Dirt can bond to the surface of an object in three
1. Electrostatic attraction:
If a surface is electrically charged with the reverse
polarity of the charge of the dirt, a bond occurs as a
result of the inherent attractive forces.
2. Chemical reaction:
A chemical reaction changes the composition of the
surface which causes it to look dirty.
3. Structural interlocking:
Dirt gets caught and trapped in rough surfaces.
How are the principles of dirt adhesion applied to the cleaning process?
The objective of cleaning is to destroy the bond between the
dirt and the surface. High pressure cleaning utilises
mechanical, thermal and chemical energy to achieve this.
There are four primary variables which affect the performance
of a high pressure cleaner: flow rate, pump pressure,
spraying distance and spraying angle.
Impact force, or the penetrating force of the water jet in
relation to the unit of surface area to be cleaned, is most
important. This is dependent on
Spraying distance: A distance of 10 to 30 cm is
recommended, as the pressure curve drops quickly at
Spraying angle: This angle should be selected
according to the degree of soiling. Stubborn dirt
requires an angle of 0 - 25°, medium soiling 25 - 50° and
light soiling an angle of 50 - 80°.
Nozzle pressure: As a function of water flow rate
and the cross section of the nozzle, only a
disproportionate increase of nozzle pressure can generate
greater impact force.
Water flow rate: A quick increase of impact force
is achieved by increasing the quantity of water. This
also makes it easier to remove dirt, as there is minimal
atomisation even at greater distances.
Chemical processes are accelerated when heat is applied,
which means grease and oil can be dissolved more quickly.
Since this also warms up the object being cleaned, drying
time is also reduced. This leads to better results, and the
cleaning time is reduced by as much as 40 %. However, there
is a corresponding drop in temperature as the spraying
distance is increased.
If an increase in impact force or temperature does not
produce satisfactory results, the use of chemical cleaning
agents will be necessary. This has a positive effect on
wetting power, emulsification and direct chemical reactions
with particles of dirt.
The suitability of a cleaning agent is determined by pH and
the surface being cleaned. Acidic agents with a pH of 0 - 6
are used for calcium deposits, urine deposits, rust and other
oxides, and alkaline agents with a pH of 8.5 to 14 are used
for oils, greases, tar and soot. Neutral cleaning solutions
are the right choice for sensitive surfaces which are
contaminated with small amounts of oil or grease. Extremely
acidic or alkaline levels can, however, result in damage to
the high pressure cleaner and the object to be cleaned
itself, and may even violate water protection laws. The
prolonged application of chemical cleaning agents can also
cause damage. Increasing the duration of the application time
is generally only effective up to certain point, as cleaning
intensity approaches a threshold with the progression of
time. Pre-soaking coarse layers of dirt with water can have a
positive effect on cleaning time, as this can reduce the
amount of cleaning time required with the high pressure
cleaner by as much as 50 %.
Information about pressure specifications in MPa (mega
As a result of the migration to safety testing standard IEC
60335/2/79, pressure values will no longer be specified in
"bar", but rather in "MPa". This how to convert the values:
10 bar = 1 MPa.