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

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

Where:

$$\large{ F_p }$$ = 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.

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

$$\large{ d }$$ = 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.