Backwash Products
A CGF filter plant can be manually operated to provide simple and economical performance. It can also be an elaborate, fully automatic system that is customized to suit specific requirements.

CGF’s single lever valve is designed to reduce the chance of Operator error and to simplify the backwashing process. The equipment is simple, sturdy and effective.

In the “lock-down” position, the valve is the normal “filter mode”. When backwashing is required, simply stop the pump, unlock the valve and raise the backwash lever. This changes the normal “downflow” operation into an upward backwash flow that will effectively expand the filter bed and remove the collected solids.

Single lever valves are available in two sizes (either 100mm or 150mm). The single lever valve can also be automated if so required.

The ELBATROL controller continually monitors and automatically controls the operation of your CGF filter.

When a predetermined pressure rise is detected, the ELBATROL controller will automatically initiate a planned backwash process. After backwashing the first filter, the controller will scroll through the program and progressively backwash any remaining filters.

The whole backwashing process is subject to extensive management. Failure to reduce the system’s pressure (after the backwash operation) will activate a second, then a third attempt. After the third attempt, the ELBATROL will automatically shut down the system and display an alarm. A programmable timer is also included so that backwashing can occur at times that suit you. Connections are also provided to start & stop the pump at predetermined times. For this option, it is strongly recommended that the pump be equipped with a softer starter or other approved device.

The ELBATROL control system includes the following:-
  • Polycarbonate Enclosure
  • PLC (for up to 8 filters)
  • Valve Control Relays
  • Adjustable PD Switch.
  • Common alarm relays.
  • Flashing alarm beacon.
  • Audible Alarm.
  • Push button manual override.
  • Time clock for backwash
  • Main power switch.
  • Conduit electronics and fittings.
  • PLC software
  • Internal Wiring & Terminals
  • Fully workshop test.
  • Data CAD drawings
  • Operational manuals.
  • Project Specific Information


When using a traditional “sand” filter media, a backwash rate of 42m3/hr/m2 is a common and fundamental requirement. Whilst different medias may have different backwash rates, it is essential that the required bed expansion be provided. Failure to do so can result in a cumulative build-up of solids that will detract from the filter’s long-term performance. This loss of performance can include unnecessary service problems, replacement of the filter media and possible damage to the filter’s underdrain.

The choice of backwash method is largely determined and dictated by the required filter rate and the number of filter vessels that are selected for the specific project.

For single tank systems (with filter areas of up to 3.5m2) single lever backwash valves are available as an optional item.

These valves are currently available in two standard sizes (dn100 and dn150). Single lever valves can also be automated with a pneumatic actuator and associated controls. The CGF single lever valve is a simple mechanism that is designed to obviate the need to operate a number of commercially available valves in a very a specific Four Tank MHS1500 filters with 100mm Multiport Valves and controlled sequence.

CGF single lever valves have special relevance when the services of a trained plant room operator are not necessary available, eg., as is often the case with a school pool.

For projects that require a two-tank system, a standard “tandem” installation is strongly recommended. In this instance, the filters are arranged in parallel to operated at a conservative rate of 21m3/hr/m2. This filter rate is established on the basis of being half of the required backwash rate (ie., 42m3/hr/m2.) Backwashing a “tandem system” is achieved by using the full duty of the pump through one individual filter module. When backwashing is undertaken, the other unit is isolated and is temporarily taken “off-line”.

Whilst deviations of the above “tandem system” include pump selections that are based on using the maximum filter rate of 42m3/hr/m2 this method requires very careful planning. Furthermore, it does not provide the same dirt holding capacity that is available with the “tandem” filter system that operates at a conservative filter rate of 21m3/hr/m2.

“Shunt Backwashing” has been developed to permit the use of conservative filter rates without compromising the need to obtain the specified/mandatory backwash rate. In many high load applications (such as indoor heated pools and many industrial processes), filter rates as low as 15 to 25 m3/hr/m2 are often technically required. Since CGF first introduced shunt backwashing to the commercial swimming pool market (in 1992) this backwash method has been widely used and specified by many leading Consultants.

