What factors affect pressure drop across a strainer in clean condition?

One of the major factors considered during selection of a strainer is the pressure drop (DP) caused in the pipeline. Pressure drop is inevitable as the strainer obstructs the smooth flow of the fluid. Turbulence is caused as the fluid hits the filtration area of the strainer. This turbulence causes the pressure to decrease at the outlet of the strainer when compared to the inlet. This decrease in pressure is termed as “Pressure Drop” (PD) or “Drop in Pressure” (DP).

So what are the main factors that affect pressure drop in a strainer at 0% clogged condition? In general, two factors, the flow rate of the fluid and the size of the strainer itself. Theoretically, it is simpler to reduce the pressure drop across a strainer by lowering the flow rate of the fluid. Lower flow rate means slower output of the fluid. In most cases this is not ideal for operating team as this may impact the production or other process functions.

Increasing the strainer size can also lower pressure drop across a strainer. Let’s assume a DN150 (6”) line currently has a DP of 0.6 bar caused due to a 6” basket strainer. This DP can be lowered to 0.2 bar-0.3 bar by changing the strainer size to 8”. A bigger strainer means lesser turbulence thereby decreasing the pressure drop across a strainer. Other factors such as space restriction and use of reducer connections need to be considered before upgrading the strainer size.

One of the common myth is DP can be reduced by increasing the hole size of the mesh or the filter. Increasing the mesh hole size has a bigger impact on the Open Area and little or no significant impact on the DP. So the next time you are faced with a high DP across a strainer in clean or 0% clogged condition, consider reducing the flow rate or increasing the size of the strainer.