Spray gun air pressure query

Any questions about tools or supplies. Post your compressor/gun questions here.



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Thu Nov 18, 2021 10:10 pm
Hi

With regards to setting the pressure on my HVLP primer gun -

I have say 80 psi line pressure, then I adjust the gun regulator so when I pull the trigger it drops to 30 psi but if wont hold there and if I continue to hold the trigger it will drop down another 5-10 psi and hold 20-25 psi all day long. I can turn up the line pressure to say 95 psi and it will initially hit 40 psi for half a second but will drop down to 30 psi working pressure. Note, this is without the compressor running so it's not an issue.

Does this just mean that my hose setup is too long / has some bottlenecks? I did get a bit fancy putting in multiple moisture filters all with quick connect fittings etc and I have probably 30 metres of air hose.

I suppose an easy test is to rig up a small hose line from my tank and see if the pressure holds.

Appreciate any help

Adam



Top Contributor
Posts: 6735
Joined: Tue May 19, 2009 7:10 pm
Location: OREGON COAST
PostPosted: Thu Nov 18, 2021 10:27 pm
i would do your test to see what it says. it sounds like you have restrictions that are cutting down the air volume. there's not enough volume to keep the pressure up.
thats my idea anyway. I just reread your post so i think what you need to do is pull the trigger an adjust the gun regulator to the lbs. you need 30 psi. some of my guns have regulators some don't. i just set my main regulator to where i get the proper spray and go to work. the viscosity of the paint will determine the air you need.
Jay D.
they say my name is Jay



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Thu Nov 18, 2021 10:32 pm
thanks mate....

The issue I am thinking I will have if I don't address it is that everytime I release and repull the trigger its going to over atomise the paint for that first second while it sits at a higher psi and then settles into its pressure drop and give me inconsistent finish.
Last edited by LittleJerry on Thu Nov 18, 2021 10:44 pm, edited 1 time in total.



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Thu Nov 18, 2021 10:40 pm
I just read this about air regulators at the gun:

Air pressure controlled with an air-adjustment valve-type restrictor will first exit the air cap with an initial burst of pressure, then level off to the adjusted pressure and may fluctuate with changes in system pressure.

But most videos I see of people using at the gun air regulators dont seem to have the subsequent pressure drop.



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Thu Nov 18, 2021 10:50 pm
I recorded a video of the issue (note lower your sound volume)

https://youtu.be/_JCqVEU1-Uc

you can see how it slowly drops about 10 psi down to the 30 psi...I was under the impression it should rapidly drop down to the desired setting and hold it.

User avatar

Board Moderator
Posts: 9878
Joined: Fri Oct 20, 2006 12:40 pm
Location: ARIZONA
PostPosted: Fri Nov 19, 2021 6:16 pm
What is the size and CFM output of your compressor?
What is the make and tip size of your spray gun?
1968 Coronet R/T


ACTS 16:31



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Fri Nov 19, 2021 6:32 pm
The gun in the video is Iwata AT3 HTE2 HVLP.

The air compressor is 348l/m FAD 120l tank - not sure if this is an issue given all my testing is without compressor running and just tank air.

With regards to the gun pressure dropping slowing from the tank pressure to the gun pressure when the trigger is pulled (as opposed to rapid change) I feel like its almost some turbulence or something in the system?

I am going to start isolating the system and if I can get it fixed, slowly add back components (or replace / remove them) as I have 30 metres of 3/8 hose (probably need to halve that), too many quick connects, a couple moisture traps and an amaxi phase 3 filter (which I think is creating a restriction maybe).

f that fails i will hook up my GTI pro lite and see if the problem replicates or is the gun playing up.



Settled In
Posts: 53
Joined: Wed Feb 12, 2020 1:41 am

Country:
Australia
PostPosted: Fri Nov 19, 2021 6:39 pm
Dumb question - with regards to the slow pressure drop I mentioned above...with a HVLP gun having low psi at the air cap, if I am running higher psi at the tank to offset pressure drops would that mean that the psi would drop slower at the gun regulator moreso than a gravity fed gun because it's pushing less air out at the cap so its slower to drop?

User avatar

Board Moderator
Posts: 9878
Joined: Fri Oct 20, 2006 12:40 pm
Location: ARIZONA
PostPosted: Fri Nov 19, 2021 9:22 pm
Read the chart below and find your gun's tip size.
Follow that line to the right and read the Air Pressure at Gun Inlet required PSI in ( ).
Then look at the Air Consumption column for your gun. It will state the CFM in ( ) that is required for your gun to operate properly.

PSI is air pressure. CFM is air volume.

In the HVLP category (at bottom of chart) the PSI at the gun is 30. The air consumption is 12 CFM which means cubic feet per minute.

You need to know if your air compressor is putting out a large enough "volume" of air to handle your gun. So check the specs on your compressor and see how much air it is actually capable of producing.

Iwata Specs.jpg
Iwata Specs.jpg (32.94 KiB) Viewed 10510 times
1968 Coronet R/T


ACTS 16:31

User avatar

Top Contributor
Posts: 2762
Joined: Sun Dec 16, 2012 4:46 am
Location: Canberra
Country:
Australia
PostPosted: Sat Nov 20, 2021 6:21 am
Your AZ3 uses 340l/min and your compressor is only rated for 348l/min. I'd say you're running that a bit close to the line.

30m of hose? You painting next door's car? In the booth I run a 10mm hose that is 9-10m long - just long enough to get half way around the car, go back the other way and get an overlap. The longer your hose the more it will distend under pressure and the more you'll lose.

Although I use regulators on ALL of my guns, some of them are a royal PITA. The passageways are so narrow inside that they restrict the flow so much that you do have to run quite high pressures at the wall and I get exactly the same drop-off. I'm used to it and it's not as bad as yours, but it does mean I have to pull the trigger and use that excess pressure before starting to actually paint. My compressor is rated in the high 400s, so I don't have a problem with the pump struggling to catch up, which is part of what is happening to you. Depending on the brand/design of the regulator, some can be drilled out - makes a huge difference. I've done it with the most affected guns I have, so I think 4 of the 20 odd and a couple more would benefit from the modification.

Running a test with only tank air, i.e. compressor not turned on is a bit of a waste of time, IMHO, even with a 120 litre tank.

As for all your filters, be careful. Very easy to get filters that knock your air pressures or flow rates down. Start with a straight line and test each filter individually. You'll be surprised. :wink:
Chris
Next

Return to Tools and Supplies

Who is online

Users browsing this forum: xF100x and 53 guests