It may not sound or seem possible to some but it's true and happens quite offen!

 Next time you're booming out 'flat' while pumping a moderate steady flow pay attention. Just as the boom reaches 70 to 80 percent of it's reach it will belch out a pocket of air. It's violence will depend on the mix and reduction etc. It's usaully not too awful bad but it can be!  When the 3rd, 4th or fifth sections are in a vertical position the concrete is falling through a portion of the vertical system. A steady flow is reached once the concrete begins to backup/stackup in the tip hose, reducer & tip elbows leaving a small section of air that the concrete is falling or sliding through. As the boom is extended the tip section no longer drains and the pressure increases when the system is horizontal. The small pocket of air gets compressed behind the concrete that has stacked up in the whip, redcucers etc. and juuust before you run out of boom POP!.. Now the boom is FULL.

 It's what I reffer to as a "False Flow" that is created with the assistance of gravity and reduction. It's hardly noticable with a five inch tip hose but like I said, it all depends on slump, reduction, pump volume etc. It happens to me every single time I'm walking a guy around a foundation wall with a five inch slump & a 3" whip?

...oh and for those that think I'm totaly NuTz... You're right! I even have papers to prove it ... 

Very True indeed

 and it can be very violent.the hoseman will look at you like ur trying to kill him. there must be a safety patrol on this web site the way everyone talks is that true... did anyone call in today. im avaliable will travel.......distance anywhere. i just want to pump concrete!

I like to keep the tip section flat or tilted a bit up. In my head this helps, any meaning about this?