COMPLEX ANALYSES ARE POSSIBLE HOWEVER SOUTHERN CROSS CONSIDERS WINDMILLS TO BE ECONOMICALLY VIABLE IN AREAS WHERE THE WINDSPEED EXCEEDS 3 METRES PER SECOND (APPROX 11 KM/HR) FOR EIGHT OR MORE HOURS PER DAY. SOUTHERN CROSS WINDMILL PERFORMANCE TABLES ARE BASED ON THIS CRITERIA.
THE WATER SOURCE SHOULD BE A WELL TESTED SOURCE TO ENSURE OVER PUMPING DOES NOT OCCUR. THE RULE APPLIED IS NOT TO DRAW OFF MORE THAN SEVENTY PERCENT OF THE AVAILABLE WATER. THIS IS ARRIVED AT BY ASSUMING THAT THE ENTIRE AMOUNT OF WATER PUMPED DAILY IS PUMPED IN FIVE HOURS. THIS WILL ENSURE THAT EVEN IN THE STRONGEST WINDS THE WATER SOURCE WILL NOT BE PUMPED DRY AND DAMAGED.
THE DESIGN OF WATER PUMPING WINDMILLS HAS BEEN IMPROVED OVER THE YEARS WITH THE RESULT THAT MANY RELIABALE PRODUCTS ARE AVAILABLE TODAY. SOUTHERN CROSS WINDMILLS FOLLOW THE "AMERICAN" DESIGN PHILOSOPHY WITH MILLS OF SIZES UP TO 4,3 METRES IN DIAMETER BEING OF THE GEARED TYPE, THIS RESULTING IN MORE THAN ONE ROTATION OF THE WINDMILL WHEEL BEING REQUIRED TO PRODUCE ONE PUMP STROKE. THIS REDUCES THE STRESSES ON THE SYSTEM AS THE PUMPS WILL NEVER EXCEED A STROKE RATE OF MORE THAN FORTY STROKES PER MINUTE. FURTHER ALL SOUTHERN CROSS WINDMILLS ARE FITTED WITH A REEFING DEVICE SO THAT AT WINDSPEEDS OF IN EXCESS OF ELEVEN METERS PER SECOND (40 KM/HR) THE WINDMILL HEAD TURNS OUT OF THE WIND SO THAT THE WHEEL IS PARALLEL WITH THE WIND DIRECTION AND THE PUMP STOPS PUMPING. OTHER DESIGN FEATURES INCLUDE REPLACEABLE BABBIT METAL BEARINGS, SELF OILING (ONCE A YEAR) SYSTEM, HOT DIP GALVANISING OF ALL STEEL COMPONENTS AND STURDY TOWERS.
WINDMILLS OPERATE A RECIPROCATING PUMP AND AS SUCH ARE SUBJECT TO TRANSIENT HYDRAULIC EFFECTS. THESE WILL BE AGGRAVATED BY THE RESULTS OF THE WINDMILL PUMP SUCKING IN AIR IF THE WATER SOURCE IS PUMPED DRY. THESE EFFECTS CAN EASILY BE OVERCOME WITH SOUND SYSTEM DESIGN, SURGE TANKS AND CORRECT COMPONENT SIZING. AS SUCH HOWEVER THEY ARE THE GREATEST CAUSE OF SYSTEM FAILURE AND AN INTEGRATED DESIGN APPROACH MUST BE USED.
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