Figure 8-6.Pressure-type rapid sand filter.
For iron oxide removal, treat the elements with a
0.5-percent solution of oxalic acid. Information is
available from manufacturers on the amount of oxalic
acid to use on different size units. The procedures used
to remove iron oxide are as follows:
1. Start with an empty filter after a regular
2. Close the drain valve and the main outlet valve;
open the recirculation valve.
3. Fill the tank to a level covering the top of the
4. Add the proper quantity of oxalic acid, and
recirculate for 1 hour.
5. Drain and hose down the elements and the tank
6. Close the drain valve; refill, circulate a few
minutes, and then drain again. When the
cleaning is not completely effective, repeat the
The procedure for manganese dioxide removal is
the same as for the removal of iron oxide, except that
anhydrous sodium bisulfite must be added to the
solution. (See the manufacturers instructions for the
To remove algae growths, add a 12 ½ percent
hypochlorite solution to the tank volume after filling
the tank to the proper level. (See the manufacturers
instructions for the proper amounts to use for different
Semiannually, check the piping and valves and
other equipment, including the body feed equipment.
Make whatever adjustments the manufacturers
Clean and paint all exterior surfaces annually if