How To Backwash A Sand Filter

All the sand filters use the same mechanics: when they are set to filter, water will flow from the pool via the filter and then back into the pool. The sand that’s in the filter system will block dirt, oil and debris. A normal sand filter multiport usually has 6 various settings; filter, circulate, backwash, rinse, waste and closed.But when you vacuum your pool, a lot of dirt and debris is deposited in the sand. What results is a dirty and clogged sand filter that if not checked, it will reduce the ability of the sand to filter and get back again into your pool.

Backwashing the sand filter will prevent this. The backwash will change the way the water is flowing, raising up and rinsing the sand and then getting rid of the dirty water through a waste line right into the drain or ground. To be sure there’s no residual blowback into the pool, after you have finished backwashing it, it’s important that you rinse the filter. As the backwash raises and cleanses the sand, the cleanse goes back into the sand in its original position for effective filtration.

sand filter
How do sand filters work?

A sand filter cleans your pool water by a process known as depth filtration. As dirt and other debris get into the sand bed, they get trapped in the tiny spaces that are between the sand grains.

Does backwashing make any difference?

Backwashing your pool sand filter often is the secret to trouble free filter problems. If the filter is not backwashed regularly, there will be a buildup of dirt particles on the surface of the sand bed. This causes short cycles, channeling and ineffective filtration. Still, if you backwash the sand filter too regularly, some of the dirt particles may pass through the bed and get back into the swimming pool.

How to backwash a sand filter

• Turn off the pump
• Close the valves that are located in the suction and the return lines
• Unlock the cover of the pump and pour out the filter basket
• Lock the cover
• Open the valve that leads to the drain outlet
• Turn around the lever to backwash
• Open the suction valves and return lines
• Start the pump. Cleanse the filter for about 2 minutes or until the water visible is crystal clear. NOTE: All electric heaters must be off
• Turn off the pump
• Turn around the lever to rinse, restart the pump and cleanse for approximately 30 seconds. Turn off the pump and then turn the lever to filter. This is usually the usual operating position.
• Turn off the drain outlet valve and start the pump. If you have an electric heater, switch it on.

backwashing a pool sand filter
How regularly should you backwash a pool sand filter

Your pool sand filter should be backwashed and rinsed off once in a week but this depends on how heavily your pool is used. The best time to do this is usually immediately after you have vacuumed the pool. If your pool has been used more than it is normally, then it’s advisable to backwash two times in a week.

In addition, if your pool is located under trees that shed a lot, then you may have to backwash the pool filter frequently as leaves and any other debris from trees and contaminants from insects will be getting into your pool.
Still, you can always tell when it’s time to backwash the pool by assessing the sand filter systems pressure gauge. The normal operating pressures are usually from 50 to 75Kpa (kilopascal). However, when the sand gets dirty and clogged up, the pressure reading goes up. If the Kpa pressure on the gauge is appearing high at about 80Kpa, then it means it’s time to backwash your pool sand filter.

When should you not backwash the pool sand filter?

If the pool has abnormal high dirt levels for example, due to being neglected over a long period of time, runoff that may occur due to flooding or due to dirt from a construction site nearby, it may be prudent not to backwash the filter.
Further, if your water has algae growth, backwashing the sand filter may not be wise. Live algae can easily pass via the filter and then get back into the pool. The same case applies for dead algae after shocking the pool. In the above cases, instead of vacuuming and then backwashing, it would be advisable to waste directly and release the vacuumed water right down into the drain.

Backwashing Tips

how to backwash a pool sand filter
• Do not backwash more than its necessary or for extended periods of time. A sand filter system will operate at its best in the middle of the filtration cycle. This is due to the location of the sand filter and also to some extend the built up of gathered debris and dirt in the filter. The effects of too much or frequently backwashing is that the sand filters efficiency is reduced.
• Ensure your pump is always turned off before moving or resting the filter valve setting. If you do not turn off, then you will damage or destroy the entire system.
• Since backwashing cleanses out some sand with dirt and debris, it is important to increase more sand in the filter from time to time. When you increase the amount of sand, put the filter system on rinse for a few minutes to decrease the amount of sand blowback into the swimming pool.
• The problem of backwashing the sand filter is that since water is removed from the system and released to water, there is water wastage. Although this cannot be avoided, the important thing is not to overdo the backwash process and expel only the amount of water that necessary. Keep an eye on the quality and color of water in the sight glass to avoid water wastage.

When should one change the sand?

It’s recommended that the sand filter is emptied and replaced after every 6 years for a residential swimming pool. However, if your pool runs all year round, you have to change it earlier.

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