At general overhauls on exhaust valves in
Diesel engines running on fuel oil in Cogeneration Plants, the principal
typical anomalies displayed by the valves are as follows:
This is the total
perforation of either one of the valve seats (or of both, i.e., the
cylinder head, or valve basket, and the valve cone). This necessitates the
complete replacement of the valve or the component affected (the valve cone
or the valve basket) or the mechanical rectification of the valve seat of
the cylinder head. It is localised corrosion at one point, and is not
necessarily accompanied by generalised corrosion of the valve seat.
This is generalised corrosion, to greater
or lesser depths, of the valve seats, causing the need to rectify the
surfaces of the seat to a depth proportional to the severity of the
corrosion. This is mainly caused by sodium vanadates produced by
combustion, when the fuel oil is not suitably treated to prevent it. The
greater the depth of corrosion, the greater the depth of valve seat
rectification required, which in turn shortens the operational life of the
valves, because they are able to withstand fewer subsequent rectifications.
This is the failure, due to heat, of the
mechanical resistance of the valve and is detectable by the appearance of
circular cracks on the flat surface of the valve cones, following thousands
of hours in operation. The extent of the fatigue should be evaluated before
deciding on replacement.
This appears in the form of marks and
deformation of the surface of the valve seats and is caused by the great
quantity of solid residues generated by combustion of fuel oil, which can
become trapped in the seats when the valves close. This is remedied by
slight mechanical rectification of the valve seats.
This refers to marks on the metal left by
compacting, when the solid residues are not retained on the seats. This is
similarly remedied by slight mechanical rectification of the seats.
Throughout our many years of activity, the technical department has participated
in numerous engine overhauls, gathering information about all these
anomalies. We must emphasise that the anomaly of "corrosion"
can easily be minimised by treating fuel oil with the additive "rb bertomeu"
beco F1/ASF, whereby at overhauls a superficial rectification
of the valve seats is sufficient (instead of deep rectification) and the
operational life of the valves tends to be prolonged up to the limits
determined by the appearance of "thermal fatigue of the
metal" because the valve is able to withstand a greater
number of rectifications. In our experience, it is possible at least to
double the operational life of the valves if the fuel oil is treated with
the additive "rb bertomeu" beco F1/ASF.
For further information on this subject,
please consult the following documents from rb bertomeu
(click on the chosen title).