Tractorsport Flowbench Forum Archive

Posted: **Sat Mar 20, 2004 11:26 am**

I just came up with a simplified equation to calculate the flow through a sharp edge orifice that pretty closely coincides with the Efunda web site calculator.

This equation assumes an orifice discharge coeffient of .62 (Tony thinks this is a bit low, but it is what I have been using. I have seen a lot of debate over this figure, but .62 is the number I see used most often) and calculates Standard CFM (Air density is assumed to be standard, or .075 lb/ft^3).

Edit: Corrected equation: (Thanks Thomas)
Orifice area in feet*2479.5*SQRT(pressure differential in inches of H2O)

Here is a good link on discharge coeffecients of orifices:

John

Posted: **Sat Mar 20, 2004 11:03 pm**

Posted: **Sun Mar 21, 2004 1:32 am**

Thanks for that Thomas. I corrected the equation above.

For orifice area in square inches:

Orifice area in inches*17.25*SQRT(pressure differential in inches of H2O)

Posted: **Sun Mar 21, 2004 9:42 am**

Ok math wizards out there (simple country boy here), how would I do the math if I knew the CFM's I wanted at a given flow depression but wanted the orifice dia? I can then machine any dia of orifice for standard ranges of flow. Ie if someone wanted 0-100. 0-200, 0-300 cfm's @XX depression etc . . .

Posted: **Sun Mar 21, 2004 11:08 am**

Tractorsport Flowbench Forum Archive

Orifice flow equation