Blockage of the drip emitters and sprinkler nozzles is avoided by using High volume irrigation filters. Heavy-duty irrigation filters are used where the pressures are very high and inline self-cleaning filters are capable of cleaning themselves automatically. Examples of high-volume irrigation filters are sand filters, large disc filters, large screen filters, and centrifugal filters.

The selection of the type of filter to use greatly depends on the particle size and particle weight of the contaminants. Under the weight of the particles, the particles can either be settleable or non-settleable. Settleable particles are those that are heavier than water whereas non-settleable particles are those that are lighter than water.

Sand filters

Sand filters are high-volume irrigation filters used to trap solid particles in water. Sand filter tanks are made from stainless steel or carbon steel. Water is allowed to flow into the tank from above and exit at the bottom. Sand filters are not able to remove dissolved salts. The sand filter is comprised of sand particles that have varying particle diameters depending on the size of the filter tank, the level of filtration required and the flow which is desired.  The arrangement of sand particles in the filter is such that the fine particles are placed on the upper layer and the size of particles increases up to the coarse sand particles placed in the bottom layers. Sand particles offer a large surface area for the solid particles in water to adhere as water passes through the soil pores. If the sand particles are too fine there will be increased cleaning efficiency of the filter and also increased resistance as water flows. The increase in resistance means more pumping energy will be required.

Sand filters are high volume irrigation filters suitable for removal of contaminants especially organic contaminants in water. Sand filter are able to remove large quantities of organic matter due to the large surface area offered by the sand particles. As more and more contaminants are trapped in the sand the pressure loss increases hence there is need to remove the contaminants. Cleaning of the sand filter is achieved by a process known as backwashing. This is where the flow of water in the filter is reversed  and the inflow pipe is closed. The sand media is filled with water and the suspended contaminants are removed through a separate outlet.

Large disc filters

 

 

Large disc filters are a type of high volume irrigation filters used in heavy duty water cleaning operations. It contains a number of discs which are attached together one over the other with a hole passing at the center of the discs. During the filtration process, water passes through the discs leaving behind dirt on the discs. Clean water drains from the discs through the hole at the center and into the outlet. Large disc filters are capable of cleaning both dirt particles and organic matter. Although by cleaning organic matter disc filters tend to clog at a faster rate that when removing inorganic particles. The frequent clogging means there will be need for frequent backwashing.

Backwashing is the process by which trapped organic and inorganic particles are removed from the filters by reversing the flow of water. Disc filters have the advantage of being easy to backflush and using little water compared to other high volume irrigation filters. The quality of water being cleaned by a disc filter depends on the size of the discs, the length of the disc filter and the number of intersections within the disc filter.

Types of filter discs available for high volume irrigation filters

High volume irrigation filter discs come with different types of discs and each type varies with the purpose. The different types are;

  1. Mesh filter discs – they can come either being pleated or flat and provide a large surface for filtration
  2. Fiber filter discs- these discs also come in pleated or flat versions. The flat version is not suitable for liquids with few contaminants
  3. Powder filter discs- they come in a variety of diameters ranging from 0.5 mm to 203 mm. They also come in a variety of thickness
  4. Automatic filter discs – these come equipped with an automatic backflushing mechanism
  5. Manual filter discs – this is a collection of discs clamped together in order to filter out contaminants out of water.

How to choose the right filter disc for high volume irrigation filters

It is important to choose the right filter for high volume irrigation filters to avoid damage that can occur to the irrigation components due to poor filtration. The following factors should be considered:

  1. The number of layers of discs – the number of layers of discs in high volume irrigation filters determines the cleaning efficiency of the system. The more the number of layers the higher the cleaning efficiency
  2. The shape of the filter disc – the shape of the disc should be considered according the piping system available
  3. The material – the material used in the discs should be strong and durable to ensure the filter disc operates for a long time.
  4. The type of weaving used – the type of weaving used in high volume irrigation filters affects the cleaning efficiency.
  5. The edge processing method used – examples of edge welding processes used are butt welding, spot welding, edge wrapping and seam welding. This factor should be considered when considering the pressures to be expected in the disc filter.
  6. Technology used – when selecting the filter disc to use it is best to choose a disc which has the best technology in filtration.

