Question: I have a small reciprocating concrete pump powered by a 25-horsepower gasoline engine. I tried to make it work faster by using a 6-inch pipe from the machine and gradually reducing the line to 2 inches. It didn't work, whether I tried to pump an 8-bag or 9-bag grout mix. I get only about 8 yards of grout an hour through the pump. What is wrong?
Answer: Although a 6-inch line is large for such a small pump, the reduction in size causes great resistance. The capacity of the 2-inch line is as much as the 6-inch line; it takes a great amount of energy to squeeze the concrete down to the smaller volume and thereby increase the velocity at the small end. Possibly a 4-inch line for the full distance would be more effective.