Pressure Loss

The Pressure Loss calculator estimates the loss in pressure of a pipe or duct based on the friction coefficient, the length of pipe, the hydraulic diameter of the pipe, the flow velocity and the density of the material.

INSTRUCTIONS: Choose units and enter the following:

• (L)  Length of Pipe
• (Q)  Flow Rate of Fluid
• (D)  Hydraulic Diameter (Inner Diameter of Pipe)
• (C)  Friction Coefficient for Pipe Material (see below).

Pressure Loss (P_loss): The pressure is returned in pounds per square inch (psi).  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The pressure loss in pipes and tubes depends on the flow rate, pipe length, hydraulic diameter, and a friction factor based on the roughness of the pipe whether the flow us turbulent or laminar - the Reynolds Number of the flow.  The formula used in this calculator to estimate pressure loss is:

`p_(loss) =4.53 * L * (Q/C)^1.852 / D^4.857`     

where:

•     p_loss = pressure loss (psi)
•     L = length of duct or pipe (ft)
•     D = hydraulic diameter (in)
•     Q = the flow rate of the fluid.
•     C = the coefficient of friction

Coefficient of Friction

The pressure is affected by the inner smoothness of the pipe material.  In general the coefficients are as follows:

• 150 for plastic PVC
• 120 for aluminum with connections or fittings.
• 140 for galvanized pipe
• 100 for cast iron or old steel.