FREQUENTLY ASKED QUESTIONS
WHY DO YOU CALL IT A “GRANULAR” FILTER INSTEAD OF A “SAND” FILTER?
The CGF product range is designed for both mechanical and chemical filtration. Conventional silica “sand” is only one of the many filter medias that can be used in a CGF filter. Depending upon the project requirements the range of alternative medias includes biological & chemical filter medias, like Aquaclay®, Granulated Active Carbon (GAC), Active Filtration Media (AFM), Zeolite, manganese greensand, Garnet, etc., Chemical process can include the removal of chlorine, chloramines, ammonia, iron, manganese, hydrogen sulfide, etc.,
WHY IS AUSTRALIAN MADE IMPORTANT?
Buying Australian-made makes good economic sense. Historically, imported filters are only as good as the Distributor of the day. Historically, this can often be a transient affair that is subject to all sorts of variations & surprise. Even if everything goes OK, what happens if you find that you need some urgent advice or some spare parts? How confident are you that you can get this support when you need it? Given the proven assets that exist and are widely used in Australia, the logic of importing filter vessels is questionable.
WHY FRP CONSTRUCTION?
Unlike most other materials, fiberglass is a composite material. Its principal component is a fibrous reinforcement that is encased within a thermosetting matrix. These fibers are the load bearing component and the provider of both strength and elasticity. The function of the resin is to protect the fibers from corrosion, render the composite watertight, and transfer the loads from fiber to fiber.
Due to the infinite combinations of reinforcements & resins, FRP pressure vessels can be manufactured to suit specific design requirements. Rather than be limited to a nominal plate thickness or a wall section, FRP laminates can be designed to suit specific load analysis. FRP laminates can often be up to one-sixth the weight of carbon steel for the same duty.
Whilst the problems associated with traditional metals are well documented, it should be noted that inappropriate materials of construction could often result in expensive replacement costs. Quite apart from any cost implications, corrosion can be critical in terms of the inconvenience caused by a major disruption to plant and services. In some applications, such disruptions could even create a potential health risk.
WHAT SHOULD I LOOK FOR WHEN CONSIDERING A FILTER SUPPLIER?
A filter manufacturer with engineering and design capabilities will be able to support you with standard and custom made products and features that are able to suit specific requirements. It is unreasonable to expect that all filter requirements can be simply satisfied by making a selection direct from an equipment catalogue.
In many cases, it is often prudent to select the manufacturer that would be best to work with, rather attempt to select what may seem to be the best/most appropriate filter. Either way, it is important to consider who you are buying from. Check their references, visit local installations and talk to plant Operators of similar systems. Check the financial status of the manufacturer, verify their record for meeting delivery dates, identify the availability of technical support and service, inquire about the availability and the price of spare parts and inspect the manufacturer’s warranty carefully.
Apart from being readily accessible, your filter supplier should also have sound working knowledge of valves, piping systems, pumping equipment, operating requirements, faultfinding, and water chemistry.
WHAT SHOULD I BE PARTICULARLY CAUTIOUS ABOUT?
Be wary about look-alike products that are made by fiberglass fabricators. There is more to a good filter, than just the filter shell. Be also wary of proposals that feature a multitude of small diameter filter vessels. These filters are commonly used in residential (backyard) swimming pools and they cannot be reasonably expected to provide the type of performance that is required in a commercial application.
Banks of smaller domestic filters do not necessarily consume less plant space. This can only come about if higher filter rates and less filter media are provided. Check the warranty provided with a domestic filter, you might find that commercial pool use is specifically excluded.
HORIZONTAL FILTERS DO NOT WORK AS WELL AS VERTICAL FILTERS”
Whilst CGF filters are available in both a vertical and a horizontal format, filtration efficiency has very little to do with the actual shape of the filter. Filtration efficiency is all about the type of filter media, the media size, the bed depth, the filter rate, the water temperature, filterability, likely dirt concentrations, and the adhesive qualities of the likely suspended and colloidal particles.
Subject to appropriate engineering, the plan area of an effective filter bed could be circular, square, rectangular, or a mixture thereof. A study of the granular filters available on the world market will quickly reveal the existence of sand filters with vastly different shapes, sizes, and quality.
