Why does pressure loss occur in filtration systems?
System pressure reduces when fluid flows through a filter system due to the fluids interaction with the filter media, housing components and piping arrangement. The interaction between the fluid and aforementioned components cause energy to be lost due to friction, the losses are influenced by a number of different factors including piping configuration, velocity, viscosity and fluid density.
The degree of pressure loss also differs depending on the fluids flow regime which can be classified as either turbulent, intermediate or laminar. Fluids that are more viscous in nature will tend to be laminar having several flow layers within the fluid, leading to frictional energy losses due to shear stress. Flows that exhibit turbulent flow tend to be fluids travelling at a higher velocity.
When sizing a filter system, the combined losses across the filter element and accommodating filter housing is used. Industrial filtration typically sizes to achieve a combined clean pressure drop of no more than 0.08 bar. Once in operation the pressure drop of the system is monitored via calculating the difference between pressure gauges measuring the pressures upstream and downstream of the filter housing, alternatively differential pressure gauges are supplied with the housing to simplify the measurement. The biggest cause of pressure loss within the filter is the contaminant retained by the media filter which over time increases the pressure drop. To maintain optimal performance Industrial Filtration recommends that filters are changed out when a pressure drop of 1.8 bar is achieved, of course this is not a hard and fast rule and the value can change depending on the type of filter element used and the nature of the application.