For parallel flow, the total Lohm rating is:
Please note that this relationship is identical to the electrical equation.
Example: Parallel flow
For series flow, the total Lohm rating is:
One of the reasons for using two restrictors in series is to allow fine-tuning of a total resistance value. If L1 is known and is more than 90% of LT, then L2 may vary by ±5% without altering the value of LT by more than ±1%, even though the value of L2 may be as high as 40% of LT. This effect becomes even more pronounced as L1 approaches LT.
To determine the intermediate pressure between two restrictors in series, the following formulas may be used.