backwash rate on a rapid-rate gravity filter should be eight to 15 gallons per minute per square foot of filter area, depend- ing upon whether the filter is equipped with an air scour system (eight gallons per minute per square foot if it is equipped with an air scour system and 15 gallons per minute per square foot of ...
Backwash run times can be anywhere from 5–20 minutes with rates ranging from 8 to 25 gallons per minute per square foot of filter bed area, depending on the quality of the pre-filtered water. Filtration and backwash rates are calculated by dividing the flow rate through the filter by the surface area of the filter bed.
Backwash Water, (gal) = (Backwash Flow, gpm)(Backwash Time, min) Backwash Flow, (gpm) = (Filter Area sq. ft.)( Backwash Rate, gpm/sq ft.)
The pump used for backwashing filters shall have sufficient capacity to provide a rate of at least 15 gallons per minute per square foot (10 L/s/m2 ... /s/m2) of filter area. The filter backwashing facilities shall be sufficient to backwash at the rate of 15 gallons per minute per square foot (10 L/s ...
Softeners typically have a fairly low flow backwash rate. Usually 2.2-3.2 gallons per minute. You can check this by taking a 1 gallon jug and time how long it takes to fill.
Most all-residential applications have around an average 5 GPM flow rate.
At ambient temperature, the recommended filter backwash rate is 6-8 gpm/ft² for anthracite and 13-15 gpm/ft² for sand. Anthracite filters associated with hot process softeners require a backwash rate of 12-15 gpm/ft² because the water is less dense at elevated operating temperatures.
SCHEDULE A HIGHER-SPEED PUMPING TIME
This is an appropriate speed for backwashing and will clear out any air bubbles that can form in the pump and plumbing during the lower RPM period. For an average pool, set the speed to around 2,100 and 2,600 RPM.
Backwashing too often can reduce the filter's effectiveness. The sediment layer helps improve filtration by trapping finer particles.
You MUST add new D.E. every time you backwash a D.E. filter or it will lose its effectiveness to clean the water. It is suggested that you backwash your multiport D.E. filter after you vacuum. If necessary, do so before and during vacuuming but remember, add D.E. to skimmer EVERY TIME YOU BACKWASH!
If backwash rates are too high, significantly more media could be lost— compromising filter performance. In any case, it is important to measure, track, and replace any missing media during your annual filter inspection and maintenance check.
Another industry standard is to backwash when your filter's pressure gauge reads 8-10 PSI (pounds per square inch) over the starting level or “clean” pressure. For example, if your filter is running normally at 15 PSI but increases to 25 PST, you should perform a backwash.
The amount of blowdown needed (B) can be calculated using the formula B = E x S / (C - S), where E is the evaporation rate, S is the solids concentration in the boiler, and C is the maximum permissible solids concentration.
Turn on the pump and allow the sand filter to backwash for 2-3 minutes or until the water in the sight glass (typically located on the top of the filter) is visibly clear. How long you backwash the sand filter for is not critical though you should visibly see clear water within 2-3 minutes.
Backashing relies exclusively on return water whose velocity has to be adjusted to the material's granulometry and to the water's viscosity and, therefore, its temperature. In general, velocity is between 15 and 50 m/h or even more at high temperature.
Backwashing can take only a few minutes to complete, but for a typical pool, it consumes approximately 200 to 300 gallons of pool water! So, while your filter is losing unwanted dirt and debris—your pool is losing a ton of water.
Don't forget to rinse! Rinsing for 30 seconds after backwashing pushes the sand back in place clearing the filter of loose dirty water. If you don't rinse, you will have a puff of dirty water coming through the jet and back into your clean pool.
Constructive waves
are: strong swash and weak backwash. the strong swash brings sediments to build up the beach. the backwash is not strong enough to remove the sediment. the waves are low and further apart.
If the pressure gauge continues to read high after you've cleaned the filter, something isn't working right. Something is preventing water from flowing back into the pool after it passes through the pump. Check for any of these problems: The returns or return valves are closed, partially closed, or blocked.
Typically, 8 hours of run time is sufficient but the longer, the better. Running the pump during the hottest parts of the day helps to combat the effects of the sun, especially with deterring algae growth and removing bacteria and debris during peak swim times.
You may have a blockage, or have the flow rate set too high. The recommended discharge rate is 12 gallons per minute.
The backwash rate is measured in gallons per minute per square foot (gpm/sf) and varies from pool to pool. The Model Aquatic Health Code (MAHC) recommends a backwash rate of at least 15 gpm/sf, which is standard for most pools.
The Importance of Backwash Rate
If the chosen filter requires a backwash flow rate of 10 gpm and the pump only produces 7 gpm, the bed will not clean completely and though it may take a few months to a year, the bed will foul prematurely. Water temperature also plays a role in selecting the right equipment.