FREQUENTLY ASKED QUESTIONS

Q:  How do bubblers work?

A:  Bubblers, are all hydrostatic measurement devices. This technology is used in vessels (tanks) that operate under atmospheric pressure. A dip tube having its open end near the vessel bottom carries a purge gas (typically air, although an inert gas such as dry nitrogen may be used when there is danger of contamination of or an oxidative reaction with the process fluid) into the tank. As gas flows down to the dip tube’s outlet, the pressure in the tube rises until it overcomes the hydrostatic pressure produced by the liquid level at the outlet. That pressure equals the process fluid’s density multiplied by its depth from the end of the dip tube to the surface and is monitored by a pressure transducer connected to the tube. 

Q:  Where are bubblers used?

A:  Pneumatic air bubbler systems contain no moving parts, making them suitable for measuring the level of water, viscous fluids, liquids with large quantities of suspended solids, slurries, sewage, drainage water and  sludge.  The only part of the sensor that contacts the liquid is a dip tube which is chemically compatible with the material whose level is to be measured. Since the point of measurement has no electrical components, the technique is a  good choice for most fluids and especially good for fluids classified as“Hazardous”.  What makes the bubbler more safe is that the bubbler controls are located outside the tank  in a separate enclosure with only the  pneumatic plumbing running to the tank,  isolating the hazardous from the safe area. 

Air bubbler systems are an excellent choice for open tanks at atmospheric pressure and can be built so that high-pressure air is routed through a bypass valve to dislodge solids that may clog the bubble tube. The technique is inherently “self-cleaning”.  It is highly recommended for liquid level measurement applications where ultrasonic, float or microwave techniques have proved undependable or when tanks are irregularly shaped.  

Q:  How does a pulsed bubbler differ from a continuous flow bubbler?

 A: Both bubblers work off the same hydrostatic principle.  They measure the level of a liquid by measuring the air pressure required to blow air bubbles out of a sense line that is inserted into the tank. 

Continuous flow bubblers generate a constant flow of air in the sense line to make bubbles.  For maximum accuracy the air flow rate must be greater than the fastest rate of anticipated level change.  The pressure reading is then calculated  into a level measurement.  Continuous flow bubblers accuracy is dependent on the integrity of the system. If the sense line gets plugged, the air pressure changes or a leak develops somewhere in the system, a continuous flow system will continue to give you a reading although and it will be in error.

The LC-100 pulsed bubblers function by sending a purge of air into the sense line and into the tank. In normal operations the LC-100 automatically performs a sensor zero check every half hour.  The sense line is automatically purged at regular intervals to keep the line clear before or after the reading. Self diagnostics enable the LC-100 to check the system both pneumatically and electronically, if any problems are found the LC-100 will display the appropriate error message or activate an alarm to alert the operator.  Common problems that can not be determined with a continuous flow bubbler are leaks, plugged lines, high or low air pressures and hardware errors.

Q:  How does the LevelCom LC-100 determine the volume of the liquid it is measuring?

A:   The LevelCom’s microprocessor derives the volume based on the vertical height of the liquid that it measures and the “Tank Capacity Curve” data that the user supplies.

Q:    How does the LevelCom LC-100 determine the weight of the liquid it is measuring?

 A:   The LevelCom’s microprocessor calculates the weight using the derived volume information and the specific gravity of the liquid.  The specific gravity can be a constant value entered by the user, or the LevelCom can automatically determine the specific gravity in real time if it has been configured with a second sense (bubble) line.

 Q:   What type of materials are used for the dip tube inside the tank?

A:   Typically most of our installs use stainless steel tubing inside the tank.  316 series stainless is very common and provides good service life.  Other materials commonly used are copper and some plastics.  Recently we have been evaluating a tubing material called “Tungum” , an alloy of aluminum, nickel and silicon brass.   Tungum is very corrosion resistant and is said to outlast stainless by  4-6 times in marine environments.

Q:   What is a “Tank Capacity Curve”?    

 A:   This is a plot of true vertical height versus volume.  Simple, symmetrically shaped tanks (square, rectangular and cylindrical) have linear capacity curves that are relatively easy to calculate.  Hopper tanks and tanks with irregular shapes and/or intrusions (such as piping running through them) require specific plots of height versus volume, usually supplied by the tank manufacturer, or determined empirically after construction.

Q:    How is a “Sounding Table” different than a “Tank Capacity Curve”?

 A:   A sounding table provides information about the volume of a tank based on sounding depths.  Sounding tubes are almost never straight — they often are routed around piping internal or external to the tank and they are usually terminated in a location convenient for the user.  Nor are they installed perpendicular to the bottom of the tank.  Thus, the sounding depth is rarely equal to the true vertical depth.

Q:  What is the average service life of a LevelCom unit? 

A:  Good question!   We know by our records  that 98% of all levelcoms made since 1994 are still in service today.  

Q:  What are some of the process fluids that the LevelCom’s are used on?

A:  LevelCom’s have been on a wide variety of liquids such as; acids, oils, water, wastewater, runoff, suspensions, foaming liquids, solutions, asphalt, heavy fuel oil and molasses.

Q:  Can LevelCom’s be used in a sealed tank?

A:  Yes!  We can equip LevelCom’s with a Differential Pressure (DP) option.  

Q:  Can the LevelCom be programmed for specific gravity?

A: Yes!  We can equip the LevelCom with a Specific Gravity (SG) option.

Q:  How far away from the tank can you place the LevelCom?

A:  Using 3/8″ diameter sense line, the LevelCom can be placed up to 500 feet away from the tank. 

Q:  Can LevelCom’s be incorporated into a SCADA system?

A:  Yes!  We have many installations where single or multiple LevelComs are configured for process controls, alarms and data gathering.  LevelComs connect via MODBUS protocol to an HMI or Smart Panel.   Profibus and Devicenet options are available.   There are numerous application specific software programs available.