Emerson Process Management 99 - Manual (Page 5)

Type 99
5
The monitoring pilot should be upstream of the working
monitor regulator. This enables a closer setpoint
between the working regulator and the monitoring
pilot. Special Types 161AYW and 627-109 monitoring
pilots with quick-bleed operation have been designed
to give faster response to abnormal downstream
conditions. Table 4 gives the spread between normal
distribution pressure and the minimum pressure at
which the working monitor regulator can be set to take
over if the working regulator fails open.
Wide-Open Monitor
The control line of the upstream regulator is
connected downstream of the second regulator
(Figure 5), so that during normal operation the
monitoring regulator is standing wide open with the
reduction to distribution pressure being taken across
the working regulator. Only in case of open failure of
the working regulator does the wide-open monitoring
regulator take control at its slightly higher setting.
The upstream regulator must have an O-ring seal on
the valve carrier assembly. This seals off the leak
path that otherwise would let line pressure ahead of
the working regulator inlet try to close the wide-open
monitoring regulator.
Figure 4. Working Monitor Installation
Figure 5. Typical Wide-Open Monitor Installations
FLEXIBLE aRRangEMEnT THaT PERMITS WIDE-OPEn
MOnITOR TO BE EITHER UPSTREaM OR DOWnSTREaM
FLEXIBLE aRRangEMEnT THaT PERMITS WIDE-OPEn
MOnITOR TO BE EITHER UPSTREaM OR DOWnSTREaM
10A1388-A
A2504
UPSTREaM
REgULaTOR
(REqUIRES O-RIng
STEM SEaL)
OPTIOnaL PILOT
SUPPLy REgULaTOR
10A1386-A
A2503
UPSTREaM
REgULaTOR
(REqUIRES O-RIng
STEM SEaL)
WORKIng
REgULaTOR
OPTIOnaL PILOT
SUPPLy REgULaTOR
20A1389-A
B2484
DISTRIBUTIOn PRESSURE
COnTROL LInE
TyPE 161ayW MOnITORIng
PILOT (aLSO REPRESEnTaTIvE
OF TyPE 627-109)
PILOT SUPPLy LInE
WORKIng
MOnITOR PILOT
InTERMEDIaTE
PRESSURE
InTERMEDIaTE PRESSURE
COnTROL LInE
LOaDIng
PRESSURE
UPSTREaM
PRESSURE
OPTIOnaL
PILOT SUPPLy
REgULaTOR
WORKIng
MOnITOR
REgULaTOR
WORKIng
REgULaTOR
OPTIOnaL
PILOT SUPPLy
REgULaTOR
PILOT SUPPLy PIPIng FOR WORKIng REgULaTOR
WHEn PILOT IS REqUIRED TO BE SUPPLIED FROM
UPSTREaM PRESSURE
DISTRIBUTIOn
PRESSURE