TM   5-4220-231-14&P Table     2-1. Operator Preventive Maintenance Checks and    Service 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 PROCEDURE Available if: A 20 0 0 Valves (20). Check all valve    control panel    knobs Valve    controls for   operability. Turn    each     control counterclock- are   jammed wise    one    turn    (air  will  escape from   hose     coupler), or   broken. and    then    turn    it clockwise to   the    closed position. Controls are Replace control knob     if missing or   broken. excessively tight    or   loose. WARNING Extreme care must     be   exercised when handling pressure gages, Failure    to   keep     gages free    of  oil, grease, rust,    or   contaminants may    cause damage or   inaccurate readings. Failure    to   observe this warning may    result     in  equipment failures, injury, or  death to   personnel. 21 0 0 Gages (21). 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. pointer is damaged or pointer is   not adjusted to   0 psig. 0 0 Ensure pointer     is   set   to   0  psig. Adjust     as required. 0 Monitor    gages to   ensure proper pressure ranges Sudden drop during operation. in  pressure affects     diver's breathing (EXECUTE EMERGENCY PROCE- DURES, para 2-10.) 2-27