Purchasing decisions in filtration are frequently made on the line item that is easiest to compare: the price of the element. It is also the smallest of the four costs a filtration system incurs.
The four costs
Across the installations we have modelled, on a typical continuously-operating liquid line, the annual cost distribution looks approximately like this:
- Elements: 15 to 22% of total annual cost
- Labour for change-out: 18 to 30%, and higher where confined-space or permit work is involved
- Production downtime during change-out: 20 to 40% on lines that cannot run through a change
- Pumping energy against differential pressure: 15 to 35%, rising sharply where systems run near terminal pressure drop
- Disposal, including hazardous classification where applicable: 5 to 12%
Why the cheap element loses
A lower-cost element usually has less effective area, a less optimised pleat geometry, or a media with lower dirt-holding capacity. Each of those shortens service life, and service life multiplies directly into the two largest costs — labour and downtime.
An element that costs 30% less but lasts 45% fewer hours increases the number of change-outs by more than 80%. On a line where a change-out costs four hours of production, the saving on the purchase order disappears in the first quarter.
The same logic runs the other way on pressure drop. An element with more effective area starts at a lower clean differential and reaches terminal pressure later, which reduces both pumping energy and change frequency at once.
How to model it in ten minutes
Take annual element spend. Add change-out hours multiplied by fully-loaded labour rate. Add downtime hours multiplied by contribution margin per hour. Add average differential pressure multiplied by flow, divided by pump efficiency, multiplied by tariff and running hours. Add disposal.
Then run the same calculation with the alternative element's service life and pressure drop. The comparison is usually decisive, and it takes less time than negotiating the discount that prompted the question.