Howl-Mann Equation

Back in 1965, D A Howl and C A Mann published “The back-pressurizing technique of leak-testing”. The technique of leak-testing sealed objects is examined in which the object is first pressurized in a tracer gas and afterwards tested for re-emission of the gas. The technical article establishes an equation which gives the measured leak rate (R1), for a leak showing purely molecular flow, as a function of the leak size (L), internal volume (V), and pressurization parameters.

The “Howl-Mann” equation is now present in Mil-Std-883 TM-1014 and Mil-Std-750 Test Method 1071 documents, and is mainly used to set test parameters and Pass/Fail criteria for Helium Fine Leak Testing.

The interactive form below helps you compute the R1 Pass/Fail criteria based on your leak test parameters. The form also does the reverse computation (i.e. it computes the Total Leak Rate (L) from the Measured Leak rate (R1)).