My Schwing BPA 500 seems to accumulate a lot of dry concrete in the rock valve and the discharge port. Will a new rock valve solve this or is it normal with an older machine? It happens especially with a pea gravel mix. I have been breaking it down and cleaning every 2 trucks but it sucks.

I would check the condition of your wear parts or you are pumping extremely slow.

I hope that's it. They came in yesterday! New cups, spec plate, mirror plate, cutting ring, bushings and agitator rebuild kit. 

Yea I've found when the cutting ring and pressure spring are wearing out, obviously the rock is not sealed as tight. Especially when pumping at hi pressures, grout will push in that space and hold on tight, building up the more yardage you pump. How is builds up half the valve is beyond me lol but it happens