Hydraulic Filters

Hydraulic Filters

Hydraulic Filters

Filter types according to their structures;

    A. Surface Type Filters: follow a flat and smooth flow path. The contaminating particles are held at the surface of the filtration element. The dirt holding sensitivity of the filter is proportionate to the allowed pore size on the filtration element. 
     The pore are of equal sizes. All the particles bigger than the filter pore size can be filtered. The particles with a small body but with a lengthy height can pass. As the filter continues to hold dirt, the filtration sensitivity increases and smaller particles can be trapped. 

    Like all the filters, the sensitivity of these filters are defined by the size of particles they can hold. The unit of length is micron (µ). 1 µ = 0,001mm. For example, a filter which can hold particles of 60 microns and above is defined as a 60 micron filter. 

    B. Depth Type Filters: It has a labyrinth like structure. These filters have a high capacity of dirt holding. Three types of filter elements are used such as cellulose, micro-glass and composite materials. Micro-glass filter media provide a more sensitive filtration when compared with other media by means of its fine fibered structure. 
    Depth type filters aren’t cleaned, they are replaced when they are dirty. This type of filters are manufactured with a casing.   When dirty, the cartridge is replaced. They have a higher capacity of filtration when compared with surface type filters.
    Depth type filters are named after the size of particles they can hold. For example, For example, a filter which can hold particles of 20 microns and above is named as a 20 micron filter.

    It has the advantage of being manufactured with smaller sizes of pores. Most of the filters used in the return piping and pressure lines are depth type filters. 

 
Filtration Element Dirt Holding Capacity Pressure Drop Life Price
Micro-glass High Medium High Medium
Cellulose (Paper) Medium High Medium Low
Wire Netting Low Low Medium High

There are standards formed according to the amount and size of the solid particles in oil. These are ISO 4406, Nas 1638 and SAE standards. 
 
ISO 4406 (ISO 11218) Nas 1638 (1964) Particle / Millimeters
4 microns 6 microns 14 microns
23/21/18 12 80 000 20 000 2 500
22/20/18 - 40 000 10 000 2 500
22/20/17 11 40 000 10 000 1 300
22/20/16 - 40 000 10 000 640
21/19/16 10 20 000 5 000 640
20/18/15 9 10 000 2 500 320
19/17/14 8 5 000 1 300 160
18/16/13 7 2 500 640 80
17/15/12 6 1 300 320 40
16/14/12 - 640 160 40
16/14711 5 640 160 20
15/13/10 4 320 80 10
14712/9 3 160 40 5
13/11/8 2 80 20 2,5
12/10/8 - 40 10 2,5
12/10/7 1 40 10 1,3
12/10/6 - 40 10 0,64

​The main feature of the filter is to decontamination of the oil from the contaminating and corrosive particles that originate with time.  Therefore, at least one filter needs to be used in the hydraulic circuits. This filter consists of the filter casing and the filter cartridge. There may be elements on the casing such as check valves and contamination displays. 
    The filter cartridge accommodates the filtration element. When the filtration element is dirty, the cartridge is replaced. 

BETA NUMBER
                Beta rate expresses the rate of solid particles held by the filtration element during the pass of the fluid through the filtration element. The beta rate is regarded as the efficiency of the filtration element.
                Filtration rate Px= The number of solid particles going through the filtration element / The number of solid particles coming out of the filtration element.
                For example, a filtration element with a beta rate of β10 = 2 holds 50% of the particles bigger than 10 µm. A  filtration element with β10 = 200 beta rate holds 199 of 200 particles passing and has an efficiency of 99,5%. The beta rate is one of the most important criteria when defining the quality of the filtration element. A 20 µm filtration element with a beta rate of 200 is always better than a 10 µm filtration element with a beta rate of 2. 

Let’s assume that the particle number before the filter is 100,000 X MICRONS
The amount of particles that the filter couldn’t hold Beta Value β(x) Filter Efficiency
50.000 2 50,0%
5.000 20 95,0%
1000 100 98,7%
500 200 99,5 %
100 1000 99,9%
 
Micro-glass Media Particle Size β(x)≥200 Partikül Boyutu  β(x)≥1000 Dirt Holding Capacity  (gram/m2) ΔP=5 bar
MG 03 < 4  µm (c) 4  µm (c) 218
MG 06 7,1  µm  (c) 8,7  µm (c) 200
MG 10 13  µm (c) 15,7 µm (c) 215
MG 20 20  µm (c) 21,5 µm (c) 238
MG 25 23,6  µm (c) 29,6 µm (c) 127
Hydrotech Filter manufactures high quality equivalent products of all the big hydraulic filter manufacturers. Hydrotech Filter is manufactured in Turkey and it is the first and only filter brand that is β(x)≥200.
    The micro-glass filter media we use are “Multipass Test” and dirt holding capacity test approved.

FILTER MEDIA CERTIFICATE
Typical Properties USA Units Metric Units Test Methods
 
Basis Weight 52 lbs/3000ft2 87 grams/m2 T.A.P.P.I-T-410
A.S.T.M.-D-646
Thickness 23 mils 0.56 mm T.A.P.P.I.-T-411
Efficiency (Flat Sheet)          
Beta 200 13.0 micron 13.0 micron ISO-16889
Beta 1000 15.7 micron 15.7 micron ISO-16889
Dirt Holding Capacity (Flat Sheet) 2 bar 99 mg/in2 155 grams/m2 ISO-16889
Dirt Holding Capacity (Flat Sheet) 5 bar 138 mg/in2 215 grams/m2 ISO-16889
Air Resistance 4.0 mm H 20 39 Pa MIL-STD-282
A.S.T.M.-D2986-91
Air Permeability 37 cfm 18.8 cm3/cm2/s T.A.P.P.I-T-251
Mean Flow Pore 9.8 micron 9.8 micron PMI Porometer
Max Pore 24.4 micron 24.4 micron PMI Porometer