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About 10 years ago, I wrote an article trying to sort out and simplify the various types of HVLP sprayers. At that time it was important to separate HVLP turbine spray systems from HVLP spray guns that worked on compressed air, also known as HVLP air conversion spray guns.
Now a decade later, with many options and alternatives on the market, again, I need to sort and simplify, so you, as the finishing consumer, can make a proper equipment selection, or better utilize equipment you may have purchased a few years back.
In this commentary I would like to focus on features and differences between HVLP turbine spray systems.
Turbine systems, in the wood industries, are generally best suited to small to mid-sized finishing applications such as cabinet shops, furniture refinishing shops and mobile finishing applications — although you will often see turbine systems very successfully used in the small production shop.
It is important to note that turbine spray systems are serious professional tools for many spray finishing jobs. Unfortunately, like many tools, lower market versions of the professional tool have often reduced the credibility of a valuable tool and the serious tasks it can perform.
Turbine systems come in all different shapes, sizes, prices and configurations. First, and most notable, is understanding the size of the motor installed and its relationship to performance with a variety of coatings and finishes.
The biggest mistake made when turbine system shopping is to relate the intended time usage to the purchase of a system. Rather, a turbine system must be selected based on your choice of coatings to be used and the manner in which you choose to spray them. Simply, the more powerful the system, the wider range of product you can spray at realistic product viscosity.
Power of the air source
Turbine motors are referred to by stages: single stage, two stage, three stage and four stage. (You can even find multiple turbine motors installed for even greater power.) Stages refer to the number of impeller blades producing the air volume, which in turn creates your low air atomizing pressure.
Unlike an air compressor where it is possible to increase or decrease available atomizing pressure, turbine sprayers output one fixed maximum pressure relative to the size of the motor installed. While decreasing pressure is possible (should it be necessary), increasing pressure is not an option. This is the reason to purchase a unit powerful enough to atomize your coating to provide a good quality finish. The last thing you want is a rough, rippled (orange peel) surface from under atomization.
So, what's next? How do you compare units with similar power output? Some are big, some are small, some are round, and some are square. You want to look for adequate ventilation and air filtration since turbine motors produce warm air from the rotational friction of the motor. It is critical that this air ventilates so as not to regenerate and create additional heat. This will ensure the longevity of your equipment.
Air filtration is also critical to filter out any airborne particles. Flimsy and limited filtration can cause much grief, especially when you are coming to the final phases of your finishing. Beware of small compact units. Often there is not enough air to circulate around the motor causing them to run warmer than average. There are guidelines for air space around the motors.
HVLP turbine spray guns have come a long way in the past 30 years. Crude sand cast spray guns (which performed well early on) have evolved into precision tools. Pressure die casting along with high-grade metals add to the precision and quality. Plastic spray guns will wear quickly as opposed to metal spray guns.
No longer are we limited to a standard quart cup mounted on the bottom of the spray gun, but now we have smaller bottom-mounted cup assemblies and gravity feed cup assemblies as well. Teflon® coating is often added to the inside of cups to accommodate many of our modern finishes, notably water-based coatings.
Type of spray gun
Critical to a spray gun is how it is manufactured: the quality of the metals used, what parts are actually stainless steel and the grade of the stainless steel.
Balance and feel is so important. The last thing you want is fatigue when spraying a big job or large surface. There should be a wide range of tip/needle and air cap sizes available for the various products you might choose to use. Most people are not aware that the actual tip, needle and air cap design play an important role in the performance of the spray gun as well.
Finally, and often the most frequently asked question, how about cleanup? Always ask to be shown how a spray gun is assembled and disassembled. Simplicity is the key. O-rings need frequent replacement as they react with various solvents. Today, given critical manufacturing techniques, you can find spray guns with no O-rings, ensuring lower maintenance.
Bleed vs. nonbleed
In years past, all HVLP turbine spray guns were known as bleeder style. That meant when the turbine was turned on, air constantly came out of the air cap. This was never an issue until we started to see the appearance of what are called nonbleed spray guns. In this instance no air comes out of the spray gun until the trigger is pulled, the theory being that less air turbulence will create fewer issues in the workshop with dust and airborne matter.
In reality, bleeder spray guns were really never an issue. The truth is, you should not be spraying in an area that can kick up dust. The main concern regarding nonbleed spray guns is how to relieve the back pressure on the motor when the trigger is not pulled.
Here is what you need to be aware of: First, external air relief can cause air to blow airborne particles around. Internal air relief mechanisms should exhaust the air safely outside the turbine, so as not to regenerate the warm air inside the unit. Unfortunately, some manufactured units blow the warm air back inside the turbine.
One very minor drawback to nonbleed spray guns and air relief mechanisms is they slightly reduce the full power of the motor because a small amount of air is constantly bleeding.
Relative to that is the amount of air bleeding off. Too little air relief can put a strain on the motor. One can easily hear this by listening to the pitch of the motor with the trigger pulled or released. The greater the change would indicate poor air relief, which could lead to premature motor failure.
Air hose considerations
An often ignored part of the system is the air hose. You will find diameters from ¾ in. down to 5/8 in. Some air hoses come equipped with a flexible extension, adding greater operator comfort. The smaller and more flexible hoses reduce any chance of operator fatigue and ensure the probability of a more even application and movement of the spray gun.
In conclusion
Turbine HVLP spray systems are, and can be, a valuable and serious tool in your workshop.
Design, pressure output, ventilation and air filtration are important factors to be aware of. Spray gun design, quality, comfort and maintenance along with production variables should be considered. Air hoses should be flexible and comfortable to use.
Lower priced units generally will not offer the comfort, quality and longevity of the professionally designed models. The installed motors are usually underpowered to produce the best possible results with many of today's modern coatings and finishes leading to excessive thinning of some products and the inability to use others appropriately.
The quality of the spray guns leaves much to be desired in terms of precision and atomization. Amazingly, the price difference between a well-priced professional model and the less expensive units is not that great.
Often your work is judged by the finish. Shouldn't you strive for perfection?
Ed. note: Bill Boxer, vice president of Apollo Sprayers International Inc., is an expert consultant on finishing. Bill became a hands-on finisher 30 years ago when he had a piano rebuilding shop in New York. He has been speaking to woodworkers at shows, workshops and conventions for 20 years.
author: By Bill Boxer