Graco Express 3900 Operation page 15

Problem
Pump output is low
Excessive paint leakage into throat
packing nut
Fluid is spitting from gun
Pump is difficult to prime
Clutch squeaks each time clutch
engages
High engine speed at no load
Gallon counter not working
No display, sprayer operates
334121B
Cause
Strainer is clogged.
Piston ball is not seating.
Piston packings are worn or damaged.
O-ring in pump is worn or damaged.
Intake valve ball is not seating properly. Clean intake valve (see pump manual).
Intake valve ball is packed with mate-
rial.
Engine speed is too low.
Clutch is worn or damaged.
Pressure setting is too low.
Fluid filter, tip filter or tip is clogged or
dirty.
Large pressure drop in hose with heavy
materials.
Throat packing nut is loose.
Throat packings are worn or damaged. Replace packings (see pump manual).
Displacement rod is worn or damaged.
Air in pump or hose.
Tip is partially clogged.
Fluid supply is low or empty.
Air in pump or hose.
Intake valve is leaking.
Pump packings are worn.
Paint is too thick.
Engine speed is too high.
Clutch surfaces are not matched to
each other when new and may cause
noise.
Misadjusted throttle setting.
Worn engine governor.
Bad sensor, broken or disconnected
wire. Displaced or missing magnet.
Display damaged or has bad connec-
tion.
Solution
Clean strainer.
Service piston ball (see pump manual).
Replace packings (see pump manual).
Replace o-ring (see pump manual).
Clean intake valve (see pump manual).
Increase throttle setting (see operation man-
ual).
Adjust or replace clutch. See Pinion Assem-
bly/Clutch Armature/Clamp, page 20.
Increase pressure (see operation manual).
Clean filter (see gun manual).
Use larger diameter hose and/or reduce overall
length of hose. Use of more than 100 ft of 1/4
in. hose significantly reduces performance of
sprayer. Use 3/8 in. hose for optimum perfor-
mance (50 ft minimum).
Remove throat packing nut spacer. Tighten
throat packing nut just enough to stop leakage.
Replace rod (see pump manual).
Check and tighten all fluid connections. Rep-
rime pump (see operation manual).
Clear tip (see gun manual).
Refill fluid supply. Prime pump (see operation
manual). Check fluid supply often to prevent
running pump dry.
Check and tighten all fluid connections.
Reduce engine speed and cycle pump as
slowly as possible during priming.
Clean intake valve. Be sure ball seat is not
nicked or worn and that ball seats well. Reas-
semble valve.
Replace pump packings (see pump manual).
Thin the paint according to the supplier's rec-
ommendations.
Decrease throttle setting before priming pump
(see operation manual).
Clutch surfaces need to wear into each other.
Noise will dissipate after a day of run time.
Reset throttle to 3300 engine rpm at no load.
Replace or service engine governor.
Check connections. Replace sensor or wire.
Reposition or replace magnet.
Check connections. Replace display.
Troubleshooting
15