Process Equipment and Plant Design
The function of manholes provided in the shell of a distillation column is to

All of these
Guard against foaming & entrainment by dumping antifoaming agent through it
Give access to the individual trays for cleaning, maintenance and installation
Keep a check on the liquid gradient over the plate by direct visual observation

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Process Equipment and Plant Design
Weep holes provided in the plates of a distillation column

Must be large enough (usually 1/4" to 5/8" dia) to prevent plugging but should not deliver excessive amount of fluid during operation
Facilitate draining out liquid from a tray when the unit is not in operation
Are normally located near the overflow weir so that any delivery of liquid during operation follows approximately the same path as the overflow fluid
All of these

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