Pumping of water and flow measurement

There are channels in water transmission systems that are necessary to transport water from one point to another. In most cases, it is necessary to transport water from its source to water treatment facilities and from there to consumers. Pumping is used to provide the required energy to move water from the beginning to the end of the transmission system.

The location of pumping stations is usually in raw water catchment, treatment plant and distribution network.

Flow measurement provides information about the amount of water passing through a point in the transmission system. Usually, the places that are considered for the installation of flow measurement devices include raw water catchment, the beginning of the water treatment asurement treated water pumping stations and various points of water treatment and distribution systems.

Systems of water transfer:

The water transfer system has been set up to provide a way for water to move from the raw water catchment to the treatment plant and from there to the consumption point.

Types of transmission systems

Different types of conduits are used to transport water. The main considerations for choosing suitable conduits for the water transmission system include topography, existing height, structure type, implementation methods, economic factors and water quality. Water channels are classified into two categories, open channels and pressurized channels. Open channels have a free surface in contact with the atmosphere and pressurized channels have an enclosed surface. Several common types of transmission systems fall into each of these two general groups.

Open water transfer channels

Water transfer channels:

These channels are earthen conduits that are dug into the ground. Depending on the type of soil, the slope of the floor and the price of water, the inner surface of these ducts may have a cover or no cover. Usually, the cross-section of these channels is trapezoidal, sometimes they are made in rectangular, parabolic or other geometrical shapes.

Flumes and waterways to water transfer:

These channels are designed in such a way that water is transferred through valleys and pits. They have a rectangular, circular or horseshoe cross section.

Inclined tunnels of water transfer:

These tunnels are built in order to shorten the route or maintain water pressure in mountains or other very high altitudes. Their cross-section is often circular, but they can be made in other geometrical shapes as well. These tunnels are usually dug with special drilling machines. The inner surface of the tunnel may be coated or uncoated. In unstable soils, it is necessary to cover the inner surface of the tunnel. The materials used for the cover are usually cast-in-place concrete, precast concrete pieces, or steel pipe pieces. Sometimes, if there is a gravity flow, a pipe with a circular section may also be considered an open channel.

Pipes under pressure to water transfer

Pressurized conduit:

These ducts usually have a circular cross section, a flat concrete, cast iron, steel or plastic structure. Water flows by hydrostatic pressure, or pressurized pumping. Often, pressurized conduits (also called pressurized waterways or pressurized pipelines) follow the profile of the ground and are installed at a depth of 5/1 to 6/0 below the surface of the ground. Considering this soil cover height is to prevent freezing and damage to the surface of the conduit.

In the case the pipeline is placed under the valley, river and other depressions, it is called a curve, bent pipe or reverse siphon. Pipelines under pressure can also be passed under the hills and other high altitudes as a tunnel under pressure, or they can be used as a flume under pressure or an air passage above the ground.

Design considerations of open channel systems:

These important considerations are:

turbulence control in hydraulic instabilities, maintaining water quality, corrosion control, minimizing losses due to leakage and evaporation,

Hydraulic instabilities:

Depending on the relative velocity and the degree of turbulence, the flow condition in an open channel is classified as supercritical or subcritical. The speed is controlled by the slope of the channel and its cross section. A gentle slope leads to lower velocities and less turbulence and is called subcritical flow. A steeper slope brings higher velocities and more turbulence and is known as supercritical flow. Changes in slope or cross section can lead to change of flow from one type to another. During this event, the channel coating can be damaged by excessive turbulence.

Water quality:

Since open channel systems are often in contact with the atmosphere, this issue causes accidental, intentional or natural water pollution. Incidental pollution may occur where vehicles pass over a channel or other open conduit. In such cases, vehicle accidents can lead to hazardous chemicals leaking into the source. Incidental contamination can also occur when contaminated surface runoff is discharged into a conduit. To prevent pollution, gravity channels must be protected from all sources of pollution. Although intentional contamination is a rare event, the possibility of its occurrence should be considered. If access to open ducts is limited, the possibility of intentional contamination is reduced.

When water quality decreases through natural processes, natural pollution has occurred. Excessive growth of algae (algal bloom) and rooted plants in channels is the most common example of this type of pollution. Algae give the water a taste and smell that is difficult to remove. It is possible to reduce natural pollution by controlling nutrients (through watershed management methods) and preventing surface water from entering the channel and controlling the growth of rooted plants.

Erosion control:

To protect earthen channels against erosion, water speed and turbulence must be controlled.

Evaporation and leakage reduction: 

Channels are often used in dry areas or areas where the soil has high permeability. If any of these conditions exist, it may cause high losses due to the evaporation and leakage. To control evaporation, designers must limit the amount of water in contact with the atmosphere in dry areas. If there is a possibility of leakage, it is necessary to reduce it by covering the inner surface of the channel with clay, concrete or other impermeable materials.

Design considerations for pressurized conduit system:

Air control and unsteady pressure waves are important design considerations of pressurized systems.

Air control:

Pipes under pressure are usually subject to the unevenness of the ground, which results in the presence of low and high heights in the pipeline. The air trapped in the pipe tends to accumulate at high points and if it is not removed, the pressure drop due to friction will increase at that point of the pipeline. As the air bubbles enter the water, the passing current is reduced or an explosion occurs at the point of exit. Installing automatic air valves, which are called "air release valves", at high points to release air from the pipeline is the best way to control air.

Unsteady pressure wave:

When a velocity change occurs in a closed channel, the kinetic energy of the water is converted into a pressure wave that travels rapidly inside the pipe. These waves are often called water shocks, pressure waves, or unsteady pressures. These waves can create very high pressures that oscillate between positive pressures (high pressure) and negative pressures (low pressure). The production of these waves usually occurs with a sudden change in the speed and direction of the water flow through the quick closing or opening of the valves or the sudden stopping of the pumps. If these waves are not controlled, they will cause many damages such as breakage or displacement of the piping system. These unstable waves can be controlled by reducing the speed change rate to the extent that the amount of waves is reduced. To do this, standing pipes called surge tanks are installed along the pipeline of these unstable waves to provide a source of water under pressure to slow down the speed change. At critical points, special wave control valves can also be installed in order to reduce high pressures or allow air to enter the pipeline to prevent vacuum conditions during low pressure waves.

Analysis of pipeline instability:

Instability analysis technology is used by engineers to perform engineering assessments of pipeline instability conditions. Usually they do this analysis using appropriate computer software. The software can simulate pipeline instability conditions for different working modes. In this method, the profile of the pipeline is shown graphically, which provides important engineering information such as maximum and minimum pressure values ​​and the position and time of occurrence of instability. Then, engineers use this information to optimize the types and locations of surge protection devices along the pipeline.