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

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


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

\(\large{ d }\) = 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.


\(\large{ K_1 }\) = 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

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

\(\large{ D }\) = pipe inside diameter (ID)

Solve for:

\(\large{ K_1  = 0.5  \left( 1 \;-\; \frac{d^2}{D^2} \right)^2   }\)     (inlet expander/reducer)

\(\large{ K_1  = 1.0  \left( 1 \;-\; \frac{d^2}{D^2} \right)^2   }\)     (outlet expander/reducer)

\(\large{ K_1 + K_1  = 1.5  \left( 1 \;-\; \frac{d^2}{D^2} \right)^2   }\)     (for a valve installed between identical expander/reducer)

\(\large{ K_{B1} }\) or \(\large{ K_{B2}  = 1 \;-\; \left( \frac{d}{D} \right)^4   }\)

\(\large{ K_{B1} }\) 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