown
5.6.1 Stopping and restarting in continuous running
According to hydraulic conditions of the installa-
tion and its automation degree, stop and restart
procedures can have different forms. Neverthe-
less all of them must respect imperatively the fol-
lowing rules:
Stopping:
a) Avoid that the unit turns in the opposite direc-
tion to the normal running.
b) Make sure that the discharge line pressure does
not reach the foot valve.
c) Avoid a continuous running below the authori-
zed flow rate (see § 5.4.2).
Restart:
a) Ensure that the pump is completely full of liquid.
b) Ensure a continuous supply with a sufficient
available NPSH.
c) Ensure a backpressure so that the motor power
is not in excess.
Protect the pump against water hammer when
stopping or starting
Shutdown:
5.7
Hydraulic, mechanical and electrical duty
This product has been supplied to meet the per-
formance specifications of your purchase order,
however it is understood that during the life of the
product these may change. The following notes
may help the user decide how to evaluate the
implications of any change.
5.7.1 Specific gravity (SG)
Pump capacity and total head in meters (feet) do
not change with SG, however pressure displayed
on a pressure gauge is directly proportional to SG.
Power absorbed is also directly proportional to SG.
It is therefore important to check that any change
in SG will not overload the pump driver or over-
pressurize the pump.
5.7.2 Viscosity
For a given flow rate the total head reduces with
increased viscosity and increases with reduced
viscosity. Also for a given flow rate the power
absorbed increases with increased viscosity, and
reduces with reduced viscosity.
5.7.3 Pump speed
Changing pump speed effects flow, total head,
power absorbed, NPSHR, noise and vibration. Flow
varies in direct proportion to pump speed, head
varies as speed ratio squared and power varies as
speed ratio cubed.
The new duty, however, will also be dependent on
the system curve. If increasing the speed, it is
important therefore to ensure the maximum
pump working pressure is not exceeded, the driver
is not overloaded, NPSHA > NPSHR, and that noise
and vibration are within local requirements and
regulations.
5.7.4 Pumped flow
Flow must not fall outside the minimum and maxi-
mum continuous safe flow shown on the pump
performance curve and or data sheet.
5.8
Pumps for Food Use or Potable Water (ACS
range)
If the pump has not been specifically ordered for a
food or drinking water application it must not be
used for these types of applications. If it has been
ordered for this type of application the following
Alarm and trip values for installed pumps
should be based on the actual measure-
ments (N) taken on site on the bearing
housings of the pump in the fully com-
missioned as new condition. Measuring
vibration at regular intervals will then
show any deterioration in pump or sys-
tem operating conditions.
Motor rating kW (hp)
Maximum stop/starts
per hour
Up to 15 (20)
15
Between 15 (20) and 90 (120)
10
90 (120) to 150 (200)
6
Above 150 (200)
Refer
Respect the starting frequency imposed
by the motor manufacturer.
CAUTION!
CAUTION!
Close the outlet valve and stop the
motor. Eventually close the inlet valve.
For prolonged shutdowns and especially
when ambient temperatures are likely to
drop below freezing point, the pump and
any cooling and flushing arrangements
must be drained or otherwise protected.
CAUTION!
CAUTION!
