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The FX Leak Detector 3-Step Test
The V-R FX Series LLD is a pressure-sensing, diaphragm-operated valve designed to indicate a leak in the piping
between the leak detector and the dispenser.
When the submerged pump is turned on, a controlled amount of product, 3 gph (11 lph) is metered through the
LLD into the piping system. If a leak is present which equals or exceeds this amount, as much product escapes
from the system as is metered in through the LLD. Under this condition pressure cannot build up in the piping
system. When a nozzle is opened and the LLD poppet is in position one (ref. Figure 7), flow is restricted to
approximately 1-1/2 to 3 gpm (5 - 11 lpm). If the poppet of the LLD is in position two when a nozzle is opened,
flow is restricted to approximately 1-1/2 to 3 gph (5 - 11 lph). This is the indication to the operator that the leak is
present.
If there are no leaks, pressure rapidly builds in the system forcing the LLD to open to the full-flow position. In a
system with no leaks, it takes approximately 2 - 3 seconds for the complete test. No further line testing takes place
until the line pressure drops below 3 to 5 psi (21 - 35 kPa) depending on which LLD is installed.
Figure 7. FX Tester operating positions
1. The Trip or Relaxed Position (Closed)
Under normal operating conditions, it is assumed that the lines are filled with gasoline. When the system pres-
sure is less than 3 to 5 psi (21 - 35 kPa), the diaphragm and poppet are in their ‘down’ or ‘tripped’ position.
the position of the valve ‘poppet’ is such as to allow approximately 1-1/2 to 3 gpm (5 - 11 lpm) flow into the
delivery line through a bypass opening in the LLD valve poppet when the submersible pump starts. Since the
system is full, pressure builds rapidly and the poppet moves to the leak sensing position assuming there is no
leak present.
CLOSED
POSITION 1
OPEN
POSITION 3
METERING
POSITION 2
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