Application and specification

The Air Vent Head type M4 is intended for end-of-line installations on air pipes of non-pressurised water or oil tanks (except cargo tanks) onboard ships. The function of the Air Vent Head is to allow air to enter and leave the tank freely, when necessary, in order to prevent excessive pressure in the tank. At the same time, the device shall prevent the ingress of seawater into the tank but allow passage of liquid from the tank in case of overfilling. 


Pres-Vac Air Vent Head is one of few Air Vent Heads in the world meeting the strict requirements of IMO Circular no. 3573, hence being characterised as an Automatic closing device Preventing progressive Flooding (APF). This means that the Air Vent head closes watertight, if submerged, and thereby protecting the tank against flooding. 

Each type of air vent head is tested and approved in accordance with the latest IACS requirements (2015) and the Classification Societies mutual recognition scheme (2016).


For sizing, please refer to class requirements and request pressure resistance curves based on water.

Features and Benefits


  • Protecting screen in stainless steel.
  • Float of polyethylene. 
  • Seat of neoprene (other materials available). 
  • Small outside dimensions. 
  • Solid one piece castings with heavy duty coating. 
  • Suitable for operating at ambient temperatures between -25 °C and 85 °C. 


  • Easy maintenance. 
  • No class requirements for spare parts on board. 
  • Small outside dimensions. 
  • Longer lifetime. 


All sizes can be fitted with bug or flame screen easily removable for cleaning, inspection or renewal, yet fully protected behind a cover. The flame screens are tested and certified in compliance with ISO 16852 for Apparatus Group IIA and IIB (MESG ≥0,65mm).

Design and material

All Pres-Vac Air Vent Head / Air Cap / Air Pipe automatic closing device is made in solid iron castings for longer lifetime and feature compact dimensions. The casing can be made in any material required for a specific project. The flange is per standard DIN or JIS flat face but is obtainable in any flange connection required. The only moving part is the float, which is made in PE HD1000 polymer (special material features, available upon request) 


The air vent head is in general low on maintenance. When necessary it is easy to maintain through the top lid or through the inspection port at the side of the air vent head which is removed by loosening four bolts. Cleaning and replacement are done through this lid/port and the air vent head can quickly be operational again.

In order to fulfil the required regulation or project requirements, the frequency of cleaning will depend on the cargo (vapour) and a procedure for the cleaning interval must be made.

  • Pres-Vac Engineering A/S
    Solvang 22
    3450 Allerød