What to Do When the Gun Spits Powder: 8-Step Troubleshooting (Ordered by Probability)

Powder spitting (intermittent powder output, a spray plume that varies in thickness, and sometimes a sudden large clump of powder) is the most common fault in electrostatic coating. The key to troubleshooting is to order the checks by probability, not to replace parts on a hunch.

The sequence below is summarized from actual repair records; in most cases the problem can be located within the first three steps.

Step 1: First Check Whether the Powder Has Absorbed Moisture (Most Common)

Powder that has absorbed moisture cakes, will not fluidize, and is then delivered in bursts during transport.

How to diagnose:

Open the hopper and see whether the powder rolls and moves like a liquid (normal fluidized state)
Squeeze a handful of powder; if it forms a clump and does not break apart, it has absorbed moisture
Check the storage environment humidity and whether the powder is sealed after opening

Fix:

Dry moist powder and sieve it before reuse (discard badly caked powder directly)
Store powder sealed after opening the bag; add dehumidification where workshop humidity is high
Do not open large amounts of powder in advance in humid weather

Step 2: Check Whether the Venturi Powder Pump Is Worn

The Venturi pump draws powder by negative pressure; once the inner wall wears, suction becomes unstable and output pulses. This is a consumable, not a permanent part.

How to diagnose: remove the pump body and check whether the inner wall at the throat shows obvious wear grooves or an enlarged bore. Once worn it cannot be repaired, only replaced.

Why check this early: a pump costing a few tens wears out and causes unstable output across the whole line and rework of large numbers of workpieces. Many factories spend ages chasing electrical problems before finally finding it is the pump.

Step 3: Check Whether the Inlet Air Pressure Is Stable

Powder feed is driven by air pressure; unstable pressure means unstable output.

Check whether the air supply pressure is stable (whether other equipment in the workshop causes fluctuations)
Check whether the oil-water separator has failed — a moisture-laden air line wets the powder
Check whether feed air and atomizing air are set reasonably (the two are independent; mis-setting either causes problems)

Special note: moisture in the air line is a hidden killer. It causes the symptoms of both “moist powder” and “unstable air pressure” at the same time.

Step 4: Check Whether the Powder Hose Is Worn or Compressed

Worn inner wall changes the powder flow resistance → unstable output
Stepped on or over-bent → reduced bore → insufficient output
Cured powder residue on the inner wall → local blockage

Fix: remove the powder hose, inspect the inner wall and replace if necessary. The powder hose is also a consumable.

Step 5: Check the Hopper Fluidizing Air Pressure Setting

Fluidizing air too high makes the powder concentration excessive → a large clump is sprayed out; fluidizing air too low means the powder will not fluidize → intermittent output.

Fix: start from low pressure and raise it gradually; find the lowest pressure at which the powder rolls evenly, and record this value as the standard parameter.

Step 6: Check Whether the Nozzle and Electrode Needle Are Clogged With Powder

Powder accumulation on the nozzle causes abnormal atomization, showing up as an off-centre or intermittent spray plume.

Remove the nozzle and check for powder build-up on the inner wall
Check whether powder has clogged around the electrode needle
Test after cleaning and see whether performance returns

Prevention: clean the nozzle on a regular schedule; do not wait for a problem before cleaning.

Step 7: Check Whether the Powder Particle Size Matches the Gun

Particle size too fine or too coarse can both cause abnormal output:

Too fine → scatters easily, over-atomizes, agglomerates during transport
Too coarse → poor flowability, blocks easily
Too wide a particle size distribution → uneven output

Fix: confirm the particle size range stated by the powder supplier and compare it with the gun’s recommended value. Re-verify particularly when changing powder brand.

Step 8: Check Whether the Electrostatic Output Is Abnormal

Only check the electrical side after the previous seven steps have been ruled out.

Whether output voltage is stable (measure with an instrument, don’t just read the panel display)
Whether the high-voltage module has failed (shows up as voltage that will not rise or abnormal discharge)
Whether grounding is reliable — poor grounding affects both transfer efficiency and output behaviour

Quick Reference Troubleshooting Order

Order	Check item	Probability	Action
1	Moisture caking in powder	High	Dry and sieve, or change powder
2	Venturi pump wear	High	Replace pump body
3	Unstable air pressure / moisture in air line	High	Stabilize air supply, replace oil-water separator
4	Powder hose worn or compressed	Medium	Replace powder hose
5	Incorrect fluidizing air pressure setting	Medium	Readjust and record parameters
6	Nozzle / electrode needle clogged with powder	Medium	Clean
7	Powder particle size mismatch	Low	Change powder or verify compatibility
8	Abnormal electrostatic output	Low	Service the high-voltage module, check grounding

Daily Prevention Checklist

Store powder sealed after opening the bag; add dehumidification where workshop humidity is high
Replace the Venturi pump, powder hose and electrode needle on schedule — don’t wait for a problem
Drain the oil-water separator in the air line regularly
Purge the powder path after every color change
Keep a parameter log recording the optimum voltage and air pressure for each powder

If the problem is still unresolved after these 8 steps, send us the gun model, powder type, a video of the symptom and the items already checked, and our technical staff will suggest the next direction.