High-quality painting of a car body is not just the application of a color layer, but a complex technological process, where the result directly depends on the skill of the performer and the equipment used. The central element here is spray gun, often popularly called a bullet gun. It is on its characteristics, calibration and proper handling that it depends whether the paint will lie as an even “mirror” or become covered with ripples and shagreen. The choice of tools today is huge, and it is easy for an inexperienced master to get confused in abbreviations and technical parameters.
However, even the most expensive tool will not produce results without understanding the physics of spraying. In this article, we'll look at the differences between different paint supply systems, how to properly set up the torch, and avoid common mistakes that can cost you time and materials. Professional painting requires not only a steady hand, but also deep theoretical knowledge about the behavior of paints and varnishes in air flow.
Classification of spray guns by spray system
The main criterion for choosing a tool is the spray technology, which determines the efficiency, quality of the torch and the requirements for the compressor. Three main systems dominate the modern market, each of which has its own specific application in body repair. Understanding the difference between them is the first step to making a smart purchase.
System HP (High Pressure) is a classic and uses high pressure to crush paint. Such spray guns create a powerful torch that can “pierce” hard-to-reach places, but at the same time they have a low material transfer coefficient - a significant part of the paint simply flies into the air, forming fog. This makes them less popular in modern workshops, where material savings and environmental friendliness are valued.
Systems are considered more advanced HVLP (High Volume Low Pressure) and LVLP (Low Volume Low Pressure). They operate at low pressure, which allows up to 75-80% of the paint to be transferred to the part. HVLP requires a large volume of air, which can be a problem for weak compressors, whereas LVLP combines low pressure with moderate air consumption, being the “golden mean” for garage use.
⚠️ Warning: Do not attempt to use HP system spray guns to apply modern high solids acrylic varnishes. High pressure can lead to boiling of the solvent in the torch and the formation of porosity on the surface.
For garage painting, the LVLP system is the best choice, as it is less demanding on compressor performance and provides a high paint transfer coefficient.
Design features: nozzle size and body material
The internal structure of the spray gun determines its durability and versatility. The key element here is the nozzle (nozzle), the diameter of which is selected strictly according to the viscosity of the material used. Using the wrong size will either result in the thick paint not being able to be sprayed or excessive use of liquid primer.
The material used also plays a critical role. Nickel-plated brass nozzle and stylus are standard on most tools, but they are susceptible to wear when working with abrasive materials such as zinc-rich soils. For professional work, it is preferable to choose sets from stainless steel, which last much longer and maintain the geometry of the torch.
The body of the spray gun is most often made of aluminum with a protective coating. It is important that all seals are made of Teflon or high-quality rubber that is resistant to aggressive solvents. Cheap models often suffer from the fact that upon contact with “646” or solvent, the seals swell, which leads to paint leaking into the air channels.
Different types of work require different nozzle diameters. A basic car painter's kit usually includes several replacement heads or a separate gun for each type of material. This allows you to avoid wasting time on thoroughly washing the instrument when moving from the ground to the base.
Why can't you save on the nozzle?
Cheap brass nozzles wear out quickly, especially in the central part of the hole. This leads to a change in the shape of the torch and the appearance of paint “spitting”, which cannot be corrected by adjusting the screws.
Table for selecting nozzle diameters for various materials
Choosing the right nozzle size is 50% of success. Below is a reference table that will help you navigate depending on the type of paint and varnish material (paint and varnish material) and viscosity.
| Material type | Viscosity (DIN4) | Recommended nozzle diameter | Type of work |
|---|---|---|---|
| Base enamel (metallic) | 14-18 sec | 1.2 – 1.3 mm | Finish coating |
| Acrylic enamel (solid) | 16-20 sec | 1.3 – 1.4 mm | One-stage painting |
| Acrylic varnish | 16-20 sec | 1.3 – 1.5 mm | Varnishing |
| Soil filler | 20-25 sec | 1.5 – 2.0 mm | Leveling the surface |
| Liquid putty | 25-30 sec | 2.0 – 3.0 mm | Local repair |
It is worth noting that these values are averaged. Specific recommendations can always be found on the product can in the “Technical Data” section. The paint manufacturer specifies exactly through which nozzle and at what pressure the material will work ideally.
Preparing the compressor and auxiliary equipment
The spray gun itself is only an actuator. The quality of its work directly depends on the “power”, that is, compressed air. The compressor must provide not only the required pressure, but also a sufficient volume of air (performance) so that the pressure in the receiver does not drop critically during operation.
A critical element of the system is air preparation. The air from the compressor contains moisture and oil, which, when contacted with the surface to be painted, cause defects that are incompatible with the life of the coating. For cleaning, moisture-oil separators are used, which are installed directly in front of the spray gun or in the line.
