Air Supply Troubleshooting Chart - Graco 8900 Instructions For Use Manual

Air Supply Troubleshooting Chart

Problem
Abnormal pressure loss on air motor
pressure regulator gauge during both
changeovers.
Abnormal A and B pump outlet pres-
sure loss during both changeovers.
Reduced flow rate.
Off-ratio material.
During normal operating conditions, the feed pump (A
and B) air motors are filled with air almost instanta-
neously on both changeovers.
However, if the feed pump air supply is restricted, it can
take significantly longer for air to fill the air motor. To
check for this, observe the gauge on the air motor pres-
sure regulator during both changeovers:
• At the end of each stroke the air pressure will drop
abnormally as the air motor begins to fill.
• At the same time the A and B pump outlet pressures
will drop abnormally due to the feed pump's respec-
tive air motor's reduced pressure.
• The decrease in the pump outlet pressures causes
the flow rate at the dispense gun to be reduced.
• Once the air motor has filled with air, all air pres-
sures and flow rates will return to normal until the
end of the next stroke.
• The decreased pump outlet pressure may affect the
feed pumps' checking action, and thus mix ratio,
resulting in the dispense of what appears to be
poorly mixed material.
• Changing air pressure changes the compression of
the component A hose and material. This causes an
off ratio condition until pressures stabilize. Equip-
ment air supply pressure must always stay above
the motor regulator setpoint.
309790ZAF
Cause
Air line restriction due to quick-dis-
connect pin fitting.
Air supply line ID to each feed pump
is too small.
Undersized air compressor.
Solution
Remove quick-disconnect from the
air line and replace it with bleed-type
air shutoff valve.
Replace with minimum 3/4 in. (19
mm) ID hose.
Replace with properly sized air com-
pressor.
Troubleshooting
37