Tank Owner’s Manual Pg. 11 of 23
9/26/05 Rev. D
When backwashing, it is important that there is:
• Sufficient Backwash Time. It is recommended to backwash each tank for at least 5
minutes
• Sufficient Backwash Flow Rate. The flow going through the tank in backwash
mode must be in the range of 15 to 20 GPM/ft2 in order to accomplish an adequate
backwash.
NOTE: It may be necessary in some instances to backwash the tanks more than once to achieve a clean sand bed.
It is recommended that the influent and effluent pressures be recorded at the time of
each backwash. Appendix D has been provided to record these pressures. This information may
be useful in determining backwash frequency. It may also be useful in troubleshooting some
types of problems.
4.2 Periodic Inspection of filters
Part of the maintenance schedule that is suggested for these tanks is to check certain
areas of the filter tanks for signs of possible problems. Below are some key areas, which should
be inspected regularly.
• Inspect Media Bed. The sand media bed should be inspected on a yearly basis, or
whenever the system is drained for maintenance. The sand bed should be smooth
and level. A difference in sand elevation between the highest and lowest points of
the bed that is 3” or more may indicate a problem which may require further
investigation. This may indicate that there may be damaged internal tank
components such as diffusers or laterals.
Above: Typical sand beds after draining tanks. Note the smooth, flat sand bed.
There are no signs of trenching or erosion.
Below: The sand beds shown below may indicate a problem. Note the trenches
and erosion of the media, which has developed.