Why do only horizontal split-case fire pumps require elbows and tees to be installed a minimum of 10 pipe diameters from a pump suction flange when in a horizontal plane parallel to the pump shaft?
Placing an elbow or tee with the centerline in the horizontal plane within 10 pipe diameters of the suction flange creates an unbalanced flow of water into the impeller. An unbalanced flow causes an axial load to be placed on the pump shaft and bearings, causing excessive wear to the bearings and subsequent damage to the pump over time and/or severe cavitation if not corrected. The requirement for elbows within 10 pipe diameters of the suction flange applies only to horizontal shaft fire pumps. In an inline (vertical shaft) fire pump, gravity already creates an axial load imbalance so the imbalance from an elbow is of less concern.