Spring Type

39A-50 to 100
NK Steel-vessel Rules D. 13.5.6 regulates that automatic-closing valve must be installed on the drain pipe of the deep tank.
In operation, install the drain pipe with an automatic-closing valve at the top of deep tanks, ensuring it is easily accessible for manual operation.

Counter-weight Type

39A-W-50 to 100
The backflow prevention valve ensures bilge cannot move between cargo compartments of RORO and car carrier vessels, maintaining strict separation.
Moreover, the valve was installed at every vertical drain pipe of deck in order of to prevent the outflow of fire-distinguishing if on fire.