172-654741MA-01 (CV-COS-20/CV-COS-20D) 7 Oct 2021
25
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.
Valve Section
Problem
Cause
Diagnosis
Remedy (Countermeasure)
Valve Leakage The pressure of the air
supply to the actuator
or positioner is too
high
Check the pressure of
the air supply to the
actuator and 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.
Steam Trap Section
Problem
Cause
Diagnosis
Remedy (Countermeasure)
Steam is
blowing
There is a build-up of
dirt on the trap valve
seat or on the float
Check the trap valve
seat and the float
Clean or replace with a new
trap valve seat or float
The body is installed
tilted
Check the installation
conditions
Correct the installation
The float is deformed
Check the float
Replace with a new float
(Inspect for water hammer
or freezing)
There is vibration in
the piping
Check the piping
conditions
Remove the source of the
vibration or reinforce the
piping supports
No condensate
is discharged
The primary pressure
exceeds the trap
valve seat maximum
working pressure
Check the primary
pressure
Decrease the inlet pressure
to the maximum operating
pressure (PMO) or less
Water is inside the
float
Check the float
Replace with a new float
(Investigate to see if the
flow medium contains
corrosive substances)
Output piping is clogged Check the outlet piping Clean or modify the piping
The trap valve seat is
clogged
Check the trap valve
seat
Clean or replace with a new
trap valve seat
