The situation when the spray gun spits large drops instead of creating a fine mist, is familiar to many craftsmen. This is not just an irritating defect, but a serious problem that can ruin the appearance of the part being painted, leaving shagreen marks and streaks on the surface. Often, when newbies encounter this, they immediately blame equipment malfunction, but in most cases, the root of the evil lies in improper preparation of materials or basic settings.
Ignoring the problem leads to excessive consumption of paint and varnish materials and the need to redo the work, which is especially critical when painting cars or furniture. To avoid defects, it is necessary to clearly understand the physics of the spraying process and know which parameters affect the stability of the spray. The main reason for spitting is an imbalance between the outlet air pressure and the viscosity of the supplied paint.
In this article we will analyze in detail the mechanics of the occurrence of a defect, consider the influence of the human factor and technical faults. You will learn how to quickly diagnose and troubleshoot problems yourself without contacting a service center.
Effect of paint viscosity and filtration quality
The first thing you should pay attention to if spray gun began to shoot drops - this is the preparation of the paint itself. Material that is too thick does not have time to be broken down into microparticles by the air flow. Viscosity is the resistance of a liquid to flow, and each type of gun (HP, HVLP, LVLP) has its own optimal values. If you use thick enamel without thinning, air pressure simply will not disperse it effectively.
However, even properly diluted paint may contain foreign inclusions: dried particles, dust or lumps of pigment. These microscopic obstructions clog the feed passages or partially block the outlet nozzles. At the moment when the air flow tries to overcome the obstacle, a sharp jump in pressure occurs, and the paint is thrown out in a large portion. That is why high-quality filtration is a mandatory step.
To check the readiness of the material, professionals use a viscometer - a funnel with a calibrated hole. The time it takes for a certain volume of liquid to flow out indicates whether more solvent needs to be added. Neglect of this tool often leads to the fact that the master adds solvent “by eye,” which rarely gives an ideal result.
To eliminate problems with the quality of the mixture, follow these recommendations:
- 🧪 Always use a viscometer to accurately select solvent proportions.
- 🌡️ Consider the temperature in the paint booth, as cold paint becomes thicker.
- 🕸️ Strain the material through special funnel mesh filters before pouring it into the tank.
- 💧 Mix the ingredients thoroughly to avoid separation and the formation of lumps.
Insufficient air pressure and compressor operation
The second most important factor is the air supply parameters. If pressure at the gun inlet is too low, the air flow speed is insufficient to break the paint. Instead of being sprayed, the liquid simply flows out of the nozzle under the influence of gravity or residual pressure in the tank, forming large droplets.
Often the problem lies not in the regulator settings, but in the performance of the compressor itself. If the receiver is empty and the engine does not have time to pump up the required pressure, when you pull the trigger, an instant drop in performance occurs. At this moment the torch “spits”. It is also worth checking the condition of air filters and moisture separators: clogged elements create resistance, reducing the efficiency of the tool.
⚠️ Attention: Using an air hose that is too long or thin (less than 8-10 mm in diameter) can significantly reduce the pressure at the outlet of the compressor, creating the illusion of a malfunctioning spray gun.
For stable operation it is necessary to ensure a constant flow of air. Check the pressure regulator (pressure gauge) settings directly on the gun handle, not just on the compressor. The difference in readings can be significant. Also make sure that the type of gun you choose matches the capacity of your compressor: system HVLP requires a large volume of air at low pressure, and HP - high pressure with less volume.
If the compressor is weak, try painting in two thinner coats with drying in between to reduce the stress on the air supply system.
Wear and mechanical damage to the nozzle and needle
When the material preparation and pressure are normal, but the spray gun continues to spit, it is worth inspecting the mechanical part of the spray head. Duza (nozzle) and needle are a precision pair, where the gap between them is a fraction of a millimeter. Any scratch, chip at the end of the needle or deformation of the nozzle hole violates the tightness and geometry of the torch.
Most wear and tear occurs due to the use of metal brushes for cleaning. Aggressive mechanical cleaning scratches the inner walls of the nozzle, after which the paint begins to flow into these micro-irregularities and is ejected unevenly. It is also possible that the sealing gasket, which is located between the body and the tank or in the needle attachment point, may wear out.
