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3 Hydraulic Oil Filters
Electric Solenoid Valve
Spool To Bore Fit
Spool
Cage
Spool
in Cage
Clearance
.4369 / 4371 DIA.
.4375 / 4378 DIA.
.0004 MIN
.0009 MAX
Total
Particulate Contamination
Relative Sizes of Particles
Sizes of Familiar Objects
Substance Micron Inch
Grain of Table Salt
Human Hair
Lower Limit of Visibility
White Blood Cells
Talcum Powder
Red Blood Cells
Bacteria (Average)
100
70
40
25
10
8
2
.0039
.0027
.00158
.001
.00039
.0003
.000078
Spool scored by
contamination
To give an example of some of the clearances in a
hydraulic system, If we look at the spool section of
an electric solenoid valve we can see that we will
have a clearance of .0004 to .0009. These tight
clearances will not accept contamination from the
oil with out experiencing a problem. It is therefore
important that the oil remains clean.
This is a comparison chart of come common
particles and their micron size.
We can see that talcum powder is larger then we
will let through our normal hydraulic filter
Here we see a solenoid valve spool that has been
scored by contamination.
The marks on this spool can not be felt but they
are deep enough to cause problems with this
valve
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