(revised 11/29/01 to correct CO2 units factor)
(Revised 7 Mar 06 changed default downstream pressure to 14.7)
(Revised 7 Jan 10 changed from input Lohms to input Dia.  Original from www.theleeco.com)

For gas flow through an orifice the Lohms Laws are:

Sonic Flow -- P1/P2 > 1.9 Sub-Sonic Flow -- P1/P2 < 1.9
Sonic flow formula Sub-sonic flow formula
Important Nomenclature:

K = Gas Units Constant
fT = Temprature Correction Factor
P1 = Upstream absolute pressure
 
P2 = Downstream Absolute pressure
Q = Gas flow
DeltaP = P1 -P2




Step 1: Enter temprature of Gas:
degrees F
C

Temp Correction factor:
 Step 2:

Select a Gas:
Air
Argon
CO
CO2
Ethane
Freon-12
He
 		H2
N2
N2O
Nat. Gas
Neon
O2
SO2
Step 3:

Select a Pressure Unit:
Psia
Bar
kPa
kg/(sq. cm)
ft H2O
mmHg
 Step 4:

Select a Flow Unit:
Standard Liters per Minute
Standard milliLiters per Minute
Standard cu. Meter per Minute
Standard cu. inches per Minute
Standard cu. feet per Minute
Automatically calculated from the gas and unit information entered, the units factor (K) is

Step 5:

Enter data into the input area of one of the scenarios below, and click the calculate button in that box. Results will appear in the answer area.

A. If you know the pressure and flow and need to find Lohms:

Inputs:

Upstream:
Downstream:
Flowrate:

Answer:

 
Lohms =
Dia[in] =

B. If you know pressure and Lohms and need to find flow:

Inputs:

Upstream:
Downstream:
Dia[in]:  

Answer:

 
Lohms =
Flowrate =
 

C. If you know Lohms and Flow and need to find Upstream pressure:

Inputs:

Dia[in]:  
Downstream:
Flowrate:

Answer:

 
Lohms =
Upstream =
 




Always verify flow calculations by experiment. The Lee Company expects the users of this calculator to be responsible for proper design and fabrication of their systems.