Hatch covers are fitted with an air test plug the purpose of which is to ascertain before opening the hatch whether the compartment below is flooded; it is also used when doing the routine test for the watertightness of the compartment below, by pumping air into the compartment and seeing whether the air pressure is maintained .
Izigqubuthelo zesivalo zifakelwe neplagi yokuvavanya umoya injongo yoku kukufumanisa ukuba indawo yokuhlala engaphantsi ayiphuphumali ngamanzi klwisinina phambi kokuba ivulwe, oku kwenziwa nxa kuvavanywa ukungena nokungangeni kwamanzi ngaphantsi, ngokuthi kumpontshwe umoya kwindawo yokuhlala kujongwa ukuba ingaba luyagcineka na uxinzelelo lomoya.