Notes On Suction And Delivery Lines - Graco 127642 Instructions Manual

I.2

NOTES ON SUCTION AND DELIVERY LINES

EN
DELIVERY
EFFECTS ON
FLOW RATE
HOW TO REDUCE
EFFECTS ON
FLOW RATE
NOTICE
SUCTION
FOREWORD
NOTE
NOTICE
CAVITATION
HOW TO PREVENT
CAVITATION
NOTICE
NOTICE
NOTICE
NOTICE
CHARACTERISTICS
OF THE SUCTION
PIPES
10
Length and diameter of pipe, flow rate of dispensed liquid,
accessories fitted, can create back pressures above those allowed.
In this case, the pump mechanical control (bypass) will trip to reduce
the flow rate.
To avoid these problems, system flow resistances must be reduced
using shorter and/or larger diameter pipes, as well as line accessories
with low resistances (e.g., automatic nozzle for higher flow rates).
The delivery pipe must have the following technical
characteristics:
- recommended minimum nominal diameter: ¾"
- recommended nominal pressure: 10 bar (145 psi)
Diaphragm positive-displacement pumps are self-priming and
feature good suction capacity.
During the start-up phase, when the suction pipe is empty and the
pump is wet, the electric pump unit is able to suck liquid from a
maximum vertical distance of 2 mt.
Priming time can last a few minutes. We suggest
performing priming operations without automatic
nozzle and making sure the pump is properly wet.
Always install a foot valve to prevent the suction pipe
from being emptied and to keep the pump wet at all
times. In this way, the pump will always start up im-
mediately the next times it is used.
The pump is able to work with vacuums of up to 0.5 bar (7 psi) at the
suction mouth. Over this value, CAVITATION can occur that causes a
fall in flow rate and increase in noise levels.
It is important to ensure low vacuums at suction mouth by using:
- short pipes with larger or identical diameter to that recommended
- reduce bends to the utmost
- use large-section suction filters
- use foot valves with minimum possible resistance
- keep the suction filters clean because, when they become clogged,
they increase the resistance of the system.
The vertical distance between the pump and the fluid
must fall within the 2 mt.(6.5 ft) maximum required
for priming. If the distance is greater, a foot valve
must be installed to allow the suction pipes to fill up
and the diameter pipes must be larger. It is recom-
mended that the pump not be installed at a vertical
distance greater than 2 meters.
If the suction tank is higher than the pump, an anti-
siphon valve should be installed to prevent acciden-
tal product leaks. Size the installation to contain the
back pressures caused by water hammering.
It is a good system practice to immediately install
vacuum and air pressure gauges at the inlets and
outlets of the pump which allow verification that
operating conditions are within anticipated limits. To
prevent the suction pipes from being emptied when
the pump stops, a foot valve should be installed.
The suction pipe must have the following technical
specifications:
- recommended minimum nominal diameter: ¾";
- recommended nominal pressure: 10 bar (145 psi);
- use pipes suitable for vacuum operation (e.g. with
metal core)
M0307