The first step in planning a concrete pumping system is to determine the capacity and pressure requirements of the system. To move concrete of a given slump through a pipeline of a particular length and diameter at a given rate of flow, a specific line pressure will be required. In general, the larger the inside diameter of a pipeline, the less pressure required to move a given quantity of concrete through the line at a given rate. Line pressure requirements also depend on pipeline layout. The length of straight and horizontal pipeline, the vertical rise, the number and severity of bends, the amount of flexible hose used in the line—each has an effect on pressure needed to move the concrete.
DIAMETER OF LINE
While a larger inside pipeline diameter cuts down on the pressure needed, it also has one enormous drawback: the larger the line, the more labor, blocking and bracing it will require. With regular weight concrete, a 5-inch pipeline is generally considered a practical maximum without losing the advantage of maneuverability of the pipeline system. In heavy construction, contractors may use 6-, 7- or even 8-inch line because they know that harsh, low-slump mixes require a greater ratio of cross-sectional area to surface in the pipeline.
ACI 304.2R-71, "Placing Concrete by Pumping Methods," recommends that the maximum size aggregate be no more than one-third the inside diameter of the delivery system. It is, however, difficult to pump any 4-inch slump concrete a substantial distance through a 4-inch line using 1-inch top-size coarse aggregate—and almost impossible if it is lightweight aggregate that has not been thoroughly water-saturated by pretreatment.