Graco ProMix PD2K Operation page 78

Setup Mode Screens
Differential Pressure Pressure and
Differential Differential Pressure
A primary means of maintaining ratio assurance for
the ProMix PD2K system is through monitoring of
the differential pressure between the A-pump and
B-pump outlets. Ideally, these two pressures would
be identical, but factors such as line sizing, viscosity,
and mix ratio lead to some variation. Understanding
where your system typically operates is imperative
when setting up an effective differential pressure
check that notifies the user of potential mix ratio
inaccuracies while avoiding nuisance alarms.
It is recommended that, once the system is fully
installed and ready to use, the user load a recipe and
then spray the mixed material. While spraying, note
the outlet pressures of both the A and B pumps (per
the ADM's main screen or the PLC) and spray long
enough to ensure the pressures have stabilized to
a nominal value. The difference between the outlet
pressures of the A and B pumps is an established
baseline for the Mix Pressure Tolerance set point.
The Mix Pressure Tolerance set point allows the
B-side pump outlet pressure to vary a specified
percentage away from the A-side pump outlet (spray)
pressure. For example: In the following figure, if the
spray pressure (A-side pump outlet pressure) is 100
psi, and the Mix Pressure Tolerance is set to 25%,
the B-side outlet pressure is allowed to float between
Dual Solvent Solvent
Dual Dual Solvent
Figure 50 Dual Solvent Recipe Screen
If Mix-at-Wall is enabled on System Screen 3, Dual
Solvent becomes an option on the Recipe screen.
Selecting 'Dual Solvent' enables the sequencing of
flushing mixed material for a system using two types
of solvent (i.e., water and solvent based) that should
not be mixed together.
Table 6 6 6 The The Progression Progression of of of Purge
Table Table The Progression
Mixed
➜
Material
78
and the the Mix Mix Pressure Pressure Tolerance
and the Mix Pressure
Purge Sequence Sequence and and Fill
Purge Sequence and
2nd Fill 1st Fill Ma-
Material terial (If
(if appli- applica-
cable) ble)
Tolerance Set Set Point Point
Tolerance Set Point
75 and 125 psi (100 psi ± 25%) without generating
an alarm.
140
120
100
80
60
40
20
0
Figure 49 The acceptable B-side pump outlet
pressure range for a system with a target spray
pressure (A) of 100 psi and a Mix Pressure Tolerance
of 25%.
It is recommended that you keep the Mix Pressure
Tolerance set point as low as possible to alert the
user of anything affecting the mix ratio accuracy.
However, if your system is generating several
differential pressure alarms, or will be mixing a wide
variety of materials at different mix ratios, you may
need to increase the Mix Pressure Tolerance.
Purge Purge 1, 1, 1, 2, 2, 2, and Purge
Select the sequence for purging the mixed material
from the mix hose and spray device. Each stage
of the sequence can be set to either 'A' or 'B'.
The solvent corresponding to each material will be
dispensed out the spray device for the Gun Purge
Time of the Flush sequence assigned to that material
for each stage. See Table 6 for a progression of the
successive stages of the purge sequence.
Fill Fill Fill
Select the sequence for dispensing material into the
mix hose and spray device. The choices are: 'A
then B', 'B then A', and 'Parallel', if no fill sequencing
is necessary. The fill sequence is typically dictated
by the last material used in the purge sequence.
See Table 6 for a progression of the fill sequence
following the last stage of the purge sequence.
Fill Sequence Sequence in in in a a a Dual Dual Solvent
Fill Sequence Dual
Purge 3 Purge 2
Solvent Solvent
and 3 3 3 and
Solvent System System
Solvent System
Purge 1 Mixed
Solvent Material
A
B
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