scallop lines

just had the packing replaced on the pump. Now the lines are scalloping, its never done that before. Any suggestions? Its a Graco 3900.

Is the filter and rock catcher clean and un restricted? Are you using the long hose?

Skeens, When you say "scallop" do you mean hour glass lines or curved ends during your starts? Tom

hour glasss lines. Also changed out both the rock catcher and filter. I think that Rock is on to something though about the hose. I was using the short whip hose. I'll try the longer hose tomorrow...we'll see if that's the problem.

We always use the whip hose and never have problems with hour glassing. The only time we ever even bleed out the long hose is to shoot double lines. Sometimes thinning the paint can help but that is probally not the cause of the problem. You say the problem started after the pump rebuild. If you wasn't having that problem before the repack I would almost bet money a packing was installed upside down or in someway wrong.

If you're using latex and did not purge paint through the long hose, the paint where it meets the water can harden up into a plug. Usually not too far up the hose from the pump. If this happens it negates the shock absorber effect of the long hose.

If its hour glassing then it's dropping pressure on one stoke and building on the other, redo the packing and check all the balls.

I striped another lot today, it seems to have worked itself out. Nice sharp lines again. Strange.

skeens wrote on Oct 29, 2011:Go to #8

I striped another lot today, it seems to have worked itself out. Nice sharp lines again. Strange.

Could have been the paint too, maybe too thick or something.

If it worked itself out, my guess is that maybe something was caught in the ball/seat or the perhaps one set of the packings (upper or lower packing stacks was adjusted to tightly)was working like a brake. When evaluating hourglassing issues, an important diagnostic note is to determine the frequency of the of the hourglassing. Every few inches is in the pump (or shorter intervals - vibration related), while every 3 - 5 feet is engine speed, clutch, etc. the surface condition or marginal paint can "telegraph" hourglassing as well.

Glad to hear it worked itself out, but almost every time I've had problems with lines hourglassing it's been on the suction side of the hose. It may just have worked itself out of the way, waiting to give you fits another day. If it were me I would go ahead and take the suction hose off and take a gander at the piping going up into the housing. You may be surprised at the gunk that has built up there.

skeens wrote on Oct 29, 2011:Go to #8

I striped another lot today, it seems to have worked itself out. Nice sharp lines again. Strange.

Could have been the paint too, maybe too thick or something.

If it worked itself out, my guess is that maybe something was caught in the ball/seat or the perhaps one set of the packings (upper or lower packing stacks was adjusted to tightly)was working like a brake. When evaluating hourglassing issues, an important diagnostic note is to determine the frequency of the of the hourglassing. Every few inches is in the pump (or shorter intervals - vibration related), while every 3 - 5 feet is engine speed, clutch, etc. the surface condition or marginal paint can "telegraph" hourglassing as well.

Glad to hear it worked itself out, but almost every time I've had problems with lines hourglassing it's been on the suction side of the hose. It may just have worked itself out of the way, waiting to give you fits another day. If it were me I would go ahead and take the suction hose off and take a gander at the piping going up into the housing. You may be surprised at the gunk that has built up there.

I thought it fixed itself. It went right back to doing what it was doing. To date, I've changed the pump packing, thouroughly cleaned entire system from rock catcher to tip of guns. Changed pressure valve. I'm at a loss here. Changed paints, thinned paints. Nothing seems to fix this. Looking for other ideas. I'm thinking boat anchor. The pic shows what the line is looking like. http://www.flickr.com/photos/26572419@N04/6709440067/in/p…

Did you try switching tip?

yes used several different tips, old and new. Also, noticed that the pressure slowly drops while not in use fluctuates between 25 to 50 pounds while spraying. Is that normal? I wouldnt think it is, but the fine folks at our authorized Graco repair shop say it is.

Check your pressure relief valve, could be leaking when the pressure is built up. Build up the pressure and put your ear to diffrent parts of the striper. have the lid off and see if paint is coming out the prime tube when it is just sitting. Thats my kick at the can!!

i already put a new pressure relief valve on. There is no bypass coming through from there...I thought that might have been the problem. I'm starting to wonder...is the paint too thick? I've been using this brand paint for years, never an issue.

That looks like the pressure is falling and rebuilding, check for leaks in the intake lines the check the pressure controll system. Could also have a ball check ball. And the paint could also be too thick.