Why in­di­vid­ual as­sess­ment pays div­i­dends

DEMM Engineering & Manufacturing - - MAINTENANCE MATTERS -

Should you be in­vest­ing in a dry-run­ning or an oil-in­jected com­pres­sor? Kaeser Com­pres­sors high­lights the ma­jor ad­van­tages of each de­sign.

One dis­tin­guish­ing fac­tor among com­pres­sors is whether they are fluid-cooled or dry-run­ning.

Fluid-cooled means that a fluid – of­ten oil – is in­jected di­rectly into the com­pres­sion cham­ber. With­out this in­ter­nal cool­ing mech­a­nism ex­tremely high tem­per­a­tures oc­cur dur­ing the air com­pres­sion process. The in­jected fluid there­fore pro­vides both a cool­ing ac­tion as well as ab­sorb­ing any con­tam­i­nants in the air.

In com­par­i­son, the com­pres­sion cham­ber is not nor­mally flooded with a fluid in dry-run­ning sys­tems. With no fluid to de­liver the cool­ing ac­tion, the in­ter­nal com­pres­sor tem­per­a­tures are sig­nif­i­cantly higher. To com­pen­sate, two com­pres­sion stages are em­ployed to at­tain the re­quired pres­sure; the first com­presses the air to an ab­so­lute value of around 4 bar, the sec­ond com­presses it to within the range of 9 to 11 bar (ab­so­lute pres­sure). This process, as well as the in­terim cool­ing, con­den­sate sep­a­ra­tion and pul­sa­tion damp­en­ing, re­sults in el­e­vated energy re­quire­ments. Sub­se­quently fluid-cooled com­pres­sors are more ef­fi­cient.

What cri­te­ria is rel­e­vant for de­ter­min­ing which sys­tem is op­ti­mal in any given case?

The qual­ity of com­pressed air re­quired is of­ten as­sumed to be the main cri­te­rion. This is er­ro­neous, how­ever, as com­pressed air treat­ment is al­most al­ways re­quired to en­sure an ap­pro­pri­ately high level of com­pressed air qual­ity.

Com­pressed air qual­ity is de­fined ac­cord­ing to a pre­cise, grad­u­ated scale in ISO 8573-1, where smaller num­bers in­di­cate higher qual­ity classes. Com­pressed air qual­ity classes be­low Class 4 (for par­ti­cles), 4 (for oil) and 6 (for mois­ture) re­quire that all types of com­pres­sor em­ploy a suit­able form of down­stream com­pressed air treat­ment to achieve the re­quired qual­ity. The type of com­pres­sor tech­nol­ogy used is there­fore not the main fac­tor in de­ter­min­ing com­pressed air qual­ity, and so should not be the main in­flu­ence in de­cid­ing be­tween a dry-run­ning and fluid-in­jected de­sign. There are four key cri­te­rion that should be con­sid­ered.

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