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For parallel flow, the total Lohm rating is:
Please note that this relationship is identical to the electrical equation.
Example 1: Parallel flow
L1 = 2000 Lohms
L2 = 3000 Lohms
L3 = 5000 Lohms
and therefore LT = 970 Lohms
For series flow, the total Lohm rating is:
Please note that this relationship is not the same as in electrical problems. The difference is due to the non-linearity of:
Example 2: Series flow
When L1 = L2 = L3, then LT = L √N
N = Number of equal resistors in series
For passageway size, DT = D/N1/4
DT = Diameter of a single equivalent orifice, with a Lohm rate = LT
D = Diameter of the actual orifices, each with a Lohm rate = L1
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.
Always verify flow calculations by experiment.
*There are many parameters to consider when determining V-Factor. Click here for more information.
