Pratissoli MW Serie Manuel D'utilisation Et D'entretien page 51

9.3 Changing version and reduction unit
positioning
The pump version is defined as right when:
observing the pump facing the head side, the pump shaft
must have the PTO shank on the RH side.
The pump version is defined as left when:
observing the pump facing the head side, the pump shaft
must have the PTO shank on the LH side (see Fig. 5).
The version can only be modified by trained and
authorised personnel and carefully following the
instructions below:
1. Separate the hydraulic part from the mechanical
part as indicated in chapter 2 in par. 2.2.1 and
2.2.3 of the Repair manual.
2. Turn the mechanical part 180° and reposition
the rear casing cover in such a way that the
oil dipstick is turned upward. Reposition the
lifting brackets and relative hole closing plugs
in the upper part of the casing. Reverse the two
inspection covers making sure that the open
one is positioned at the bottom. Finally, properly
reposition the specification label in its housing
on the casing.
Make sure the drainage hole of the bottom
inspection cover is kept open.
3. Unite the hydraulic part to the mechanical part
as indicated in chapter 2 in par. 2.2.2 and 2.2.4 of
the Repair manual.
In addition it is possible to position the reduction unit in 5
different positions as per Fig. 6.
RH SIDE
The position of the reduction unit can only be
changed by authorized specialized personnel
meticulously following the instructions in the
repair manual.
9.4 Hydraulic connections
In order to isolate the system from vibrations produced by
the pump, it is advisable to make the first section of the duct
adjacent to the pump (both suction and outlet) with flexible
piping. The consistency of the suction section must be such as
to prevent deformations caused by vacuums produced by the
pump.
9.5 Pump supply
MW pumps must always be installed with a positive suction
head, that is they must receive the water by gravity or by
forced feeding, but never draw it from a lower level.
The pumps are able to withstand minimum suction heads of
even 1 metre, however, for the best volumetric efficiency and
above all to avoid cavitation, the available positive suction
head (NPSH avail) measured at the suction flange in the head
must be equal to or greater than the values below:
MW32
MW36
MW40
MW45
MW50
MW55
For the greater displacements, MW 45 - 50 - 55 pumps, forced
feeding by a booster pump is highly recommended in order to
avoid cavitation, considering the geometry of the hydraulics
and the considerable flow rates.
The booster pump must have at least twice the flow rate of
the rated flow rate of the plunger pump and a pressure of
between 2 and 3 bar.
These supply conditions must be observed at all operating
speeds.
The booster pump must always be started up
before the plunger pump.
It is advisable to install a pressure switch on the
supply line downstream of the filters protecting
the pump.
9.6 Suction line
For a smooth operation of the pump, the suction line should
have the following characteristics:
1. Minimum internal diameter as indicated in the graph in
par. 9.9 and in any case equal to or exceeding that of the
pump head.
LH SIDE
Localised restrictions should be avoided
along the run of the duct, as these can cause
load losses resulting in cavitation. Avoid 90°
elbow bends, connections with other piping,
constrictions, counterslopes, inverted U- curves and
T-connections.
2. With a layout that is set in such a way to prevent
cavitation.
3. Completely airtight and constructed to ensure sealing
over time.
4. Prevent that pump stopping causes emptying, even
Fig. 6 partial.
5. Do not use 3 or 4-way hydraulic fittings, adapters, swivel
joints, etc. as they could jeopardise pump performance.
6. Do not install Venturi tubes or injectors for detergent
suction.
7. Avoid use of base valves or other types of unidirectional
valves.
8. Do not recirculate by-pass valve discharge directly into
suction.
51
NPSH (m)
r
4.5
5.5
6.5
7.5
8
9