Pipe Fittings Loss Calculations with K Factors
Pipe fittings, valves and bends usually have some associated K factor or local loss coefficient, which allows the calculation of the pressure loss through the fitting for a particular fluid flowing at a specified velocity. Manufacturers of pipe work fittings and valves often publish a fitting's associated 'K' factor.Pipe Fitting Loss Formula
Fluid head loss through a fitting can be calculated by the following equation:
h = K x v² / 2g
where
h = pressure loss in terms of fluid head, i.e. fluid head loss
K = manufacturer's published 'K' factor for the fitting
v = velocity of fluid
g = acceleration due to gravity
Where the length of the pipe is relatively long, the effect of the fitting losses are usually considered as minor losses, and are often ignored during initial analysis of the pipe system.
If the piping design contains a partially open valve then the effect and head loss through the valve should always be included since the valve head loss may turn out to be significant.
Pipe Fittings and K factors database
Our Pipe Flow Expert software has a database that contains the K factors for many different types of valves and fittings. It also has special wizard helpers that can calculate the K factor for special types of fittings such as:
- gradual enlargements
- gradual contractions
- sudden enlargements
- sudden contractions
- rounded entrances
- long pipe bends
Addition information about losses through pipe fittings is published in 'Flow of Fluids through valves, fittings and pipe' - Crane Technical Paper No. 410.
Equivalent Length of Pipe for Pipe Fittings
Sometimes the pressure loss of a fitting is expressed as an 'Equivalent length' of pipe, where by the engineer calculates a further length of pipe that will produce an extra friction loss in the pipe that is equivalent to the loss through the fitting. In this way, adding a notional extra length to each pipe can model the further pressure loss that would have occured due to the fittings.
The 'K' factor of a fitting may be calculated from the 'Equivalent length' (in m or ft.) if the friction factor and the Internal diameter (in m or ft.) are known.
The 'Equivalent length' and 'Internal diameter' must be in the same units to calculate the 'K' factor.
K = (EL * ff) / i.d.
where:
EL= Equivalent length of pipe (in m or ft)
ff = Friction factor
i.d. = Internal Diameter of the pipe (in m or ft, same as for EL)
