So always confirm that the air is readily
lined up to the control valve through the
air filter.
a.
Ensure that the control valve is
isolated.
b.
Ensure that both the unit
operator and the panel operator
have communication
devices.
c.
Open the valve to the maximum
and close it suddenly, then
reopen it to any position
and confirm the real
opening out onsite. It
is recommended that
the percentages of the
opening can range
from below 0%, 25%,
50%, 75%, 100%, and
above 100%.
d.
Return the valve to a close
position while leaving it in the
isolated status.
When errors are discovered the values
should be recommended for rectification.
The maintenance personnel should
readily check to confirm the faults and
urgently address it. When that is done the
valve should be lined up for operation.
T o B y - pass a C ontrol V alve :
When a valve during operation is to be by-
passed, care must be taken not to disturb
the flow, pressure or whatever parameter
it controls.
Valve by-passing is the diversion of the
floe direction of the process stream away
from the valve.
a.
Inform the panel operator your
readiness to divert the valve
flow to the valve by-pass.
b.
Gradually commission the by-
pass valve (globe) to give a
slight increase in flow.
The flow increase can be noticed
on the side indicator.
c.
Thereafter start to block in the
downstream valve of the control
valve while increasing the
percentage opening of
the by-pass valve so as
to maintain the same flow rate
through the by-passing.
Valves are by-passed when they are faulty
or when more flow than the maximum
flow through the control valve is needed.
This requirement is usually abnormal and
is applied in rare occasions. By-passing
valves are not regular control valves,
therefore as soon as the fault is rectified
or the flow stabilises, the by-pass valves
should be returned to its close position.
Most by-pass valves are globe valves
because they are regulatory in operation.
C onclusion
Good understanding and operation will
go a long way towards prolonging the
service life of the control valve. Team
work and management between the field
operator and panel operator is integral.