70psi at compressor regulator to get 23psi at gun?

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PostPosted: Sat Jun 13, 2020 11:55 am
Hi, newbie here and newbie at paint guns. My 1st attempt at priming an entire car with Slick Sand. I have a Devilbiss FLG-678 Finishline primer gun (2.2 & 1.8 tips). The gun says use 23psi at the gun inlet. I have a gauge at the gun inlet and a regulator at the compressor. Hose is 3/8" and only 25' long. To get 23psi at the gun gauge (with the trigger on), I have to set my regulator at about 70psi. This seems high, even the gun instructions say I should only need about 50psi with a 5/16"- 50' hose. The air coming out of the gun is super strong it seems, but like I said I'm a newbie at this. I even switched air gun gauges and still get that same result, so I ruled out the gauge as the culprit.

Is it normal to need 70psi at the compressor to get 23psi at the gun using 25' of 3/8 hose?

Thank you!

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PostPosted: Sat Jun 13, 2020 5:12 pm
Sounds right to me. You could set the regulator higher and just control it at the gun.

The main factor to consider is whether your compressor puts out enough volume of air (CFM) to satisfy the spray gun's requirements. I believe that gun requires 13 CFM to operate.
1968 Coronet R/T


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PostPosted: Sun Jun 14, 2020 8:42 am
'68 Coronet R/T wrote:Sounds right to me. You could set the regulator higher and just control it at the gun.

The main factor to consider is whether your compressor puts out enough volume of air (CFM) to satisfy the spray gun's requirements. I believe that gun requires 13 CFM to operate.


Thank you for the response. Compressor is 33gal, 6HP, specs say:
Displacement CFM 21.2
SCFM@40psig 15.0
SCFM@90psig 11.5.

Should I be ok?



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PostPosted: Tue Jun 16, 2020 3:06 pm
box986 wrote:
'68 Coronet R/T wrote:Sounds right to me. You could set the regulator higher and just control it at the gun.

The main factor to consider is whether your compressor puts out enough volume of air (CFM) to satisfy the spray gun's requirements. I believe that gun requires 13 CFM to operate.


Thank you for the response. Compressor is 33gal, 6HP, specs say:
Displacement CFM 21.2
SCFM@40psig 15.0
SCFM@90psig 11.5.

Should I be ok?


That"s a Big HP claim for such a small tank? big claim on CFM rating as well 21.2 cfm?
drops quick with any pressure red flag! Air compressor specs are over rated in almost all cases what brand and model is it?
Dennis B.
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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PostPosted: Tue Jun 16, 2020 3:52 pm
What Dennis is seeing is the jump in CFM from 11.5 at 90 psi to 15 cfm at 40 psi.

I have a 6 hp and it only gains .4 CFM with a 75 psi drop in pressure. Yours is saying it increases 3.5 CFM with a 40 psi drop in pressure. That's a hard to accept as accurate.
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PostPosted: Wed Jun 17, 2020 9:51 am
I set all my compressors at 150 psi cut off, kick on at 110 psi.

I like how el'cheapo compressor mfg show the cfm ratings at 40 psi like it matters ? who operates at 40? lol

Free air cfm matters as does cfm at pressure at or above 90 psi
thats the min pressure for most air tools to operate. If the Pump isnt making any cfm above 90 its not gonna keep up with your air consumption its always going to be running its gonna stay hot and make a lot of water and oil and burn up.

Heat is your air compressors enemy. Water is your air tools enemy. water and Oil is your painting enemy.
If your compressor is constantly running its getting HOT making water if its running constantly Hot its wearing out fast leaking oil into your lines.

Your gonna battle Heat, water and oil.

The Bigger your compressor pump is the more air flow you have and you can turn the pump slower making less heat, so your Pump lasts longer & makes less oil and water.
Dennis B.
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Wed Jun 17, 2020 12:19 pm
Doright wrote:
box986 wrote:
'68 Coronet R/T wrote:Sounds right to me. You could set the regulator higher and just control it at the gun.

The main factor to consider is whether your compressor puts out enough volume of air (CFM) to satisfy the spray gun's requirements. I believe that gun requires 13 CFM to operate.


Thank you for the response. Compressor is 33gal, 6HP, specs say:
Displacement CFM 21.2
SCFM@40psig 15.0
SCFM@90psig 11.5.

Should I be ok?


That"s a Big HP claim for such a small tank? big claim on CFM rating as well 21.2 cfm?
drops quick with any pressure red flag! Air compressor specs are over rated in almost all cases what brand and model is it?


Sears Craftsman 919.152931 "Twin-V Oilfree"



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PostPosted: Wed Jun 17, 2020 12:21 pm
Doright wrote:I set all my compressors at 150 psi cut off, kick on at 110 psi.

I like how el'cheapo compressor mfg show the cfm ratings at 40 psi like it matters ? who operates at 40? lol

Free air cfm matters as does cfm at pressure at or above 90 psi
thats the min pressure for most air tools to operate. If the Pump isnt making any cfm above 90 its not gonna keep up with your air consumption its always going to be running its gonna stay hot and make a lot of water and oil and burn up.

Heat is your air compressors enemy. Water is your air tools enemy. water and Oil is your painting enemy.
If your compressor is constantly running its getting HOT making water if its running constantly Hot its wearing out fast leaking oil into your lines.

Your gonna battle Heat, water and oil.

The Bigger your compressor pump is the more air flow you have and you can turn the pump slower making less heat, so your Pump lasts longer & makes less oil and water.


Yes, it ran the entire time when I was priming the truck. Is water in the line while priming with poly as bad as water while spraying base or clear?



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PostPosted: Thu Jun 18, 2020 3:00 pm
box986 wrote:
Yes, it ran the entire time when I was priming the truck. Is water in the line while priming with poly as bad as water while spraying base or clear?


Yes. water BAD!

My Neighbor has same compressor. its fine for filling tires with air and running a Nail gun but I would not try Painting a car/truck with it.

That has an Oil free Vane type pump they wear out fairly quickly.
I have had to fix wiring on his before due to heat damage from running a lot.
Dennis B.
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Fri Jun 19, 2020 7:04 am
something to think about:
33 gallons is 4.4 cubic feet.
oiless compressors run HOT. HOT= major moisture problems.
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