172-65742MA-01 (CT20/CT20D) 7 Oct 2021
20
Troubleshooting
When disassembling or removing the product, wait until the internal
pressure equals atmospheric pressure and the surface of the product
has cooled to room temperature. Disassembling or removing the
product when it is hot or under pressure may lead to discharge of fluids,
causing burns, other injuries or damage.
CAUTION
When the valve unit fails to operate properly, use the following table to locate the
cause and remedy. When the actuator and positioner fail to operate properly, refer
to the applicable manual.
Problem
Cause
Diagnosis
Remedy (Countermeasure)
Valve Leakage The pressure of the air
supply to the positioner
is too high
Check the pressure of
the air supply to the
positioner
(confirm product
specifications on the
nameplate)
Adjust the pressure of the
air supply for the positioner
to match the pressure in the
product specifications
Refer to the instruction
manual for the positioner
for zero point adjustment
The positioner’s zero
point is miscalibrated
Check the actuator air
supply pressure (on
the positioner’s
pressure gauge) when
the operation signal is
at zero point
If the pressure on the
pressure gauge is elevated,
adjust the positioner’s zero
point (refer to the instruction
manual for positioner)
The inlet pressure for
the control valve is too
high
Check the inlet
pressure for the control
valve
Decrease the inlet pressure
(Cv value and the spring
range must be changed)
The valve plug and
valve seat are off-
center
Move the valve plug &
stem up and down and
check to see if it
catches
Reassemble the valve
bonnet section correctly
Wear of the sealing
surfaces of the valve
plug and valve seat
Check the valve plug
and valve seat
Replace the valve plug and
valve seat.
Consider replacing with a
valve plug and valve seat of
a more durable material.
