Narrow line and hourglassing

Have a Graco 3500.While spraying it gives a narrow line which starts wider then narrows, repeats this about every foot and a half. Rebuilt pump two years ago. Seems to build pressure fine with water. I have replaced the 50 foot line. 60 mesh filter. Looking a troubleshooting in manual. Any help would be appreciated. Dan... Stripes I'll try the video once more.

It could be starving for paint and the pump not filling completely on each stroke. Check for clogs in the intake. Also could be a stuck valve. Also could be that the paint is too thick...

TGL Got the video. Impressive!

TGL, I have a 3500 that also "hour glasses" from time to time. It is usually an indication that the pump packings need to be replaced. Mine will also spray fine with water but as soon as you load it with paint it does not build the proper pressure. Just my 2 pesos. Domingo

Have the pump apart now, packings look fine. Realy don't want to replace if it may go to shop. Last ones I replaced were shredded. It was obvious the needed replacing. Is the anything visual to look for?...Dan

My last rebuild of the pump. The packings looked fine. The plastic packings had scratches on the inside rim. I replaced them and it worked fine. The rebuild previous to that, I had to replace the piston on the pump. It had minor scratches on it. It was apparently enough to keep the pressure from building properly. Domingo

What video Stripes?

I'm a new guy but...I had the excact same issue with a brand new machine. Called the Graco rep and he suggested thinning the paint just a touch. Tryed it and it worked. Adding a shot of Tueluene to my Oil based RC marking paint is Automatic now and I have not had the problem since. I have at least 200 "Hard" hours on my Lil' 3400 and it has not missed a beat!

I have a 3500 that did same thing. Repaced most everything, pressure controller, repacked pump, hoses, tips, pickup tub and though all that helped it would still hour glass slightly. Started thinning pain just a little and worked great. Have a new 3900 being delivered tomorrow that should cure problem. Milt

It is almost always a viscosity problem. Just usually the paint is cold. Just thin it a bit it should stop doing that. The other main cause is a blocked screen

Milt, A new 3900??? remember first thing..throw paint on it...

We used some paint in the past that had different viscosities from one pail to another, the line would widen after spraying a few stripes with a fresh refill, then we would refill again and get narrow lines, had to keep resetting pressure lowering and lifting the whole nine yards....we didn't use the paint anymore after that.

ASI - what brand paint was it?

Sometimes packing may look fine but they get hard and dont seal as good , i have 6 machines and they get rebuilt on average 2 times a year. if you leave paint in the machine the pant will start to dry and clog the suction tube and strainer. one time i had a problem with p-control box it wouldnt turn on at proper intervals( although its rare)it was doing the same thing.