In general, **the hydraulic head**, or total head, is a measure of fluid’s **potential** at the measurement point. It can be used to determine a hydraulic gradient between two or more points.

**In fluid dynamics**, the head is a concept that relates the energy in an incompressible fluid to the **height of an equivalent static column** of that fluid. The units for all the different forms of energy in Bernoulli’s equation can also be measured in **distance units**. Therefore these terms are sometimes referred to as “heads” (pressure head, velocity head, and elevation head). Head is also defined for pumps. This head is usually the **static head** and represents the **maximum height** (pressure) it can deliver. Therefore the characteristics of all pumps can usually be read from their **Q-H curve** (flow rate – height).

There are four types of potential (head):

**Pressure potential – Pressure head:**The pressure head represents the flow energy of a column of fluid whose weight is equivalent to the pressure of the fluid.**ρ**_{w}: density of water assumed to be independent of pressure**Elevation potential – Elevation head:**The elevation head represents the potential energy of a fluid due to its elevation above a reference level.**Kinetic potential – Kinetic head:**The kinetic head represents the kinetic energy of the fluid. The height in feet is that a flowing fluid would rise in a column if all of its kinetic energy were converted to potential energy.

The sum of a fluid’s elevation head, kinetic head, and pressure head is called the **total head**. Thus, Bernoulli’s equation states that the total head of the fluid is constant.

**continuity equation**tells us that as the

**pipe diameter increases**, the

**flow velocity must decrease**to maintain the same mass flow rate. Since the outlet velocity is less than the inlet velocity, the kinetic head of the flow must decrease from the inlet to the outlet. If there is no change in the elevation head (the pipe lies horizontally), the decrease in the kinetic head must be compensated for by an increase in pressure head.