Continue from Pump Total Differential Head

The static head difference across the pump is the difference in head between the discharge static head and the suction static head.

Static head difference = discharge static head – suction static head

Discharge Static Head

The discharge static head is sum of the gas pressure at the surface of the liquid in the discharge vessel (expressed as head rather than pressure) and the difference in elevation between the outlet of the discharge pipe, and the center line of the pump. Discharge static head = Discharge vessel gas pressure head + elevation of discharge pipe outlet – elevation of pump center line
The discharge pipe outlet may be above the surface of the liquid in the discharge vessel or it may be submerged as shown in these below 3 diagrams.

Suction Static Head
The suction static head is sum of the gas pressure at the surface of the liquid in the suction vessel (expressed as head rather than pressure) and the difference in elevation between the surface of the liquid in the suction vessel and the center line of the pump.

Suction static head = Suction vessel gas pressure head + elevation of suction vessel liquid surface – elevation of pump center line

Note: gas pressure can be converted to head using: Gas head = gas pressure ÷ (liquid density x acceleration due to gravity)