Visual examination is often inconclusive, so diagnosis is made by exclusion. Try replacing the drill bit and needle with new ones that are known to be good. If the problem disappears, then the reason was due to wear of the parts. Remember that the needle and nozzle must be strictly the same size and, preferably, from the same manufacturer.
| Type of damage | Symptom | Solution |
|---|---|---|
| Scratches on the end of the needle | Constant leakage, spitting when releasing the trigger | Replacing the needle |
| Nozzle hole deformation | Uneven torch, spitting in one direction | Replacing the nozzle pair |
| Gasket wear | Air leaks, unstable supply | Replacing the seal |
| Air duct contamination | Spitting air with paint | Channel cleaning |
Errors when working with the trigger and application technique
Often the reason is trivial and lies in the actions of the operator. If you press the trigger sharply and all the way, the air supply channel opens first, and then the paint. But if the movement is done carelessly or the trigger sticks, the simultaneous opening of the channels may occur with a delay, which causes the initial "spit".
Another common mistake is tilting the spray gun. When working at an angle of more than 15-20 degrees to the surface, the paint level in the tank shifts. In gravity flow guns, this can cause air to become trapped along with the paint, causing spitting. In bottom feed guns (paint tanks), the angle of inclination is less critical, but still matters.
Movement technique also affects the result. Driving the gun too slowly or uneven speed creates conditions for the formation of sagging, which is visually perceived as spitting in large drops. It is important to hold the gun perpendicular to the surface and maintain a constant distance (usually 15-20 cm).
☑️ Correct technique for pulling the trigger
Clogged air channels and head
Even if the nozzle is clean, the cause of unstable operation may be clogged side horns of the air cap or air supply channels. Dried paint in these nodes distorts the shape of the air flow that should flow around the paint stream. Instead of symmetrical blowing, vortices are formed that tear out pieces of material.
Cleaning should be done with special brushes included in the kit or wooden toothpicks. The use of metal is strictly prohibited, as it changes the geometry of the holes. The solvent helps to soften the dirt, but mechanical removal of the residue is necessary.
Pay attention to the condition of the air cap. If it is chipped or cracked, it must be replaced. Also check that it is screwed tightly to the gun body. A loose fastening leads to air leaks and a violation of the tightness of the system.
How to properly clean the air cap
Soak the head in the solvent for 10-15 minutes. Use a soft brush to remove softened paint. Blow out all holes with compressed air. Never poke holes with metal objects.
Problems with tightness and seals
The last group of reasons is associated with loss of tightness in various components of the spray gun. If there is a microcrack or a worn oil seal somewhere, the system begins to “grab” excess air. This disrupts the vacuum required to lift paint from the tank (in gravity flow models) or the stability of the flow.
Pay special attention to the junction of the tank and the gun body. There is a gasket installed there, which becomes dull or breaks over time. Also check the needle seal: if it is overtightened, the needle will move tightly, which will lead to jerking when feeding paint. If it is loose, there will be leakage.
For diagnostics, you can lubricate suspicious joints with soapy water or water and apply air. The appearance of bubbles will indicate the location of the leak. Timely replacement of consumable seals extends the life of the tool and guarantees the quality of painting.
⚠️ Attention: When assembling the spray gun, do not tighten the fasteners “all the way” by force. Excessive force will distort the gaskets and may cause cracks in the air cap housing.
90% of cases of spray gun spitting are solved by adjusting the paint viscosity, increasing the pressure or replacing a worn nozzle pair.
Frequently asked questions (FAQ)
Why does the spray gun spit at the very beginning of pressing the trigger?
This is a classic sign that the opening sequence of the channels is incorrect or the paint is too viscous. At the beginning of the trigger stroke, the air has already flowed, but the paint has not yet risen, then a sharp jump occurs. Try adding solvent or adjusting the feed screw.
Can I use car polish to clean the nozzle?
No, the polish contains abrasives that will scratch precision surfaces. For cleaning, use only special paint solvents (646, 647, branded cleaners) and soft brushes.
Does paint temperature affect spitting?
Yes, cold paint has a higher viscosity. If you store materials in an unheated garage during the winter, be sure to warm them up to room temperature (about 20°C) before working.
What to do if the new nozzle does not help?
Check the needle for bending and the condition of the needle seal. Also make sure that the compressor pressure is stable and the hose is not kinked.