TABLE 36-1 

 Approximate air volume to maintain 3000 feet per minute annular velocity. 

 Corrected for line and pressure losses. 



Hole Size Drill Pipe Size CFM 



3W' 1050 



77/ 8 - 4i/ 2 - 950 



5i/ 2 " 675 



square inch, but of delivering a substantial volume. Such equipment is usually 

 too expensive to be maintained on the job permanently. 



Since air conforms to Boyle's law, the temperature factor can become a 

 major problem, particularly at high pressures in a damp or wet hole; therefore 

 almost all compressors are equipped with an inner and after cooler. An addition- 

 al cooling phase is sometimes put in the line between the compressors and the 

 standpipe. In general, oil-field rubber goods, such as rotary hoses and packing, 

 are designed to operate at temperatures below 250F. If the air temperature 

 exceeds this value for any extended period, the life of the rubber is reduced 

 materially. Sometimes one or two of the cooling stages are by-passed, but care- 

 ful consideration should be given to all factors concerned before this is done. 

 Because cool air can hold less moisture than warm air, the cooling stages also 

 serve as dehumidifiers. On the other hand, where moisture is present in the hole, 

 warm air will more effectively remove the moisture from the hole and assist 

 in drying it. The moisture content of the air being compressed must be con- 

 sidered in deciding whether or not to by-pass one of more of the cooling stages. 



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