Emerson FISHER EZH Series Instruction Manual page 10

Types EZH and EZHSO
Figure 11. Type EZHSO DN 25/50/80 (Spring-to-Open Version) Operational Schematic
Upper diaphragm
Filter
V
Inlet pressure (P )
INLET PRESSURE (Pu)
u
Motorization pressure (P
MOTORIZATION PRESSURE (Pm)
Pilot feeding pressure (P
PILOT FEEDING PRESSURE (Pup)
Outlet pressure (P )
OUTLET PRESSURE (Pd)
d
Atmospheric pressure (P
ATMOSPHERIC PRESSURE (Pb)
Type EZHSO - Spring-to-Open Version
Type EZHSO Single-Pilot Regulator
(Figures 11 and 12)
CAUTION
!
The pilot-operated Type EZHSO (Spring-to-
Open version) will fail in open position in
case of main valve diaphragm failure or lack
of pressure supply to the pilot (see Table 4
for Failure Mode Analysis).
Type EZHSO uses inlet pressure as the operating
medium, which is reduced through pilot operation to load
the actuator diaphragm (lower chamber). Pilot feeding
pressure (P ) is provided to the regulator actuator
up
diaphragm (upper chamber). This pressure opposes the
main spring force that tends to open the regulator and
the motorization pressure (P
pressure (P ) opposes the pilot control spring.
d
10
Type
PRX/120
Type
SA/2
S
B
R
L
A
M
Lower diaphragm
R2
)
m
)
up Type PRX:
S - Bleed port
) B - Supply port
b
). Outlet or downstream
m
Pilot disk
Type EZHSO
Type SA/2:
V - Sensing
L - Motorization port
R - Pilot
A - Sensing port
M - Inlet
PRX Series pilot is supplied with pressure coming from
pre-regulator Type SA/2, which reduces inlet pressure
(P ) to the value of outlet pressure (P
u
3 bar.
When outlet pressure drops below the setting of the
pilot control spring, pilot control spring force on the pilot
diaphragm opens the pilot valve plug, providing additional
motorization pressure (P
This diaphragm motorization pressure opens the main
valve plug, supplying the required flow to the downstream
system. Any excess motorization pressure on the actuator
diaphragm escapes downstream through the bleed
restriction in the pilot.
Regulator
diaphragm
R3
R4
) plus approximately
d
) to the actuator diaphragm.
m