172-65175MA-13 (COS Pressure Reducing Valve) 16 Feb 2022
6
4. Precautions for the Installation of Additional Fittings Before or After the Reducing
Valve
In order to ensure stable steam flow, the piping upstream and downstream of the
COS must be straight runs. If a COS is installed either directly before or after an
elbow or control valve, unevenness in steam flow may result in chattering and
unstable pressure.
To ensure stable steam flow, it is recommended that the COS be installed on
straight runs of piping, as illustrated below.
1) Inlet (primary side) of the COS
NOTE: d = pipe diameter
Maintain a straight piping run of
10 d or more
when a manual
valve, a strainer or an elbow, etc. is
installed.
(Example: if nominal size is 25 mm
(1 in), have 250 mm (10 in) or more)
Maintain a straight piping run of
30 d or more
when an automated
valve (on-off valve) is installed.
(Example: if nominal size is 25
mm (1 in), have 750 mm (30 in)
or more)
Maintain a straight piping run of
30 d or more
when another
pressure reducing valve is
installed. (Two-stage pressure
reduction)
(Example: if nominal size is 25
mm (1 in), have 750 mm (30 in)
or more)
2) Outlet (secondary side) of the COS
Maintain a straight piping run of
15 d or more
when a manual
valve, a strainer or an elbow,
etc. is installed.
(Example: if nominal size is 25
mm (1 in), have 375 mm (15
in) or more)
Maintain a straight piping run of
30 d or more
when a safety
valve is installed.
(Example: if nominal size is 25
mm (1 in), have 750 mm (30
in) or more)
Maintain a straight piping run of
30 d or more
when a control
valve or an automated valve
(on-off valve) is installed.
(Example: if nominal size is 25
mm (1 in), have 750 mm (30
in) or more)
COS
10d or more
Valve, strainer,
elbow, etc.
COS
Valve, strainer,
elbow, etc.
Less
than
10d
COS
30d or more
Automated
Valve
COS
Automated
Valve
Less than
30d
30d or more
COS
Less than
30d
COS
COS
15d or more
Valve, strainer,
elbow, etc.
COS
Valve, strainer,
elbow, etc.
Less than
15d
COS
30d or more
Safety
Valve
COS
Safety
Valve
Less than
30d
COS
30d or more
Control or
Automated
Valve
COS
Control or
Automated Valve
Less than
30d