The Phenomenon Of Water Hammer; Operation Of Pumps With A Frequency Converter - Packo AX Instruction Manual

become so hot that it starts boiling with all the
risks related to this. There always has to be a
minimum fl ow of 1 m³/h per kW installed motor
power. Except for FMS and NMS pumps where
the minimum fl ow is 0.5 m³/h. Pumps that were
built to handle large fl ows, but are operated at
low fl ows, will, even when respecting the above
mentioned minimum fl ows, operate unstable and
therefore be subject to abnormal wear.
A pump must never operate with a closed
valve in the suction pipe! In this case the
pump will cavitate, resulting in abnormal wear
and the possibility that the mechanical seal may
be sucked out of its seat. Special attention is to
be paid to automated installations. Make sure in
the program that all valves in the suction pipe are
opened before the pump is started.

5.2. The phenomenon of water hammer

When a mass of liquid is stopped quickly or has
a large acceleration, the pressure wave gener-
ated will have peaks that can reach tens of bars
with a heavy load on the pump and pipes as
a result. The longer the pipe works, the easier
"water hammer" occurs.
"Water hammer" may be prevented
by starting the pump with an almost
closed valve in the discharge pipe and

5.3. Operation of pumps with a frequency converter

Controlling the pump fl ow (automatic or not) by
regulating the speed of the motor is the best way
to save most energy. But please keep in mind
the following before connecting the pump to a
frequency converter. Standard PACKO pumps
are designed to operate at 50 Hz or 60 Hz. When
a pump is running faster, a high pressure can be
produced in a small pump. Moreover, the power
consumption of the pump increases signifi -
cantly when it is running quicker. Motors pow-
ered by a frequency converter get hotter than
motors connected to a harmonic sinus shaped
power supply. Pump and motor will produce
more noise when running faster. For reasons of
In order to guarantee the lubrication of the
mechanical seal in air-handling pumps (types
CRP, IRP and PRP) and self-priming pumps
(type MSP), they need to suck fl uid in at least
20 % of the time (and thus no more than 80 % of
the time air). A period in which only air is sucked
in must never last longer than 5 minutes.
For pumps with a heating jacket on the pump
casing or on the back plate, the suction valve
and the valve in the discharge pipe must never
be closed together as long as the heating is pres-
ent; not even when the pump is switched off. By
heating a closed quantity of liquid, extremely
high pressures can be produced and can lead
to pump damage and serious burns.
by opening and closing valves slowly. In order
to stop the pump, fi rst close the valve in the dis-
charge pipe slowly and then switch off the motor
of the pump. Solenoid valves that open or close
quickly should not be used. Any and all damage
due to "water hammer" does not come into
account for warranty.
Never try to stop a pump quickly by quick
closure of a valve!
reliability, safety and comfort the maximum
allowed speed of the pumps is limited by:
• the maximum pressure in the pipe word (see
above 2.3);
• the motor power. When the pump runs faster,
it needs more power;
• the maximum speed however, can never be
higher than 3600 revolutions/minute.
When a motor is running very slowly, its' own
cooling could suffer. The minimum speed is
15 Hz for pumps with a 2-, 4- or 6-pole motor and
25 Hz for pumps with an 8-pole motor.
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