Q.: On our first pumping job we had unending trouble with the pump. We got very low output and every little while we would have a blocked line. We were pumping about 500 feet horizontally, using a mix that had consistently worked well for other pumpers in our area. We got started in the business by buying a used pump and 5-inch line plus some more used 5-inch line from another source. We learned from the previous owner of the pump as well as others familiar with his work that he had never experienced the troubles we had. We've exhausted all the attempts to explain why we can't pump successfully with the same equipment and materials that other contractors use routinely. Do you have a clue?

A.: It's just possible that you have obtained two kinds of pipeline that do not exactly match. The fact that two pieces of line have the same nominal size does not necessarily mean that they will fit together properly. They may come from two manufacturers who make their pipe to very slightly different dimensions. Or even if they come from the same manufacturer they may have different styles of ends. In either case you may have noticed some slight difficulty in coupling them. In either event, turbulence develops where there are minor constrictions, even though the inside diameter may diminish by as little as 1/8 inch from one pipe section to the next. Mortar also builds up at such locations, restricting the flow. Mismatching of line causes far more impedance to flow than one would ever expect.

The whole subject of pipeline systems is discussed in a new book by Robert Crepas, Pumping Concrete: Techniques and Applications. The book is mainly devoted to the principles of safe and efficient layouts and is replete with illustrations for using standard accessories or fabricating equipment for unusual situations. It is available for $87.50 from Concrete Construction Publications, 426 South Westgate, Addison, Illinois 60101.