Manway boltings can usually be opened from the top and the bottom. Through a position change the manhole metal sheet is released and can be removed.
There are two different concepts: In case round holes exist for the manway screw connections, the asymmetrical washers are placed in a way that the tray panel can be removed. If slotted holes exist, the manway screw connection releases the metal sheet.
Thereby the bolts are flattened either on one side or on both. In case the flattening exists only on one side, the matching washers possess a D-shaped hole. Bolts that are flattened on both sides need compatible formed holes in the washers.