# Take apart Graco 390ST fluid section?



## Kingstud (Jul 11, 2010)

I just was finishing cleaning my sprayer when it wouldnt build pressure. It was working flawlessly. I tapped it to free check ball but nothing.

So I want to tear down the fluid section and go thru it but I can't figure out how to get the pickup hose off the elbow. I"m guessing the collar is a lock that needs to be pushed back to release the hose but mine is glued with paint.
Is that it?


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## Pete'sfeets (Mar 20, 2011)

Not sure which connection exactly but pull and turn . I used to just pull out the packing piston and hose out that hose part, switching from oil to latex is half the problem, if a dried up chunk of paint gets lodged onto the intake ball it'll happen over and over till ya lose your head , a good flushingof the hose not the head. Take apart the snap on hose too often will lead to loss of suction too.


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## Metro M & L (Jun 3, 2009)

My general pressure procedure is to 

check intake for obstruction
tighten hand turned elbow joint
hammer the hammer on fitting tight
Run thinner through machine
hammer off the hammer on fitting and clean the ball

I've only gotten to the last step once in the three years I've owned my 390. Running thinner for five ten minutes works wonders!


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## Pete'sfeets (Mar 20, 2011)

Mine lasted fourteen years, ,was going to get parts but a little late. I got it in the shed like a skeleton..


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## Kingstud (Jul 11, 2010)

Got it torn down, cleaned and reassembled. Works again after removing a lot of build up. Packing looked ok, replaced 1 O-ring on pressure relief valve. But now leaks bad out of the shaft and seal.

I didn't want to repack this but must have damaged throat packing in process.


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## Pete'sfeets (Mar 20, 2011)

be sure you glued on the piston pack right is all I'd say , which is why the 390 I have is dead,scratched, plus just alot of wear on the piston walls, if it were a car there would be a huge plume of smoke following. Pictures would be nice, still thinking of learning myself.


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## Kingstud (Jul 11, 2010)

ok here is the diagnoses after tearing it down again.

I had damaged a plastic packing on the piston when I put it back in AND apparently dropped a throat packing ring (found on the ground).


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## Pete'sfeets (Mar 20, 2011)

It's always something with sprayers I tell ya, next it'll be the gun,, the spray gun, not to the head you know but as a matter of good business, a reliable sprayer is essential, even bought an extra cheapie just in case , hardly use it but I can't even imagine having one bust and I have a 3000 sq house to prime and they want it now not later, am I gonna just roll it, or hire an extra help, I don't think so, it's worse than having no spare tire.


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## grecoandson (Dec 22, 2011)

*Grayco 390*

Hi, I am a general contractor who is sick of brushing and rolling jobs that can be sprayed. Years ago I worked with a barn painter and got lots of experience spraying but little setting up, and learning details about the machines. I just got a Grayco 390 used for a great price. I want to learn all I can from the basics up. Can someone please give me a crash coarse that can get me started? I want to make sure I get the hang of it before I bring it to a job site. I am painting 2 medical offices in the new year and would like to get practice at home while I can. Thank you and Happy Holidays.


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## Kingstud (Jul 11, 2010)

its not a complicated rig and very reliable.
Add mineral oil to the cup (or TSL), its the brass collar on the piston, I pop up the plastic collar, it doesn't take much. This will lubricate and breakdown any paint in the packings.
drop the big pick up tube in your paint bucket, after boxing and screening your paint. the little tube I stick in a small bucket at first to flush out whatever water or homemade pump saver is still in it. I try and store it pickled with a mix of spray oil base and mineral spirits in it. With this mix you won't need to flush before use. Flip the valve on the right straight down to flush it and get it primed. Once paint comes out I stick it in the paint bucket too.

Once primed flip the valve horizontal this shuts the bypass and fills the hose. Adjust the knob for pressure, your setting can change depending on viscosity of product. Dial up pressure til you get the atomization and coverage you want. 

When I get low on material but know there is enough in the hose I put the pickup in a bucket of water, run til your paint gets "wet". A 50 ft hose holds about 1 qt of paint.

For cleanup I just drop the gun in a bucket of water and lock it on and let it cycle for a few. Then switch the valve to prime and let it cycle water (or solvent for your product). Be sure to turn the pump OFF BEFORE switching the valve! 
if you flip it to prime and the pump is pressurized the small tube will jump out of the bucket and spray you and your client and his driveway..
I have a habit now of putting one hand on the tube whenever I switch it.

I always tear down my gun. To finish up I prime it with the oil/thinner mix and leave this in it. Leave hoses and gun hooked up or this stuff will leak all over.

Get a few filters for your gun to have on hand, a bad filter in the middle of a job can be a real b****. 60's are for latex 100's for lacquer and cabinets.


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## Pete'sfeets (Mar 20, 2011)

That "U" section of the intake pipe is always a mystery, as you switch from oil to latex a build up of dried paint, loosened from a solvent and you'll never get a prime. That's what I like about the 490, a quick release feature means you don't need a bunch of tools to rinse off the first check ball. I still don't get why there's a filter in the gun, if dirt gets that far ,just blow it out, why save it. I probably need a new gun, the spitting is annoying but I don't think it is dirt so much as low pressure. Would love to splurge on the newest gun, supposed to have less spit, Anyone seen the difference?


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## grecoandson (Dec 22, 2011)

Thank you very much for the info. I got the machine working well.


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## Kingstud (Jul 11, 2010)

Pete, spitting is usually an air leak somewhere. check all your fittings. dont forget to check the pickup tube too.


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## fixitbraintree (Feb 23, 2010)

your gun is spitting because the ball and or the seat in the diffuser is worn out. The diffuser is the piece that you screw the tip guard onto and on the inside has a seat for the gun needle assembly to sit in. there are gun repair kits available and it takes about 10 minutes to rebuild one and it is pretty easy. there are usually only two pieces the needle assembly and the diffuser


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## Pete'sfeets (Mar 20, 2011)

Yah I figure that, I have about five spray handles that are sort of on the way out but I never quite toss them, and the parts are not often interchangable , sometimes but there is new guns out there, ,, with a closed type spring to resist gumming up, not spit it said but the price is what more than a new piston? kinda severe


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