Amplitude Modulation

[Willyou]

I recently purchased a small spray gun ( I think it is referred to as a conversion (HVLP) gun). I also have an older touch-up (non-HVLP) spray gun. The old gun has two main controls, fluid control and air control. The new gun, similar to this one:
http://www.amazon.com/SPRAYIT-SP-352-Gra...words=speay+gun
has a third control that I'm trying to figure out which is a screw knob located just above the fluid control on the back of the gun. The sketchy instructions refer to the part with a chinese word. When I google the word, it seems to have something to do with "amplitude modulation". Googling that phrase results in nothing useful. Does anyone here know what that control is for and how to use it.

[JR1]

Most likely controls th spray pattern from a circle o a fan and the width of the fan. ry it on some cardboard using water and see.

[Willyou]

I got a chance to work with it some this afternoon. The upper knob is, in deed, the fan control. However, while I thought it would be straight forward, I am having a problem understanding the air controls. First, the gun operates between 30 & 60 psi and 2.5 to 6 cfm. My compressor puts out 6.5 cfm at 90 psi according to the specs. I don't know what the cfms are at a lower pressure.

I started by setting the compressor to 90 psi and connected a Harbor Freight pressure regulator to the gun. I tried to use that configuration to control the pressure at the gun, but the HF regulator would not reduce the pressure to less than about 60 psi (with the gun trigger pulled) and then it would shut the air completely off. For some reason, it provides better control when using it with my airbrush. Also, with water in the gun, I was able to get a nice fan shape and, what appears to be, good fluid flow with those two controls. However, adjusting the air volume control between the two extremes didn't seem to have any effect on the spray. Maybe it only effects the quality of paint spray on the project??

I've checked several videos on utube, etc. as well as some print documents on the various settings. Most were vague or confusing regarding air volume control. One said to adjust it until it sounds right. Another said that you could use this control instead of a pressure regulator and stated that this control could be used to shut the air complete off. Another two sources had full on and full off going opposite directions.

For my last attempt, I left the pressure regulator off and set the compressor to limit pressure to 50psi. Again, with water in the gun, the fan and fluid control adjustment worked OK, but the air control seemed to have no effect on anything and it would not shut off the air (if, indeed, it is supposed to).

I appreciate any suggestions.

[jteneyck]

Yes, most likely the fan width control knob. The info. says it only has a control range of 5.5 to 7.5 inches, however. That would have made it a no go for me. Didn't several folks here give you specific recommendations recently?

John

[Willyou]

I rather thought that it might be fan control. I won't have an opportunity to try it out until I finish my current project and get it out of my way. Thought I would try to get an answer in the mean time.
The link I provided is not the one I bought, but rather just a convenient picture showing the knob location. Yes. some here recommended one of the Harbor Freight models. I actually bought one from TCP Global that has features, I think, I will like better. We'll see.
BTW, the word in the "manual" used to label the control in question is "fudutiaojiezujian".
Thanks

[Snipe Hunter]

Bottom knob by the air inlet is "Air Volume". The next knob up controls the travel distance of the needle from closed to wide open which allows more or less fluid to pass through the spray tip. So it's "Fluid Volume". The knob on the top is "fan control". It controls the width of the fan pattern. You have the same amount of fluid passing through the tip and the same amount of air passing through the air cap no matter how the "fan control" is set. If it's set too narrow, it will apply to much paint in too small an area assuming you have sufficiency air and fluid passing through the gun to get a good finish coating. If you open the fan pattern wider, that same amount of finish will coat a wider area... which is what you typically want.

Loosen the ring around the air cap to allow you to rotate the air cap. That way you can adjust the fan from vertical to horizontal... You'll probably use it vertical 99% of the time.

I rarely open my fan wide open, usually somewhere around 80% - 90%. A good way to see the pattern is to turn the gun sideways with a dark area in the background. You should be able to easily see the pattern when you pull the trigger.

You can also use the trigger to to vary fluid control but the fan and air volume stay put once adjusted.

[Snipe Hunter]

The air volume control at the bottom of the gun won't have anything to do with pressure. That should be regulated at the compressor and at the regulator installed at the air inlet if one exists. It sounds like your HF regulator is bad. The one at the gun should be set around 45psi. You should be able to take off the non operational HF regulator and just set the one on the compressor at 45psi. It's not ideal but it will work.

The gun you bought is rated at "Air consumption 4.2 to 6.0 CFM @ 30 PSI"... which is kind of odd, they usually rate them at 45psi so you can easily compare to other guns. At 45psi, you can expect higher numbers than 4.2 and 6.0.... maybe 50% more? 6.3 to 9 cfm at 45psi.

[Willyou]

Snipe,
Thanks. I've pretty well figured out that the control at the bottom has nothing to do with pressure. The question is: how do you set the volume and does it ever need to be changed depending on other settings ?

Please ignore the link in my op. It was only intended as an example. Sorry I did that. The gun I actually purchased is this one:
http://www.tcpglobal.com/TCP-F3-SET.html#.VfghZ1MdPr4

Can you recommend a better pressure reg that won't break the bank? Are the ones with "diaphragm control" that automatically adjust for fluctuations better?

[Snipe Hunter]

You're probably going to leave that air volume pretty much wide open. I would. You can choke it down later if you can't get the gun spraying right. Leave it wide open and set your regulator to 45. I'd set the fan width at about 80-90%. Then play with your fluid/needle setting. Hold your gun 10-12 inches off your work, make your passes at about 1ft per second. If it's runs, close the fluid some until you get a nice wet edge where the fan hits the work without running. I like shooting the Deft because you can shoot the second coat in about two - three minutes. You might have to wait a while with the Urethane.

Keep the gun at 90 degrees to your work and try to keep your work vertical. Shooting down on a horizontal surface is begging for trouble... orange peel, bugs, dust, dragging your hose on the work, spilling etc.

Set the gun up that way and experiment with "Speed and distance". Speed of the pass and distance from the work. You can almost always compensate with adjusting speed and distance. It becomes second nature after a while. You can practice with Deft "Brushing lacquer" and Min Wax Urethane.. shoot the glossy, it makes you concentrate. The satin is easy to shoot. I recommend those because they're cheap and spray reasonably well. Thin either one with 10% Lacquer Thinner and spray in the shade. Wear your respirator.

[Willyou]

Snipe,
Thanks. That gives me a place to start. I guess I need to get another regulator. I think the HF is just too cheap. Having said that, the company where I purchased the gun also has a couple for about the same price. One is apparently self regulating. Do you (or anyone else) have any insight?