An Introduction to Reverse Osmosis Pre-Filtration

RO filtration is used to remove the tiniest contaminants such as dissolved salts from water. For example, RO is used for desalination – to create fresh drinking water from sea-water, or to purify fresh water to remove trace contaminants and make drinking water even healthier. In industrial applications, RO is used to remove harmful scalants and damaging residues to minimize deposits in expensive boilers, or to recycle waste waters into water that can be re-used for washdown, irrigation or evaporative cooling , thus prolonging the availability of freshwater resources. Many of our customers and distributors have a lot more experience with traditional dead-end cartridge filters than with some of the more advanced forms of membrane filtration. For newcomers to water purification, any discussion of Reverse Osmosis can be intimidating at first, but this paper is intended to facilitate effective discussions about pre-filters between buyers and sellers.

String Wound Filters – The Best Pre-Filters?

On some levels, string wound filters might be considered to be of unsophisticated technology, but they are often the most intelligent choice. Experienced plant personnel and new-system designers select string wound filters because these filters have proven effective, because advances in the manufacture of string wound filters have continued to advance filter performance, and because this filter design continues to provide value (favorable price/performance ratio).

String wound filters are used for pre-filtration in a myriad of applications, ranging from protecting potable water systems using RO desalination membranes in large municipal water facilities to protecting under-sink RO units in home water systems; from cleaning up amine for gas sweetening in petrochemical plants to chemical filtration in a “tank farm” at pharmaceutical API (active pharmaceutical ingredient) plants; from ensuring circuit board quality in plating solution bath recirculation systems to protecting geological formations via water filtration in a geothermal plant.

Basics of Filtration

This white paper includes definitions and descriptions of






Pressure drop


System pressure drop


Cartridge Pressure Drop


Housing Pressure Drop


Open, Parallel and Series Filtration Systems

Glossary of Produced Water & Fracking Terms

If you are in the liquid filtration industry but terms like “produced water” and “flowback water” are unclear to you, download and print out our Produced Water and Fracking Terms glossary.

How to Prepare to Buy a New Chemical Filter Assembly

A properly functioning filter for a chemical process is usually one that has been carefully selected. Collecting the right information for a new filter assembly (housing and filters) lays the groundwork for all involved to thoroughly understand requirements.

Delta Pure Filtration has prepared a questionnaire to help with the filter selection process. Preparing answers to these questions will help you to get the right recommendation and pricing from your supplier, will significantly speed-up the quoting process, and might even provide you important new insights into your own process.

TIP: Special filter vessels can often take many months to design and fabricate, so it is best to plan ahead and order as early as possible.

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"I've been doing business with Delta Pure for many years and you will find that all of the people there are real stand up folk."

- Marshall B.

“Delta Pure has been one of my manufacturers that will drop everything to help my customers out of a bind. I have called them at the drop of a hat to do an emergency order and no matter how small or large the order has been they have always come through for me and my customers. Delta Pure has been available to me days, nights and weekends, almost without fail. We have been able to offer our customers the DP product as a replacement / alternate for manufacturers that our customers have been set on for years and the DP filter has been tested and approved by many of our major customers across the USA.

We appreciate their ability to work with us on customizing filters and their dedication to customer service that I find so lacking in some of the manufacturers in our industry in today’s world. Donna and Steve are always willing to jump right in with both feel to assist in a resolution to issues that come up – even on Friday at 4:45PM.”

“Over the last few months the team at Delta Pure has been truly jumping through hoops to supply desperately needed string-wound filters to our customers. I can tell you that this dedication to excellence has enabled us to drive sales deeper and wider into these accounts and engendered total trust from our contacts.. When we sell your products to our customers we stand behind the Delta Pure name and I can tell you that this is easy to do as your outstanding reputation is well-deserved.

Thank you again for the hard work and late hours your team has put in to make our joint efforts count when it’s most needed in the plant.”

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