How Swimming Pool Sand Filters Work

Swimming Pool Sand Filters

Sand filters are a popular option for keeping swimming pools clean. These filters use natural sand as a filtering agent, trapping debris as it passes through so that only clean water is pumped into your pool. Because sand filters don’t have paper or fiber parts to clog or tear, they can often go for years with only minimal maintenance being required to keep them in good running condition. If you are looking for a pool filtration solution, take the time to consider the benefits of sand filters to see if one is right for you and your swimming pool.

How Sand Filters Work

Sand filters work by allowing water to cycle through a canister that contains sand. The water flows through the sand with ease, but larger particles are unable to pass through. Once the debris and other particles have been filtered out by the sand, a pump moves the clean water back into the pool. As more debris becomes collected by the filter, the efficiency of the filter will start to increase as well; the debris will actually help to keep smaller particles from passing through the sand. In order to ensure consistency and make sure that most if not all of the debris that might be in your pool water is filtered out, sand of a specific makeup and grain size is used. Sand filters use #20 silica sand with grains that fall within the 45 to 55 millimeter range. Any sand that you buy as “pool sand” or “filter sand” will meet this standard, since it is sold specifically for use in sand pool filters.

Materials Filtered by Sand

A range of materials will be captured by your sand filter. Larger materials such as leaves, gravel, and insects won’t be able to pass through the sand at all, and even smaller materials will be stopped as the water from your pool moves through the filter canister. Even small particles between 20 and 100 microns in size will be captured by the sand within your sand filter, and particles smaller than that can potentially be contained as the filter collects debris. Particles that pass through the filter initially may be filtered out later as the water in your pool cycles back through the filter.

Maintenance Requirements

As material is captured by your sand filter, occasional cleaning and maintenance is required. The more dirt and debris your filter has in it, the more pressure will begin to build within the filter canister. Take note of the initial reading of the pressure gauge on your swimming pool’s sand filter, then check it every week or two to see if there has been an increase in pressure. Once the pressure has increased by 8 to 10 pounds you will need to clean the filter by performing what is known as a “backwash cleaning” to remove the excess dirt and other debris from the sand. Backwashing a sand filter is easy. Shut down the pump cycling water through the filter and allow it to stop completely. Once the pump has stopped, unroll or attach the backwash hose and turn the pump’s setting valve to “Backwash.” Turn the pump on and let it run. The water will start coming out clear, and then will begin to get darker as more dirt and debris comes out. Allow the water to run until it becomes mostly clear again, then shut the pump off. Turn the setting valve to “Rinse” and allow the pump to run in the rinse cycle for 30 to 45 seconds. After you’ve rinsed the filter, put up the backwash hose again and reset the pump to its normal setting before starting it up again.

Changing the Sand

Unfortunately, even regular backwashing won’t keep a sand filter running efficiently forever. Eventually the sand within the filter container is going to need to be changed, though this will generally only have to be done once every 5 to 7 years. Changing the sand isn’t difficult, though it can be slightly time-consuming depending on the size of the canister that the sand filter uses. Start by performing a backwash, leaving the pump turned off once it is finished. Open the pressure valve on the top of the filter canister to release the pressure from within the sand filter, then open the drain valve on the bottom of the canister to release the water inside. Begin loosening the bolts holding the canister together, alternating from one side to the other in order to prevent damaging the container with excessive stress on one side. Remove the top of the canister, then scoop out the sand contained inside of the filter canister. Once you’ve removed the sand from the filter, check the lateral components inside to see if they are overly loose or broken. Replace any laterals that have broken or come loose, then fill the container half full of water to help protect them from damage as you start adding sand. Pour or scoop clean sand into the container, filling it to within an inch or two of the top; consult your pool filter’s owner’s manual if you aren’t sure of exactly how much sand you should add. Once the filter is full of sand, reattach the top of the canister and perform another backwash before you begin pumping water through the filter again.

Above Ground Pool Sand Filters

Inground Pool Sand Filters