Shunt back washing is applicable to installations that use three or more filter modules that are arranged in a filter bank. In practical terms, shunt backwashing should not be applied to any more than six filter modules in any one filter bank.
The use of shunt backwashing simplifies the application engineering that is often required when selecting a pump’s duty point to best suit the “filter” & the “backwash” requirements. Shunt backwashing also has the benefit that it uses clean filtered water for backwash purposes.

Compared to all other conventional methods of “reverse flow” backwashing, extensive field-testing has established that shunt backwashing is capable of maintaining filter beds in a far more permeable condition.

Maintaining a permeable filter bed is particularly relevant in high load applications where body oils and fats are an issue. It is also relevant where a high level of solids is expected; such as encountered with equine pools and aquaculture. In these applications, reverse flow backwashing is not recommended on the basis that underdrain systems can be very easily blocked with solids. Blockages of this type can result in premature failure of the filter’s underdrain, poor filter performance, and
high service/maintenance problems.
Typical Shunt Backwash with Stainless Steel Face Plumbing

Apart from simplifying the commissioning process, shunt backwashing also provides the opportunity to increase the backwash rate to resolve filter bed maintenance problems. With the shunt backwashing each filter is backwashed by operating three simple butterfly valves. Shunt backwashing can also be readily upgraded to include various levels of automation.

Apart from reducing the chance of Operator error, shunt backwashing provides a constant albeit reduced process flow during the backwash cycle. As minor as what this benefit may seem, it has a very considerable impact on the extent of automatic control loops that are required.

When using a shunt backwash system, the shunt backwash valve must be modified so that it cannot be
fully closed. Once the required backwash flow has been established (by volumetric analysis or other means), the notch plate setting on the shunt valve should be marked and recorded as being the setting required for normal backwash.

The maximum recirculation rate for a shunt backwash system should be considered to be no more than the total number of filter vessels, minus one, times the filter area of each filter module, times the maximum filter rate of 42m3/hr/m2. This requirement ensures that when one filter module is being backwashed the filter rate through the remaining “on-line” filters does not exceed the filter’s maximum filter rate of 42m3/hr/m2. The minimum recirculation rate for a shunt backwashing system must not be less than the required backwash flow for one filter (in m3/hr) times 1.2. This requirement obviates the need for the shunt backwashing valve to ever be fully closed.


Apart from providing the required amount of filter area, the system designer (& the installing contractor) has an obligation to ensure that the proposed filters are capable of being effectively backwashed. Regardless of which backwash method you may choose, it is important to get it right. Whilst system flaws may not be readily apparent upon the initial start-up, failure to achieve the correct backwash rates will affect the long-term performance of your filter system.

CGF’s technical literature nominates the required backwash flow for each filter Model. This “litre per second” flow is based on a required backwash rate of 42 m3/hr/m2. It is also extended to reflect the amount of washwater (in cubic metres) that is required for a standard four-minute backwash. This washwater consumption helps to establish the size and the capacity of the required detention tank, sludge lagoon, and or washwater recovery system.

The above backwash requirement is based upon the use of “silica filter sand” that has been produced in accordance with AWWA B100-89 Standard. CGF’s recommend grade of filter sand provides an effective grain size of 0.8mm to 2.0mm with a specific gravity of 2.65. Whilst other filter Medias may be used, backwash rates (& the required bed expansion) may vary according to the media’s specific gravity.


The shunt backwash method uses clean filtered water for backwashing purposes. It is applicable to at least three filters arranged in parallel. Individual filters can provide up to 7.25m2 of effective filter area. This backwash method enables the use of conservative filter rates, without compromising the need for aggressive wash rates.

This backwash process is particularly relevant to applications that may have a high level of suspended solids. The process will help to maintain the permeability of your filter bed. Precise backwash rates can be readily obtained by regulating the shunt valve located in the filtered water outlet.

Since CGF first introduced hunt backwashing to the commercial pool market in 1992, this method has been widely used and specified by many of Australia’s leading pool professionals. 


