Energy of Water

STATIC – Water not moving or not Flowing – When water is in the static state, the weight of a column of water creates the pressure, usually a water tower or the difference in elevation in a pipe system.

DYNAMIC – Moving or Flowing – When water is moving or flowing in a pipeline, friction in the pipe creates a loss of pressure. As the velocity of the water increases, there is a greater drag or turbulence within the piping system. As the water flow over the roughness of the pipe, the friction increases creating a greater pressure loss. The end of the pipeline operating pressure is reduced to a lower pressure due to this dynamic situation.

As water flows through a constriction such as a converging section of pipe, the velocity of the water increases; as a result, the pressure is reduced. Under such conditions, negative pressures may be developed in a pipe.

If the constriction is great enough, water is forced to flow through the smaller pipe at an increased velocity. The increases velocity creates a negative pressure within the constricted pipe arrangement. This phenomenon is known as the Venturi Effect and is caused by water traveling through a pipe constriction at high velocities. If the throat diameter, pipe or restriction is small enough in the converging section of pipe, the pressure can become sub-atmospheric or negative. In this pipe arrangement, a decrease in the supply pressure may also cause sub-atmospheric or negative pressure to develop at the pipe convergence.

If this point of reduced pressure is linked to a source of pollution, backsiphonage of the pollutant can occur. This backsiphonage occurrence is caused by what is known as aspiration, aspirator effect, or simple aspiration. Aspiration is the withdrawal of a substance by suction.

The simple aspirator is based on the principle that negative pressure is developed in a fluid pipe system or arrangement when the velocity of the fluid increases due to piping constrictions or restrictions

A simple aspirator would be a garden pesticide or fertilizer applicator.

If the water velocity in the water main increases sufficiently due to obstructions in the pipe, negative pressure may develop creating a siphon situation at the connection. The water in the service line and domestic water system in the building could backflow into the water distribution main because of the backsiphonage situation.