The Engineering Reference Section of the IMH website is a handy compilation of facts that every hydraulics engineer can use. It starts with a comprehensive discussion of Lohm Laws which make every hydraulic and pneumatic calculation easy. It includes formulas for comparing the effectiveness of different mesh size safety screens called ROB numbers, and finally, extensive reference material including standards, conversion factors, graphic symbols and definitions.
Every engineer will be interested in our simple system of defining the fluid resistance of Lee hydraulic components.
Just as the OHM is used in the electrical industry, we find that we can use a liquid OHM or “Lohm" to good advantage on all hydraulic computations.
When using the Lohm system, 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 testing 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 1 Lohm restriction will permit a flow of 100 gallons per minute of water with a pressure drop of 25 psi at a temperature of 80° F.
The graph here relates Lohms to hole diameter in inches and millimeters.
The Lee Company offers a specially designed Hydraulic and Pneumatic Flow Calculator to help in the transition to the Lohm System. This handy, free slide rule can be used to solve basic Lohm calculations.