Working with Gases

The Lee Company has developed the Lohm Laws, a simple method of defining and measuring resistance to fluid flow for pneumatic components. Just as the Ohm is used in the electrical industry, we find that we can use a liquid Ohm or “Lohm” as an advantage when performing fluidic computations.

The benefit of using the Lohm Laws is that you can forget about coefficients of discharge and dimensional tolerances on drilled holes. These factors are automatically compensated for in the Lohm calculations and confirmed by our testing of each component to establish flow tolerances. The resistance to flow of any fluid component can be expressed in Lohms.

The Lohm has been selected so that a 100 Lohm restrictor will permit a flow of 250 standard liters per minute of nitrogen at a temperature of 59°F, and an upstream pressure of 90 psia discharging to atmosphere.

Due to the differences in fluid properties between gases and liquids, the equations for calculating the relationship between flow restriction, pressure differential, and flow rate are different.

View the resources below to learn all about Lohm Laws in applications for gas flow:

• How to Calculate Flow Resistance in Pneumatic Systems
  Define and measure resistance to pneumatic flow to ensure the proper flow rate
• Gas Flow Characteristics
  Learn about how the compressibility of gas causes it to have unique flow characteristics when compared to a liquid
• ACFM to SCFM Conversion
  Understand the relationship between actual conditions and standard conditions
• Gas Flow Factor (Multi-Orifice Restrictor)
  Determine how multiple orifices in series will be impacted by the total pressure ratio
• Formulas for Combinations of Flow Restrictors
  Learn how gas Lohm equations apply to restrictions in series and in parallel
• Momentum Forces
  When a flowing stream of gas is subject to a change in velocity, forces arise which are the reaction to the change in momentum of the stream
• Lohm Calculator
  Use the online tool to have Lohm rate, flow rate, or pressure differential easily calculated for you.