Successfully navigating a filtration challenge requires a multi-disciplined engineering approach to the selection of the pump, filter, and control technologies best suited the task at hand, more so, each vendor must recognize and appreciate his role and the influence his component will have upon other process entities to make a competent, somewhat critical contribution and recommendation. Once installed and commissioned, it is not uncommon for high filtraiton costs to drive post installation efforts to reduce cost per filtered gallon.

Understanding the process characters
To effectively reduce filtration costs without compromising other process components requires acknowledging and identifying with each component. When conducting a filtration cost analysis and contemplating a filter media technology or retention change emphasis must be placed upon the impact the perspective change(s) may have on the primary system components, i.e., pump and filter. To simply change or swap filter media, retention, or sacrifice filtration area and flow profile without acknowledging the effects on the installed centrifugal pump will more often than not prove detrimental the effort.

Centrifugal pump performance
Centrifugal pumps by their nature represent a forgiving method of transferring non-viscous fluids within a process stream. Ironically however; their ability to handle reasonable changes in flow and pressure is what leads to their demise, downtime, and that famous phrase… "Next Day Red"

Incorporated within a filtration process, a centrifugal pumps performance should complement the load (differential pressure), at flow required. When analyzing the pump operating envelope both the filter clean and debris loaded pressure differentials must fall within the pump manufacturers performance envelope while meeting the process minimum and maximum flow demands. When marrying a pump and filter in a system it should be understood the pump must remain within the manufacturer’s operating limitations. To size the pump for a 15psid filter load could prove hazardous to the pumps health should clean filter media cause the pump to exceed the maximum recommended flow. It is not uncommon to control clean filter differential flow by artificially creating a load at the pump using an orifice or modulating control. Likewise, to protect a pump from a debris loaded filter, by-passing flow at the pump to meet the manufacturer’s minimum mechanical and thermal flow requirements is often recommended to secure pump and process reliability.

Process fluid thermal issues
As filter media accumulates debris available surface area or void volume is decreased resulting in an increase in pressure seen at the pump. As system pressure rises a centrifugal pumps flow decreases. As a filter media continues to remove debris the rise in pressure will eventually result in no flow, commonly reffered to as pump dead head condition. As a centrifugal pump trails left within its performance envelope approaching shut-off, imparted energy results in a temperature rise. In many applications this rise in temperature is somewhat insignificant when the condition exists for a short period. However, fluids with high vapor pressure, and those applications where pump operation far left continues for extended periods temperature rise may become a process consideration as phase change occurs within the pump and product or process integrity may be compromised.

The pump performance curve (above), illustrates the flow at pressure of two pumps both meeting a clean filter requirement of 3gpm @ 20’tdh (8.6psid). The blue curve represents a supply pump where the rise to shut-off is shallow, 5 feet. When incorporating the blue pump the filter media at retention is afforded a 5psid or less debris load. The red curve shows a much steeper rise toward shut-off, when used within the same filtration system the filter media is afforded a 15psid debris load.

Optimum performance
Once the influences of the pump and filtration systems have been identified, optimizing the best of each component can prove the most difficult of challenges. Ideally, the rated clean and debris loaded filter differential pressure loads at maximum and minimum process flow requirements will fall within the pump manufacturer’s limitations (with a little help of control here and there).

Once a filtration system design has been selected a series of objectives must be established to reach maximum filter media life. As described in the example, it is not uncommon for a centrifugal pump to limit filter media life to 20% or less, likewise, an undersized filter will result in frequent change and downtime. Optimum filter performance would be 100% of media use at planned intervals, intervals being dictated by batch size, transfer flow rates/time or simply scheduled as preventive maintenance. Ideally, the process dictates media change at a time when the filter media is nearly exhausted, opposed to a process component or condition decreeing change.

Reducing filtration costs through media technology
Only a methodical, diagnostic, and creative approach to filtration will decrease total cost per filtered gallon. To accommodate versatility and flexibility one must recognize and appreciate the importance of "fitting" a given requirement to reduce total filtration costs. A filtration professional respects one technology will never fit all applications and optimum preformance within a technology spectrum requires acknowledging the influence the prime fluid mover has upon filter life cycle and the filters effect on pump flow with debris generated pressure rise.

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