Hydraulic Connections; Pump Supply; Suction Line; Filtration - Pratissoli MW Serie Manual De Uso

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:
NPSH (m)
r
MW32 4.5
MW36
5.5
MW40 6.5
MW45
7.5
MW50 8
MW55
9
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.
9.7

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
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.
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
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.
9. Provide for proper guards inside the tank to prevent that
water flow from the bypass and the tank supply line can
create vortexes or turbulence near the pump supply pipe
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 again
downstream from the filters.
1 Filter 1
2 Booster Pump
3 Filter 2
4 Pressure gauge
5 Pressure switch
6 Plunger pump
Bypass
51
7 Pressure gauge
8 Safety valve
9 Accumulator
10 Control valve
Fig. 7