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Discussion Starter · #1 · (Edited)
My pump works fine but I want it to work perfectly. It pumps and sprays well but when not being sprayed it loses pressure and has to pump once. It will hold for a few to many seconds then pump once. It happens more with water or thinner and only with full pressure. Replaced packings and valve seat so far wonder whats up.
 

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A Brush Above
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Here is the key culprits:

1. Air leak in system -Tighten connections
2. Air leak in siphon hose -Tighten, check for leaks
3. Inlet valve not seating -Service or clean
4. Worn Packings -Replace
5. Dirty or worn Ball valves -Clean or replace
6. Worn Valve Seats -Reverse
7. Worn Prime/Spray Valve -Replace

Typically #4 or #7

Hope that helps. When in doubt send it in to a pump service shop. Ask your local paint store. ;)
 

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A Brush Above
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Graco 600 plus is discontinued so, it is probably something worn out. Graco is really good about keeping discontinued pump parts still in circulation/manufacture.
 

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I must have one of the 7 symptoms on that list too.
I noticed this spraying trim, finer work where the pumps sits inactive more.

My Graco Ultra 695 was shop repacked about 4 years ago (after relatively light use). After a few more years and light-moderate use, I notice when gun is being pressured at 3/4 , the motor will try and get to pressure but keeps making quick short little pumps to get there.

I've repacked my gun, but haven't ever broken down and rebuilt an airless. Don't have the time or, more recently, the area to do it in.
 

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Paint Store Owner
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Sometimes if its only pumping once, its the pressure equalizing in the line. Your spray hose will actually expand and contract slightly causing this extra cycle to happen. If its doing this more than once, its either worn packings, damaged ball or seat, worn gun, or worn prime valve.
 

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Discussion Starter · #7 ·
My thought is

My valve seats can be reversed? I think its my inlet seat or dump valve. I already replaced packings and piston valve. It was doing the same thing before I replace them.
 

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Sometimes if its only pumping once, its the pressure equalizing in the line. Your spray hose will actually expand and contract slightly causing this extra cycle to happen. If its doing this more than once, its either worn packings, damaged ball or seat, worn gun, or worn prime valve.
It's that motor humming noise heard as the piston is trying for its top part of the stroke cycle. . LOL, when it stopped, I thought I'd thrown a circut breaker. Lately mine been humming and me thinking, "this can't be good for the motor". I think its the circut board and motor doing their thing. A less then new motor too, heh.
 

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Discussion Starter · #9 ·
still learning

So if the prime valve is bad does fluid come out the dump tube, or if the ball seat is bad does it run down the pickup tube.
 

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Paint Store Owner
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So if the prime valve is bad does fluid come out the dump tube, or if the ball seat is bad does it run down the pickup tube.
If the prime valve is bad, yes fluid will leak from the return hose. That's the most common symptom. If the lower ball is bad, no prime.
 

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If the prime valve is bad, yes fluid will leak from the return hose. That's the most common symptom. If the lower ball is bad, no prime.
Just a quick note we probably all already know. After storing or not using your airless for a time, the ball will become stuck in the seat and not prime. This happens even if you keep your rig well cleaned. A firm tap to the exterior where the ball is located will free it and allow the unit to prime.
 
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