Showing posts with label bubbler system. Show all posts
Showing posts with label bubbler system. Show all posts

Wednesday, October 26, 2016

Continuous Liquid Level Measurement Using Bubbler Method

bubbler or downpipe liquid level measurement schematic
Bubbler or Downpipe Liquid Level Measurement Schematic
Courtesy King-Gage
Measuring liquid level in a tank or vessel can be accomplished in a number of ways, all of which require some arrangement of instrumentation to either infer the liquid level through measurement of a related physical property, or directly deliver the liquid level visually using a scaled gauge arrangement. One indirect method of level measurement, referred to as the bubbler or downpipe method, is so named because it employs a purging gas that continually vents from the bottom of a dip tube extending into a tank of liquid. Through a simple apparatus, the level of a liquid can be inferred by the amount a back pressure exerted upon the gas flowing through the tube.

Probably the greatest advantage of this method of liquid level measurement is that the subject liquid does not contact the sensing instrumentation. The only portion of the apparatus in contact with the liquid is a tube immersed into the tank. Selecting the proper material for the immersed tube is left to the user. An additional feature of this method is the entry of the sensing tube from the top of the tank, eliminating the need for a fitting below the liquid level surface.

Basically, a purge gas flows through the immersion tube and may bubble out the immersed end of the tube, which is open to allow the contained liquid to exert a hydrostatic pressure on the purge gas. The back pressure on the gas that is exerted by the liquid contained within the tank will vary directly with the depth of the liquid. The back pressure can be correlated to a liquid level. Further calculations, which would include the tank shape, dimensions, and the liquid density can provide an indication of the volume and mass of the liquid.

It is possible for a user to assemble the components necessary to put a bubbler level indicator into operation, but King-Gage produces a device which consolidates purge control, pressure measurement, level signal transmitter, and necessary connections into a single compact device. There are versions of this level transmitter for electric and pneumatic output signals. They also include an additional level of protection in the form of an internal diaphragm that further isolates the device from the measured medium.

More details, along with some good illustrations, are provided in the document below. Share your process measurement challenges with application specialists, combining your process expertise with their product application knowledge to develop effective solutions.

Wednesday, December 10, 2014

Improving Maintenance and Reliability of Bubbler Systems

According to Wikipedia "an air bubbler system uses a tube with an opening below the surface of the liquid level. A fixed flow of air is passed through the tube. Pressure in the tube is proportional to the depth (and density) of the liquid over the outlet of the tube."

A common problem with many bubbler systems used in water and wastewater systems is long term accuracy and reliability issues. The need for scheduled maintenance is required because of the possibility of  tampering, failed solenoids, changing air flow rates, or clogged downpipes due to crystal formation - particularly in wastewater applications with high entrapped solids.

A better approach is to use a level transmitter for purge control. This solution offers a highly engineered single component that is easily retrofitted to bubbler installations. These purge transmitters automatically maintain an extremely low flow continuous purge (less than 0.02 scfm) regardless of liquid depth, and minimizing formations of crystals in the downpipe. The lag time during dynamic level changes is also eliminated. Furthermore, bubbler operation is tamperproof because there is no external regulator or needle valve (or rotameter) – internally a fixed differential is maintained over a precision flow orifice.

Transmitter purge (or bubbler) technology works reliably in the presence of vapors, and, unlike ultrasonics, can be used in media temperatures of more than 350°F. Bubblers are normally used in applications where foam, solid debris, sewage sludge, or turbulence make ultrasonic, radar, or float switch devices ineffective. The purge transmitter is relative compact in size and allows for installations in tanks where other systems won’t fit.

The purge control transmitters require a compressed air supply (35-150 psig/2.4-10.3 bar) and provide a two-wire 4-20mA output that can be transmitted over substantial distances. The transmitter can be mounted directly outdoors or within small enclosed spaces at the measuring point or up to a hundred feet away.

More information on the purge transmitter may be download here.