HVLP Needle sizes

I'm failing to understand what the point is of all the different sizes of needles/tips for HVLP sprayers. The needle to tip gap is adjustable (at least on my Earlex 5000) from wide open to pretty much closed. It seems to me that this adjustment should allow just about any fluid viscosity and flow rate that you would ever want besides maybe really thick latex paint or epoxy. What am I missing? Could someone please try to explain this to me?

Besides my inability to understand this, there is an underlying reason for me asking this question. I removed my tip to clean it and upon reinstalling it, the tip cracked because the needle got stuck somehow and I forced the tip on with the wrench which cracked the tip. I learned my lesson on that one...always install the tip before the needle to avoid this. Now I need a new tip. The 2.0mm needle/tip that I have been using has worked just fine for what I have been spraying (stain, shellac, lacquer, etc.) so I'm wondering why I would ever want or need any other size tip.

I'm no expert but I think that the smaller tips give better atomization with thinner materials. If you're not aware of it, here are some tips for the Earlex 5000:
http://www.earlex.com/hv5000-accessories.php and scroll about 2/3 of the way down the page.

A larger diameter needle/nozzle will allow more fluid to pass when the needle is open. Every n/n will at the fully closed not allow any fluid then increase with each turn of the fluid adjustment knob. The larger n/n will flow more fluid with each turn, albeit just fractionally at first. For each turn of the fluid control knob, the larger n/n will flow a greater volume of fluid than a smaller size. Remember that while the ratio of nozzle diameter to needle diameter is the same, the diameter of the "ring" between the nozzle and needle is greater - that is the difference.

The reason for the variety of sizes (air caps, needle, and nozzle) is to facilitate fine control for different viscosities. The sweet spot - proper atomization - for identical fluids can change with temperature and humidity, as well as air volume and pressure. For a given fluid, you could probably use two, possibly three different n/n combinations - but each would have different fluid knob settings and probably different air control settings.

You might find that spraying a low viscosity fluid such as water based dye possible with your 2.0mm n/n, but proper atomization might only occur within a 1/4 turn range of your fluid control. With a 1.0mm n/n proper atomization would probably occur over a broader span of the fluid control knob giving you much greater control of your spray pattern. If you are spraying a sunburst on a guitar body, control is everything. If you are spraying a single tone of dye over a cabinet, that degree of control is less important.

Many woodworkers only spray lacquer or shellac and never have a reason to use anything else than the n/n that came with their gun. Move to waterborne finishes or dyes, and having a size up or down from center can make a difference.

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Originally Posted by Kyle Kaldor

I'm failing to understand what the point is of all the different sizes of needles/tips for HVLP sprayers. The needle to tip gap is adjustable (at least on my Earlex 5000) from wide open to pretty much closed. It seems to me that this adjustment should allow just about any fluid viscosity and flow rate that you would ever want besides maybe really thick latex paint or epoxy. What am I missing? Could someone please try to explain this to me?

Besides my inability to understand this, there is an underlying reason for me asking this question. I removed my tip to clean it and upon reinstalling it, the tip cracked because the needle got stuck somehow and I forced the tip on with the wrench which cracked the tip. I learned my lesson on that one...always install the tip before the needle to avoid this. Now I need a new tip. The 2.0mm needle/tip that I have been using has worked just fine for what I have been spraying (stain, shellac, lacquer, etc.) so I'm wondering why I would ever want or need any other size tip.

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the needle to tip is adjustable. Right but the size it is still adjustable . Don't matter how big . it is adjustable I use 2mm for my lacquer. Now if it were bigger it would still be adjustable . Now a bigger one you may have to use with paint.?? I haven't use mine for paint? So maybe another poster will chim in ? my 2 cent's

Larger needle/nose sizes for thicker paint/varnish.
Smaller needle/nose sizes for thinner paint/varnish.

What you are looking for is:

1) a workable spray patten so you can cover your surface evenly.

2) atomization that gives a smooth finish with no runs and acceptably low amount of orange peel.

This is accomplished by thinning (or reducing the paint), varying the air pressure and tip size. And just to stick another fly into the ointment, some paints just seem to level out and work better.

How to approach this?

1) As someone earlier posted, read everything you can find and watch dvds on the subject.

2) Purchase the best equipment you can afford.

3) Purchase the best paint and thinner/reducers.

4) Practice

5) Practice

6) Practice

7) If all this fails, hire an experienced painter.

It must be remembered that this is professional skill that men make their living at, feeding families, purchasing houses, cars and saving up for retirement years. Sometimes they are worth every penny and them some.

That doesn't mean an amateur cannot produce excellent paint jobs. Some amateurs paint cars with brushes and rollers, then sand and polish to obtain a shine the pro's would die for if they could get it right off the gun.

So even when my amateurish jobs come out with a few runs and extensive orange peel, that just means I get to spend some time sanding and polishing before the job is finished. Don't ask me how I know! :>)