Backwashing your Pool Filter Tips & tricks

 Backwashing your D.E. Filter or Sand Filter is a task that can seem difficult if you are new to pool ownership. It is relatively easy once you understand the nature of your particular backwash valve and the typical problems you may run into with that valve. Here are the two most common backwash valves, the Piston Type and the Multi-Port Valve, and the things to note about each one.

First, what exactly is backwashing a filter? This is basically reversing the flow of water to loosen up any dirt and debris in the filter when the filter PSI or pressure gets too high. The filter PSI can be found on the gauge on top of your filter. Since starting filter pressure varies it is a good idea to mark your gauge at the point when you just cleaned your D.E. filter or when you either installed your sand filter, changed the sand, or gave it good backwashing. It becomes time to backwash when your filter PSI goes up by 10 PSI from the clean mark on the gauge. 

When you engage the backwash two things can happen depending on the type of valve and type of filter. For a D.E. filter with the Piston Backwash Valve, the water is reversed through the D.E. grids which pushes the dirt and D.E. off the grids and out the waste line. For the Multi-Port Type Valve backwashing just stirs up the water in the filter washing the debris out of the filter. These types of valves are most common on Sand Filters but can also be found on D.E. Filters. Note that a cartridge filter because of the nature of how the water flows through it cannot be backwashed and you will not find a backwash valve on this type of filter.

A typical backwash cycle can last from as little as 30 seconds to 1 ½ minute. You typically do not want to backwash for more than 2 minutes. Most of the dirt and debris will be discharged in the first minute and running it for longer periods of time is just unnecessary and a waste of water. Whenever you engage the backwash valve the pool pump must be off. So if you are pulling up on the piston the pump is off. Once you have it up and open turn on the pump to start the backwash. For the Multi-Port Valve, each time you are turning the handle to a different setting the pump is off. 

The piston-type backwash valve also known as the “Push/Pull Valve” is probably the most common backwash valve found on a D.E. filter. It looks like an actual piston and it has a long handle on top that you turn to unlock and then pull up on to engage the backwash. It is simple to use and pretty easy once you get the hang of it. The most common issue with the piston is that the o-rings inside will expand over time, making it difficult to open and close the piston. The fix is pretty easy. Simply unscrew the plastic ring or nut holding on the piston and pull it out to change the o-rings. Or change the entire piston if it s getting old. Once you do the piston will slide in and out very easily. 

The Multi-Port Valve has several different settings on it, but the three you are interested in while backwashing is the “Filter,” “Backwash.” And, “Rinse.” To successfully backwash using this type of valve, simply turn it clockwise to “Backwash.” Once you have run the pump for a minute or so, turn it off and then turn the valve to “Rinse.” Turn on the pump and let it run for 30 seconds. Then turn it off and turn it back to “Filter.” The “Rinse” mode is important as you need to clean the line of any left-over dirt from the backwash cycle. If you skip the “Rinse” mode chances are some dirt will return to the pool once you start it back up.

A Sand Filter does not need to be recharged with anything after backwashing it. The sand is not removed during the backwash cycle, just dirt. For a D.E. filter, it should be recharged with some D.E. after each backwashing because old  D.E. is expelled during a backwash. The amount to add in varies by filter size but a good Rule of Thumb is that you need to add back in about half the D.E. that you originally added when you cleaned it. For example, if you added 6 lbs of D.E. you will need to add in 3 lbs. after backwashing it. For a D.E. filter, I wouldn’t backwash it more than two and maybe three times before I would take it apart and clean off the grids completely. After the 2nd backwashing, the process becomes less effective. 

There are other types of backwash valves but these are the two most common and if you do pool service once you master these two the rest are very easy to learn. 

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