A pump will generate a pressure or back pressure as it tries to pump material through a filter.  The pressure or back pressure is measured in psi. for pounds per square inch.  The finer the filter is the greater the backpressure will be.  When filtering through a 3-micron filter the backpressure is approximately 7 psi.  When filtering through two filters the back pressure is approximately the sum of the back pressure of both filters so it is 5 psi for the 5 micron filter plus 10 psi for the I micron filter at a nominal flow rate of ten gallons per minute.   

As the pressure increases the flow rate will decrease.  As the filters get clogged the amount of force required to pump through them will increase.  As the filters get used and start to clog up they will also do a better job of filtering.  Take a look at some of our Machine Coolant Filters or see the difference filtering your machine coolant can make by viewing some of our Machine Coolant Filtration Articles. 

At a flow rate of 10 gpm

1-micron filter creates 10 psi

3-micron filter creates   7 psi

5-micron filter creates   5 psi