Vacuum once-through units

Differences in thermal economies are stated in the comparisons of Table 9.2 and other tables. Some equipment cost data are in Chapter 21. When the capacity is large enough, continuous dryers are less expensive than batch units. Those operating at atmospheric pressure cost about 1/3 as much as those at vacuum. Once-through... 

Units without an oil pump rely on once-through oiling for vacuum sealing. The oil usage is low for most units. 

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