There is a relation between the system resistance and the flow through the system. As more liquid flows, the system resistance increases. From the start of the system to the end of the system there is a pressure loss of a given flow. This pressure loss is a result of the system resistance.

The relationship between the flow through the system and the system resistance is given by:

h = KQ²
h = head loss in metres
K = constant
Q = flow in m³/sec.

Head loss is always measured in metres of liquid.

System head flow characteristics<	Interaction pump/system
Effective of a total variable static head	variations in system resistance
effect of reducing impeller diameter