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FILTRATION IN BRIEF Contamination Control in Hydraulic Systems
Filter element life is signifi cantly effected by the pollution level at the machine location and by the maintenance level of the machine.
Considering these parameters the actual fl ow rate should be multiplied by the following “Environmental Factor”:
After having stated the fi lter media and the REAL fl ow rate, the fi lter must be chosen from the “fl ow rate tables” on the catalogue.
The values shown there take in account the pressure drop Äp met by the fl uid passing through the fi lter, that must be within a certain
value. In practice, the “assembly Äp” (Äp fi lter housing + Äp fi lter element) with clean fi lter element should be
· 3 kPa (0,03 bar)
max for suction fi lters
· 35 ÷ 50 kPa (0,35 ÷ 0,5 bar)
max for return fi lters
Lower is the initial pressure drop, better is the fi lter effi ciency and longer fi lter element service life.
N.B. The fl ow rate values given in the tables are referred to mineral oil with viscosity “V” di 30 cSt and density “ps” = 0,9.
When using oils with different features, the following correction factors must be applied at the Äp0 values obtained on the curves:
FILTER HOUSING: the pressure drop is directly proportional to the oil density “ps”, so in
case you have ps1 ‚ 0,9 Äp1 = (Äp0 x ps1) : 0,9
FILTER ELEMENT: the pressure drop through the fi lter element varies in function of the oil viscosity, so in case you have a viscosity
V1 (cSt) different from cSt:
· for oil viscosity 150 cSt Äp1 = Äp0 x (V1 : 30)
· for oil viscosity > 150 cSt Äp1 = Äp0 x [V1 : 30 + (V1 : 30)] : 2
Some fl uids have fi lterability problems (diffi culty in passing through a “multilayer” (glassfi ber) fi lter media).
In such cases a correction factor must be considered when sizing the fi lter: this factor must be verifi ed with the fi lter manufacturing,
specifying all the features of the fl uid.
PRESSURE DROP (Äp) - according to ISO 3968:2005
ENVIRONMENTAL FACTOR
System maintenance level Environment contamination level
LOW MEDIUM HIGH
• tank with good protection, effi cient air breathers
• few actuators, with very good protection from contaminant ingression
• frequent monitoring of fi lter conditions
1,0 1,0 1,3
• tank with protection, good air breathers
• many actuators, with good protection from contaminant ingression
• scheduled monitoring of fi lter conditions
1,0 1,5 1,7
• tank with poor protection
• many actuators, with low protection from contaminant ingressions
• random monitoring of fi lter conditions
1,3 2,0 2,3
F. i. system located
in climatized room
F. i. system located
in industrial building
F. i. system located
in hostile environment
(foudry, wood
working machines,
mobile machines)
· 35 ÷ 50 kPa (0,35 ÷ 0,5 bar)
max for pressure fi lters 11 MPa (110 bar)
During the system operation, the pressure drop through the fi lter increases as the element clogs, due to the contaminant retained.
The fi lter element must be replaced when clogged and anyway before the pressure drop reaches the bypass valve set value.
For this reason it is recommended a clogging indicator on the fi lter. It gives a visual or electrical indication and must have
a set value lower than the bypass valve set value, to get an exact indication of the right time for fi lter element replacement.
On return and low pressure fi lters the clogging indicator can be a pressure gauge or a pressure switch, measuring the pressure
upstream the fi lter. On some return fi lters and on high pressure fi lters, the clogging indicator can be of differential type: measuring
the pressure upstream and downstream the fi lter and activating a signal when the differential pressure reaches the set value.
On suction fi lters the clogging indicator is a vacuum gauge or a vacuum switch, measuring the depressure downstream the fi lter.
All the UFI fi lters have the port for the indicator as a standard feature; if the fi lter is ordered without indicator the port is plugged with
a removeable plug allowing the indicator to be added easily at any time.
CLOGGING INDICATOR
