POSSIBLE Causes of, “Positive Rate Increases”

1. Incorrect temperature coefficient entered during setup.

Verify that the temperature coefficient of thermal
Expansion is set correctly according to the TLS Setup Manual specifications listing for various product grades.

2. Manifold Tank Siphon Bar Leakage

Rate increases can occur in siphon manifold tanks due to a leaking siphon system. Since the siphon piping
is normally full of fuel this can become a source of rate increases. If the siphon does not hold, product will drain
Back slowly into the tanks during idle periods. The fuel from the siphon piping will increase the volume in the
Tank which will cause a CSLD rate increase warning. Test and repair the siphon system per the manufacturers
Recommendations.

3.    Leaks In Submersible Pumps

Around the packer O-ring.
At the threads of the two-inch pipe coming from the turbine motor.
The gasket between the turbine motor and mounting flange.
At any seal which would allow the column of fuel being held in the pump by the check valve to leak back slowly
Into the tank.

4.    Manifold tanks are programmed incorrectly in In-Tank setup.

Tanks in a manifold set must be programmed as a set, and you must select CSLD as the Leak Test Frequency
For each of the tanks.

5.    Defective Line Check Valves

Fluid from the line piping leaking back into the tank through a defective Line Check Valve may cause a rate increase.
Verify that the line piping holds pressure after pumping stops.

6.    Thermal Expansion In The Lines

When the product temperature in the tank is lower than the ground temperature, product in the line will expand
after dispensing. After pumping ceases the line check valve or pump check valve will maintain pressure in the
line. As the ground warms the product in the line expands. This expansion causes a corresponding pressure increase
in the line therefore the pressure relief valve opens. The relief valve, relieves this increased pressure by
allowing fuel to flow back into the tank. The flow from the line back into the tank can be a source of rate increase
warnings. Typically thermal expansion’s impact on CSLD is short lived. However, in extreme cases thermal
expansion can be a source of CSLD rate increase warnings. If thermal expansion is suspected as the
source of CSLD rate increase warnings you should inspect the site layout to determine if it is susceptible to
extreme thermal expansion due to site specific conditions (i.e. shallow line depth combined with extreme temperatures,
etc.).

7.    Stage II Vapor Recovery System Related Problems

Condensed vapors and liquid drawn into the vapor recovery system can leak back into the tank causing increases.
Check with the manufacturer of the vapor recovery system about possible solutions such as the addition of a
vapor pot to collect these condensed vapors.
Have the Stage II vapor recovery system inspected and tested.
Verify that liquid product in the vapor lines cannot drain directly back into the tank. A liquid trap can be installed.
The product that collects in the trap can be siphoned back to the tank via the pump siphon system.
This will prevent the introduction of liquid into the tank during idle periods.

8.    Water Leaking into the Tank

Water can leak into the tank and cause rate increase warnings.
Check the water level in the tank.
Monitor the tank for increasing water levels.
Check the alarm history for prior water level alarms.


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