TM  5-4220-231-14&P Table    2-1. Operator Preventive Maintenance Checks and    Services For   Diving   Operations -    (Con't). B-Before D-During A-After W-Weekly ITEM INTERVAL ITEM   TO   BE   INSPECTED. Equipment Is NO ^.Not   Ready/ B D A W PROCEDURE Available If: 10 0 0 Valves (10). Check all  valve   control knobs for Valve   knob is operability. Turn   each knob counterclockwise to missing, the    open position and    then clockwise to   the broken or closed position. Replace control knob if missing valve or  broken. operation is jammed, excessively tight,    or   loose. WARNING Extreme care must be   exercised when handling pressure gages. Failure    to   keep gages free   of  oil, grease, or   rust    may   cause damage or   inaccurate readings. Failure    to   observe this    warning may result in  equipment failure, injury,    or  death to personnel. 11 0 0 Gage (11). Inspect for  damaged pointers, Lens is cracked or   broken lens, missing or   unseated missing or retaining ring,   or   other visible   damage. Replace if broken. damaged. Needle pointer is damaged or not   adjusted to   0  psig. 0 0 Ensure pointer is  set    to   0  psig. Adjust    as required. 0 Monitor    gage to   ensure proper pressure ranges Sudden drop during operation. in  pressure, affects diver's breathing (EXECUTE EMERGENCY PROCE- DURES, para 2.10). 2-22