HVLP Hose Question

[jpearson]

I bought a pair of HVLP spray guns to paint a car with. It will be my first paint project. I am wondering about the air supply. I have a 5hp, 60gal, two stage Ingersoll Rand compressor. My question involves the hose. I understand you want to preserve as much CFM as possible with these guns. I have read that 3/8 is the ideal ID for the hose + it is recommended to use high flow couplers. My question is that all the 3/8 hose I have found has 1/4 fittings, is that OK? It seems that the CFM would only be as high as the most restrictive part so why have the bigger hose with small fittings? Do they make hoses with bigger fittings? Do I need one?
Someone please set me straight.
Thanks

 

[tcianci]

The fittings are 1/4 inch IPS (iron pipe size) and the hole through them is somewhat larger than 1/4 but certainly not 3/8. The high flow fittings are 1/4 IPS too. Regular fittings have 1/4 IPS but the hole through them is actually less than .200. So, while your system is not really 3/8 all the way, it will flow sufficient air for your gun. You can push a lot of air through a small hole but when the holes are too restrictive, you get excess pressure drop. That's why it's imortant to set the pressure at the gun with the gun triggered. It takes the pressure drops due to restrictions in the hose system out of the equation and keeps the gun compliant. The pressure the manufacturer recommends at the gun gives the correct pressure at the air cap which results in transfer efficiency that the manufacturer intended.

 

[jpearson]

Thanks - I know that was a simple question but I've been struggling to find the answer.

 

[rburke65]

Thanks "tianci" for taking the time to explain this.

 

[Heavy Metal Doctor]

The fittings are 1/4 inch IPS (iron pipe size) and the hole through them is somewhat larger than 1/4 but certainly not 3/8. The high flow fittings are 1/4 IPS too. Regular fittings have 1/4 IPS but the hole through them is actually less than .200. So, while your system is not really 3/8 all the way, it will flow sufficient air for your gun. You can push a lot of air through a small hole but when the holes are too restrictive, you get excess pressure drop. That's why it's imortant to set the pressure at the gun with the gun triggered. It takes the pressure drops due to restrictions in the hose system out of the equation and keeps the gun compliant. The pressure the manufacturer recommends at the gun gives the correct pressure at the air cap which results in transfer efficiency that the manufacturer intended.

To add to what he said -- all of this ^ is why I run a regulator right at the the connection of the hose I use for paint work --- and I set it per the recommendations for the particular gun / paint with the the trigger pulled / flowing air through the gun. I'm not a painter by trade, but I worked with traditional siphon feed guns forever doing the occasional small jobs here and there and only recently went to HVLP -- setting the regulator this way / following the directions worked like a charm and everyone who see's my work still thinks I'm a professional painter

 

[rlitman]

I'm no expert at this by any means, but here's what I did, that works for me:

I got a 3' swivel extension air hose. I screwed that into my HVLP handle, put a disposable filter at the other end, followed by the regulator, and THEN the QD fitting. Then, I put a big hook between the regulator and filter, so I can hang them from my belt, and only be holding the gun in my hand.

That way, there are no QD fittings between the regulator and the gun, so you know just what pressure you're getting.

 

[NUTTSGT]

Always good advice (well most of the time) on GJ.

 

[nehog]

To add to what he said -- all of this ^ is why I run a regulator right at the the connection of the hose I use for paint work...

I think many of us do the same thing: the regulator at the gun helps eliminate most of the air delivery problems you will find. This also will help prevent pressure sagging.

 

[Shadowdog500]

+1 on setting the pressure on the gun with the trigger pulled. Not an expert, but have painted a few things with my HF HVLP paint gun. I used the same lines you used on my detail gun with no problem.

Here is the procedure that I used to set up my HF HVLP gun and it worked great.

http://purplesagetradingpost.com/sumner/techinfo/HVLPspraygun.html

Once you get the gun set up practice on something you don't care about. I used a propane tank before I painted this gas tank. Make sure you put one of the disposable water separators at your gun as one last chance to get the water out(see the red thing at the bottom of my paint gun). This was my first paint job using the gun. I used an $8 can of tractor paint because I'm a Cheap Rat ******* (CRB).