Piping Geometry Factor

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Piping geometry factor, abbreviated as \(F_p\), a dimensionless number, is the pressure and velocity changes caused by fittings such as bends, expanders, reducers, tees, and Y's if directly conected to the valve.  

 

Piping Geometry Factor Formula

\(\large{ F_p = \frac{1}{  \sqrt{1\;+\;\frac{\Sigma K}{0.00214} \; \left( \frac{C_v}{D_v^2}   \right)^2   }   }   }\)   

Where:

\(\large{ F_p }\) = piping geometry factor

\(\large{ D_v  }\) = nominal valve size

\(\large{ C_v }\) = flow coefficient

\(\large{ \Sigma K }\) = algebraic sum

Solve for:

\(\large{ \Sigma K = K_1 + K_2 + K_{B1} + K_{B2}   }\)   
 \(\large{ \Sigma K }\) (is the algebraic sum of the velocity head loss coefficient for all the fittings that are attached to the valve)

Where:

\(\large{ K_1 }\) = resistance coefficient of upstream fittings

\(\large{ K_2 }\) = resistance coefficient of downstream fittings

\(\large{ K_{B1} }\) = inlet Bernoulli coefficient

\(\large{ K_{B2} }\) = outlet Bernoulli coefficient

\(\large{ D_v }\) = nominal valve size

\(\large{ d }\) = pipe inside diameter

Solve for:

\(\large{ K_1  = 0.5 ;\ \left( 1 - \frac{D_v^2}{d^2} \right)^2   }\)  (inlet expander / reducer) 
\(\large{ K_1  = 1.0 \; \left( 1 - \frac{D_v^2}{d^2} \right)^2   }\)  (outlet expander / reducer) 
\(\large{ K_1 + K_1  = 1.5 \; \left( 1 - \frac{D_v^2}{d^2} \right)^2   }\) (for a valve installed between identical expander / reducer) 
\(\large{ K_{B1} }\) or \(\large{ K_{B2}  = 1 - \left( \frac{D_v}{d} \right)^4   }\)  
\(\large{ K_{B1} }\) or \(\large{ K_{B2} }\) (are only used when the diameter of the piping approaching the valve is different from the diameter of the piping leaving the valve)

Tags: Equations for Pressure Equations for Valves