For filters with up to 3.5m2 of filter area.
Available in two valve sizes (either 100mm or 150mm). Applicable to single filters with dedicated pump sets or filters within a filter bank. Single Lever valves; reduce the chance of operator error. The orientation of the valve ports may be manufactured to suit your specific installation requirements.


(Using Commercially Available Valves)

Applicable to all filter models, either as single filters or filters within a filter bank. The number of operating cycles will vary depending upon the use of either a four or five-valve matrix. Most applicable to systems that require air scouring



Tandem systems refer to two filters arranged in parallel to “filter” at a rate of 21m3/hr/m2. With this arrangement, each filter is individually backwashed with the full pump duty to obtain a rate of 42m3/hr/m2.

Tandem systems can apply to all filters with filter areas up to 7.25m2. As shown in this case, the tandem arrangement is equipped with single lever backwash valves. Tandem arrangements can also use a valve matrix.

Tandem filter systems provide all of the benefits associated with a conservative filter rate ie., high dirt holding capacity & improved process efficiency.

Models VHT & VDF are particularly suitable for dual media filtration, using a capping of Anthracite (or filter coal) on top of a conventional silica sand bed. Whilst the depth of each filter media may vary according to the application and the specific media details, Table 5 in DIN19643 nominates that both anthracite and the filter sand beds should be 600mm deep in order to provide a total bed depth of 1200mm. In cases where deeper filter beds are required, CGF’s taller range of Vertical Column Filters (VCF) are available for this specific purpose.

The potential benefits of dual media filtration include extended filter cycles and improved water quality, particularly when high-suspended solids may be encountered. Other benefits include a higher retention of solids and generally lower pressure losses.


In a mono-sand filter, the reverse flow of the backwash process can inevitably cause the smallest particles to be lifted to the top of the filter bed. This condition is known as “inverse stratification” and it is largely responsible for problems that are associated with the formation of mud balls and channeling. In order to minimize this effect best practice suggests very careful selection of the filter media and generally good filter management by the plant Operator.

Ideally, the ultimate stratification for a granular filter would place the coarsest, largest granules being placed at the top of the filter bed. This would provide a technically “coarse to fine” filter with larger matter being detained by the filter’s top layers. This arrangement would also tend to prevent the bottom (fine) layer from being prematurely loaded and blocked.

In essence, dual media filtration permits much finer materials to be used in the bottom of the filter bed than can be otherwise tolerated in a conventional mono-sand filter. In a mono-sand filter, only a comparatively small part of the total voids are used to store particulates. When high-suspended solids are encountered, the head loss increases quite rapidly. Under certain circumstances, this may result in unacceptably short filter cycles.


Anthracite is the ideal top layer in a dual media filter. Anthracite has a greater surface area and a greater dirt holding capacity than sand. More importantly, when correctly applied and operated, the Anthracite will remain at the top of the filter bed after backwashing has subsided.

During its service life, sand tends to lose its entrapment capacity as it is progressively eroded from sharp-edged and irregular granules to roundly smooth, uniformly sized, smaller granules. The hard-carbon nature of anthracite resists erosion and therefore is not subject to a loss of efficiency due to the upward migration of the smaller particles that can be produced in a mono-sand filter.

With dual media filtration, the upper layer of the media provides in depth filtration and large dirt storage capacity.
The finer sand in the bottom of the filter (with its low uniformity co-efficient) remains largely unpolluted and it is available to provide very effective filtration. By remaining relatively clean, the sand’s layer’s dependence upon backwashing is also reduced. Similarly, the chance of the bottom sand layer becoming biologically corrupt is greatly reduced.


Despite the fact that the dual media concept was established in the early 1060’s, the use of a mono-sand filter remains the most reliable and convenient mainstay of the commercial swimming pool Industry. The use of dual media filtration is more commonly and correctly applied to the industrial water treatment Industry, where the nature of the dirt load is usually more fragile and sticky. Equally many processes in general water treatment require single pass performance, whereas the swimming pool Industry is largely founded upon the Law of Consecutive Dilution with filtration being provided by multiple passes.

