Pratissoli MXXR Serie Manuel D'utilisation Et D'entretien page 30

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 suction hose must be sufficiently rigid to prevent
deformation due to the negative pressure exerted by the
action of the pump.
9.5 Pump supply
The MXXR-MXSR pumps must always be installed with a
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 meter, 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
manifold must be equal to or greater than the values below:
NPSH
MXXR40 - MXSR40
4.5
MXXR45 - MXSR45
5.5
MXXR50 - MXSR50 6.5
MXXR55 - MXSR55 7.5
MXXR60 - MXSR60
8
MXXR65 - MXSR65
9
For the greater displacements, MXXR/MXSR 55 - 60 - 65
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 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.
9.7 Filtration
Two filters must be installed on the pump suction line, positioned as indicated in Fig. 7 and Fig. 7/a.
With a manually activated control valve
Inlet
Supply tank
(m)
r
9.6 Suction line
For smooth operation of the pump, the suction line must have
the following characteristics:
1. Minimum inside diameter as indicated in the graph in par.
9.9 and in any case greater than or equal to the diameter
at the pump manifold.
Localized restrictions should be avoided along the
piping, as these can cause pressure drops resulting
in cavitation. Avoid 90° elbows, connections with
other piping, restrictions, reverse gradients, inverted
U-curves and Tee connections.
2. The layout must be such as to prevent cavitation
problems.
3. Completely airtight and constructed to ensure a perfectly
hermetic seal through time.
4. Prevent the pump from emptying when it is stopped,
including partial emptying.
5. Do not use 3 or 4-way hydraulic fittings, adapters, swivel
joints, etc. as they could jeopardize pump performance.
6. Do not install Venturi tubes or injectors for detergent
suction.
7. Avoid use of foot valves or other types of unidirectional
valves.
8. Do not recirculate the by-pass valve drain directly to the
suction line.
9. Install suitable baffles inside the tank to prevent the water
flow from the bypass and the tank supply line creating
vortices or turbulence near the pump supply outlet port.
10. Make sure the suction line is thoroughly clean inside
before connecting it to the pump.
11. Install the pressure gauge for checking the booster
pressure near the plunger pump suction port and always
downstream from the filters.
1 Filter 1
2 Booster Pump
3 Filter 2
4 Pressure gauge
5 Pressure switch
6 Plunger pump
Bypass
30
7 Pressure gauge
8 Safety valve
9 Accumulator
10 Control valve
Fig. 7