Bubbler Level Calculator
A bubbler (purge or dip tube) system measures level from the gas pressure needed to push bubbles out of a tube near the bottom of the tank. Convert back pressure to level, or level to the pressure you should read.
- Head above tube = P ÷ (SG × ρwater × g) = 20,000 Pa ÷ (1 × 1000 × 9.80665) = 2.039 m
- Level = head + tube offset = 2.089 m
Bubbler Level Formula
Gas flows slowly through the dip tube until bubbles escape at its open end. The pressure in the tube then equals the hydrostatic head of liquid above the tube end.
Level = h + tube offset
Worked example
A bubbler in a water tank (SG 1.0) reads 200 mbar = 20,000 Pa. h = 20,000 ÷ 9806.65 = 2.039 m. With the tube end 50 mm above the bottom, the level is 2.089 m.
Frequently Asked Questions
Where are bubbler level systems used?
They suit corrosive, slurry or hot liquids and open sumps or pits because only the dip tube touches the liquid, and the transmitter stays outside the tank.
Does tank pressure affect a bubbler?
In a closed pressurised tank the vapour space pressure adds to the reading. Use a DP transmitter with the LP side connected to the vapour space.
Why is the dip tube offset important?
The bubbler cannot see liquid below the tube end, so that height must be added to the measured head to give level from the tank bottom.
Learn more on the blog
Basics of level measurement
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article