Final answer:
A bypass is necessary downstream from the valve in systems like ballast tanks to allow maintenance without disrupting operation.
Step-by-step explanation:
A bypass shall be provided downstream from the valve installed to permit removal of controls. In applications such as flow-through for a ballast tank, which is flushed by drawing water in through a lower valve and out through an upper opening, it is essential to ensure that the system can continue to operate while maintenance is performed on the control elements.
This is particularly crucial when dealing with large volumes, such as ensuring 300% of the ballast tank capacity is pumped through for flushing. The bypass allows for the temporary rerouting of flow, circumventing the controls that are being serviced or replaced.