How To Backwash A Pool Filter
If you are not installing the filter now but need to determine the clean operational pressures then this can be accomplished by backwashing the filter for 3 minutes followed by a 90 second rinse cycle. After this you can consider the filter to be clean in all but the most extreme cases.
Note the clean operational pressure of the system. The best way to determine when you need to backwash is to wait until the pressure in the filter has climbed 6-10 PSI above the clean operational pressure. Typically you do not want the pressure in the system to increase over 30PSI. While most newer filters have a maximum pressure rating of 50PSI, anything over 30PSI is considered to be very high. If you have a filter that operates at high pressures such as this you may like to backwash more often to reduce the pressures that your system operates at.
If you are going to rely on the filter gauge to tell you when you need to backwash the filter then you should check to make sure the filter gauge is functioning properly. These filter gauges are known to commonly fail and you could inadvertently have higher pressures that you realize in your filter. This could cause potential damage to the filter and in a worst case scenario actually be dangerous.
To check the functionality of your filter gauge then turn off your plumbing system and you should see the filter gauge drop to zero. If the filter gauge does not drop all the way to zero then you should replace it as it is no longer in calibration and could in fact be giving false reading s for pressures in all pressure ranges. For the low cost that it would be to replace the filter gauge it is strongly encouraged that you replace the gauge if you are unsure of its condition or accurate.
The actual backwashing process should be completed when the operational pressure of your system has increased by 6-10PSI. The length of time that you backwash for will depend on how dirty the filter is. For a new filter or new filter sand it is recommended to overfill the pool and backwash for a full 3-5 minutes to help remove smaller filter sand from the system that would otherwise make its way back to the pool.
For all other conditions the correct procedure would be to backwash while using a timer and watching the sight glass which is located adjacent to the backwash port. The function of this sight glass is so that you can physically look at the water as it leaves the filter. Through the sight glass you should be able to see the water clear as the debris os removed from the filter. This should take anywhere from one minute to three minutes depending on how dirty the filter is. You should continue to backwash until the water in the sight glass is clear as this is an indication that the debris has been removed from the filter.
Good practice dictates that you should run your filter through a rinse setting that is half the length of time that you have just backwashed for prior to returning the filter to 'filter' setting. This will rinse any debris out of the filter head and will eliminate the potential for debris to be returned to the pool.
When changing the filter settings it is critically important that you turn off the pump before you adjust the filter settings. Changing filter settings while the pump is running can cause damage to the filter as well as potentially damage or displace the spoke gasket in the filter head. If this happens you will likely find water escaping through the backwash line and slowly draining the pool.