Basic Filteration

0.0001µm           0.001µm                                  0.2µm                                 10µm*

1A⁰ <———–> 10A⁰           <———–>    200A⁰     < —————–>  100,000A⁰

Reverse                                          Ultra                                                Microfiltration
Osmosis                                         Filtration

•  µm – Micron
• Smallest pencil dot, which we can see by necked eye, is about 40µm.

There are various filtration & seperation procedures follows by industry for removal of un-wanted particles (contamination) like :

Filtration for the removal of suspended particles from the range of 0.2 mm to 100 or 150 mm is generally known as micro filtration or cartridge filter. This is pressure filter in line as shown in the picture.

Pressurized fluid comes in to the housing and due to pressure, passing from the cartridge, where actual filtration takes place and contamination retain on/over the cartidges and clear fluid comes out from the center of the cartridge. This is out to in system.

One needs to monitor the filter by pressure difference (ΔP – the difference inlet pressure and outlet pressure). Initially, when cartridge is clean, clean pressure drop will be minimum and as it got contaminated, pressure drop will increase gradually. At 2.5 or 3 Kg/cm2 g pressure drop, one needs to change the cartridge in case of disposable cartridge.

If the flow rate is more, we need to give number of cartridges in one housing as shown here.

Depending on filter media we can classify the filter cartridges as depth or surface filter. Also they are available in various materials like, Polypropylene, Cotton, Cellulose, Glass- fibre, Nylon, PTFE, PES, Ceramic, S.S. Screen, Sintered S.S. or Bronze etc.

In pleated cartridges, actual filter media is in pleated from to cover more surface area. It is pleated on perforated core. It is supported with any other media, which is coarser to give minimum pressure drop and good strength to the cartridge. Outer cage is provided to give mechanical strength to the cartridge.

Most precise filter elements for guaranteed removal efficiency is pleated polymer cartridges.

Paper, S.S. wire-mesh, polypropylene, Nylon – N66, Polyethersulfone, Fluropolymer, Glassfibre or PTFE material pleated filter cartridges are widely available.

Polypropylene, Cotton, Nylone, Ceramic & Sintered S.S. media are available in depth type cartridges. Many manufacturers make graded pore structure depth media, which gives efficient filtration because of proper pore distribution. (Cross section of Depth cartridge)

Cross section of graded pore structure cartridges, bigger particles retain on the outer surface of the cartridge and most upper layer of the cartridges. While smaller particles retain at inner and very small particles retains at the inner layer of the cartridge. Thus entire depth of the cartridge utilizes and hence filtration is very economical.

Thus graded pore structure depth filter cartridge are good pre-filer, because it traps bigger particles then its rating.

Following parameters are to be considered for selection of the filter :