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Issue
Date: April 18, 1997
Revision Date: August 23, 1999
Universal
Sensors and Devices, Inc.
LTC-2000
(Differential Pressure Probe)
BULK
UNDERGROUND STORAGE TANK LEAK DETECTION METHOD (50,000 gallons
or greater)
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Certification
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Leak
rate is proportional to product surface area (PSA).
For tanks with PSA of 14,244 ft², leak rate is 3.0 gph
with PD = 98.8% and PFA = 1.2%.
For other tank sizes, leak rate equals [(PSA in ft² ÷
14,244 ft²) x 3.0 gph].
Example:
For a tank with PSA = 20,000 ft²; leak rate = [(20,000
ft² ÷ 14,244 ft²) x 3.0 gph] = 4.2 gph.
Calculated minimum detectable leak rate is 2.15 gph with
PD = 95% and PFA = 5%.
Leak rate may not be scaled below 0.2 gph.
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Leak
Threshold
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Leak
threshold is proportional to product surface area (PSA).
For tanks with PSA of 14,244 ft², leak threshold is 0.7
gph.
For other tank sizes, leak threshold equals [(PSA in ft²
÷ 14,244 ft²) x 1.5 gph].
Example:
For a tank with PSA = 20,000 ft², leak threshold = [(20,000
ft² ÷ 14,244 ft²) x 1.5 gph] = 2.1 gph.
A tank system should not be declared tight if the test
result indicates a loss or gain that equals or exceeds
the calculated leak threshold.
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Applicability
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Gasoline,
diesel, aviation fuel, fuel oil #4.
Other liquids may be tested after consultation with the
manufacturer.
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Tank
Capacity
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Use
limited to single field-constructed vertical tanks larger
than 50,000 gallons.
Maximum product surface area (PSA) is 35,610 ft² (approximately
213 ft diameter).
Performance not sensitive to product level.
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Waiting
Time
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Minimum
of 3 hours, 30 minutes after delivery.
Valve leaks and pump drain-back may mask a leak.
Allow sufficient waiting time to minimize these effects.
None between dispensing and testing.
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Test
Period
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Minimum
of 48 hours, 18 minutes.
There must be no dispensing or delivery during test.
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Temperature
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Measurement
not required by this system.
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Water
Sensor
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None.
Water leaks are measured as increase in mass inside tank.
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Calibration
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Probe
must be checked and, if necessary, calibrated in accordance
with manufacturer's instructions.
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Comments
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Tests
only portion of tank containing product.
As product level is lowered, leak rate in a leaking tank
decreases (due to lower head pressure).
Consistent testing at low levels could allow a leak to
remain undetected. Evaluated in a nominal 2,000,000 gallon,
vertical underground tank with product surface area (PSA)
of 14,244 ft².
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Universal
Sensors and Devices, Inc.
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Evaluator: Ken Wilcox Associates
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9205
Alabama Ave.
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Tel: (816) 443-2494
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Chatsworth,
CA
91311
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Date
of Evaluation:
05/17/96
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Tel: (800) 899-7121, (818) 988-7121
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