1/4" or 3/8" hose

[AlxxNova]

I have a Craftsman 150 psi 30 gallon tank with 6 hp putting out 8.6 scfm at 40 psi. It came with a quick disconnect attached and 10' of 1/4" hose. I have been reading about using 3/8" hose. But I would have to use an adapter to reduce the 3/8" line to connect to the tank. So since I would have to reduce the size to connect the 3/8" line do I still need to change over or does it not matter since the adaptor will cause a bottle neck in the line?

 

[Mac_Muz]

Why can't you remove the 1/4" set up right at the compressor?

I have a similar compressor that came with no lines, just a fancy fitting that will take about any 3/8" fitting...

You want all the air you can get for painting, running air tools with more air is usually for the better...

I would can that 1/4" stuff in a hurry.... Mac

 

[Motornoggin]

Absolutely ditch that 1/4" air line! There are some formulas for figuring it all out, but it takes about 8 times (if I remember right) the pressure in 1/4 to get the same volume of air as 3/8 line! For example, if you can get(hypothetically) 40cfm @10 psi with 3/8 line, you would need 80psi to get the same 40cfm with 1/4 inch line. Big difference! If you have an HVLP gun you could (probably would) ruin the air cap diaphram trying to run enough pressure to get enough air with 1/4 line.

 

[AlxxNova]

What happened was this. When I bought the compressor it came with a hose. The hose was supposed to be a 3/8" so I bought a second to go from the filter to the gun. The filter was for 3/8" NPT couplings. When I went to connect it I found out that the hose has 1/4" NPT couplings so I assumed that was also the inside diameter of the hose. and bought some adaptors to connect the hoses to the filter. I was just out in the garage and noticed the label for the second hose laying around and took another look at it. It is a 3/8" inside diameter hose but it has a 1/4 NPT coupling. Looking at the tank the tube coming out to the second gauge just might have a 3/8" ID. I'll have to take it apart tomorrow and measure it. I guess that explains why when I cranked the pressure at the gun up to 60 psi it worked better.

So I am I correct in assuming that even though the inside diameter of the hose is 3/8" that the 1/4" NPT fittings are choking off the air supply?

 

[Mac_Muz]

Ok You are running standard 3/8" hose then and the fittings while steping down, as they all do as far as I know will be ok.

Choose 1 type of fitting and stick to it.

If you really had, had 1/4" the step down for that would be even smaller!!!!

To see what I mean take a look at most any air brush in a art store..... The fittings on them are very small....

I have never seen a compressor the size of yours come with 1/4", but I figured you knew what you had...

What are you going to paint?

I am way new to painting, and have only painted my bike todate.... 1 gas tank, and 2 side covers. My compressor will do it, but it really works in the doing.

I am getting ready to do my car, which needs body work first. I know very little of that.

Once I get the body work done, I will have to figure out a pattern to shoot the car,, so the comp can have a wee rest between shooting.

I will be asking all sorts of newbie questions on my thread. Your welcome to read, and join in... Mac

 

[rex]

Since things are missmatched check the whole system.If you have 3/8 fittings a pencil will go through them,where it wont in 1/4 hardware.The couplers might be hard to tell so take one to the store and compare them.A 30 gallon tank might run down quick on a car though.If you want to know do a dry run.With a clean and empty gun plug her in and start 'painting' your car.Even if the compressor runs constantly,you need to maintain pressure to put a complete coat on.A pickup can be painted bed and cab separate,but there's really no stopping point on a car.You could fake it on the base but you'll be screwed on the clear and end up with dry spots where you stop and come back to finish after the air supply built back up.She might work though,do a dry run to be sure.

 

[AlxxNova]

Hi,

Right now all I have room to do are motorcycles and that was the biggest compressor I could get without going over my start up budget. Though as things progress I really want a bigger compressor. I just need to show the wife that I can make some money at this and that it's not just more toys for the garage <g>.

