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Mechanical Leak Detector Problems Associated with Manifolded Piping
The following addresses problems typically associated with
piping systems that consist of single wall piping, multiple turbines manifolded
together, and the use of mechanical line leak detectors.
Manifolded piping systems present unique problems that
affect mechanical line leak detection. These
problems are associated with the ability of the mechanical leak detector or leak
detectors to detect a 3 gallon per hour leak rate as per EPA guidelines. The attached drawing illustrates three configurations of
single wall piping systems and how mechanical leak detectors are often used. Configuration # 1 Two Pumps / Two Leak Detectors This configuration illustrates two tanks, each with one
turbine. Each turbine has one leak
detector, piping is tee’d together to a single line. Problem: Each
leak detector, when in the leak search position, allows 3 gallons per hour to
pass to line. If both pumps come on
at the same time, each leak detector will be testing for a leak at the same
time. This results in 6 gallons per
hour line leak detection, not 3 GPH as per EPA guidelines. One proposed solution is to delay one of the pumps long
enough for the primary pump / leak detector to search for a leak and then
activate the second pump. This solution has a similar 6 GPH problem.
Even though one turbine starts and performs line leak detection, the
second turbine is not prevented from coming on if the leak detector in turbine #
1 detects a leak. If pump # 2 does
start when there is a leak in the line, the combined volume passed by both leak
detectors is 6 GPH, exceeding the 3 GPH threshold. Configuration # 2 Two Pumps / One Leak Detector This configuration illustrates a two turbine installation
with one turbine/ leak detector and one turbine/ check valve. Problem: The
installation of a leak detector in the pump that is activated first (pump # 1)
and the installation of a check valve at the discharge of pump # 2 results in
virtually no leak detection. Unless
pump # 2 is prevented from turning on when the leak detector in pump # 1 is in
slow flow, no leak detection occurs. This
cannot be achieved without additional sensing and control equipment. Configuration # 3 Two Pumps / One Leak Detector - At Tee Manifold This illustration shows two turbines piped to a tee
connection where the leak detector is installed and a single pipe continues to
the dispensing area. Problem: Without
double wall piping and sump containment, any leak between the pumps and the leak
detector will go undetected. This configuration is acceptable only if both turbines and
the leak detector are in the same sump, or if double wall piping, sump
containment, and sensors are used up to the discharge of the leak detector.
Additionally, in this configuration the leak detection
equipment needs to be sized to handle the flow capacity of both turbines
combined.
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Last modified: November 15, 2008 Vaporless Manufacturing, Inc. 8700 E. Long Mesa Drive Prescott Valley, Arizona 86314 E-mail: vmi@vaporless.com 1-800-367-0185 Fax (928) 775-5309 |
