Irrigation Water Filtration Techniques

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Questions and Answers

What affects the filtration grade in disk filters?

The material of the disks

The angle in the alignment of disks

The pressure applied during back flushing

The size of the groove in the disks (correct)

What is the required back flushing pressure range for cleaning disk filters?

4 to 5 kg/cm2

2 to 3 kg/cm2 (correct)

1 to 1.5 kg/cm2

3 to 4 kg/cm2

What is the purpose of check valves in a filtration system?

To regulate pressure

To prevent unwanted flow reversal (correct)

To increase flow speed

To filter out sediment

Which type of injection system is known for its easier control of the injection rate?

Injection pump Signup and view all the answers

What is one of the components of a chemigation unit?

Chemical solution tank Signup and view all the answers

What materials are typically used to construct chemical solution tanks?

Poly or fiberglass Signup and view all the answers

Which method creates suction to draw chemicals into the venturi injector?

Creating a pressure differential Signup and view all the answers

What is the simplest method to avoid problems of high pressures in a system?

Implementing a bye pass arrangement Signup and view all the answers

What is the purpose of pressure gauges in filtration systems?

To measure the head loss across the filter Signup and view all the answers

What happens when the head loss exceeds 30 kPa in a sand filter?

The filter needs back washing Signup and view all the answers

How do screen filters prevent clogging in micro-irrigation systems?

They filter out minute particles ensuring clean water flows Signup and view all the answers

What characteristic of centrifugal filters allows them to be effective?

They utilize centrifugal force to separate heavy particles Signup and view all the answers

What type of materials can disk filters efficiently filter?

Organic material and algae Signup and view all the answers

What should the aperture size of a screen filter opening be in relation to the orifice size of emission devices?

Between one seventh and one tenth of the orifice size Signup and view all the answers

What occurs during the filtration mode of a disk filter?

The disks are pressed together to capture debris Signup and view all the answers

What is a common application of screen filters in irrigation systems?

Final filtration to prevent clogging Signup and view all the answers

Study Notes

Media Filtration

Media filters are essential for primary filtration of irrigation water from open water reservoirs, canals, or reservoirs where algae may develop
Water is introduced at the top, while a layer of coarse gravel is put near the outlet bottom
Filters are cleaned by reversing the direction of flow and opening the water drainage valve
Pressure gauges are placed at the inlet and at the outlet ends of the filter to measure the head loss across the filter.
If the head loss exceeds more than 30 kPa, the filter needs back washing

Screen Filters

Screen filters are always installed for final filtration as an additional safeguard against clogging.
Minute sand particles and other small impurities pass through the sand filter
The screen filter contains a screen strainer, which filters physical impurities and allows only clean water to enter into the micro-irrigation system.
The screens are usually cylindrical and made of non-corrosive metal or plastic material.
Screen filters are available in a wide variety of types and flow rate capacities with screen sizes ranging from 20 mesh to 200 mesh
The aperture size of the screen opening should be between one seventh and one tenth of the orifice size of emission devices used.

Centrifugal Filters

Centrifugal filters are effective in filtering sand, fine gravel, and other high-density materials from well or river water.
Water is introduced tangentially at the top of a cone and creates a circular motion, resulting in a centrifugal force, which throws the heavy suspended particles against the walls.
The separated particles are collected in the narrow collecting vessel at the bottom

Disk Filters

Disk filters contain stacks of grooved, ring-shaped disks that capture debris and are very effective in the filtration of organic material and algae
During the filtration mode, the disks are pressed together.
There is an angle in the alignment of two adjacent disks, resulting in cavities of varying size and partly turbulent flow.
The sizes of the groove determine the filtration grade.
Disk filters are available in a wide size range (25-400 microns).
Back flushing can clean disk filters.
However, back flushing requires high back flushing pressure (2 to 3 kg/cm2).

Pressure Relief Valves, Regulators, or Bypass Arrangement

These valves may be installed at any point where possibility exists for excessively high pressures, either static or surge pressures to occur.
A bypass arrangement is the simplest and cost-effective means to avoid problems of high pressures instead of using costly pressure relief valves.

Check valves or non-return valves

These valves are used to prevent unwanted flow reversal
They are used to prevent damaging backflow from the system to avoid return flow of chemicals and fertilizers from the system into the water source to avoid contamination

Chemigation and Chemical Injection Equipment

Micro-irrigation's high distribution uniformity gives it great potential for uniformly and efficiently applying agricultural chemicals
The main components of a chemigation unit are a chemical solution tank, an injection system, and chemigation safety devices.

Chemical Solution Tanks

Chemical solution tanks are generally constructed of poly or fiberglass.
A conical form at the tank bottom facilitates flushing it completely so that no material is wasted.
Tanks should have an easy-clean screen downstream of the valve to make them easier to clean.

Injection System

The main types of chemical injectors are the venturi injector, injection pump, and the differential tank.
Criteria for selecting the proper injection system include cost, ease of use/repair, durability, and susceptibility to corrosion.

Venturi injectors

Water is extracted from the main line, then (1) pressure is added with a centrifugal pump or (2) a pressure differential is created by a valve in the mainline forcing water through the injector at high velocity.
The high-velocity water passing through the throat of the venturi creates a vacuum or negative pressure, generating suction to draw chemicals into the injector from the chemical tank.
Although the venturi is cheaper than a positive displacement pump, its injection rate is more difficult to control.

Injection Pumps

Water is pumped into the system using pistons, diaphragms, or gears.

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Description

This quiz covers the principles and methods of media and screen filtration in irrigation systems. It highlights the importance of these filtration techniques for managing water quality, including the processes of back washing and the maintenance of pressure gauges. Test your knowledge on how these systems purify water for agricultural use.