I checked the hoses. I couldn't fit a pencil through the coupling. So I measured them and the couplings are all 1/4" even though the hoses say they are 3/8". My Finishline 2 (hvlp gravity feed) arrived today. I did notice that all the couplings DeVilbiss advertised on the back of the manual have 1/4" NPT fittings so I'm wondering if I'm okay with my hoses or should I ditch them for the larger couplings. I picked up a couple of Kosmoski's videos and he was mentioning to making sure you use 3/8" hoses or else you starve the gun. But even though the hose is the right size I would think that it has to be acting like a funnel. No matter how big the opening is you still have to wait for air to pass through the smaller end. I also saw that Sears sells 3/8" line with 1/4" or 3/8" couplings. So the question is am I all right with this setup, do I need to swap the hoses, or is it possible to just change the couplings?

Can't wait to try out the new gun tomorrow. Especially after last night. While taping off the flames on the rear fender I knocked over the front fender. So today I spent some time with that fender, a rubber mallet, and my old airbrush. Now it's good as new again.

 

[rex]

Hey Alex.Kind of wierd DeVilbiss didn't recomend the 3/8.The 1/4 will work OK alot of people still use them,but your gun will work more efficiently with a complete 3/8 setup.Probably isn't much difference between Sears and DeVilbiss fittings besides price,but use fittings and couplers from the same source just in case.With DeVilbiss couplers you just push the tool in,you don't have to pull the lock ring back-I like it.

 

[Scott Gardner]

I wouldn't worry about it too much. I think we have the same compressor, except mine is the horizontal 33 gallon model. I also have the 3/8" hose with the 1/4" NPT couplings. There's a short length of 3/8" hose between the compressor and my shop plumbing, which is 100 feet of 1" black gas pipe, and then about 15 feet of 3/8" hose to the spray gun. I have had no problems whatsoever with maintaining adequate flow. Don't forget that there's a WORLD of difference between a 3/8" hose with 1/4" couplings and a hose that's 1/4" all the way through.</cr>
</cr>
That being said, I agree that a "dry run" would be a good idea. The specs for your new Devilbiss are 11.4 CFM at 23 psi. With your compressor fully charged, you have 30 gallons of 150 psi air. If you turned off the motor on your compressor and just used the air in the tank, that's only going to give you a little over two minutes' worth of 23 psi air. This means that you will definitely be relying on the compressor motor to re-pressurize the tank while you're spraying. I'll do a little experimenting on my compressor as well to see how long I can spray air through the gun before the inlet pressure drops below 23 psi. I'll try to post my results in the next day or two.
Scott

 

[Scott Gardner]

Originally posted by rex:
<<snip>>A pickup can be painted bed and cab separate,but there's really no stopping point on a car.You could fake it on the base but you'll be screwed on the clear and end up with dry spots where you stop and come back to finish after the air supply built back up.She might work though,do a dry run to be sure.

<font size="2" face="Verdana, Helvetica, sans-serif">If this is the case, what happens when you have to stop to re-fill your cup while painting the clearcoat on a car? I don't know, since I haven't painted anything yet that I couldn't either finish with one cup's worth of paint or break up into smaller pieces. Do you just re-fill the cup as quickly as possible and pick back up where you left off?</cr>
Scott

 

[rex]

Yeah,that's it Scott.I fill up between panels ie: your doing the door but don't have enough left to do the 1/4 panel,so fill up before starting the 1/4.You have a little time you can stop and come back allowing the overspray to melt in,but the length of time it takes a compressor to fill up is usually pretty long.Actually you can do a car in stages,but when you get to metallics and pearls the liklihood of seeing the difference between the panels increases.3 stages are taboo this way.If there is a breaking point in the 1/4sails like chrome,seams or moldings you can zone it out into the 2 sides and the whole top.Alot of cars don't have a break in the sails though so the roof and 1/4s need to be done together.Kind of a pain under limiting circumstances like this.