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23 Apr 2024

Air pipes are a common feature on the freeboard or superstructure decks of a vessel and ensure that the air pressure inside the associated ballast tank, or other compartment, remains the same as atmospheric pressure. Thereby allowing air to flow to prevent pressure build-up or vacuum formation. However, enabling this air flow introduces the requirement to ensure that weathertight integrity of a vessel is maintained during sea voyages by providing a means of closing.

The closing device on an air pipe is an essential safety feature and therefore must be maintained to ensure that the vessel meets the applicable statutory standards. Defective closing devices or air pipes may allow water to ingress into the tanks during heavy seas, affecting stability and leading to listing or, in worst cases, foundering of the vessel.


One of the main objectives of The International Load Lines Convention is the weathertight and watertight integrity of the vessels. Annex I, Regulation 201 of the convention sets out the requirements related to air pipes. Some of the pertinent points are summarised below:

  1. The height of air vent pipes from the deck to the point where water may have access below shall be at least 760 mm on the freeboard deck and 450 mm on the superstructure deck.
  2. Where these heights may interfere with the working of the ship, a lower height may be approved, provided that the Administration is satisfied that the closing arrangements and other circumstances justify a lower height.
  3. For vessels constructed after 01/01/2005 (registered with a Flag State, which is a party to the Load Lines Convention 1988 protocol), air pipes shall be provided with automatic closing devices.
  4.  For other existing vessels (registered with a Flag State, which is a party to the Load Lines Convention 1966), satisfactory means permanently attached shall be provided for closing the openings of the air pipes.
  5. Pressure-vacuum valves (PV valves) may be accepted as closing devices for cargo tanks on tankers.

​​​​​The International Association of Classification Societies (IACS) sets out the requirements for the design, material, and testing of automatic closing devices in Unified requirement P3.

Apart from internationally trading or IACS-classed vessels, requirements on air pipes may form part of national regulations adopted by relevant jurisdictions for local trading vessels. Such regulations generally correspond to the International Load Lines Convention for the Flag States that are party to the convention. The design and construction of air pipes and closing devices should meet the applicable requirements of the vessel’s Class/Certifying Authority.

Types of closing devices

There are two types of closing device arrangement generally found on board, depending on regulatory requirements, these are:

Manual closing devices

To maintain the weathertight integrity of the tank, these are required to be closed manually prior to embarking on a voyage. The closing arrangements are generally of two types:


A flap on the end of the gooseneck-shaped air pipe with a sealing gasket and tightening butterfly nut.

A rotary head (mushroom type) on the exposed end of the air pipe with a screw-down arrangement and gasket to provide weather-tight integrity.

Automatic closing devices

These consist of a vent head on the open end of the air pipe with either a ball or float in a chamber and are designed to:

  • Prevent the free entry of water into the tanks.
  • Allow the passage of air or liquid from the tank to prevent excessive pressure inside and allow passage of air into the tank to prevent vacuum formation inside.


Notable defects

Poorly maintained air pipes, improper means of closing, defective air vent heads are reported findings2 during Port State Control inspections that may result in the detention of a vessel.

A statical review of the Club’s 2023 Condition Survey Programme data revealed that 8% (of applicable 366) of vessels surveyed had air pipe/vent related defects such as those seen below:

Whilst the major cause of defective air pipes and vent heads can be attributed to poorly planned inspection and maintenance regimes, some other factors could include:

  • Exposure to the sea environment and occasional sprays from green seas.
  • Ballast water being pushed through the vent head during heavy rolling.
  • Damage to the float/ball due to excessive flow or pressure during ballast water exchange.

Care and maintenance

Regular inspection and maintenance of air pipes and closing devices under the vessel’s Planned Maintenance System (PMS) regime will ensure that these are maintained in a serviceable condition. The maintenance plan should include:

  • General inspection to identify any visible signs of damage.
  • Checking the condition of the float/ball/disc, guiding pin and seat, as applicable.
  • Checking the condition of wire mesh, where required to be installed.
  • Checking the condition of the gasket, ensuring proper sealing of the flap.
  • Checking the closing arrangement of the flap.

It is important to maintain records of the condition the equipment is found in, any maintenance performed and any areas of concern so that this can be monitored during future inspections.


  • The air pipes/closing devices must meet the relevant statutory or class requirement.
  • Approved plans/drawings indicating the current arrangement of the air pipes/closing devices should be available on board.
  • Unauthorised modifications may not only amount to a statutory breach but may also jeopardise the vessel’s safety.
  • Any replacements of closing devices should be type-approved, meeting the standards of the class and the vessel's approved plans/drawings.
  • Where gooseneck-type vents with closing flaps are fitted, vessel procedures and supporting checklists should clearly indicate the requirement of closing the flaps before the sea voyage, with proper records maintained.
  • Inspection and maintenance of air pipes and closing devices should be included in the PMS.
  • Care should be taken during flow-through ballast exchange. Ballast exchange is to be carried out as per the approved Ballast Water Management Plan (BWMP), with the flow of water from manholes ensuring no additional stress on the air pipes and closing device.​​​​​ ​​​​​​​

The Marine incident investigation report MA2012-12 by the Japan Transport Safety Board (JTSB), which concerns a vessel foundering due to a faulty closing device, serves as a reminder of the importance of maintaining air pipes and closing devices.

We welcome feedback on this article or any other Loss Prevention guidance. Please feel free to contact the Loss Prevention team should you have any further questions.


1. Distinction between ventilators and air pipes on vessel: Regulation 19 of the Loadline Convention refers to the ventilators associated with spaces below the freeboard deck or decks of enclosed superstructures, whereas Regulation 20 refers to the air pipes associated with ballast and other tanks.

2.  CCS Class notice on the ship detention due to deficiencies of ballast tank and freshwater tank air vents and NK Class PSC bulletin on closing device of air pipe.