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Table 8. Fluid Sensing Level Options

Pivoting Float

A float is located on the end of a rod that pivots

Float on Rail

at the opening of the tank. A linkage or cable is then used to transmit float position to through the riser to the surface. Use of a float that can move along a non linear path, such as along a rail.

Method

Description

Unpowered Fiber Optics

Uses fiber optic lines at discrete points to detect liquid level. Would require operator at surface to provide light source to lines.

Powered Fiber Optics

Use fiber optic lines at discrete points to detect liquid level. Light applied automatically and results interpreted electronically.

Pressure Sensors

One pressure gauge reads the pressure of the vapor space. A second pressure sensor is submerged at the bottom of the tank. Uses the difference in pressure to calculate fluid height.

Guided Wire Radar

A cable is fed through riser into the tank. Microwaves are transmitted down the cable and used to detect the liquid level.

Laser

A laser is transmitted down the riser and into the tank. The reflection of the beam is used to detect the liquid level.

Advantages

Common method level measurement Reduced cost Provides continuous liquid level Does not require electrical power Reduced cost Provides continuous liquid level Does not require electrical power

Potential for reduced cost due to simplicity of design Does not require electrical power Could be uninstalled/ removed from the surface without unearthing the tank. Potential to be installed/ removed from the surface without unearthing the tank.

Potential to be installed/ removed from the surface without unearthing the tank Provides continuous liquid level Hardware may be available off-the-shelf

Potential to be installed/ removed from the surface without unearthing the tank Provides continuous liquid level Method has been used for measuring Propane Off-the-shelf hardware is available.

Laser could be installed from the surface Provides continuous liquid level Method has been used for measuring liquid levels.

Alternative Underground Propane Tank Materials, Phase II—Final Report

14

Disadvantages

No off-the-shelf options available Installation/Removal would require removal of the riser

Horizontal section through the vessel opening could cause the float to bind up Rail installation through the vessel and riser would be difficult

No off-the-shelf options available Not a technology currently used by sensor manufacturers Only provides levels at discrete points

Off-the-shelf options available, but are not intended to be submerged Requires a power source Only provides levels at discrete points.

Many off-the-shelf options available may be too large to install through riser/vessel openings Requires a power source The hydrostatic pressure from the propane is not very significant, which may result in poor accuracy.

Wire would make contact with riser walls and return false signals Off-the-shelf hardware is expensive Requires a power source.

Would require prisms to navigate beam through riser Requires a power source.

September 2009 Battelle and Lincoln Composites

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