If there’s one piece of equipment that epitomizes the painter and the paint shop, it’s the spray gun. That’s not the case with painters in other industries, but for us, a painter isn’t a painter without the spray gun.
Over the Years
We’ve certainly seen many spray guns over the decades. Although there are operating principles and functions that remain the same, some have been improved upon, and some even outright changed. Yet through all the changes and improvements, the one variable component that has remained unquestionably the most important is the operator. Not-withstanding, even the most experienced and forward-thinking painter cannot overcome physics, the limitations of design or the lack of equipment maintenance.
Market demands have driven most spray gun innovations over the years, but we must also consider the regulatory compliance requirements that have changed the landscape of our industry. The regulations followed the market-driven innovations, but by now, I believe the two factions are pulling the wagon toward greater transfer efficiency. Of course, that’s not the only consideration or else we would still be using a paint brush or electro-static painting and achieving 100 percent transfer efficiency. There is no brush or electro-static rig I’m aware of that can adequately duplicate any suspended metallic paint, let alone a three-stage paint job. Speed of the operation has also been a driving force in market innovations, and I suspect it will continue to be.
Changes and Challenges
Before we discuss a painter’s obligation to his spray gun and the efficiency equation, I can’t resist cruising down memory lane and considering some of the changes and challenges we’ve conquered to underscore the importance of proper equipment.
My first spray gun was a Bink’s #7 from my father. What a workhorse! Fifty-five pounds of pressure, and you had fantastic atomization of even the most viscous enamel. Push the material through a pressure pot and you could get yourself a 24-inch fan pattern. Talk about fast on the big jobs. But that came with a price: lousy transfer efficiency. It wouldn’t be considered a viable tool choice today by a material-conscious owner/manager.
The gravity feed spray gun achieved a better rate of transfer by simple physics. There was no need for the air-pressure a standard syphon feed gun required to draw material up and out of the cup, so there was less blow back and overspray. Back when I knew everything, I laughed at the clumsy gravity feed gun the Europeans were using and knew it would never catch on here. Today, I know painters who have never used anything but a gravity feed gun and couldn’t imagine life without one. It truly is a fantastic design.
High Volume Low Pressure (HVLP) equipment, while not new, turned out to be the answer to the regulatory demands we experienced in Southern California in the 1980s. The decades-old vacuum cleaner-type HVLP wasn’t going to solve the problem for us, so existing spray gun technology was “converted” to HVLP. Hey, they were scrambling too! An additional hurdle was high solids – thicker material with less pressure to atomize it.
The engineering in the current stable of spray guns has eased painters’ grief – guns with interior air passages designed for optimum air flow; air caps with air shear considerations built into the design; fluid nozzles that are sized and aimed specifically at a given paint technology, such as waterborne. There was no way to choke down that old No. 7 and deliver less material with less pressure and achieve satisfactory results; that’s akin to trying to get good gas mileage from a big-block V-8 by feathering the accelerator or installing a single barrel carburetor. There’s better support and guidance from the spray gun manufacturers today as well. They leave little room for error by working with paint manufacturers to establish the best setups for the various paint products and then by educating painters.
There are three main areas to consider for gun efficiency. First is the proper gun setup for the paint product being used. Don’t guess. Regardless of your preferred gun manufacturer, get the proper nozzle/needle/cap combination for the product. That’s No. 1, and at times it will mean a new spray gun.
No. 2 is the proper application of the product, according to both the paint and spray gun manufacturer. Again, don’t guess. There are specific air pressure, distance and overlap recommendations as well as temperature and humidity considerations. Therefore, get the proper information for your environment. While critical to get right, these two variables alone – gun set-up and application – will become second nature. As such, you won’t even really give it much thought once you’re over the learning curve. Don’t let that be the way you approach No. 3. But before I get to No. 3, which is key to consistency, I think it’s important to stress the absolute necessity of consistent air pressure when talking about spray gun efficiency. One of our goals is consistency and repeatability. This is what allows us to paint fenders and hoods off of cars and have them match and what makes the color library so valuable. Air pressure has a tremendous effect on consistency, and to minimize that, we must regulate the air.
If your booth is like most, the air is regulated to about 120 pounds of pressure. We utilize that kind of pressure when we’re blowing off the vehicle. We then “regulate” the pressure down with a cheater valve attached to the gun. That is not regulating the air. The cheater valve is like putting your thumb over a garden hose; you’ve cut down the volume but increased the velocity. So you further throttle down the air volume to achieve the “pressure” you’re after.