Dual media filtration does require application engineering and proper selection of appropriate filter medias to suit specific applications. Backwashing rates, bed expansion, and freeboard height needs to be carefully established in relation to the media’s effective size and its uniformity of co-efficient. Operational care is also required to prevent hydraulic surges that could cause bed disturbance.

The effectiveness of dual media filtration (particularly for the water treatment industries) was clearly the catalyst for the further development of the true “multi or mixed” media filtration. In this case, a layer of Garnet is provided at the bottom of the filter bed.

Recent industrial trends indicate the use of coarser media sizes and lower uniformity co-efficient in deeper beds operating with higher hydraulic loading rates. This approach has been developed to increase the amount of storage volume within the filter bed (per square meter of filter area) for generally better plant economics and performance.



“Effective Size” (es)

The size opening that will pass 10% (by weight) of a representative sample.
“Uniformity Coefficient” (UC) The ratio of the size opening that will just pass 60% (by weight) divided by the size opening that will just pass 10% (by weight) of the same sample


This Table demonstrates the “range” of typical dual media filters.


series is specifically designed as a Vertical Column Filter. Whilst a VCF can also be used as a contact tank (for ozone processes) its primary purpose is for “chemical filtration”.

Given a clear understanding of the application, just about every conceivable requirement can be accommodated with a well engineered fiberglass vessel. Whilst important (& often critical) fiberglass is not only selected for it corrosion resistance; other features such as strength, relative lightweight construction and high abrasion resistance will provide significant cost savings and benefits.

Being manufactured from selected resins systems, the VCF series offers a totally non-corrosive solution for a wide range of processes and applications.

Features at a glance

  • Wide range of sizes with single vessels providing tank volumes of up to 17.8 cubic meters
  • Standard fitments include internal opening access hatches, media dump port, screen drain, vent, vacuum breaker, lifting lugs, etc.,
  • May be used as an upflow or downflow filters with an extensive range of filter internals
  • Simple to operate with a choice of backwash methods.



Industrial-quality, fiberglass pressure filters that are specifically designed for a wide range of water treatment and industrial processes using “dual media” filter technology.

With dual media filtration, the upper layer of the media provides “in-depth” filtration and large dirt storage capacity.

The finer sand in the bottom of the filter (with its low uniformity co-efficient) remains largely unpolluted and is available to provide very effective filtration.

By remaining relatively clean, the sand’s layer’s dependence upon backwashing is also reduced. Similarly, the chance of the bottom sand layer becoming biologically corrupt is greatly reduced.

Features at a glance:-

  • Vertical tank offering a 1200mm bed dual media filter bed.
  • Equally suitable for mono-sand and other granular filter medias
  • Standard fitments include media dump port, screen drain, vent, vacuum breaker, lifting lugs, etc.,
  • Extensive product range with single filters providing up to 7m2 of effective filter area
  • Hydraulic balance internals using injection moulded laterals
  • Simple to operate with a choice of backwash methods.


For those that prefer vertical filter vessels, the VHT series has been specifically designed and manufactured to satisfy the requirements of the commercial swimming pool industry.

Unlike many filters of its type, the VHT series is designed and manufactured in Australia for Australia’s harsh conditions.

Furthermore, if you need any technical and engineering support, you won’t have to phone overseas to get it.

Chadson Granular Filters has been a leading supplier of commercial swimming pool filters for almost thirty years. Being “contact moulded” standard and custom-made features can be readily provided.

Features at a glance

  • Uncompromising quality, at a price you can afford
  • Straight, vertical tank wall offering a 1200mm bed deep.
  • Equally suitable for dual-media other granular medias
  • Large diameter flanged access hatches.
  • Standard fitments include media dump port, screen drain, vent, vacuum breaker, lifting lugs, etc.,
  • Extensive product range with single filters providing up to 4m2 of effective filter area
  • Comprehensive underdrain using injection moulded laterals.
  • Simple to operate with a choice of backwash methods.

