6
4. Precautions for the Installation of Additional Fittings Before or After the PN-DR
In order to ensure a stable flow of air or steam, the piping upstream and
downstream of the reducing valve must be straight runs. If a pressure reducing
valve is installed either directly before or after an elbow or control valve,
unevenness in flow may result in chattering and unstable pressure.
To ensure a stable flow, it is recommended that the pressure reducing valve be
installed on straight runs of piping, as illustrated below.
172-65119MA-01 (PN-DR) 13 Jun 2013
Inlet (primary side) of the pressure reducing valve
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)
Pressure
Reducing
Valve
10 d or more
Valve, strainer,
elbow, etc.
Pressure
Reducing
Valve
10 d or more
Valve, strainer,
elbow, etc.
Pressure
Reducing
Valve
Less than
10 d
Valve, strainer,
elbow, etc.
Pressure
Reducing
Valve
Less than
10 d
Valve, strainer,
elbow, etc.
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)
Automatic
Valve
Pressure
Reducing
Valve
30 d or more
Automatic
Valve
Pressure
Reducing
Valve
30 d or more
Automatic
Valve
Pressure
Reducing
Valve
Less than
30 d
Automatic
Valve
Pressure
Reducing
Valve
Less than
30 d
Outlet (secondary side) of the pressure reducing valve
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)
Pressure
Reducing
Valve
Valve, strainer,
elbow, etc.
15 d or more
Pressure
Reducing
Valve
Valve, strainer,
elbow, etc.
15 d or more
Pressure
Reducing
Valve
Valve, strainer,
elbow, etc.
Less than
15 d
Pressure
Reducing
Valve
Valve, strainer,
elbow, etc.
Less than
15 d
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)
Pressure
Reducing
Valve
Safety Valve
30 d or more
Pressure
Reducing
Valve
Safety Valve
30 d or more
Less than
30 d
Pressure
Reducing
Valve
Safety Valve
Less than
30 d
Pressure
Reducing
Valve
Safety Valve
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)
Pressure
Reducing
Valve
Pressure
Reducing
Valve
30 d or more
Pressure
Reducing
Valve
Pressure
Reducing
Valve
30 d or more
Pressure
Reducing
Valve
Pressure
Reducing
Valve
Less than
30 d
Pressure
Reducing
Valve
Pressure
Reducing
Valve
Less than
30 d
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