“ALL HORIZONTAL ARE THE SAME”
Not horizontal filters are created equal. Since the initial success of the HS-16 filter in 1965, (now called an MHS-1500) the CGF filter range has been continually refined and expanded. Although the performance of CGF filters (in hundreds of varied installations) has attracted several look-a-like products, these imitations very rarely have the parallel flow and hydraulic balance that provides the low maintenance water quality that possible with a well engineered horizontal filter. Many filters in the CGF range (ie., those larger than MHS3500) include patented FloModuLatas™ – you won’t find this level of engineering in other filter brands.
“FILTERS CAN BE DESIGNED BY THEORY”
Although physical and mathematical Laws are very useful for modeling purposes, CGF filter design is based on proof testing and careful interpretation of the test results. Each Model within the CGF range has been carefully engineered, proof tested, and subsequently proven by its successful case history. There is no doubt that an effective flow pattern over the full length of the filter does require considerable engineering. There is almost thirty years of applied experience behind each an every CGF filter.
“HORIZONTAL FILTERS DO NOT PROVIDE A FULL AND EFFECTIVE FILTER AREA”
The physical dimensions of CGF horizontal filters have been carefully established to account for losses due to media loading above the centre-line of the filter. Whilst this physical over-sizing makes an allowance for any perceived losses within the domed tank ends, the reality is that the use of shaped tank ends does not impose any undue restrictions of the particular streamlines that are created during the filter and the backwash mode.
“HORIZONTAL SAND FILTERS ARE PRONE TO SURFACE CLOGGING”
Surface clogging and cracking is usually caused by the rapid accumulation of solids on top of a fine filtering media. This may be corrected by reviewing the media selection (in relation to the application/solids loading) or by reducing the dose rate to permit deeper bed penetration and better management of the filter bed’s porosity.
“HORIZONTAL FILTERS ARE PRONE TO BED SHRINKAGE AND CRACKING”
Bed shrinkage and cracking at the perimeter of the filter bed is usually caused by inadequate or infrequent backwashing. Alternatively, if the incoming water is saturated with air, resultant gases can come out of solution and form air bubbles that will increase the resistance to flow and encourage channeling of the filter bed.
The factors affecting insufficient or infrequent backwashing usually relate to the installed conditions or the plant Operator’s management; both of which are outside the manufacturer’s control.
“HORIZONTAL FILTERS ARE PRONE TO ENCOURAGE MUDBALL FORMATION”.
Mudball formation is attributed to inadequate or infrequent backwashing. CGF Sand Filters are provided with clear Instruction that requires a mandatory backwash rate of 42 m3/hr/m2. Mudball formation can also be encouraged by fine sand particles accumulating at the top of the filter bed.
In cases where the media classification is found to be outside the normal tolerances, it is often required to remove the top 20mm of the filter bed after the initial fluidization. This will remove the small, under-size grain sizes and reduce the chance of mudball formation. Improper or excessive chemical coagulation can also contribute to surface clogging and mudball formation. The dose rate of all coagulants must be managed and adjusted to suit specific needs.
“HORIZONTAL FILTERS ARE PRONE COLLECT CRAP BELOW THE UNDERDRAIN”
The CGF underdrain comprises injection moulded laterals with inward tapering “v” shaped slots. These slots face downwards so that when in the backwash mode a conventional current creates as very strong “boiling” process over the full length of the filter. This water-wash process effectively purges the zone underneath the bottom header.
“COMPLIANCE WITH DIN STANDARDS”
Although the German Standard (DIN 19605) is widely considered outdated, Section 188.8.131.52 makes clear references to the suitability of horizontal filters. Subject to detail, CGF filters can and do satisfy DIN Standards. Nevertheless, the use and relevance of DIN Standards is confined to a handful of European countries. By modern standards, many of these requirements are cumbersome and are not technically justified. Water treatment plants in Australia (and most other parts of the world) have no obligation to satisfy DIN Standards.
It is also worth noting that whilst some countries in Europe prefer vertical tanks (with DIN media compositions) the American market is dominated by horizontal sand filters. At the end of the day, the choice between horizontal and vertical is at best academic, and it is not particularly relevant to the choice of optimum filtration.
THE LAST WORD
The CGF product range can accommodate different flow rates, different media volumes, and different types of filter medias. They can also be customized to suit specific purposes and Client preferences. This includes the provision of flat filter floors, air scour, surface wash, pulse backwash, high-pressure tank ratings, automation and other options.