Large screen filters

A large screen filter is a high volume irrigation filter which uses a flexible or rigid wire woven screen to separate dirt from water. Screen filters are suitable for use when it comes to cleaning minimal to moderate contaminants. This type of filter works well with both heavy and suspended particles. However, screen filters are not recommended to be used for cleaning water containing organic matter as the organic matter will be able to pass through the screen. Screen filters can be cleaned manually or by flushing. Manual cleaning can be used in the case of small filters where as flushing is used in large screen filters. There are three main methods by which screen filters can be flushed. i.e., filter flush outlet, focused backwash method and directed flow flush.

Filter flush outlet methods

In this method an outlet is opened on the screen filter while water is still flowing. This water is used to clean out the screen of the filter. After the filter is cleaned the outlet is closed allowing the cleaning process to continue.

Focused backwash method.

This method can be done in two ways; the first way is by using two screen filters where by the water cleaned by one screen filter is forced to flow into the other filter forcing the trapped particles to be expelled. The second method involves creating suction whereby  water is forced to flow backwards helping in clearing particles from the screen filter

Directed flow flush

This method is similar to the filter flush outlet method. It involves opening of the outlet on the screen filter so that the cleaning water can come out like in the filter flush outlet method. The difference comes in in the design, whereby in the directed flow flush water is allowed to flow over the screen washing away the particles.

Selection of a screen filter

When deciding on the size of screen filter to use the following qualities should be considered.

  1. The quality of water required – screen filters are not suitable for cleaning water contaminated with organic materials.
  2. The volume of water to be passed through the filter – if the amount of water passing through the filter is too much in relation to the size of the filter then the pressure loss will be large, the system will require frequent cleaning and the life span of the screen filter will reduce.
  3. Filtration area of the screen filter – it is recommended that the area of the openings in the screen should be at least two times larger than the cross-sectional area of the pipe.

Advantages of large screen filters

These type of high-volume irrigation filters have the following advantages:

  1. The cost of a screen filter is relatively cheap compared to other methods
  2. The use of a large screen filter requires minimal on-site preparations compared to methods like sand filtering
  3. Screen filters are able to work with different types of water flows and qualities.

Centrifugal filters

Centrifugal filters are high volume irrigation filters that are used to separate water and solid particles based on their different densities. Centrifugal filters are especially useful when used to separate large particles from irrigation water and are even more effective when combined with other filtration methods e.g., screen filters or disc filters. The materials used to make the centrifugal filter is made to be rust, corrosion, acid and alkaline resistant to ensure the filter operates for a long time. The sand collector is easy to open and clean out after usage. The centrifugal filters use the force of gravity and centripetal force to achieve the separation.

Working principle of a centrifugal filter

Gravity is the force that acts on any substance that has mass causing them to attract each other whereas centripetal force is the force that makes a substance to always follow a curved path. The centripetal irrigation filter is designed in an inverted conical shape with a sand collector at the bottom. Water enters at the top of the filter and on reaching the conical shaped filter a vortex is created. The solid particles drop into the sand collector at the bottom of the filter. Water which is a high-density liquid will flow out of the filter whereas low density liquids such as oil and grease will remain in the filter.

Pressure loss due to high volume irrigation filters

High volume irrigation sprinkles act on the principle of hindering the flow of water so as to separate the different particles from water. Disc filters, sand filters, screen filters force water through a material so as to trap the particles where as centrifugal filters make the water to undergo gravity and centripetal forces to separate the particles.  The way the filters operate they hinder the flow of water hence reducing the pressure which the water was flowing with initially. The implications of this loss in pressure will  increase cost of pumping. To overcome the pressure loss more pumping power will be needed.  Though there are filters like disc filters which have a low pressure loss during cleaning as compared to sand filters.

Backflushing is an important process that ensures the filters are clean so as to function effectively. Although its an important process backflushing also leads to increased pressure loss. Backflushing typically reverses the flow of water so as to clean the filter resulting in loss of pressure. In the case of self- cleaning filters, the backflushing pressure losses are above the pressure losses during the water cleaning process.

How to minimize pressure loss across a high-volume irrigation filter

  1. The first method involves cleaning of the filters. As the filters accumulate more particles the number of pores available for water to pass through decreases resulting in pressure loss. Cleaning the filter is the best way to counter this problem. Sand separators can be cleaned by backflushing whereas screen filters can be manually cleaned or backflushed.
  2. Another way of avoiding pressure loss in high volume irrigation filters is by using filters that have minimal pressure losses. A disc filter will have minimal pressure loss compared to a sand filter. A centrifugal irrigation filter will always have a constant pressure loss unlike the disc, screen and sand filters whose pressure loss increases with increase in particles.

