| In essence, an HVLP gun is still an air spray gun as it | | | | eddies and currents which add to the turbulence. All |
| uses air as its primary atomization force. Both HVLP | | | | guns create their own turbulence during atomization |
| and conventional air spray guns use the same two | | | | but guns with high atomizing pressures or high volumes |
| components of compressed air, pressure and volume | | | | of air will create more turbulence than guns that use |
| but in different quantities. The pressure, which is | | | | low pressures and very low volumes of air. |
| normally noted in terms of pounds per square inch or | | | | So aside from these characteristics that are shared |
| PSI and volume, which is noted in terms of cubic feet | | | | by conventional air spray, HVLP, LVLP and RP guns, |
| per minute, are both necessary for either gun to work. | | | | one should also understand the benefits and limitations |
| Originally HVLP guns where designed to use | | | | of HVLP. For the most part the benefit is reduced |
| extremely high volumes of CFM that were generated | | | | coating usage as HVLP has been proven to increase |
| by turbines rather than compressors. These turbines | | | | ones' transfer efficiency. In essence transfer efficiency |
| delivered, in some cases, hundreds of CFM but very | | | | is than percent of paint solids that leave the spray gun |
| little pressure. In order to remain competitive with the | | | | during atomization that actually end up on the substrate |
| turbine HVLP guns, the manufacturers of the traditional | | | | and not in the spray booth filters, booth walls or the |
| air spray guns soon figured out how to convert their | | | | booths floor. Some manufacturers have seen coating |
| guns to HVLP using compressed air rather than turbine | | | | savings per square foot of up to 50% while others |
| air. Today HVLP guns are as common as the old | | | | may only see savings of 15 to 20%. Much depends on |
| conventional guns. | | | | your coating, your environment, your finishers and how |
| HVLP technology proved that if you used a lot of | | | | well your conventional gun was set up in the first place. |
| volume of air instead of a lot of pressure like | | | | As for the limitations, HVLP guns use substantially |
| conventional guns did, you could not only atomize | | | | more CFM than conventional guns. This means that |
| coatings but also do so more efficiently. The efficiency | | | | you will most likely be paying more for electricity to run |
| improvement was mostly related to the fact that the | | | | your compressor at best or you might need to |
| atomized paint particles traveled at a slower speed | | | | upgrade to a larger compressor at worst. Although the |
| than paint particles that were atomized with high air | | | | overall atomization of HVLP has greatly improved, |
| pressure. We refer to this characteristic as spray | | | | atomization quality can be negatively affected by high |
| particle velocity. The higher the velocity of the paint | | | | viscosity and or high flow rates. Most states require |
| particle the lower the efficiency would be. | | | | that HVLP guns be limited to 10 psi at the air cap |
| I like to use the analogy of a tennis ball and a cement | | | | because pressures higher than that begin to decrease |
| wall. The paint particle is representative of the | | | | the guns' efficiency substantially. So if your material is |
| atomized paint particle and the wall represents the | | | | viscous or if you are running high flow rates you may |
| substrate being coated. The harder you throw the ball | | | | be hampered by this 10-psi limit or by the declining |
| against the wall, the further the ball bounces from the | | | | efficiency should you exceed 10 psi. |
| wall. During air spray atomization the paint particle can | | | | Low Volume Low Pressure |
| travel at speeds greater than 30 feet per second or | | | | To help users with limited compressed air availability, |
| FPS. When the same coating is atomized with HVLP | | | | some gun manufacturers have introduced Low |
| technology, the FPS drops to 10 to 23 FPS. The | | | | Volume Low Pressure guns. These guns are designed |
| slower the particle velocity, the less bounce back and | | | | to reduce spray particle velocity like HVLP guns, but |
| over spray, the more efficient the technology will be. | | | | can actually use less air than a conventional gun. This |
| In addition to spray particle velocity, another | | | | can help reduce the high electricity costs associated |
| characteristic that affects guns that use a lot of | | | | with the high cfm demand of HVLP guns. However, it |
| volume of air such as HVLP is air damming. Here I like | | | | is recommended that you evaluate these guns |
| to use the analogy of a 2' high by 2' wide by 2' deep | | | | thoroughly for finish quality and efficiency before |
| box and blocks that are 1' high by 1' wide by 1' deep. In | | | | automatically switching to this technology. The money |
| this scenario the box is the inside of a cabinet and the | | | | you save in electricity may be outweighed by a loss in |
| blocks represent a cubic foot of air from your gun. Try | | | | efficiency or finish quality. Then again, you may find |
| to imagine these blocks of air as they exit the spray | | | | that some of they are actually more efficient or give |
| gun and enter the box. When you spray into the box | | | | you a better finish and save you money on your |
| you are filling it with the blocks of air. The inside area | | | | electric bill. The only way to be sure is to try them at |
| of the box can only hold 8 cubic feet or 8 blocks, but | | | | your facility, with your coatings and your finishers. |
| the gun you are using is putting out 20 cubic feet per | | | | Another advantage of this technology is their ability to |
| minute or 20t blocks per minute. | | | | deliver pressures substantially higher than HVLP. For |
| The result is that within seconds you are putting too | | | | companies or industries that are not restricted by state |
| many blocks into the box and those extra blocks are | | | | environmental regulations concerning the 10-psi limit, |
| preventing you from putting in more blocks and they | | | | these guns can handle higher viscosities and flow |
| are spilling out all over the place. The volume of air has | | | | rates than HVLP guns but most likely at lower |
| to go somewhere because it usually can't pass | | | | efficiencies. However, the efficiencies are usually |
| through the item you are trying to spray. The high | | | | significantly higher than Conventional Air Spray. LVLP |
| volume of air from the gun is preventing more air and | | | | guns are considered HVLP compliant but only if |
| most importantly, the coating from getting into the box. | | | | operated at 10 psi or less at the air cap. |
| This is an example of air damming and the higher the | | | | All of the above low fluid pressure, air spray |
| volume of air the more damming you will get. | | | | technologies are available in siphon, gravity and |
| In addition to air damming there is the problem of air | | | | pressure feed formats. However, keep in mind the |
| turbulence. Turbulence results from sudden changes in | | | | limited siphoning ability of some of these guns, |
| wind direction and velocity. This causes the aircraft to | | | | especially if your material is viscous or if you need to |
| bounce and move rapidly in directions that are not | | | | spray at high flow rates. It is also important that you |
| intended. Anyone that has ever flown in an airplane or | | | | make sure that the gun you select can be operated |
| jet has probably experienced it first hand. As the | | | | within the compliant pressure range (10 psi for HVLP) |
| atomizing air exits the spray gun it begins to interact | | | | or that it is recognized as a compliant technology, if |
| with the coating and the surrounding air in the | | | | you are required to do so by any state environmental |
| atmosphere creating turbulence. Additionally, the air and | | | | regulations. |
| coating interact with the substrates' geometry creating | | | | |