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Pressurized Steel Filters

  • When do you need filters?

Pressure filter are typically used when the raw water turbidity is greater than 1 NTU or there is an unacceptably high presence of Iron or Chlorine.

They are used to protect downstream treatment equipment from becoming plugged or fouled.

  • What is pressurized filters?

Pressure Filters contain filter media chosen to remove specific water impurities.

There are three types of pressure filters:

Multi-Media Filters use layers of different filter media to remove suspended solids from water. A typical multi-media filter has anthracite in the top layer, sand in the middle, and garnet on the bottom. They are often used in conjunction with a polymer feed system and/or coagulant aid feed system to improve filtration efficiency.

Activated Carbon Filters remove free chlorine, an oxidizing agent that damages most resins and/or membranes in water treatment systems.  While they also remove organic material, enki does not recommend their use to reduce organics due to their slower flow rates and shortened life in this application. We do not suggest using this technology ahead of a reverse osmosis system because it tends to pass carbon dust on to membranes and may generate biological contaminants within the carbon bed.

Sand Filters are used to remove suspended solids in water. Three different sand media are used at the top and gravel is used at the bottom. It is preferable to multi media because it is cheap.

Iron Manganese Filter is used to remove iron and manganese dissolved in water from the water by oxidation. The amount of media is determined according to the pollution concentration in the water. Oxygen must be present in the water for oxidation.

  • How does it work?

Raw water enters the Pressure Filter through a multi-branch inlet distributor at the top. It flows through the media, removing specific contaminants.

Filtered water leaves the Pressure Filter through a hub/lateral underdrain in a non-filtering subfill support layer at the vessel’s bottom. When impurities collect in or on the media bed, a backwash cycle cleans the filter.

  • Backwash Cycle

The standard backwash cycle for multi-media and active carbon filters is a two-step operation “backwash and rinse”. During backwash, water flows through the media bed and carries impurities from the vessel through the inlet distributor and backwashoutlet. The rinse step rids the filter of backwash water and compacts the bed before returning it to service.

When coagulants or polymers are added ahead of multi-media filters, the cleaning cycle is expanded to include an air scour step, further cleaning the media. This expanded cycle includes:

  • Drain Down
  • Air Scour
  • Backwash
  • Rinse

The vessel must be drained to just above the media for the air scour cycle. Air blown into the air scour distributor and through the media bed causes filter particles to scrub impurities off each other. After the air scour cycle, the vessel is refilled and backwashed to remove loose impurities and to re-classify the media. The bed is rinsed before being returned to service

Filter tanks are of vertical cylindrical type as standard. Horizontal cylindrical filters are used for high flow.Valves are standard butterfly valve type. Pneumatic or electrically operated butterfly valves are used in automatic filters.

The pressure class is normally 6 bar and is designed with higher pressures if required.