subject: Dual Media Filter Specification [print this page] Dual Media Filterfeature automatic backwashing, which employs a combination of air and water to maintain unit efficiency. Air scouring loosens suspended solids and dirt, sand removes suspended particles and anthracite removes odor and color, etc., so as to make the water fit for different applications.
Advantages:
Automatic self backwashing.
High filtration efficiencies.
Able to operate at very high flux rates.
Custom designed packages.
We implement pilot run for such water management to examine the implementation of the project and measure its success to make sure that desired performance is received when actually implemented in a holistic way across the plant of our customers. This comprises of sand and anthracite as filtering media and polishing media respectively. Internally it is fitted with inlet distributor and a bottom collecting system. Externally, it is fitted with frontal pipe work and isolation valves.
Sand is used for removing the suspended particles and anthracite removes the odor and colour etc to make the water fit for various application. Pebbles and gravels are provided to support to both the media. This filter is to be backwashed after accumulation of suspended solids over the cycle, however, before carrying out the backwash, air scouring (optional) is also to be done for loosening of dirt and suspended solids. Limit for the backwash in these filers is governed by differential pressure across the filter. Type of filters in vertical/horizontal configurations are:
Sometimes called "high rate" sand filters, these cost a few hundred dollars. Sand filters are a bit messy to set up compared to cartridge filters. Bags of special
filter sand (not sold with the filter) need to be manually poured into the filter.
The filter is cleaned by "backwashing." Turning a valve reverses the direction of water flow in the Dual Media
Filter, washing out trapped dirt (the actual procedure is a bit more complicated than this). The water is drained away, not returned to the pool. Backwashing is
stopped when the drained water is clear, which is after about 100 gallons.
Advantage
Low maintenance effort. Backwashing the filter once a week or once a month, is sufficient. Hayward recommends replacing the sand in their filters, every five years.
Disadvantages
Lowest filtration performance (size of dirt particles trapped) of the three types of filters, but is good enough for swimming pools.
Easier to install and maintain than DE filters, but more difficult than cartridge filters (see link to Pentair owner manuals, below).
Large, requires a lot of sand. A typical filter will use over a hundred pounds of sand and is one to two feet wide.
Water is wasted during backwashing.
Zeolite can be used instead of sand. It is sold under brand names such as Zeobest and Zeobrite. Zeolite provides better filtration performance than cartridges, and
approaches DE performance.
Diatomaceous Earth (DE) Pool Filters
Also called diatom filters, DE filters are the finest of all the pool filters, capable of removing the smallest dirt particles. They are like sand filters in that the
filter needs to be manually filled with loose DE powder. However, the DE powder is not poured directly into the filter. It is mixed in with the water in the pool
skimmer, and then pumped into the filter. Only a few pounds of DE powder are needed for one filter.
Advantages
High filtration performance (size of dirt particles trapped).
Medium maintenance effort. Backwashing every week or month, regeneration (remixing) every month, DE powder replacement every year.
Disadvantages
Most complex of all the filters, for installation and maintenance.
Breathing in the fine dust can be hazardous to health. A dust mask should be worn when handling dry DE powder.
