Type 399A-161-112
16
and speed of response. The restrictor can be used to
fine tune the regulator for maximum performance by
decreasing the restrictor setting for tighter control (in-
creased opening speed and decreased closing speed);
or increasing the restrictor setting for maximum stabil-
ity (decreased opening speed and increased closing
speed). A lower setting also provides a narrower pro-
portional band for better accuracy. The START posi-
tion has the largest flow passage and should be used
during startup and shutdown. The ‘‘0’’ setting has the
smallest (minimum) flow passage; at no point of rota-
tion will the Type 112 restrictor be completely shut off.
Shutdown for Both Single-Regulator and
Monitoring Installations
CAUTION
If pilot supply pressure is shut down first,
the downstream system may be sub-
jected to full inlet pressure.
1. If the pilot setting must be disturbed, be sure to
keep some spring setting in the pilot. This will prevent
trapping inlet pressure during blow down.
2. Close the valves shown in figure 3, in the follow-
ing order: (1) inlet block valve A, (2) outlet block valve
B, and if used (3) control line valve(s) E.
3. Open the vent valves from downstream to up-
stream in the following order: (1) C1, (2) C2, (3) C3,
and, if used, (4) vent valve(s) F.
PrinciplePrinciple ofof OperationOperation
As long as the outlet (control) pressure is above the
pressure setting, the the pilot valve plug remains
closed (figure 5). Inlet pressure bleeding through the
Type 112 restrictor provides loading pressure to keep
the Type 399A diaphragm tightly shut off.
When the outlet pressure decreases below the pilot
control spring setting, the pilot valve plug opens. Load-
ing pressure bleeds downstream through the pilot fast-
er than it can be replaced through the Type 112 re-
strictor. This reduces loading pressure on top of the
Type 399A diaphragm and lets the inlet pressure un-
balance open the Type 399A diaphragm from the bot-
tom.
As the outlet pressure rises toward the pressure set-
ting, it compresses the pilot diaphragm against the
pilot control spring and lets the pilot valve plug close.
Loading pressure again builds up to close the Type
399A diaphragm. The diaphragm support moves with
the diaphragm to provide motion indication and to sup-
port the diaphragm when open.
The motion indicator can be used to determine the
position of the diaphragm support when inspecting the
regulator, but the motion indicator cannot be used to
estimate flow. The diaphragm is free to flex a small
amount and allow initial flow before it contacts the dia-
phragm support and moves the indicator assembly.
Also, the diaphragm has some additional travel avail-
able after the indicator assembly and diaphragm sup-
port have traveled fully.
A downstream wide-open monitoring system (figure 3)
reduces pressure and throttles while the upstream
working regulator is in operation. Due to the Type
399A regulator flow-to-open design, the downstream
monitoring regulator opens only far enough to pass the
required flow and changes position with each flow rate
change. The upstream working regulator automatically
supplies the correct intermediate pressure required to
keep the downstream monitoring regulator open to the
correct position. This arrangement offers continual
movement of the diaphragm in the downstream moni-
toring regulator and allows it to take control at any
time.
The working monitor regulator is always upstream and
acts as a first-stage regulator by using the working
pilot during normal operation. This arrangement allows
the working monitor’s performance to be observed at
all times. Then, should the downstream seconds-stage
regulator fail-open, the upstream working monitor reg-
ulator assumes the entire pressure reduction function
of the system through the monitoring pilot taking con-
trol of the downstream pressure.
MaintenanceMaintenance
Regulator parts are subject to normal wear and must
be inspected periodically and replaced as necessary.
Due to the care Fisher takes in meeting all manufac-
turing requirements (heat treating, dimensional toler-
ances, etc.), use only replacement parts manufactured
or furnished by Fisher.
The frequency of inspection and replacement depends
upon the severity of service conditions and upon appli-
cable codes and government regulations. Table 9 lists
various regulator problems and possible solutions for
them.
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