BMHR 2016
36 \
World Cement
Level probes should also be inspected for damage,
cleaned and tested.
Pressure relief valves and pressure sensors
Besides ensuring the PRV is clean inside and out, it
should be checked to ensure the seal is not leaking
and that the open/shut mechanism
is in good working order. However,
the most important factor of PRV
maintenance is also the trickiest to
ascertain; namely, if the valve will lift
at the correct pressure as per its design
specification. If it lifts at too low a
pressure the valve will vent product
onto the silo top during fills, risking
blockage. If the valve does not lift
at the recommended pressure then
the build-up of compressed air may
damage the silo, even to the point
of rupturing it. As outlined above,
historically it has not been possible to
pressure-test PRVs in situ.
There is certainly no way of
checking the pressure set point for
either the PRV or pressure sensor
visually and historically they always
would go untested. Hycontrol have
now engineered a solution to this in
the form of specially-designed pressure
and load-test rigs that ensure this
vital safety equipment responds at
the correct set points and meets the
specification required to protect the
silo. It should be noted the set point
of these devices is as low as 40 mbar
or 0.7 psi – so testing without the
correct equipment is almost impossible.
However the latest Silo Protection
Systems include a self-testing facility
for both devices.
Comprehensive testing
It is self-evident that an effective
and comprehensive service should
inspect every key safety element of
the silo from top to bottom. Hycontrol
engineers follow a rigorous 60-point
service checklist when conducting
inspections, allowing them to detail
any issues that are uncovered and
make recommendations for resolving
any issues. This provides site operators
with written proof of the extent to
which a silo has been safety-checked,
should such documentation be called
upon at any time in the future. Indeed,
best practice guidance from the UK’s
MPA states explicitly that: ‘In all cases,
there should be a written maintenance
programme and detailed records should be kept of
such maintenance as it is carried out.’
Certain silo protection systems currently available
have the added benefit of automatically logging
events such as over-pressurisation or PRV lifts. This
information enables competent servicing engineers
A Hycontrol engineer servicing a control panel.
Product covering silotop.