If the pressure before the “valve” fluctuates, then the pressure after the “valve” also fluctuates. You need an actual diaphragm-type regulator to throttle down the pressure properly. If you choke down the pressure with a cheater valve, you leave yourself open to air line fluctuations due to the pressure in the compressor’s tank dropping and building as other techs tap into the air supply. This leads to inconsistent pressure and inconsistent application. It may not matter if you’re painting school bus yellow, but I suspect the lion’s share of your jobs are metallic. Consistent pressure does matter. The answer is either throttling down the wall-mounted regulator or having an actual gun-mounted regulator. A bit larger than a gun-mounted cheater valve, the regulator has a diaphragm.
An easy test to see if you’re using a cheater valve or regulator is to set it at 15 pounds or so and pull the trigger, then dial the fan adjustment to the smallest pattern. If you have a cheater valve, the pressure will increase by a noticeable amount. If it’s a regulator, it won’t. By the way, the vast majority of painters, in my observation, use a cheater valve and blame the inconsistencies on the product being sprayed.
In addition to a regulator, high-flow air fittings should be utilized, as well as an air line with 5/16-inch I.D. minimum, 3/8-inch being even better.
Finally, in ring No. 3, we have gun maintenance. It’s so easy, but so commonly neglected. Oh I know, the gun looks great, and it’s going in the automatic gun washer after each job. And I know, not only is that seldom enough, a poorly maintained gun washer does more harm than good.
Ever wash dishes? Or the car? Do you use a sponge or rag of some sort, or just spray things off with a hose? Of course you wash it first, then rinse. Or perhaps you put the dishes in the dishwasher. The dishwasher is not recycling dirty, greasy dishwater. Fresh, clean, pressurized water every time. Not so with the automatic gun washer as it recycles the cleaning solvent.
If the gun washer is your own, and if only you use it and properly clean the sludge and paint from your gun prior to using it, then maybe you have decently clean solvent for a month or two, depending on the volume of vehicles you paint. That’s a lot of “ifs” and one “maybe.” Take away those ifs and you probably have a shop-owned gun cleaner that never gets maintained and is full of sticky, soupy gravy. Worse yet, perhaps you’re operating on the edge of insanity and using an open “birdbath” full of thinner for cleaning purposes. While these methods are temporary at best and dangerous at worst, they represent only a precursor of spray gun maintenance. I have yet to meet a painter (myself included) who tore his gun down each time and re-lubed it during reassembly. I spent 30 years as a flat-rate collision repair refinisher, and I didn’t always maintain my equipment properly. I didn’t think I had time. I didn’t understand the relationship that exists between spray gun maintenance and accuracy and consistency, nor how that relates to efficiency.
You might be tired of me droning on about it, but there is nothing faster than accuracy. Accuracy is a by-product of consistency. How does this relate to spray gun maintenance? Here’s a question for painters: Have you ever torn down a gun, soaked it, scrubbed it, rinsed it, lubed it and reassembled it, test drove it, then proclaimed, “I forgot how awesome this gun sprays?” Me too. I made that statement in front of my brother, a Marine Corps helicopter mechanic, who replied, “You should never be able to tell the difference.” From his perspective of keeping a Huey from falling out of the sky, you performed routine scheduled maintenance rather than waiting for a sputtering engine to fail.
So how often do you need to perform that routine maintenance? That depends on your daily gun cleaning habits previously mentioned, as well as volume. Don’t be the guy who needs to keep a fire extinguisher close by in order to have the wire holding the maintenance/inspection card handy for poking out dirty air cap holes. Instead, be the guy whose daily maintenance keeps those holes clear. There are fantastic cleaning kits available today that simply didn’t exist in days gone by. Invest in your own gun washer. They’re pretty affordable these days, and you’ll wonder why you didn’t make that investment sooner.
One more thing to mention regarding automatic gun washers and air pressure: If you fail to isolate the interior air passages of your spray gun while it’s in a gun washer, or otherwise fail to keep the air passages clean, consistency will suffer due to an incremental buildup of crud in the air passages. This can restrict passage size, which in turn acts like the cheater valve and increases velocity despite what the gauge says. Dirty, sticky cleaning solvent hastens this effect.
Carl Wilson has been painting for nearly 30 years, with formal training from the GM Training Center, ASE, I-CAR and multiple product and color courses. He currently works as a technical rep for Hi-Line Distributors in Oahu, Hawaii. He can be reached at [email protected].