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Pressure Loss


Comparing Volumetric Flow Rates for Equivalent Pressure Loss

Standard volumetric flow rates of a fluid are often used to describe the capacity of a vent or pressure relief device. To determine how this capacity compares for another fluid under different pressure and temperature conditions a conversion must be made on the basis of equivalent pressure loss. This article describes the method for calculating the volumetric flow rate of a gas which will give the equivalent pressure drop to another gas through a fixed restriction such as a vent.


Bernoulli's Equation
Bernoulli's Equation

Bernoulli’s Principle is an important observation in fluid dynamics which states that for an inviscid flow, an increase in the velocity of the fluid results in a simultaneous decrease in pressure or a decrease in the fluid’s potential energy. This principle is often represented mathematically in the many forms of Bernoulli’s equation. This article presents some useful forms of Bernoulli’s Equations and their simplifying assumptions.


Pressure Loss in Hoses
Pressure Loss in Hoses

The Pressure loss through a hose is often approximated using coarse heuristics, but utilization of more accurate correlations increase the efficiency of pump and piping designs. This article presents more accurate methods to estimate the pressure loss in various type of hoses using multiples of the pipe length. Methods of estimating pressure loss caused by couplings, curves and coiled hose are also detailed.


Pressure Loss from Pipe Entrances and Exits
Pressure Loss from Pipe Entrances and Exits

When a fluid moves from a tank or vessel into a pipe system or vice versa there are pressure losses. This article provides K-values for pipe entrances and exits of various geometries. These K-values may be used to determine the pressure loss from a fluid flowing through these entrances and exits.


Pressure Loss from Fittings - Expansion and Reduction in Pipe Size
Pressure Loss from Fittings - Expansion and Reduction in Pipe Size

This article provides methods to calculate the K-value (Resistance Coefficient) for determining the pressure loss cause by changes in the area of a fluid flow path. These types of pressure drops are highly dependent on the geometry and are not usually covered in simple pressure loss estimation schemes (such as a single k-value, equivalent length etc.)


Pressure Loss from Fittings - 3K Method
Pressure Loss from Fittings - 3K Method

Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the 3K method.


Pressure Loss from Fittings - 2K Method

Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the 2K method.


Pressure Loss from Fittings - Excess Head (K) Method

Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the K-value method, also known as the Resistance Coefficient, Velocity Head, Excess Head or Crane method.


Pressure Loss from Fittings - Equivalent Length Method
Pressure Loss from Fittings - Equivalent Length Method

Fittings such as elbows, tees and valves represent a significant component of the pressure loss in most pipe systems. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the equivalent length method. The strength of the equivalent length method is that it is very simple to calculate. The weakness of the equivalent length method is that it is not as accurate as other methods unless very detailed tabulated data is available.


Velocity Head

This article describes the method of calculating the velocity head of flowing fluid. The velocity head uses units of length as a measure of the kinetic energy of the flowing fluid.


Conversion Between Head and Pressure
Conversion Between Head and Pressure

This article presents the method to convert between pressure and head for several common unit sets. Head relates the pressure of a fluid to the height of a column of that fluid which would produce an equivalent static pressure at its base. It is particularly useful for the specification of pumps as it provides a measure of pressure as it is independent of fluid density.


Converting Between Cv, Kv and K
Converting Between Cv, Kv and K

There are several common ways to express the losses caused by pipe fittings and equipment. Depending on the calculation programs or methods available and engineer may require to convert between one form or another. This article details the equations required to convert between the resistance coefficient and flow coefficient methods (K, Cv and Kv).


Cavitation in Restriction Orifices and Valves
Cavitation in Restriction Orifices and Valves

Restriction orifices and control valves are commonly used for pressure reduction and measurement of flow rates, however for a liquid system, excessive pressure drop across these items of equipment may result in cavitation. This article describes methods of predicting cavitation across restriction orifices and valves and proposes designs which may be used to avoid cavitation.


Pressure Loss from Fittings in Pipe Summary

Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems. This article discusses the differences between several popular methods for determining the pressure loss through fittings. The methods discussed for fittings are: the equivalent length method, the K method (velocity head method or resistance coefficient method), the two-K method and the three-K method. In this article we also discuss method for calculating pressure loss through pipe size changes as well as control valves.


Friction Factor for Flow in Coils and Curved Pipe
Friction Factor for Flow in Coils and Curved Pipe

In order to determine the pressure drop in a pipe or coil the friction factor must first be calculated. This article presents the equations which may be used to determine the friction factor in coils and curved pipe.


Pressure Loss Cv and Kv Method
Pressure Loss Cv and Kv Method

Cv and Kv are singles values in units of flowrate that may be used to characterise the relationship between flowrate and pressure loss for fittings and equipment. This article demonstrates how to calculate the Cv or Kv values, and how to use these values to determine the pressure loss for a given flowrate.


Pressure Loss in Pipe
Pressure Loss in Pipe

To determine the pressure loss or flow rate through pipe knowledge of the friction between the fluid and the pipe is required. This article describes how to incorporate friction into pressure loss or fluid flow calculations. It also outlines several methods for determining the Darcy friction factor for rough and smooth pipes in both the turbulent and laminar flow regime. Finally this article discusses which correlation for pressure loss in pipe is the most appropriate.