How to Keep Your Airbrush Working
Science is the Key
If you don’t know how the works, it will always be a magical device that works when it wants to and stops any time it feels like it. Well it’s not magic, it's science, and if you take the time to learn the scientific basis, you will always be able to keep your airbrush in operating condition. airbrush
The physical laws that govern airbrushes were discovered by Swiss mathematician, Daniel Bernoulli. He published his studies in a book he titled Hydrodynamica in 1738. Bernoulli noticed that moving fluids in an enclosed vessel (such as a tube or pipe) responded to the shape of the vessel in unexpected ways. He discovered that:
•Pressure, flow rate and velocity of a moving fluid within a vessel are constant in all locations within a vessel that’s constant in shape.
•An increase in fluid velocity within a vessel is accompanied by a simultaneous drop in pressure at the location of the increased velocity.
Pressure is how hard the fluid is pressing against the walls of the pipe. Flow Rate is how much fluid volume is transferred through the pipe over time. Velocity is how fast the fluid is moving inside the pipe.
As an example, let’s take a piece of pipe that is the same diameter throughout its entire length. Below is a cutaway of our pipe with fluid in motion. The word fluid can apply to air or a liquid. In the example below, the fluid is a liquid.
Pipe with Fluid Flow
Now, let's modify the pipe by making a restriction midway along the flow path. It's at this restriction, called a venturi, that changes in the flow dynamics begin to take place.
Pipe with Fluid Flow and a Venturi
A Closer Look at the Venturi
A Marriage of Art and Science
At the venturi, the velocity of the fluid goes up, the pressure of the fluid goes down and the flow rate of the fluid remains unchanged. Why does this happen? In simple terms, in order for the same volume of fluid to pass through the venturi as flows through the unrestricted regions, the fluid must move faster through the venturi. Scientifically however, it's due to the law of "conservation of energy". The law of conservation of energy states that energy cannot be created or destroyed. Energy can only be converted from one form to another. In our case, the increase of kinetic energy in fluid velocity is equalized by a loss of energy in fluid pressure, this keeps the energy total in balance. This physical dynamic described by Bernoulli is employed by many devices, such as airplanes, carburetors and airbrushes.
When you press the trigger button on an airbrush, you open a valve that allows air to move through the airbrush. An area of low pressure is created by the venturi located at the tip of the airbrush. In fact, the pressure at the tip of the airbrush, and by connection the entire paint circuit, is lower than the air pressure in the room surrounding you. This pronounced drop in pressure is what powers the airbrush. Low pressure at the tip allows the higher pressure of the atmosphere to push paint from the bottle (or reservoir) all the way to the venturi, where it's atomized by the airstream. In the hands of a creative person, it's a wonderful marriage of art and science.
Let’s take one more look at our pipe and venturi example. At sea level, the pressure of the air is 14.7 pounds per square inch (psi). If our venturi is configured just right, it can produce a fluid pressure of less than 14.7 psi. If a small vent tube is placed at the venturi, air is introduced to the fluid stream.
Venturi with Vent Tube
Ordinarily, putting a hole in a pipe would get you wet. In this case however, the higher pressure of the atmosphere forces air into the pipe as a stream of bubbles. In the case of the airbrush however, the roles of air and liquid are reversed. , or some other liquid color, is injected by atmospheric pressure into the air stream at the tip of the airbrush. Airbrushes have a control mechanism that meters the amount of paint that enters the airstream. A single-action airbrush requires the user to preset the metering valve before each use. A dual-action airbrush allows the user to vary the metering valve "on the fly". Most artists prefer dual-action airbrushes as they permit precise paint volume control. Paint
Below is a cutaway diagram describing the internal workings of a typical dual-action airbrush. The flow of paint is indicated in blue, and the flow of air is purple. The needle and cone components work together as a valve to control the release of paint. The point where the paint is released is precisely within the venturi created by the airstream.
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Diagnose the Problem
OK, so now you know the science that powers the airbrush. How do you put your new knowledge to use? Well, you’ll have to be a bit of an airbrush doctor. First, note the symptoms. How is the airbrush performing? If it doesn't spray any paint at all, then there is a blockage in the paint circuit somewhere between the paint reservoir and the venturi. Airbrushes have very narrow liquid passageways and they're easily stopped-up with dry paint. The best way to avoid this problem is to regularly (and carefully) clean your airbrush. The best way to clean a stubborn clog is to use an ultrasonic cleaning device. Using plain water, ultrasonic cleaners will break up the toughest dried-up paint and they will not harm any of the delicate internal parts. Bottles often become clogged, so be sure to check them first before taking your airbrush apart.
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Does your airbrush skip or leave blank spaces. This is a common complaint and it’s the easiest to figure out. There’s an air leak somewhere. Air is always trying to leak into the paint circuit. If there is a place where air can leak in, it will form a bubble within the paint and pass quickly to the venturi and come out as a blank space in the spray pattern. Carefully inspect your airbrush. Any break in the liquid circuit will allow air to leak in. A worn pilot bearing that no longer provides an airtight seal around the needle is often at fault. Some airbrushes allow you to fine-tune the “tightness” of the pilot bearing by adjusting a threaded bushing that holds it in place. If you use paint bottles and some bottles skip and others do not, then there is an air leak in the bottle cap. Sometimes the bottle neck (the part that slides into the airbrush) is not a perfect fit and air leaks in. Skipping almost always means an air leak somewhere.
Grainy Spray Pattern
Many airbrushes are very delicate – as fine as a Swiss watch. The slightest flaw in the needle and cone configuration will produce an irregular spray pattern. The most common flaw is dried paint on the needle tip. It creates an off-centered pattern that’s very often grainy on one side. I like to remove dried paint from the needle tip with a small paper stump made by tightly rolling a small piece of paper towel into a pointed, pencil-like shape. A cracked cone (sometimes called a nozzle) has a similar effect. Always be very gentle when you seat the needle in the cone. Cracked cones are almost always the result of careless handling.
Your Airbrush can Take Wings
I hope you found this article helpful. In future HubPages I will review other conditions that can cause an airbrush to perform poorly.
Now that you understand the scientific principles, you can employ thoughtful diagnostic analysis to restore the "magic" to that finicky airbrush and get back to using Mr. Bernoulli's principles to create beautiful artwork.
By the way, isn't it very interesting that the principle that powers the airbrush is the same that provides lift to the wings of an airplane. Science allows us to soar in many ways.