- 🔧 Filtration: Use fine filters (5 microns or less) for the final layers of varnish and base.
- 🔧 Hoses: Use spiral or special hoses for spray guns that do not twist and have a sufficient internal cross-section.
- 🔧 Pressure: Operating pressure is measured at the gun outlet and not at the compressor gauge. The difference can be from 0.5 to 1 atmosphere.
Technique for setting up and adjusting the torch
Before starting work, it is necessary to carry out a test spray on a test card or unwanted part. The spray gun is adjusted using three main screws located on the body of the tool. Ignoring this stage is the main mistake of beginners.
The air supply screw regulates the outlet pressure and, accordingly, the size of the torch. The material feed screw limits the needle stroke, controlling the amount of ink that comes out. The third screw (or rotary head) changes the shape of the torch from round to oval. For painting large surfaces, a wide oval torch is used, for local transitions and complex reliefs - a round one.
The setting process is as follows: first, the maximum torch width is set with the material supply fully open. Then, making test passes, reduce the supply of material until the torch becomes uniform, without thickening in the center or at the edges. The air pressure is selected so that the paint lies wet, but does not flow.
☑️ Setting up the spray gun before work
Painting process: techniques and movements
The paint application technique itself requires constant practice. The spray gun must be held strictly perpendicular to the surface at a distance of 15-20 cm. Changing the distance or angle of inclination leads to an uneven distribution of material: there will be more in the center of the layer than at the edges, or vice versa.
Movements should be smooth, parallel to the plane of the part. Starting and stopping spraying occurs outside the boundaries of the painted area. The overlap of each subsequent pass should be approximately 50% (for base) or 30-40% (for varnish). This ensures an even color and no streaks.
The speed of the pistol also plays a role. Moving too fast will leave “dry” shagreen, too slow will cause smudges. The optimal speed is about 40-50 cm per second, but it varies depending on the viscosity of the paint and the temperature in the chamber.
⚠️ Attention: Never stop moving your hand while the spray gun trigger is pressed. Stopping even for a split second is guaranteed to lead to the formation of a local thickening of the layer (smudge), which will have to be sanded.
Tool care and troubleshooting
The longevity of a spray gun depends on how you take care of it. Washing the tool should be done immediately after finishing work, before the paint has time to polymerize inside the channels. For this you need to use an appropriate solvent.
Disassembly of the instrument must be done carefully. The needle and nozzle cannot be cleaned with metal brushes or wire - this will scratch the polished surface and disrupt the spray geometry. For cleaning, special soft bristle brushes and rags moistened with solvent are used.
When storing, it is recommended to lightly lubricate the spray gun needle with oil to prevent corrosion and seizing. You should also avoid dropping the tool: even a microscopic chip on a ceramic or brass nozzle will make it unsuitable for high-quality work.
- 🧼 Rinse the tank and channels with solvent until the stream is clean.
- 🧼 Blow the gun with compressed air from all sides.
- 🧼 Do not soak the entire gun in solvent - this may damage the seals.
- 🧼 Store the tool in a special case in a dry place.
If the paint has dried inside the channels and cannot be washed off with a solvent, you can use an ultrasonic bath for small parts (nozzles, needles), but only if the tool manufacturer allows such cleaning.
Frequently asked questions (FAQ)
What pressure should I set on the compressor for painting a car?
The pressure at the outlet of the compressor is usually set in the range of 3-4 atmospheres, but the pressure at the inlet to the spray gun is more important. For HVLP systems this is usually 2-2.5 atm, for LVLP - 2-3 atm. The exact value depends on the viscosity of the paint and the recommendations of the gun manufacturer.
Why does the spray gun “spit”?
The main reasons: clogged air channels of the head, a loose tank or head, damaged seals, or too low a paint level in the tank when air is sucked into the system.
Is it possible to paint a car with an electric spray gun?
Theoretically, it is possible, but the quality of the coating will be significantly lower than that of its pneumatic counterpart. Electric models produce coarse shagreen and have low performance, which makes them suitable only for painting fences or walls, but not for car bodies.
Which spray gun should I choose for a garage with a weak compressor?
If your compressor produces less than 300 liters per minute, choose an LVLP system spray gun with a nozzle diameter of 1.4 mm. They require a minimum volume of air for stable operation.
Do I need to filter the paint before pouring it into the tank?
Yes, definitely. Even a new jar may contain clots or debris. Use special funnels with a built-in mesh filter (watering cans) or separate spider filters. This will save the nozzle from clogging and the body from defects.