Air Compressor Modification?

[Andrew Benedetto]

That cfm is not much so the regulator is not the issue. You can add an extra air tank for more volume, and use HVLP type connectors which provide more flow than the std QD type. Lowes and HFT has them.
check gleempaint.com for good advise. I do not like oiless compressors for any continuous job, best left for brad nailers IMHO.

[momo44]

Ok. just went and checked. With the blower nozzel on and the tank full and pressure to the hose at 150PSI it drops at least 20 PSI when I pull the trigger. It will run 30-45 seconds before the pump kicks in.
Let it fill up dropped the pressure to 40 and hooked up my paint gun and had at least 10-15 psi drop when I pulled the trigger.
Would a new regulator fix this? or putting a regulator at the other end and keeping enough pressure in the hose to maintain 40 PSI at the gun? Or do you think the pressure would drop after that regulator too?
I also have a water filter right after the regulator. It turns off at 175 PSI and turns on at 150PSI. I can't get more than 150 PSI past the 2nd regulator.

Onedash,

Just looking through forums and came across your post.
The calculation for avg cfm use is pretty simple to do. In your case, you have a 30 gal tank, I assume. There are 7.48 gal/cu ft. So your tank is 30/7.48 = 4.01 cu ft.
Now you need to know atmospheric pressure where you live. At sea level, it is 14.7 psia (0 psi on a gauge). In VA, it is probably 14.5, unless you live on the coast.
So 4.01 cu ft/14.5 psia = 0.2766 cf.psi
This means the pressure will drop 1 psi in your tanks for every 0.2766 cf you remove.
You said it takes 35 sec to drop 25 psi. So,
0.2766 cf/psi * 25 psi = 6.91 cf removed from the tank
(35 s) / (60 s/min) = 0.583 minutes
6.91 cf / 0.583 min = 11.85 cfm average use for 35 seconds.

Now if the compressor will make 5.1 cfm, then once the compressor comes on, you will be at a negative rate (5.1 - 11.85) = -6.75 cfm in the tank.

(-6.75 cfm) / (0.2766 cf/psi) = -24.4 psi/min in the tank (.41psi/sec)

This means you will lose pressure @ 24.4 psi every minute.

If your hose and regulator will allow the pressure to drop in the tank to 60 psi, then you will have 35 s + ((150-60)/0.41) = 254 seconds until the tank is at 60 psi.

Let me know if you need any more info on this.

Regards,

Momo

[momo44]

It looks as though the regulator and the hose are probably the culprits. I would suggest a 1/2" regulator, 1/2" fittings and 1/2" hose to be on the safe side.
Normally for painting, you want a compressor that makes >10 cfm. I would recommend a good 3 hp or larger, quality compressor. An Ingersoll-Rand SS3L3 (11 cfm, 3HP) would be a good example.
Regardless of the compressor, good hose and a good regulator are a must.

Your gun flow rate of 11.85 cfm looks typical.

Regards,

Momo