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jmoffett
03-18-2007, 10:12 AM
I have a couple of inexpensive ($125) Astro Pneumatic spray guns. They both do a decent job (good enough that I probably will not be investing in a more expensive gun) but I would like to know how to get the most out of these. I have spent some time trying to fine tune them through the adjustments they provide: the fluid needle control knob, the fan width adjustment, and the air pressure control.

Fluid needle control knob: I read once that this should be adjusted so that a full trigger pull opens the needle as far as possible and to leave it there permanently. Is it always optimal to maximize the paint flow, or would there be instances when you want less coming out of the gun? In what instances would you want less paint flow?

Fan width adjustment: Do you want the widest fan width possible without a gap in between?

Air pressure: I know most products specify a certain pressure at the gun for optimal application, but I've also read references here regarding turning the pressure up or down to achieve desired effects. (i.e. Will a higher pressure increase the atomization of the paint?) What effects can be achieved by increasing or decreasing the air pressure?

Are there additional adjustments on a spray gun?

Thanks in advance.

Len
03-18-2007, 10:29 AM
With some less expensive guns like the Astro models there is very little manufacturer info available so there may not be a recommended INLET pressure. You can start around 30 PSI at the gun's inlet pressure gauge and vary the pressure until it produces the result you want.

With most guns I usually recommend opening the fan all the way then turning the knob until the fan just starts to get more narrow. This helps eliminate the soft feathery edges of the fan.

For almost all operations you'll want full fluid flow so I usually recommend that you turn the needle knob all the out until the trigger stops at the handle then turn it in until the trigger moves forward just slightly. This will give you full flow with maximum control.

The only time I restrict the paint flow to the tip is when I need to apply the paint using a narrow pattern. Even with a narrow pattern I mostly use full paint flow but sometimes I'll restrict the paint so that I'm not dumping as much paint into the small area.

If the guns you are using are HVLP then you shouldn't increase the pressure too far beyond the recommended settings or you could/will distort the spray pattern. When using conventional or compliant spray guns the pressure can be increased quite a bit more without causing problems. There are some HVLP guns that can take the increased pressure and still work fine but this is usually a characteristic of better guns. Increase pressure will result in better atomization but also in more overspray and poor transfer efficiency. You can get a smoother finish but you'll use more material while less actually is applied to the surface.

Phil V
03-18-2007, 02:06 PM
Fluid needle control knob: I read once that this should be adjusted so that a full trigger pull opens the needle as far as possible and to leave it there permanently. Is it always optimal to maximize the paint flow, or would there be instances when you want less coming out of the gun? In what instances would you want less paint flow? (There are times that less fluid flow is necessary, like doing door jambs and small pieces. In that case just don't pull the needle/trigger all the way back. control the fluid flow with your trigger finger).

Fan width adjustment: Do you want the widest fan width possible without a gap in between? (again it depends on what you're painting. For normal car exterior painting you open the fan all the way then bring it back in just a little. Then shoot a test pattern on a piece of paper or anything unlucky enough to be in front of the gun (refrain from animals, not good for them). Check the test pattern to make sure it looks like an elongated cigar shape. Not overly thick in the middle and no gaps in the middle. For doing small objects and places like door jambs you can narrow down the fan to whatever works best for you. When you narrow down the fan the air pressure becomes critical. If you narrow down the fan and leave the same air pressure then runs are easy to attain.)

Air pressure: I know most products specify a certain pressure at the gun for optimal application, but I've also read references here regarding turning the pressure up or down to achieve desired effects. (i.e. Will a higher pressure increase the atomization of the paint?) What effects can be achieved by increasing or decreasing the air pressure? ( when shooting acrylic urethane topcoat paints like single stage and clearcoat there are NO advanatges to turning the air down unless you narrow the fan way down and reduce the amount of paint going through the gun. Turning the air pressure up on a cheap hvlp gun will help atomize the paint better but then more than half the paint ends up in the air as overspray and not on the car.

Are there additional adjustments on a spray gun? (Not really).

jmoffett
03-18-2007, 03:12 PM
Very informative...thanks for the replies.


shoot a test pattern on a piece of paper or anything unlucky enough to be in front of the gun (refrain from animals,

Phil, I have a white cat that I'm not particularly fond of. You just gave me a great idea! ;)

Nevermind, I have a hard time hitting it with one of those pressurized water guns (when it jumps up and hangs from the screen door). I could never hit it with a paint gun. :(

isprayum
03-18-2007, 09:12 PM
Fluid needle control knob:

i run full flow for base only. for clear i only go about six turns out, no further. for two years, i cleared with fluid needle 2.5 turns out with wonderful results every day for my first two years.


Fan width adjustment:

yeah, what they said.


Air pressure:

Its my opinion that air pressure is everything relative to viscosity. different days, and different products bring different viscosities. feel free to always adjust air pressure to WHATEVER provides the nice pattern. too high will give a dry spray and too low will make it chunky. find the middle without looking at the gage. ya know, dont go too far off the path, but feel free to find your own pressure.

if you dont control the droplet size, the droplet size will control you. grasshoppa