On/Off Delays; Dispense Valve - Graco PCF Instructions Manual

System Setup

On/Off Delays

The PCF fluid regulator can physically respond faster
than the dispense device and its solenoid. As a result,
the fluid regulator can supply material to the dispense
device before the device has time to open. Supplying
material to a closed device can create trapped-pressure.
At the end of a cycle, the dispense device can shut off
before the pressure has dissipated. This can cause a
dispense of an excess of material at the beginning of the
next cycle.
To eliminate these two problems, change the delay time
associated with the opening of the fluid regulator/dis-
pense and/or the closing of the dispense device, see
Table 5: On/Off Delay Variables. For instructions set-
ting on/off delays, see Configure Delay Settings, page
32.
NOTE: On/Off delay can be set for each dispense
device.
In general, delays should be adjusted so the outlet pres-
sure during "no flow" is slightly below the outlet pressure
during dispense.
Table 5: On/Off Delay Variables
Variable: Sets the Amount of Time:
Valve ON Sets time from Dispense Valve High
to Valve Open command
Regulator Sets time from Dispense Valve High
ON to Regulator ON
Valve OFF Sets time from Dispense Valve Low
to Valve Close command
Regulator Sets time from Dispense Valve Low
OFF to Regulator OFF

Dispense Valve

Signal
Fluid
Regulator
Valve Open
Command
Valve Actually
Open
F . 27: Timing Delay
IG
36
A
B
E
F . 27 and Table 6: Delay On/Off Timing show delay
IG
ON and OFF timing.
Table 6: Delay On/Off Timing
A Regulator ON
delay
B Valve ON delay
C Valve OFF Delay
D Regulator OFF
delay
E Valve Open
Reaction Time
F Valve Close
Reaction Time
F
The user sets the fluid regu-
lator ON delay timing.
Usually set to zero. Can be
used to change the starting
point of a bead.
Usually set to zero. Higher
values will lower the trapped
pressure.
The user sets the regulator
OFF delay timing. Zero or
small values will lower the
trapped pressure.
Time delay for valve to phys-
ically open. Delay varies
based on pneumatic hose
length and valve air volume.
Time delay for valve to phys-
ically close. Delay varies
based on pneumatic hose
length and valve air volume.
C
D
3A2098A