What is the Resistance (K) used in the Gas discharge calculator? The program requires a minimum of K=1

Is it the K-factors for the pipe inlet and discharge?

I am trying to calculate the flow rate of air for 70 feet of 4.026 inch ID pipe with 50 PSIG inlet pressure venting to the atmosphere.

Also. I ran the same case for air in the Air pressure drop calculator and the Gas discharge calculator and got vastly different rates ( ~7200 cfm for Air pressure drop vs. ~1900 cfm for the gas discharge calculator).

I am surprised by the large difference.

I assume that the difference is is adiabatic flow vs isothermal flow or that the Air pressure drop calculations do not account for choked flow (V2 for the Air pressure drop calculator was 1439 ft/sec ~ Mach 2)

Does the Gas pressure drop calculator account for choked flow or does it just warn you when this condition occurs?

Ultimately I am trying to calculate the venting requirements for an atmospheric storage tank from a separator if the water dump valve on the separator fails in a open position.

I am trying to get an understanding of the limitations of the equations used in the calculations.

I would appreciate any help you could give.