Filter screens are cheap enough that purchase price dominates the buying conversation. That is the wrong number, because the things that make a screen expensive – change-out labour, downtime, and contamination reaching downstream equipment – never appear on a screen invoice.
What the invoice does not include
- Change-out labour. Opening a housing, cleaning the seat, fitting and closing, restarting. Usually between half an hour and several hours depending on access.
- Downtime. If the housing cannot be changed while the line runs, the change-out is a production event. This is often the dominant cost.
- Loss of product. Every change-out involves some product loss, and in some processes it is significant.
- Cleaning. Labour, chemicals, water and the drying time for screens that are reused.
- Spares holding. Floor space, management and the working capital tied up in stock.
- Failure consequences. A bypass that lets contamination through to a heat exchanger, a spray nozzle or a downstream membrane can cost more than years of screens.
Doing the arithmetic
The useful comparison between two screen options is not price per screen. It is:
(screens per year multiplied by price, plus change-outs per year multiplied by cost per change-out, plus expected failure consequences) divided by whatever unit makes sense to you – per month, per tonne, per operating hour.
The parts are not precise and they do not need to be. The point is to see the relative sizes. In most plants the labour and downtime terms are several times the material term, which means a screen that lasts twice as long is worth considerably more than twice its price.
Where the biggest lever usually is
Extending the interval. Every avoided change-out saves the whole labour and downtime cost, not just the price of a screen. So the things that extend life – a higher open area specification, a front protective stage, better cleaning, correct installation – pay back through the interval rather than through the unit price.
This is why the cheapest screen per unit is frequently the most expensive option overall. A shorter interval multiplies every other cost in the list.
What to measure
- Change-outs per housing per year. The single most useful number.
- Time per change-out, door to door, including restart.
- Whether production stops during a change-out, and for how long.
- Screens consumed versus cleaned, since the ratio shows how much cleaning is actually saving.
- Any downstream failures attributable to contamination.
None of these need instrumentation. A log kept for a month gives enough to work with.
The honest conclusion
For many plants the screen specification is already adequate and the biggest available saving is in the system – staging, support, seating, cleaning method. Those are all cheaper than buying a more expensive screen and they address the interval rather than the unit price.
Where the screen genuinely is the constraint, a better specification is worth paying for. It is worth finding out which situation you are in before deciding.
What we can do
We supply PP filter screens and will discuss the interval rather than the price, because that is where your cost is. Tell us your change-out frequency and cost per change-out and we can work out what an improvement in screen life would actually be worth – and whether a different screen is the way to get it.