Suction+and+Discharge+Head

The pressure at the pump’s suction is the static suction head minus the head loss due to piping resistance. It is called the total suction head. In centrifugal pumps, liquid pressure may be reduced even further as its speed is increased in the narrow passages leading to the impeller of the pump. Due to the repeated drop in liquid pressure, its pressure inside the casing may become significantly lower than the atmospheric pressure.