Originally Posted by
drivermark
I don't think I ever backed a mixer up to a 60m but 45m pumps usually left about 3 or 4 wheelbarrows worth on the ground after cleaning out. However big the hopper is on a particular machine, the tubes will hold about 1/2-3/4 the amount that will fit in the hopper.
You need to have the hopper at least 1/4 full when pumping or else the pump can "blow back" which means the pressure from the pump can come back through the hopper and blow wet concrete all over the place at the hopper end and blow high velocity mud out at the end of the hose (which makes it really hard to hold on to and really pisses off the guy holding the end of the hose)
When the job is close to finished the pump operator will usually tell the mixer driver to let the hopper get low so the hopper will be able to hold the material in the pipes and hoses without over flowing the hopper. (which makes another big mess and will piss off pump operators)
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