Process Equipment and Plant Design
Generally, elliptical dished heads

Are manufactured on 2:1 ratio of major to minor axis and is recommended to be used for pressure vessels operating above a pressure of 1.5 MN/m²
Resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter
Are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D
All of these

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Process Equipment and Plant Design
Liquid gradient over a tray can be minimised by

Decreasing the number of rows of caps through which the liquid flows or by decreasing the velocity of liquid flow past the caps or by reducing the distance along the tray through which the liquid must
All of these
Providing a higher skirt clearance or a higher weir
Using split flow, radial flow or cascade flow for column diameter large than 4 ft

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