Type Y693
4
Startup and Adjustment
!
WARNING
To avoid personal injury, property
damage or equipment damage caused
by bursting of pressure containing parts
or explosion of accumulated gas, never
adjust the control spring to produce an
outlet pressure higher than the upper
limit of the outlet pressure range or that
particular spring (see Table 1). If the
desired outlet pressure is not within
the range of the control spring, install
a spring of the proper range according
to the Diaphragm and Spring Case Area
section of the maintenance procedure.
With installation completed, the regulator can be
placed in operation by slowly opening the upstream
and downstream block valves, if used, while using
gauges to monitor pressure. The regulator takes
control when downstream pressure is established.
The regulator has been adjusted at the factory
to provide approximately the reduced pressure
requested. To ensure the correct pressure setting
always use a pressure gauge to verify the outlet
pressure setting. The range of allowable pressure
settings is stamped on the spring casing nameplate.
If a pressure setting beyond the stamped range is
required, install a spring with the desired range by
following the procedures for changing the spring and
diaphragm in the Maintenance section. To adjust the
pressure setting, perform the following steps (key
numbers are referenced in Figures 3, 4 and 5):
1. Remove the closing cap (key 3, if required).
2. Turn the adjusting screw (key 2) either clockwise
to increase outlet pressure or counterclockwise to
decrease outlet pressure. The regulator will go into
immediate operation. To ensure correct operation
always use a pressure gauge to monitor the
blanket pressure when making adjustments.
3. Replace the closing cap (key 3, if required).
Shutdown
First, close the nearest upstream shutoff valve and
then, close the nearest downstream shutoff valve and
the block valve on the control line (refer to Figure 2).
Next, open the vent valve between the regulator and
the downstream shutoff valve nearest to it. Then, open
the upstream vent valve and the vent valve in the
control line. All pressure between these shutoff valves
is released through the open vent valves, since a gas
blanketing regulator remains open in response to the
decreasing downstream pressure. If vent valves are not
installed, safely bleed off both inlet and outlet pressures,
and check that the regulator contains no pressure.
Principle of Operation
The Type Y693 Gas Blanketing Regulator reduces a
higher-pressure gas to maintain a positive low pressure
of blanket gas over a stored liquid (see Figure 2). Also
when the vessel (or tank) is suddenly cooled, causing
vapors to contract, the regulator replaces the volume of
contracting vapors with a volume of blanketing gas to
prevent the internal vessel pressure from decreasing. In
both cases, a positive vessel pressure prevents outside
air from entering the vessel and reduces the possibility
of atmospheric pressure collapsing the vessel.
Gas blanketing regulators respond to a slight decrease
in internal vessel pressure (caused by pump out or
atmospheric cooling) by throttling open to increase the
ow rate of gas into the vessel. When the vessel’s liquid
level has been lowered to the desired point and the vapor
pressure reestablished, the regulator throttles closed.
When the liquid level drops and vessel pressure
decreases below the setting of the control spring, the
spring force on the diaphragm opens the disk assembly
to supply the required ow of gas to the vessel. When
vessel pressure has been satised, outlet pressure tends
to increase slightly, acting on the diaphragm. When the
outlet pressure exceeds the control spring setting, the
diaphragm moves to close the disk assembly.
Maintenance
Regulator parts are subject to normal wear and
must be inspected and replaced as necessary. The
frequency of inspection and replacement of parts
depends upon the severity of service conditions
or the requirements of local, state and federal
regulations. Due to the care Emerson™ takes in
meeting all manufacturing requirements (heat treating,
dimensional tolerances, etc.), use only replacement
parts manufactured or furnished by Fisher®.
!
WARNING
To avoid personal injury, property
damage or equipment damage caused by
sudden release of pressure, isolate the
regulator from all pressure and cautiously
release trapped pressure from the
regulator before attempting disassembly.
