Jordan Valve Mark 508 Series – Tank Blanketing Valve - Manual (Page 4)

3170 Wasson Road • Cincinnati, OH 45209 USA
Phone 513-533-5600 • Fax 513-871-0105
[email protected] • www.jordanvalve.com
API -2000
Standard Information
Tank Blanketing Regulator Selection
The tank blanketing valve is not a substitute for the
vacuum relief device.
API Standard 2000 states, “The design of a gas
repressuring system to eliminate the requirement for
vacuum relief valves is beyond the scope of this stan-
dard and should be considered only when the induction
of air represents a hazard equal to or greater than failure
of the tank”.
The tank blanketing valve failure must be
taken into account when considering possible
causes of overpressure in a tank.
API Standard 2000 states, “When the possible
causes of overpressure or vacuum in a tank are being
determined, other circumstances resulting from equip-
ment failures and operating errors must be considered
and evaluated by the designer.” Failure of the tank blan-
keting valve can result in unrestricted gas flow into the
tank, reduced gas flow or complete loss of the gas flow.
Tank blanketing valve set point definition is
determined by manufacturers.
Jordan Valve defines
set point as the point where the tank blanketing valve is
just beginning to open, and the valve requires a pres-
sure above the set point in order to close completely.
Others define set point somewhere in between opening
and closing but still the pressure must go above the
defined set point in order to close completely.
CAPACITY REQUIREMENTS
The capacity requirement of the tank blanketing valve
is composed of two components. The first being inbreath-
ing due to liquid or product movement out of the tank, and
the second being inbreathing due to contraction of the
vapors/product because of weather changes.
Inbreathing due to maximum liquid or product
movement out of the tank equals 8.0 SCFH of air for each
US gallon per minute of maximum emptying rate or 0.94
Nm 3 /h of air for each m 3 /h of maximum emptying rate.
Q displacement (SCFH)=Max. Pumpout Rate (gpm)x8.0
or
Q displacement (Nm 3 /h)=Max. Pumpout Rate (m 3 /h)x.94
The second component, inbreathing due to
weather changes, is selected from Table 1 (Table 2
for metric). The tank capacity is found in column 1
and the corresponding inbreathing requirement is
selected from column 2.
The two components are added together to
give the total inbreathing requirement and the capac-
ity requirement of the tank blanketing valve.
Q total = Q displacement = Q thermal
VALVE SELECTION
If the tank blanketing supply pressure varies, use the minimum supply pressure in selecting the tank blanketing
valve and the maximum supply pressure to determine blanketing valve failure capacity. Using the minimum supply
pressure, consult the flow chart to determine if the valve will meet the Total Inbreathing Requirement (Q total). Next
determine if a specific range selection can be used to make the capacity of the tank blanketing valve more closely
match the inbreathing requirement. This will also reduce the fail open flow of the blanketing valve.
NORMAL INSTALLATION
Supply Gas
Isolation Valve
(Full Bore)
Sensing Line
Top of Tank
Tank Blanketing Valve
Tank Isolation Valve
(Full Bore)