# Graco 490 priming problem



## Lumptastic (Oct 2, 2019)

Having problems with a 490 it wouldn’t prime. Would start to but then stop. Changed out pc unit and it’s still doing the same thing. Would pull paint for a few seconds then slow to a stop. Did it a couple times over 10-15 min but won’t continue to pump checked filters and made sure siphon tube wasn’t plugged. Could it be the prime valve itself? Im stumped.


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## APPNW (Jul 9, 2019)

Had this same issue with my 495, for me it was the siphon tube plugged up where it connects to the pump just after the curve. I was told the internal check valves could be stuck open from debris or chunks of old paint and not letting it get pressure.


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## Lumptastic (Oct 2, 2019)

Yeah I Checked the siphon tube. Even threw a different one on from another pump thinking it might have a hole and be sucking air. It’s probably something stupid and simple that I’m missing. I’ve never actually had a prime valve go bad so wasn’t sure if that was the issue because I don’t know what a bad valve would cause the pump to do. Hell I’ll probably just throw one on anyway and see what happens. For now I’ve got the trusty little turd. That’s my nickname for my titan 400. It was the first pump I bought for doing side work. I’ve put that little pump threw hell and it just won’t die. Needs repacked again but besides Packings it’s never failed me. Had days I put 100gal or more threw it.


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## kmp (Jan 30, 2011)

Prime valve. Easy fix.


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## Eagle Cap Painter (Nov 14, 2016)

Valve on the inlet of my 495 has gotten stuck before after not using it for a while.


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## cocomonkeynuts (Apr 14, 2017)

You can check the prime valve with compressed air. 

Relieve pressure. remove the short hose connecting to the pump. Run compressed air into this line and feel if its coming out the siphon tube. This is probably your issue, takes 5 minutes to replace with a torque wrench. Remove pin on valve handle, drive it out with a hammer and thin metal rod. remove the old valve. Clear threads and any debris. Install replacement valve to ~15ft-lbs.


likewise easy to check if the inlet or outlet ball is stuck open. I made an emergency call out to a painter for this just last week! In this case the unit was priming slowly but not built pressure.

Put the suction hose into thinner or water. slowly cycle the pump while holding the trigger down and watch fluid output from the gun. simultaneously watch the piston rod move up and down.
If there is fluid output on the upstroke but not the downstroke, then the lower inlet ball is stuck open ( very common debri gets sucked into and lodged in the ball seat)
if there is fluid output on down but not up then its likely some debris keeping the upper ball open. Remove the piston rod and clear debris.


If non of these seem like the issue then its likely the transducer is caked in dried paint.


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