Nature Of Solid Pollutants; Types Of Particles; Coarse Pollution - Etesia HYDRO 124D Technical Training Manual

NATURE OF SOLID POLLUTANTS

The main pollutants found on examining hydraulic fluids are :
- silica (sand...)
- metallic material
- residue of plastics, fabrics and fibres of all kinds.
In general silica comes from outside the circuit inside (equipment operating out of doors),
unless it is original pollution due to sandblasting, which is definitely not recommended in
hydraulics.
"Mat" metallic material i.e. corroded material, often represents external pollution, whilst shiny
particles usually come from wear on the inside of the circuit.
Residue of plastics, or similar, such as pieces of seals, plugs, rags, sealer tape (Teflon) etc.
are almost always original pollution from when the equipment was made.
This type of pollution can also come from various topping up and oil change operations carried
out in inadequate conditions.

TYPES OF PARTICLES.

a) Coarse pollution
This corresponds to particles whose size is above 15 µm
(15µ µ µ µ m =15 millionths of a metre = 0.000015 m = 0.015 mm).
The value of 15 µm represents the average value of the clearance found in industrial
hydraulics. When taking into account the effects of coarse pollution this value should be
lowered for the small calibres. For example, a control valve slide 10mm in diameter is mounted
with a clearance of about 8 µm.
The consequences of coarse pollution are as follows :
Coarse
pollution
45 -
Seizure Instant
phenomenon
Equipment High
stops financial
cost
-