Hello Friend
First…thanks for the post.
Next…you’re right…it’s dirt.
There’s a check ball down low on the pump. When it gets stuck…the pump will just cycle.
Next…this trouble exists in other pumps too…to the point…there’s a red, plunger thing…like a relief plug…that we pull…to free up that ball. ( Our 3900s don’t have that…! )
Bottom line…you’re right…it’s dirt…well…old paint.
Here’s a thing I was told…seriously…it’s a test…or…it’s the equivalent to the “relief valve” on some simple airless sprayers…
I was told…”rap” on the “J” tube just under the pump. That should free that ball. My first thought was; “really”…?
I took a rubber mallet and lightly smacked the J tube. It immediately stopped cycling and built pressure. That said…you can’t be going around with a hammer in your pocket.
Bottom line…clean the machine best you can.
Also…I use Xylene after I use Acetone. It’s a little more aggressive when it’s cleaning. I may even let it sit a few minutes.
Last resort…take a few parts apart. Maybe disassemble from the sprocket nut. ( I am not bad with a wrench…but it’s been too long since I looked at that particular exploded view.
Last…Sherwin Williams carries the Graco parts. There’s a replacement J tube. I just don;t remember if that lower section has the ball in it or it’s just above. Check that out. Maybe replacing the entire thing may be best…easiest.
Let me know.
Dan