Role of automatic backwash filters in efficient irrigation systems

Backwash filters refer to filters with the ability to reverse the flow of water to remove accumulated filtered particles in the filter. Backwash filters can be categorized in the following ways i.e., according to the design they use and according to the filtering media they use. Backwash filters classified according to the design can be classified as either automatic backwash filters or manual backwash filters. Automatic backwash filters utilize a computer to monitor the pressure changes due to accumulation of particles in the filter and initiate the backwashing process automatically to remove the particles. Manual backwash filters must be set once in a while by the people operating the system.

Backwash high-volume irrigation filters grouped according to the filtration media used are: Micro-contaminant backwashing filters and sediment backwashing filter. Micro-contaminant backwashing filters are those that are able to filter out particles as small as dissolved salts. Sediment backwashing filters are those that can only filter out slightly large particles.

Requirements for an automatic backwash high volume irrigation filter

For setting up an automatic backwash high-volume irrigation filter the following requirements should be met.

  1. There should be adequate and constant supply of power in the irrigation scheme
  2. There should be a tank where the collected contaminated water will be disposed of by the system
  3. The filters used should be placed on a flat surface to work effectively
  4. Necessary drainage should be provided to convey the flushed contaminated water to the tank
  5. The filter should be placed in a shaded and well-ventilated area

What are the advantages of automatic backwash filters in an irrigation system?

There are advantages that come with using automatic backwash filters especially in high volume irrigation filters. These advantages are :

  1. The safety of the equipment is assured on the downstream side. Drip emitters and sprinkler nozzles are sensitive to the quality of water being used. If large particles are allowed to pass through there will be blockage in the irrigation system and some of the systems may be damaged. High volume irrigation filters are used in large projects to protect irrigation equipment downstream which would otherwise be costly to replace.
  2. Automatic backwash filters are highly effective in reducing pressure drop in the system compared to a manual system. Automatic backwash filters make use of a computer to monitor the pressure changes. When the pressure drop goes beyond the set pressure the backwash process is started automatically. Using filters that depend on manual washing make it hard to know when it is the right time to clean the filter.
  3. An automatic backwash filter is able to remove dissolved particles of about 15 – 25 microns. This characteristic makes it very effective in cleaning the filter.
  4. Automatic backwash filters are easy and cheap to maintain
  5. Automatic backwash filters use minimal amount of water during cleaning compared to manual cleaning helping in energy saving.

  Components of an automatic backwashing filter

An automatic backwashing high volume irrigation filter contains the following   components:

  1. Inlet and outlet parts – these are the parts where the water flows into and out of the filtration system respectively.
  2. Filter media – this is the multi-layered media which is use to separate the solid particles from water during the filtration process in a high-volume irrigation filter
  3. Drain valve- This is a valve that is opened to let out the water that is being used in washing the filter together with the dirt particles.
  4. Control system – the function of the control system is to monitor the pressure difference in the system and decide on whether to activate the backflushing process or not in a high-volume irrigation filter.
  5. External housing – the purpose of the external housing is to protect the filter from external conditions such as dust particles which will block the filter.
  6. Pneumatic actuator and the differential meter- the differential meter is used to measure the pressure loss of water going past the filter. The pneumatic actuator is used to translate the control’s system commands into mechanical motion.

Operating principle of an automatic backwashing high volume irrigation filters

Contaminated water flows through the multi-layered filter and the contaminants are removed as clean water flows to the outlet. Accumulation of the contaminants on the filter will result in a drop in pressure which is being monitored by the control system through the differential meter. Once the pressure drops beyond the set value the control system sends a command to the pneumatic actuator to open the drain valve. Clean water is allowed to flow over the multi-layered filters removing the contaminants and flowing out through the drainage pipe into the tank. The washing process will continue up to the pre-set time and then the control system will instruct the pneumatic actuator to close the drain valve.

When should backwashing filters be replaced in high volume irrigation filters?

The following are instances by which a backflushing filter will need to be replaced in high-volume irrigation filters.

  1. When the backflushing filters exceed their expected lifetime.
  2. Damaged cartridges- when the filter is dirty the cartridge is usually cleaned and the filter can be used again. However, when the cartridge is destroyed in high-volume irrigation filters it must be replaced since it can no longer be effective in cleaning.
  3. When the pressure drop doesn’t decrease even after washing is an indicator to replace the filter.
  4. Torn filter element- The filter element is the main part used in the filtration process. If this part has been torn there is no other choice other than to replace the filter.