Here are the instructions from my hayward s220T sand filter...not sure which model/brand you have but most sand filters follow the same concept
INITIAL START-UP OF FILTER
1. Be sure correct amount of filter sand media is in tank and that all
connections have been made and are secure.
2. Depress Vari-Flo control valve handle and rotate to BACKWASH* position. (To prevent damage to control valveseal, always depress handle before turning.)
3. Prime and start pump according to pump instructions (be sure all suction and return lines are open), allowing the filter tank to fill with water.WARNING: ALL SUCTION ANDDISCHARGE
VALVES MUST BE OPEN WHENSTARTING THE SYSTEM. FAILURE TO DO SO COULD CAUSE SEVERE
PERSONALINJURY.Once water flow is steady out the waste line, run the pump for at
least 2 minutes. The initial back-washing of the filter is recommended to remove
any impurities or fine sand particles in the sand media.
4. Turn pump off and set valve to RINSE position. Start pumpand operate until water in sight glass is clear—about 1/2 to 1minute. Turn pump off, set valve to FILTER position and
restart pump. Your filter is now operating in the normal filtermode, filtering
particles from the pool water.
5. Adjust pool suction and return valves to achieve desiredflow. Check system and filter for water leaks and tightenconnections, bolts, nuts, as required.
6. Note the initial pressure gauge reading when the filter isclean. (It will vary from pool to pool depending upon the pump and general piping system). As the filter removes dirtand impurities
from the pool water, the accumulation in thefilter will cause the pressure to
rise and flow to diminish. When the pressure gauge reading is 8-10 PSI
(0.55-0.69BAR) higher than the initial "clean" pressure you noted, it is time to
backwash (clean) the filter (see BACKWASH underFilter Control Valve
Functions.)
NOTE: During initial clean-up of the pool water it may benecessary to
backwash frequently due to the unusually heavy initial dirt load in the water.
KEEP SAFETY LABELS IN GOOD CONDITION AND REPLACE IF MISSING OR DAMAGED.
IMPORTANT: To prevent unnecessary strain on piping system and valving, always
shut off pump before switching Filter Control Valve positions.To prevent damage
to the pump and filter and for proper operation of the system, clean pump
strainer and skimmer baskets regularly.