Level Measurement : What is bubbler system ? Advantages and Disadvantages


Bubblers are often used when the application requires that the process not contact the measurement device

Advantages of Bubbler System

Enable the DP transmitter to be a top-down measurement device, which eliminates direct contact with the process
Only one tap is required
Applicable to atmospheric, vacuum, and pressurized vessels
Applicable to tanks containing slurries or corrosive or viscous processes
Measured range is limited only by the available air supply
Can measure density and interface in addition to level
Measurement device can be relocated to any convenient location

Disadvantages of Bubbler systems

Applicable to pressurized tanks, but only up to the pressure of the available air supply
Accuracy depends on the readability of the pressure indicator and a constant, repeatable air supply
Fluid density changes create level measurement errors
Installation cost (labor) is high
May not work well in viscous or sticky process fluids that tend to clog the dip tube
Regular preventative maintenance is required
If air supply fails, the process material can enter the dip tube and damage instrumentation
Exhausted air can pick up volatile materials from the process fluid that should not be released into the environment

to known more about bubbler level measurment


A couple clarifications

  1. Installation cost (labor) is high

I don’t consider the installation cost to be high - the cost of Dip tube piping and the pipe run and the labor to install it is nominal compared to other installation costs. In fact, one reason some industries still use bubblers is that the Dip tube can be easily replaced (low labor cost) with a length of pipe when it gets damaged, plugged or corroded.

The high cost of a bubbler is not installation as much as it is maintenance of the instrument air supply or incurring the costs of not maintaining the quality of the instrument air. When the air quality is not maintained at a low dewpoint (with low entrained moisture) and cleaned/filtered (without oil or particulate) the constant flow (differential relay) regulator will clog up and the bubbler will cease operation.

Years ago, maintenance would clean the constant flow regulator. Nowadays in the US, the regulator is replaced with a new one.

  1. If air supply fails, the process material can enter the dip tube and damage instrumentation

Assuming that the regulator is at grade/ground level, that statement is only true

  • for Dip tubes that enter the vessel from the side or the bottom
  • pressurized vessels using dual dip tubes with differential measurement.

When the Dip tube enters an open vessel from the top it is self draining. There is no applied energy to force the fluid up the dip tube against gravity.

But the hydrostatic head of a column of fluid will force fluid flow ‘backwards’ through a dip tube up to the regulator if the air/gas supply pressure fails or is less than the hydrostatic head when the dip tube enters the vessel from the side or from the bottom.

Likewise the vapor pressure in a pressurized tank will force fluid backwards if the bubbler supply fails to maintain its pressure.

  1. Applicable to atmospheric, vacuum and pressurized vessels

The use of a DP transmitter to reference the vacuum side is theoretically possible, but in 30 years I’ve never seen anyone use a bubbler in a closed vessel at vacuum pressure. Any process that spends money and effort pulling a vacuum is likely to be reluctant to blow air/gas (even at the low rate of 1.5CFH) into a system that’s being evacuated.

  1. Fluid density changes create level measurement errors

Yes. That should be in your list as disadvantage #1. It amazes me that so many people do not understand that hydrostatic pressure level measurement is directly related to the density/Specific Gravity of the fluid. Basic physics.