An airless sprayer that sprays intermittently or in spurts is a common issue.
It usually appears as an unstable spray pattern, pressure fluctuations, or irregular pump cycling.
In most cases, the problem is not serious, but it must be corrected quickly to avoid premature pump wear.
This article details all known causes, their mechanical principles, and proven solutions.
1. Air entering the suction system
Symptoms
- Pulsing spray
- Pressure rising and dropping
- Cavitation or rattling pump noise
Technical cause
Air enters the system when:
- the suction tube is not fully submerged,
- the bucket of water was stirred too vigorously during preparation,
- suction seals are worn,
- fittings are loose,
- the inlet strainer is clogged.
Air cannot be compressed → pressure becomes unstable.
Solutions
- Fully immerse the suction tube
- Check and replace O-rings
- Tighten all fittings
- Clean or replace the inlet filter
2. Dirty inlet or outlet ball valves
Symptoms
- Irregular pumping
- Pump losing prime
- Pressure never stabilizes
Technical cause
Airless pumps rely on check balls.
If paint residue prevents proper sealing, pressure is lost on each cycle.
Solutions
- Disassemble inlet and outlet valves
- Clean thoroughly
- Inspect valve seats
- Replace damaged balls
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- Pump assembly – 12. Thoroughly clean the seat. Refit inlet valve with seat, ball and new O-ring.
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- Graco inlet valve assembly for GX & A60 – 17J876
3. Clogged filters
Symptoms
- Pulsing spray
- Hard trigger pull
- Intermittent over-pressure
Technical cause
A clogged filter restricts flow, causing pressure spikes and drops.
Solutions
- Clean all filters:
- Use correct filter mesh size for the material
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- Graco Contractor gun filter #60
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- Graco Mark’s main filters
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- Graco #100 filter for Ultra QuickShot VPE tank (3 pcs) – 18H074
4. Partially clogged or worn spray tip
Symptoms
- Uneven fan
- Spitting
- Distorted spray pattern
Technical cause
A blocked nozzle creates unstable back pressure.
A worn nozzle allows too much product to pass through, which the pump cannot compensate for consistently.
Solutions
- Clean or rotate the tip
- Replace worn tips
- Match tip size to sprayer capacity
5. Incorrect pressure setting
Symptoms
- Pulsing at low pressure
- Smooth spray only at high pressure
Technical cause
Pressure set too low prevents continuous flow.
The pump operates in incomplete cycles.
Solutions
- Gradually increase pressure
- Set pressure to the lowest effective level, but not too low
6. Material too thick or improperly prepared
Symptoms
- Inconsistent spray
- Pump overheating
- Frequent pressure loss
Technical cause
Material viscosity exceeds pump capability.
Solutions
- Follow paint manufacturer specifications
- Thin only if allowed
- Use a sprayer suitable for thick materials
7. Worn pump packings
Symptoms
- Chronic pressure loss
- Internal leakage
- Persistent pulsing
Technical cause
Worn seals allow internal bypass, preventing stable pressure.
Solutions
- Replace pump packing kit
- Perform regular maintenance
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- Graco QuikPak Kit
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- Graco repair kit
An airless sprayer that sprays in spurts is almost always caused by air ingress, pressure instability, or worn components.
In most cases, cleaning, seal inspection, and proper setup resolve the issue.
Preventive maintenance is the key to long-term reliability.
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