Help with pressure regulator

[Mike Murray]

I hope this isn't a really stupid question. I'm fairly new to spraying finishes. I have a gravity feed HVLP. Up to now, I just hook it directly to my compressor and regulate the pressure at the compressor. I've had good results on several small projects. I just bought a regulator and installed it at the gun because I want to fine-tune it on the fly and also get a better reading of the actual pressure at the handle.

Now the stupid question. If I want 25 PSI, is that the static reading, or the reading with the trigger pulled? Reason I ask is, if I set the static pressure at the gun to 25 and pull the trigger, I get nothing but a dribble and the pressure gauge immediately drops to zero. However, if I set it at 25 with the trigger pulled (~40-45 PSI static), I get a good spray, which appears to be about the same - maybe a little stronger - than using no regulator at the gun and the compressor set to 25.

Or... is this the result of spending $11.97 at the borg?

[Byron Trantham]

Mike I use an HVLP with a regulator at the gun. My air line is set to 90 psi. I adjust regulator at the gun to 20 psi. when I pull the trigger, it drops to about 10 psi and the paint flows well. anothe issue is the viscosity of the paint - or how thick or thin it is. If its too thick more pressure is required to move it but when it does it splatters.

[Terry Bigelow]

Byron summed it up pretty well. The thickness of your product AND temperature/humidity will all affect the properties of your gun.As far as shooting with specific psi, my advice would be to simply practice at different settings on some scrap to find that smooth finish. I spray an air-assisted/airless rig so my numbers aren't quite the same. One thing is for sure:shooting with a "dribble" won't get it done!

[Mike Murray]

Guys, thanks a lot for the responses. To clarify one point... at the moment, I'm just experimenting by spraying water on cardboard so this is not a viscosity thing and the shop temp is 60.

Here's what I still don't understand... without the regulator, everything works fine. I set the compressor at 25 PSI, and everything is perfect. With the regulator installed at the gun and set to 25 and plenty of line pressure, I get nothing. Pressure immediately drops to zero when I pull the trigger. Any ideas at what might be causing this? I'm guessing it's just a cheap regulator that's causing an inordinate amount of loss. Is that possible? I can always crank things up and get a decent spray, like I mentioned in my initial post. But something seems to be not right with this regulator. Any ideas would be much appreciated.

[JayStPeter]

The regulator that came with my gun does the same thing. I set it with the trigger pulled shooting air and it works fine. I set the regulator on my drop at around 50 and hone in on the 28-29 my gun likes at the gun.

[Mike Murray]

The regulator that came with my gun does the same thing. I set it with the trigger pulled shooting air and it works fine. I set the regulator on my drop at around 50 and hone in on the 28-29 my gun likes at the gun.

Jay, thanks very much for the response. Maybe it wasn't a stupid question after all. Just to be certain... your 28-29 is with the trigger pulled. Right?

[JayStPeter]

Yes, I pull the trigger half way so it is shooting only air and set to 29 PSI. When I release, it shows something higher IIRC.
I set my regulator at the drop to somewhere around the max that the regulator on the gun can display due to concern that I'll blow out that regulator if I drive it to my usual 90 - 100 setting.

[Dennis Peacock]

Mike,

Set your compressor pressure to about twice what you want for the highest level at the gun. Regulate the air pressure at the gun with the trigger pull far enough back to get only air. Tweak the air at the gun and spray some "finish" and see what you get. The target you are trying to hit here is good atomization of your finish and a nice fan pattern for best coverage. Also, remember to overlap each pass by about 2/3 to get a more even coat when spraying. Another thing to remember as you spray is the distance from the wood surface you are spraying as well as the speed in which you are moving the gun.

To help take some of the "guess work" out of your spray finishing? Get a viscocity cup and mix to get the viscocity right before spraying. If the spray is not smooth and even then you can adjust the viscocity once again by a shorter time for the fluid to drain from the v-cup. The shorter the time to drain the cup = thinner material. Once you hit the sweet spot for that particular finish? Write down your formula for a future mix as your starting point. But...also remember that temperature also plays a factor with viscocity.

[Mike Murray]

Thanks for the great information and suggestions. I really appreciate the responses. I've got the gun working great with the regulator and it's good to know that others use the same procedure.

I have to admit I'm still a bit befuddled by why the pressure is set with the trigger pulled instead of the static pressure. Without a regulator, I was getting very good results with the compressor set at 25 PSI static, with a drop to 10-15 when the trigger is pulled. To get comparable results with the regulator at the gun, I have to set the static pressure to 40-50 at the gun. I guess this is due to pressure loss caused by the regulator itself, although the amount of drop seems excessive compared to what I would have expected.

In any case, I know how to work with it now, so thanks again for the great responses.

Mike

[Byron Trantham]

Thanks for the great information and suggestions. I really appreciate the responses. I've got the gun working great with the regulator and it's good to know that others use the same procedure.

I have to admit I'm still a bit befuddled by why the pressure is set with the trigger pulled instead of the static pressure. Without a regulator, I was getting very good results with the compressor set at 25 PSI static, with a drop to 10-15 when the trigger is pulled. To get comparable results with the regulator at the gun, I have to set the static pressure to 40-50 at the gun. I guess this is due to pressure loss caused by the regulator itself, although the amount of drop seems excessive compared to what I would have expected.

In any case, I know how to work with it now, so thanks again for the great responses.

Mike

Mike,
My line pressure is 90 psi. The pressure at the handle of the gun is set to 20 psi. When I pull the trigger, the gun regulator drops to about 10-12 psi. My object is to use as little pressure as possible and still atomize the material and reduce over spray. Remember, there are four elements that drive how the material is laid down. The nozzle/needle size, the air pressure, the fluid control valve (my mfr recommends 1 1/2 turns as a starting point and I have always used that setting) and the viscosity of the material being sprayed. I have found from experience that 20 psi at the and 1 1/2 turns of the fluid knob works in every case - so far. The next thing you need to know is the viscosity. That dictates the nozzle/needle set. If the nozzle/needle set is matched to the viscosity you generally don't have to modify the air pressure from say 20 psi at the gun or modify your fluid setting. PM me if you want more detail. Spraying is great but when you are just getting started is SOOOOO confusing!