Sediment filters
As the final layer of defence against particulate, sediment filters fine-tune your supply. By catching the extremely small impurities - including the ones the eye can’t see - they equip your taps with safe and satisfyingly clear water.
Know what you need, just need a price for supply?
What are sediment filters?
Most private water supplies contain some level of particulate, or a certain amount of ‘bits’. In more accurate terms, particulate refers to the extremely small particles of various solids that can become suspended in your water supply - some of which can be so small that they can only be viewed through a microscope. As an umbrella term, particulate can include particles of sand, silt, rock, soil, decayed vegetation, metal precipitates, fibres, bacteria or general sediment that has built up in your pipework. Every water source will have its own blend of particulate that can reduce water quality and negatively impact it’s appearance.
Sediment filters are used to remove particulate. Similarly to a net, sediment filters use materials with lots of very small holes to catch the particulate while still allowing the water to flow onward. Sediment filters come in various shapes and sizes, using different materials and structures to create different sized holes to catch different sized particles.
Since particulate can be extremely small, the unit of measurement used for the gaps in the filter (or sticking with our example, net) is micron. One micron is equal to one millionth of a metre and one-thousandth of a millimetre. For context, the average diameter of a single strand of human hair is around 70 micron.
The type of sediment filter (or net) you’ll need will depend on your water quality and usage demands.
Depth filtration vs surface filtration
Sediment filters will typically fit into one of two categories; depth filters or surface filters. The category of the filter will depend on the technique it uses to trap the particulate.
Depth filtration
Technique
Depth filtration uses a porous (meaning it has lots of tiny holes) or multi-layered material to trap particulate, utilising the full depth (or thickness) of the filter material to catch the particles as the water moves through it. The internal structure of the depth filters, often made from densely packed fibres, use a graded depth approach which means that the fibres get progressively more compact when moving from the outer surface to the inner core. This means that larger particles get trapped first, and the finer particulate will be gradually intercepted as the water moves further through the filter.
Use case
The depth filtration technique is usually selected when the size of the particulate you’re dealing with is largely unknown, unpredictable, or varied. The filters have a high dirt holding capacity and can deal with larger amounts of particulate, whilst also maintaining great durability against clogging.
Surface filtration
Technique
Surface filtration, as suggested by the name, traps particulate on the surface of the filter, using a single-layer material which is designed to target particulate of a specific size. The surface filters operate a dual approach. Firstly, they catch the size-specific particles directly as the water passes through the microscopically small and consistently sized gaps in the material. Second to this, as the larger particulate caught by the filter starts to build up on the surface (in a process called caking), a partial block forms, creating an extra layer of filtration for the incoming water by trapping some of the finer particulate in the blockage. This process consequently heightens the efficiency of the filter.
Use case
Surface filtration is usually the selected technique when the size of the particulate you want to target is known and relatively uniform. These filters are highly efficient at particle removal, whilst also providing a minimal pressure drop and the chance to clean and reuse the filters depending on the model.
The filter housing
In both cases, the water enters the inlet at the top of the unit, makes contact with the outside surface of the filter, moves through the cartridge, flows upwards through the core of the filter and exits through the outlet at the centre of the unit.
So, what are the main options on the market?
Spun
Description
Spun filters are made from thermally bonded fibres. The density of the fibre structure can be carefully controlled to create specific filters for different particle sizes. These filters are surprisingly rigid, with a fixed framework in which the fibres do not separate or migrate.
Filter technique: Depth
Relative price tier: Low
Pros
High dirt holding capacity
High accuracy
Graded-depth technology (retains a variety of particle sizes)
Cons
Can’t be cleaned
Hard to visually assess the extent to which the cartridge is clogged
The retention of the larger particles towards the surface of the filter can clog the cartridge before the inner layers have reached full capacity
Wound
Description
Wound filters are made with yarn. Similar to a cone of string, the yarn is tightly wrapped around a core support in a carefully structured diamond or ‘v’ pattern. The exact shape of the pattern will change depending on the particle sizes for which that particular filter is made to target.
Filter technique: Depth
Relative price tier: Mid-market
Pros
High dirt holding capacity
Long lasting product lifespan compared to alternatives
Graded-depth technology (retains a variety of particle sizes)
Cons
Can’t be cleaned
Hard to visually assess the extent to which the cartridge is clogged
The wound nature of the structure leaves the fibres susceptible to movement, potentially allowing particulate which is larger than the specified pore size of the filter to push through the cartridge
Pleated
Description
Pleated filters are made up of a single-sheet of filtration medium, folded in a zigzag pattern, which is wrapped around a central core support that also caps the cartridge at both ends. The pleated texture of the filtration material increases the lifespan and efficiency of the filter, offering seven times the surface area compared to a depth filter.
Filter technique: Surface
Relative price tier: High
Pros
Highest efficiency
Maintains excellent flow rates
Minimal pressure drop
Can be cleaned (only some cartridge models)
Cons
Requires cleaning (usually cleaned 2 - 3 times in a lifespan)
Blocks quicker than market alternatives
How to choose the right filter cartridge
When choosing a specific filter cartridge for your system, there are a large variety of options on the market. These range in micron size (the particle size(s) the filter will target), length, diameter and materials. Plus, there’s an assortment of pros and cons tied to all sediment filter cartridges and what will work best for you will depend on the chemistry of your water, as well as the set-up of your system and usage demands.
So, while it’s easy to try and whittle it down based on projected accuracy, lifespan or price, there may be one specific option or a combination of filters that will provide optimum results based on the specific content of your water.
Looking to add a sediment filter to your system design? Not sure what filter you need?
