Spa Filtering Systems
Part 1

There are three types of filter systems commonly used in spas:

Pressure filters, with standard 25 or 50 square filters.  There is another type of pressure filter that uses two small filters equaling 25 sq. ft. Then there are the more modern suction side filter systems.  Each of these systems will 
be discussed in more detail in a series of Spa Care Tips articles.

The Pressure Filter
For years the pressure filter was it.  It was a derivation of the cartridge filters used in small pools.  In the beginning most parts for spas were pool parts that were adapted.

In dealing with lots of pressure filter problems, the majority of which are owner ignorance related, we find the standard pressure filter is not as owner friendly as other designs.  I have had people desperately taking wooden blocks and hammers pounding on the lock ring to stop it from leaking.   This makes for a $150 repair or more for us. parts and labor.  In the winter people forget there is water in the filter housing and we see a lot of older spas with cracked filter housings.

The use of pressure filters is relatively easy, but a little more complicated.  The pump has to be shut off in order to get inside, resulting in reprogramming the filter times.  No big deal, but a little nuisance. 

Keep a brand new o'ring ready at all times.  You can pound on the lock ring 'til you're blue in the face and it may not stop leaking. Usually it leaks like crazy after you break the lock ring or crack the housing.  Keep a tube of "Magic Lube" at all times for lubricating the O'ring.
If you replace the filter and gently tighten the lock ring and it leaks, carefully  remove the lock ring, install a new lubricated o'ring and it will almost 97% of the time be good as new.
Never force plastic parts to try to stop leaks, any plastic part.

The way a good pressure filter works is on low speed 30 to 50 GPM allowing most of the water to go through the filter.  Then on high speed the "bypass spring check valve" opens to allow less restriction to the water flow.  How the bypass is built determines the amount of back pressure in the plumbing.  There is always some back pressure with this design. Water turbulence and deflection causes back pressure.

Many times people who have older style pressure filters do not perform proper filter cleaning, and leave the filter in the cartridge until it is in really bad shape.  By properly cleaning the filter you can get about two years per filter cartridge or more. The reason they leave them in so long without caring for them is the problems with leaking O'rings and the hassle getting to the filter.

When a prospective spa buyer, who is replacing an old spa with a pressure filter, comes into the store and sees how easy it is to get the filters in and out of our spas, they smile and start talking about what a hassle the old pressure filter is.

The pressure filter is a good design in terms of function, but not in terms of owner appreciation.  I feel that the system is OK, but a little patience and knowledge is a necessary part of owning one.

My favorite of the pressure filters is the Hayward C 500.  It is relatively easy to use and seems to seal without problems by turning down on the center threaded handle.  We use them on wooden hot tubs and for replacements on old custom installs.

Because the filter's cartridge is made from a polyester fiber, they do last a long time with proper cleaning. Remember those awful polyester suits that didn't wear out?

During the spa manufacturing process, installing a pressure side filter is a bit easier than using a suction system.  You often find top loading pressure filters on less expensive built spas.  Simply cut a hole in the top of the shell, drop the filter housing in, and screw the underside lock ring to hold it in place.  It's relatively quick and easy.  This is fine as long as the rest of the "filter system" is plumbed correctly.

The best way to plumb a pressure filter is in the pump first, filter second, then heater, so the back pressure from a dirty filter will shut off the heater and not cause a "meltdown".  PUMP-FILTER-HEATER.   If the filter is after the heater, the back pressure can cause the pressure switch to be on when the water is barely moving in the heater.  (This is one of the reasons why I dislike tiny, 24 Hr., circ. pumps, because they do not actuate a pressure switch.). The pressure switch is part of the heater electrical "loop".  When the "high limit", "thermostat", and "pressure" switches are on then and only then does the heater work.  Look at http://www.spaspecialist.com/aug2.html

If you have a spa with the filter last, you need to make sure the filter is clean!!
I also recommend putting in a "paddle flow switch" or a "Grid model 25" magnetic flow switch, instead of a pressure switch, when the filter is last.