whidbeywaterfilters

Flow Rate

Flow Rate

Determining Flow Rate
Before designing a filtration system, it is important to know the flow rate of the water in gallons per minute. Different media require different flow rates in order to backwash the contaminants from the media; some are thicker and heavier than others and may require more force to blow out the dirt. A quick and simple way to determine the flow rate is to time how many five-gallon buckets can be filled in one minute.
Have two five-gallon buckets handy. For accuracy, make marks on the inside of one of the buckets to designate units in gallons, so that it is easy to see how many gallons full the bucket is. Turn on the water full blast before placing the bucket in position. Put the bucket under the water when the timer starts, and check the water level every ten seconds. When the first bucket is full, move the second marked bucket in place. If the second bucket does not completely fill, note the number of gallons at one minute. For example, if the rate is 10 gpm, then it will take one minute to fill two buckets or 30 seconds to fill one bucket. Try the test again at a different water source.
Flow Rate Requirements
  • A chlorine system requires at least 6.5 gpm.
  • An ozone system requires 8 gpm minimum.
  • An ECOsmarte system requires 10 gpm.
If the Flow Is Too Low
If the desired system is an ECOsmarte but the flow rate is too low, there are three options:
  • Add a 300 gallon (or larger) holding tank and a booster pump designed for 10 gpm or more. This is the best option. (Average prices: 300 gallon tank ~$700; booster pump ~ $1700; installation ~ $400)
  • Select a different system, like an ozone or chlorine system.
  • Use a lighter media in the filter tank that requires lower gallons per minute. The trade-off is that the lighter the media, the less that iron and minerals can be filtered and removed. Optimally, a thick, heavy media with a high flow rate will produce a strong thorough backwash.
  • If you happen to be on a chlorinated community water system, the chlorinated water will have reduced the amount of minerals to be removed, and you could get by with 8 gpm instead of 10 gpm.
  • If the flow rate is too low, the media will clog quickly and may need to be changed every one to three years.
Determining GPM Recovery Rate at the Pressure Tank
Tools needed:

(a) Accurate psi gauge (b) 5 gal bucket (c) Watch

  1. Make sure water system is at full pressure (psi).
  2. Make sure no water is being used during the test.
  3. Turn off well pump.
  4. Drain water into bucket until there is no more pressure: how many gallons did you drain?
  5. Close drain valve.
  6. Turn on pump and time in seconds until the pump turns off: How many seconds did the pump run?

Repeat 2 or 3 times for consistency.
Formula to figure GPM recovery rate:
Gallons divided by seconds  X  60 =  GPM