F.A.Q.

FREQUENTLY ASKED QUESTIONS

How do I choose a material for liquid filter bags?

Material selection depends on temperature, particle size, and chemistry. Most of the filter bags we offer are made from polypropylene (POG) or polyester felt (PES) which have a wide range of chemical compatibility. Polyester can handle higher temperatures, to 275 degrees Fahrenheit, compared to 180 degrees Fahrenheit for polypropylene. High temperature (HT) aramid (also known as Nomex) is rated to 400 degrees Fahrenheit.  Many demanding applications utilize absolute rated nylon mesh (NMO).

Why aren't my bags lasting as long as they used to?

Usually because they are working harder. Bag life is limited by the amount of dirt captured, not by hours in service or gallons processed. Bags filtering relatively clean water may last a year. A bag filtering mud may last only a few minutes. A fluid can appear clean to the naked eye and still be full of particles which are too small to see.

How do I know when to change bags?

It is always advisable to monitor the inlet and differential pressure. The pressure drop across a bag rises as the active surface area is used up. When pressure drop accelerates rapidly, the bag is almost to the end of its useful life and is due to be changed. Every application is different, but a good rule of thumb is to change bags when you see 8-12 PSI pressure drop (the difference in pressure between the filter's inlet and outlet.)

How many times can I clean and reuse a filter bag?

Filter bags are designed for one-time use. This is critical to maintain the bag's micron rating. Attempting to clean and reuse a bag may damage and stretch the material, allowing its pores to enlarge and pass contaminants. Alternately, shrinkage may occur, causing the filter to plug quicker, and could lead to unplanned removal of desirable components of the filtered fluid. 

What does the 'P' in the middle of your part number mean?

In example part PES100P2SH, the first P is material PES=Polyester felt.  The second P stands for Plain (no cover over the entire filter bag.) Covered bags are now uncommon. Prior to the advent of modern non-woven fabrics and felts, it was customary for filter bags to have an outer cover. Covered bags are still available from our sister company, Midwest Filter.

Why are there bubbles in my aquarium when I replace filter bags?

You are using polypropylene felt (POG) bags that are glazed and have small traces of foreign chemical; this chemical is NOT harmful to the aquarium life. These bubbles can be reduced by pre-washing your filter bag in clear fresh water (three rinses should do it.)

Do you offer volume/distributor discounts?

We do offer volume discounts through Midwest Filter based on quantities and frequency of orders. Contact us for specifics.