**For parallel flow**, the total Lohm rating is:

Please note that this relationship is identical to the electrical equation.

**Example:**

**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:**

When L_{1} = L_{2} = L_{3} , then L_{ T} = L

N = Number of equal resistors in series

For passageway size:

D = Diameter of the actual orifices,each with a Lohm rate = L_{1}

DT = Diameter of a single equivalent orifice, with a Lohm rate = L_{T}

One of the reasons for using two restrictors in series is to allow fine tuning of a total resistance value. If L_{1} is known and is more than 90% of L_{T}, then L_{2} may vary by ±5% without altering the value of L_{T} by more than ±1%, even though the value of L_{2} may be as high as 40% of L_{T} . This effect becomes even more pronounced as L_{1} approaches L_{T} . To determine the intermediate pressure between two resistances in series, the following formulas may be used.