What is the McLeod gauge? working principle, application & uses

The McLeod gauge also known as the McLeod manometer, is a highly precise instrument used to measure low-pressure gas environments. It operates on the principle of Boyle’s Law and offers a wide range of applications in various scientific and industrial fields.

Working Principle:

The McLeod gauge operates by compressing a small, known volume of gas at the unknown pressure to a much smaller, measurable volume. This compression is achieved using a mercury column, and the ratio of the original volume to the compressed volume is used to calculate the unknown pressure.

Here’s a breakdown of the working principle:

  1. Initial Measurement: A small, known volume of gas at the unknown pressure is trapped in a capillary tube.
  2. Compression: Mercury is raised in a reservoir, compressing the trapped gas into a smaller volume within the capillary tube.
  3. Pressure Measurement: The height of the mercury column is measured, which is proportional to the pressure of the compressed gas.
  4. Calculation: Using Boyle’s Law (P₁V₁ = P₂V₂), the unknown pressure can be calculated based on the initial and final volumes and the measured height of the mercury column.


The McLeod gauge finds diverse applications in various fields, including:

  • Vacuum technology: Measuring pressure in vacuum chambers, vacuum pumps, and other vacuum systems.
  • Scientific research: Studying the properties of gases and conducting experiments in low-pressure environments.
  • Electronics industry: Monitoring vacuum conditions for manufacturing processes like thin-film deposition and semiconductor etching.
  • Chemical industry: Studying gas reactions and analyzing the composition of gases in chemical processes.
  • Aerospace engineering: Testing spacecraft components and simulating space environments.

Use and Important Information:

  • The McLeod gauge is known for its high accuracy in measuring low pressures (down to 10^-4 Pa).
  • It is a relatively simple and robust instrument compared to other pressure measurement devices.
  • The use of mercury poses environmental and safety concerns, requiring careful handling and disposal practices.
  • Alternative designs like the oil-filled McLeod gauge are available to address the mercury issue.
  • Maintaining a clean and leak-free apparatus is crucial for accurate readings.

Additional Information:

  • The McLeod gauge was invented by Herbert McLeod in 1874.
  • Several variations of the McLeod gauge exist, each with its own advantages and limitations.
  • Modern digital versions of the McLeod gauge offer improved accuracy and convenience.

In conclusion, the McLeod gauge stands as a valuable tool for measuring low-pressure gas environments across various scientific and industrial applications. Its simple yet effective operating principle, along with its high accuracy and diverse uses, make it a mainstay in the world of vacuum technology.

Leave a Comment