View Full Version : Gravity Feed Gun Question...

10-04-2004, 12:07 PM
For years I used a siphon feed gun and in between coats I would remove the cup and fill a small can with wash solvent so that I could spray a bit out to clean the gun. I recently bought a gravity feed gun and have found that if I leave paint in the cup between coats it thickens slightly and I can not get the same spray pattern for subsequent coats. I'm using Omni epoxy primer and Omni high build primer with a hardener (the worst). I've even tried pouring the cup out between coats, spraying some lacquer thinner through the gun and refilling the cup. Major inconvenience, a waste of paint and solvent, and still not 100% effective.

Am I missing something? Can someone offer some advice?

10-04-2004, 02:10 PM
I just block the fluid cap and tap the trigger a few times to back feed the settled material and mix it with the rest of the material in the cup. The trick is not blowing the cap off the cup and taking a primer shower.
Then I spray the gun out a few seconds before I start on the car or part agian.

10-05-2004, 05:06 AM
Geez, how long are you waiting between coats? It shouldn't thicken up that much. I do one of two things if I anticipate a long period between coats. Put the gun in the fridge, yes it sounds funny but the lower temps don't promote catalyzation as quickly. Secondly, as a last resort, I'll thin it a bit more.

10-05-2004, 06:23 AM
Typically 10-15 mins between coats. I've tried putting the paint in the fridge but not the entire gun. The Omni MP-182 primer surfacer is the worst. That stuff dries on the inside of the cup within 15 minutes with an ambient temp of 80 degrees or so.

I'll try the backfeed trick, I can always turn the regulator down a bit so as not to blow the top off.

10-05-2004, 06:24 AM
as tyhe guys have said it should not thicken between coats unless its 100 degrees outside or in shop, most urethane primers are 4-1-1, some say for thicker applications or more mil coverage to mix 4-1, i always thin my urethane primer, it builds more than enough thinned out.
do you have mixing cups?? how are you mixing it?? i would bet it is getting to much hardner, also what size tip are you using for the primer?? i would not go below a 1.6 or so, i personally like a 1.8 to 2.0, but now and then i will use a 1.6 for a finish coat of primer before final wetblock sanding, let us know

10-05-2004, 06:28 AM
The Omni MP182 I'm using mixes 5 - 1 with hardener and I'm spraying with a 1.8 tip. The first coats sprays awesome, the second OK, and thie third is a waste of time. Ambient temp 80 - 90 degrees.

10-05-2004, 10:52 AM
You might try adding 1 part slow reducer and trying that. It should flow alot nicer. Just be careful not to run it.

10-06-2004, 03:26 AM
you always should match your hardner with the temp it is working in, there is no reason to use a fast hardner when its 80, you want a slow, this is more than likely the problem you are having, when using the right hardner i can go 1-2 hrs without gumming up, and even if it does it comes right out of it once you spray alittle.

10-06-2004, 04:03 AM
Thanks Jake, the paint store keeps giving me the MH165 hardener. I looked it up at http://www.tricitypaint.com/docs.html, a great resource by the way, and they do make a slower hardener MH166. I'll try some of that next time I spray.

That, along with some of the other advice from the board and I'm sure I'll get it dialed in.

Thanks guys!

10-06-2004, 05:11 PM
That is actually pretty common situation. Try bigger tip set up as those surfacers are pretty thick to begin with and clog frequently. You did say surfacer right? If you have sufficient flash time use paint not time as guide. Throw a little reducer to thin it up a bit coming out of gun. Also if this is home job check your compressor as sometimes pressure drops and moisture in lines create havok and gets worse as you spray. If you still have problem you can pull off cap and tip between rounds and clean out. You will see how clogged up they get. I usually reduce a little even if not recommended by paint MFG and go up atleast one tip size and can go two to three rounds with some slow down on third.

Jim Nilsen
10-06-2004, 08:44 PM
If you have a gravity feed gun you can use a bag that seals like a ziplock that will eliminate the air from getting to it at all. Since the primer will not be exposed to air it might not thicken up.It draws the bag in until it is vacuum sqeezed out. You waste less material since you can get closer to the last drop without the usual problems.

I have a Finishline by Devilbiss that came with the bags. You can actually turn the gun upside down and never spill a drop or clog or spatter and it just keeps spraying.

You can get these bags through Eastwood and get the adapters to fit many different guns and the installation tool too!

They are worth every penny just in the savings in solvents since you never get your cup dirty so there is less needed to clean.

Once you use the bags you will never go back and I really think it may solve your problem.If it doesn't you will still be glad you are using the bags anyway.

Goodluck, Jim Nilsen

10-07-2004, 12:29 PM
Hey Jim, thanks. I'll look into the bags since it sounds like we're using the same gun!

10-09-2004, 07:18 PM
Bags are great for easy clean up but usually the problem with non primer specific guns is the thick surfacers dry and clog in the tip area. As you spray the air simply dries up the paint that is ultra thick to begin with. Easiest way out is to put amount for 1 pass in gun and after pass blow out with reducer then take off tip and clean. Leave total mixed amount in sealed cup. You are now ready to spray. A little messy but hey either that or spend the bucks for better set up. Sata guns clean very easy but then again some of the offshore stuff are almost direct knock offs and work great for the money for primer. The Finish line is ok? for thick primers? Whatever you do stay away from Sharpe Cobalt. Worst primer gun I ever owned.