Emerson Fisher EZH Series - Page 9

9
INLET PRESSURE (Pu)
OUTLET PRESSURE (Pd)
MOTORIZATION PRESSURE (Pm)
PILOT FEEDING PRESSURE (Pup)
ATMOSPHERIC PRESSURE (Pb)
V
S
B
L
A
R2
RP IP
IS
R
M
Types EZH and EZHSO
Europe, Middle East and Africa Only
Figure 10. Type EZH-OS2 DN 100/150 (Spring-to-Close Version) Operational Schematic
Inlet pressure (Pu)
Motorization pressure (P
m)
Pilot feeding pressure (P
up)
Outlet pressure (P
d)
Atmospheric pressure (P
b)
Type PRX:
S - Bleed port
B - Supply port
L - Motorization port
A - Sensing port
When the outlet pressure (Pd) drops below the setting of
the pilot control spring, pilot control spring force on the
pilot diaphragm thus opens the pilot valve plug, providing
additional motorization pressure (P
m) to the lower chamber
of the actuator diaphragm. This diaphragm motorization
pressure opens the main valve plug, supplying the required
ow to the downstream system.
Any excess motorization pressure on the actuator
diaphragm escapes downstream through the bleed
restriction in the pilot.
When the gas demand in the downstream system
has been satised, the outlet pressure (P
d) increases.
When outlet pressure (P
d) increases over the setting of
the pilot spring, the pilot valve disk will be closed, reducing
motorization pressure (P
m) to the lower chamber of the
main valve actuator. The pressure in the upper chamber
and the main spring will force the regulator to close.
Type SA/2:
V - Sensing
R - Pilot
M - Inlet
The excess of motorization pressure (Pm) acting on both
the main diaphragm and Type PRX pilot bleeds to the
downstream system through a bleed restriction in the pilot.
For Types EZH DN 100, 150 and 200 a check valve
(Figure 28) is installed between outlet pressure and
motorization pressure impulse lines; this valve is designed
to protect the diaphragm assembly from wrong procedures
during startup, avoiding a too high pressure differential
between outlet and motorization pressure.