The non-corrosive and cost effective solution for all sorts of :-

  • Swimming pools & recreational water
  • Industrial applications and process
  • Water & Waste Water Treatment
Not all fiberglass horizontal filters are created equal. Since the release of CGF’s first fiberglass filter in 1967, our product range has been continually refined and expanded. Although our success (in hundreds of varied installations) has periodically attracted several look-a-like products, these imitations commonly lack the parallel flow and the hydraulic balance that is unique to the MHS series.If water quality, low purchase costs, and minimum maintenance are important to you, the MHS series is worthy of your consideration. It will consume less plant space & provide more value for your filter dollar. It is also used by most pool professionals & commonly specified by accredited Consultants

Features at a glance:-

  • Parallel flow with precise control of velocity & water balance.
  • High backwash rates without the loss of filter media
  • Large dirt holding capacity utilizing the depth of the filtering media
  • Built tough to known engineering standards & references
  • Tried & proven in some of Australia’s harshest outback conditions
  • Extensive product range with single filter providing up to 7.25m2 of effective filter area
  • Single lever backwash valves available for all filters up with up to 3.5m2 of filter area
  • Technically superior & patented technology (FloModuLata™)
  • Transportable, easy to install & simple to operate with a choice of backwash methods
  • Australian-made with local technical & engineering support

Granular type filters are widely recognized by water treatment experts as being “effective & reliable”

Typically a granular filter will provide a large filtering volume with the ability to accommodate high levels of suspended solids. Most importantly, granular filters can be simply cleaned, by reversing the water flow through the filter. Their backwashing operation does not require complicated operations such as draining, sluicing, or precoating.

The CGF product range can satisfy almost every conceivable requirement:-

  • Rapid, Medium or High Rate filters(with filter rates up to 42m3/hr/m2)
  • Mixed or Dual Media (using Hydro Anthracite & other filter medias)
  • Single or Multi media (With different bed depths & different medias)
  • Chemical Filtration (GAC, BAC, & many other diverse removal processes)
  • Horizontal or Vertical Filters (in various sizes & filter areas)
  • Single or Multiple Vessels (with individual filter areas up to 7.25m2)
  • Standard or Custom-made product (contactors, biological filter towers, carbon adsorbers, etc.,)
  • Different Backwash Methods (reverse flow, shunt, manual/auto)

CGF filters have been used on hundreds of swimming pools and are capable of providing benefits and features that are not simply available with many other sand filters.

Whilst CGF’s reputation in the swimming pool market is widely known and accepted, they are equally suitable for aquaculture, aquarium life support systems, waste water treatment, industrial applications, and special high pressure applications.



Given that CGF manufactures a comprehensive range of horizontal and vertical filters, they do not have a vested interest in any one type or form of filtration. It is however important to accept that CGF’s horizontal filters are able to provide maximum value for your filtration dollar. Conversely, vertical vessels are often technically warranted when different filter medias and processes are required and or specified.


Whilst CGF filters may appear to operate in a very similar fashion to older filters (that were made from steel or concrete) they differ quite radically in their hydraulic characteristics and their total plant size. By operating in excess of traditional slow filter rates, solids are retained within the depth of the filter media………. not just on the surface, as was the case with many early filters.

This fundamental difference has resulted in modern Australian-made filters that are able to satisfy any given volume through a bed, which is considerably smaller than any traditional rapid filter.

Although increased flow rates may appear to be a dramatic departure from early/traditional filter rates, this does not detract from their collecting efficiency.

The basic principle of “in-depth” filtration has resulted in filter plants that offer:-

  • More compact vessel designs.
  • Lower unit costs.
  • Less shipping weight.
  • Shorter installation times.


All CGF filters are manufactured from selected and proven resin systems in accordance with standard procedures that recognize the requirements of BS-4994, DIN 18820, and AS-2634. Standard vessels are designed and manufactured for a standard test pressure of 350kPa. Higher pressure ratings are available upon request.

CGF filters are supplied with hydraulically balanced filter internals and various filter connections and fittings. This includes a choice of access hatches, flanged inlet/outlet connections, screened drain, kinetic vent & vacuum breaker, pressure indication, and detailed installation and operating Instructions. For mechanical & chemical filtration, the CGF filter laterals are injection moulded from engineering plastics (ABS) with inward tapering ‘V” shaped opens that are in general accordance with DIN19605.