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781Mini Series Spray Valve
17
Troubleshooting
Problem
Possible Cause
Corrective Action
No fluid flow
Valve operating air pressure too low
Increase air pressure to 4.8 bar (70 psi)
minimum.
Fluid reservoir air pressure too low
Increase the air pressure to the fluid
reservoir.
Needle stroke adjusted to the closed
position (0 stroke)
Open the stroke adjustment. If
adjustment is needed, refer to “Valve
Stroke Calibration” on page 10.
Clogged nozzle
Clean the nozzle. Refer to “Cleaning the
Wetted Parts” on page 11.
Actuating air and nozzle air supplies
reversed
Check the air supply connections.
Valve not providing clean shutoff, leaving
buildup on the nozzle
Needle not properly seated
Remove the nozzle, clean the needle and
nozzle, and replace worn or damaged
parts.
Fluid flows from the nozzle but will not
spray
Nozzle air pressure too low
Increase the nozzle air pressure.
Air passage between nozzle and air cap
obstructed
Remove the air cap and clean the air cap
and nozzle.
Fluid viscosity too high
If the fluid viscosity is too high, it will
not atomize. Increase the nozzle air
pressure.
Steady drip
Damaged needle, debris in needle seat,
or improper valve assembly
Replace the damaged needle. Whenever
replacing a needle, also replace the
nozzle.
Fluid leaks from drain hole
Worn O-ring seals
Replace the double-stacked O-rings.
Refer to “Cleaning the Wetted Parts” on
page 11.
Inconsistent deposit size
Value actuating air pressure and / or fluid
reservoir air pressure fluctuating or valve
actuating air pressure less than 4.8 bar
(70 psi)
Make sure that the valve and fluid
reservoir air pressures are constant and
that the valve actuating air pressure is
4.8 bar (70 psi).
Valve open time inconsistent
The time the valve is open must be
constant. Make sure the valve controller
is providing a consistent output.