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The Two Types of Filter Systems

No matter what brand of spa you own there are only two possible configurations that it uses to filter the water. The two type of systems are Pressure and Suction. We will attempt to show you the differences, and the similarities, between the two systems in order to show you the importance of a clean filter.

Pressurized Filter Systems

In a pressurized filter system the water from the spa is pushed through the filter by the spa's pump. In the diagram above you can see that the filter is plumbed in the system before the heater. In many cases the the heater may be before the filter. It doesn't make much difference in which order the filter and heater are in. The thing to notice is that the filter is on the discharge, or pressure side of the pump.

One of the nicest features of a pressurized filter system is that in most cases the spa will prime itself when it has been refilled. Sometimes when a spa has a suction filter it may be necessary to evacuate all of the air from the plumbing leading to the pump before the system will circulate water. A dirty filter cartridge can further hinder this process.

The down side to a pressurized filter system is that you are dealing with pressure. Now water does not compress. If a filter canister cracks or an o-ring gives while the canister is filled with pressurized water it will most likely cause a big leak and a major clean up. However if the filter canister is filled with pressurized air, (which can be compressed), a crack can have explosive results. Simply opening a pressurized filter can be hazardous if it is under pressure. Always open the filter's bleeder valve prior to opening the canister. Even after doing this USE CAUTION WHEN OPENING YOUR PRESSURIZED FILTER! When a pressurized filter develops a leak in an o-ring it can rapidly empty your spa. If you see water dripping from your filter canister, it may be time to replace an o-ring or two.

Suction Filter Systems

The first thing that you will notice about the suction filter system is that the filter is the first device in the plumbing. Water is pulled though the filter by the pump and then it is pushed through the heater before being returned to the spa. In some rare instances you may find a heater before the pump but this is truly the exception to the rule. More and more new spas are being produced with the suction side filter system due to its reliability and ease of maintenance. Although we show a stand alone filter in the above diagram most newer spas feature a suction filter that is built into the lip of the spa. This allows the spa owner to easily open the filter and replace the cartridge without spilling any water.

The nice thing about suction filter systems is that leaks or potential explosions of the canister are virtually eliminated. In fact even if some suction filters do have a leaky o-ring they usually won't leak while the pump is running. Since the pump is sucking the water through the filter a leak will just allow outside air to be sucked in also.

As mentioned above the down side to suction filters is that they may cause the spa to be hard to start up. This happens because air can become trapped in the pump and must be removed before the spa will circulate properly.

Suction Filters can also be built right into the spa shell itself. As you can see on our spa, the filter cartridge actually drops into a canister that is attached to the shell. This is a clean, easy to maintain setup. The only bad thing about this setup is that when a dirty filter is removed a lot of the debris from the filter can be release right back into the spa.

By-Pass Systems

Both systems are adequate for cleaning the water in your spa providing that the filter cartridge, (sometimes referred to as the filter "element") is clean enough to allow water to pass through it. What few spa owners realize is that most spa's have a by-pass system built into either the filter housing or into the spa's plumbing. This by-pass system is there to allow water to continue to flow through the system even if the filter cartridge is completely blocked. It does this by using a spring loaded valve that opens when it becomes too hard to push the water through the filter cartridge. This is called a "check-valve". The reason for bypassing the filter is simple. If water does not flow, it does not circulate. If it does not circulate it can not be heated. Most spas have a device that detects water flow either by measuring the pressure being produced by the pump or by the movement of the water. When the flow of water is detected the circuitry in your spas controls allow the heater to function. If a dirty filter was allowed to keep your spa from heating it would be a real problem. So the good thing is that your filter system will probably allow your spa to heat even if the filter cartridge is dirty. The bad thing is the water is by-passing the filter and is not getting cleaned! Even a filter cartridge that appears clean can be so filled with particles that it no longer allows the water to pass through effectively. And if water is not passing though the filter cartridge the filter is not doing its job.

Solution

The way to keep your spa clean and healthy is to replace your filter cartridge regularly. We recommend that you replace your filter at least every 6 months. The way we do it with our spa is to have two filters that we rotate on water changes. When the dirty filter is taken out of the spa we replace it with the spare one that has been cleaned and dried. Then after 3-5 water changes we replace the older of the two cartridges.

A dirty filter can reduce the power of your jets and can cause problems with your spas heater. Replace yours regularly.

If you have any questions about filters, filter systems or any other spa related topics please send email to help@spafilters.com.