There are a few rules to remember when sizing a filtration system:
With in-depth cartridge filters, the slower the flow, the more efficient the cartridge is and the longer the user can go between change-outs. At Filters.com, we typically size housings to start out with a clean differential pressure of two pounds or less. You will find that many people in the filter business will quote housings that are undersized for an application so that they quote the lowest capital equipment cost.
The differential pressure (pressure drop) across both the cartridge and housing must be considered cumulatively. The pressure drop across the housing differs from housing to housing, but in most cases, it can be obtained from the housing manufacturer.
Assuming a cartridge vessel is designed for cartridges with a one-inch inside diameter, keep in mind that the flow through the bottom of each filter should not exceed 15-25 gallons per minute (for membrane pre-filters, try not to exceed 15 gpm). These flow rates should not be exceeded because turbulent flow is created on the interior core of the filter, which frequently cause unloading of contaminant from the filter media.
Always consider the viscosity of the material to be filtered when sizing filters or vessels. Also keep in mind that the viscosity of most materials varies depending on temperature. If you have an application where the customer does not want to go over a certain differential pressure and the temperature of the product can go through a wide swing, be careful to find out what the viscosity of the liquid is at both extremes of temperature.
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