TECHNICAL REFERENCE
How Donaldson Displays Filter Flow versus Pressure Loss Data
Pressure Drop ( ' P) Correction Formulae To properly calculate pressure loss for viscosity and/ or specific gravity, use the filter and housing formulae below to determine the clean filter assembly pressure drop.
Filter, Head or Housing/Assembly Reference
Flow Rate (lpm)
0
200
400
600
800
1000
15
100
12
80
2 m
9
60
6
40
5 m
8 m
Filter Correction Calculation
3
20
14 m
New Saybolt Seconds Universal Viscosity (SSU) 150
25 m
0
0
ΔP Filter = ΔP from graph X - or -
New Specific Gravity (S.G.) .90 X
0
50
100
150
200
250
300
Flow Rate (gpm)
New Centistokes Viscosity (cSt) 32
Performance Curve Notes • All flow measurements were made with 32cSt [150 SSU] hydraulic oil at 100°F (37.7°C), fluid specific gravity of 0.9. • The performance curves displayed are for the filter, head or housing assembly. • Filter performance curves will either list media numbers or beta ratings (see circled areas on chart above). These labels correspond with the filter choice tables.
ΔP Filter = ΔP from graph X
New Specific Gravity (S.G.) . 90 X
Clean Filter Assembly Pressure Drop (ΔP) Calculation
ΔP Clean Filter Assembly = ΔP head + ΔP filter
The Importance of Temperature in Determining Pressure Drop Fluid viscosity plays an important role in restricting the flow through filters. It’s crucial to select the proper filter to maintain adequate flow and avoid excessive pressure drops. Measured in centiStokes (cSt) or Saybolt Seconds Universal (SSU or SUS), fluid viscosity is the resistance of a fluid to flow (thickness of fluid). Low viscosity fluids pass through filters with less resistance than high viscosity fluids. Higher fluid viscosities have higher pressure drops due to higher resistance passing through the media. The colder the fluid, the higher the viscosity, so the lowest potential temperature of the fluid is the best measure for calculating pressure drop. Use the chart below to determine the viscosity of the fluid to be filtered at its lowest potential temperature.
Oil Kinematic Viscosity Combined With Temperature in centiStokes (cSt)
SAE Gear Oil Hydraulic Oil ISO Grade
75W
80W 85W
90W
140W
15
22
32
46
68
100
150
220
320
460
680
°F
°C
3.7 4.4 5.4 6.7 8.5
3.5 5.5 6.8
5.7 7.0 8.8
7.3 9.0
9.3
11.7 14.9 19.4 26.0 36.2 52.4 79.6 128 220 409 838 1920 5060
14.7 18.9 25.0 34.1 48.2 71.1 110 181 320 613 1290 3070 8400
18.2 23.7 31.8 44.0 63.3 95.2 151 254 460 907 1980 4870
22.9 30.2 41.1 57.9 84.8 130 211 365 680 1380 3130 8020
248° 230° 212° 194° 176° 158° 140° 122° 104°
120° 110° 100°
11.7 15.0 19.8 27.1 38.5 57.2 98.7 150 271 536 1190 2990 8890
1
4.5
11.4
3 5
5.3 6.5 8.5
8.5
11.2 14.8 20.2 28.7 42.9
14.8 19.9 27.7 40.2 61.5 100 175 334 711 1720 4880
90° 80° 70° 60° 50° 40° 30° 20° 10°
11.0 14.8 20.6 29.9
6.2
11.1 15.1 21.5
8
12 15 22 32 51 87
11 15 21 33 52 85
32
46
68
50.7 86.7 162 340 820
75.6 135 264 585 1500
116 214 438
86° 68° 50° 32° 14°
180 375
1020 2770
13900 47000
23900 85000
0°
185
15700
27200
-10°
400
800
2350
4650
9120
16800
32300
60000
-4°
-20°
26 • Hydraulic Filters & Accessories
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