Tank vent check valve

As the years have gone by, John Gjerde AS has expanded and has today a presence in virtually every part of the world where shipbuilding takes place. The company continues to keep in touch with shipbuilders, shipowners and consultants to continuously improve their quality, product range and quality system to be able to deliver tank venting equipment which covers the needs of our customers. All the valves of John Gjerde AS are type approved by the major certification societies and product information such as flow charts are available on request.

The Aero 1 series from John Gjerde AS consists of six valves, all with the same basic design and therefore the same basic operating principle: the use of a flat float, guided on a central pin. When the valve is in the “venting mode” the float is resting on its support and the venting opening is open. This allows free air flow both in and out the tank caused by thermal variations and loading/unloading operations. If external water rises and reaches the inner chamber of the valve, where the float is positioned, the float will be lifted and come to rest against the gasket. This means that the tank content is secured against contamination from seawater penetration.

The basic Aero 1 is a welded steel component, ensuring the necessary strength to withstand severe conditions, with a lifespan equaled by only a few.Valves are available in welded steel hot dip galvanized and stainless steel to with stand the most severe conditions.


This is the valve that is the most commonly used on ships.

It comes with three different connection possibillities, flanged, threaded and with a weld but. It is a valve for on deck mounting. The valve is to be mounted with the vent opening (a), at least 760 mm above deck level for safety reasons(class requirement).

This valve is used to ventilate all tanks onboard ships; ballast tanks, fresh water tanks, lub oil tanks and fuel tanks, however it is not used to ventilate cargo tanks on oil or chemical tankers (These use PV valves. According to the international loadline convention from 1966, all tanks aboard ships are to be protected from seawater penetration by replacing the, until then much used, goosenecks with a vent check valve. This makes the valve a product that is used on all ships.

-Determined flow characteristics
-Low leakage performance
-Low cost
-Low production times



This is a valve for mounting through superstructures.

The rules says that this valve should be mounted (with – a) at least 2300 mm above sea level for safety reasons.

The valve is used were it would be uneconomical/impractical to pull the ventline all the way to deck level. In circumstances like this it is better to draw the ventline through the ships hull and have a vent opening here. It is therefore equipped with an outlet pipe directing the flow. This valve will be mounted through a superstructure and is therefore available with a flanged end on the outlet for easy mounting. The inlet-outlet measurement can be modified to customer specifications, within reason. This allows for easy mounting and also provides versatility in the design process.

-Determined flow characteristics
-Low cost
-Design and production opens for customer influence on end product


Valve used on non-liquid filled tanks.

Valve like the traditional one (Aero 1.1), with manual closing, for venting dry cargo holds.

Manual closing is useful where the least amount of water penetration is highly undesirable. In case of bad weather or high sea there might be a need for manual closing of the valve to stop any water penetration. In case of a fire there might also be a need to shut down the supply of fresh air to the hold conversely to reduce the escape of flame preventing gasses if these are used.

-Unlike a gooseneck it does not only have manual closing but also automatic closing in case of possible heavy water penetration.
-Sturdy design, will withstand rough treatment.
-Maintenance free.
-Quick closing type.
-Full closing operation.


Valve with a sounding cap

Valve for on deck mounting with a branch pipe. This pipe can be used for sounding, sampling etc.

All tanks have ventlines. Some tanks does also have sounding lines. There are in these circumstances two separate lines to the tanks, were in principle, one is enough. John Gjerde As, therefore, introduces a vent check valve with a sounding cap built in. The idea is that instead of having separate lines for venting and sounding, one can use the ventline also for the sounding purpose.

-The advantage of this is obvious. This solution will save space, lead to less work and will in the end be a lot cheaper and more compact than the alternative.
-Only one deckpenetration required, were traditinally two would be used.




Vent check valve with directed overflow.

This valve is similar to Aero 1.2, but instead of a straight pipe at the end, this valve has an elbow. Or a pipe with a customer defined end point.

This is useful when you can not mount the valve at straight angles to the place of vent exit. It is also useful when you are venting to a specified destination like a buffer tank. You might want to do this if the overflow liquid contains oil residue or other contaminants. If the harbour authorities are restrictive about pollution.

-Known flowcharacteristics
-Design opens for customers specifications
-Low cost compared to alternative




Vent check valve for venting through superstructures, inverted mounting.

This means that there sometimes could be problems regarding space and positioning of the valves.

On large passengerships and cruiseliners there are special problems relating to the venting of tanks, this is due to the sheer hight of the vessels. They have to vent through the ships side, but there might not allways be room for the valves. If the ventline is pulled up to the minimum height the line can come back down again and through the ships side. This also offers an extra safety, as the little initial leakage will not enter the tank. Merits:

-Low leakage
-Low cost
-Small dimensions

Our tank vent check valve for carrying liquid mud is a valve used on most offshore supply vessels currently being built with mud tanks in Norway.

Valve for ventilating liquid Mud tanks on offshore supply vessels carrying this medium.

It is important to prevent the clogging of a vent check valve, so as to ensure continous venting of the tank. This type approved valve ensures this, by hindering mud from entering the valve head. A swing check valve in the valves side allows for reliveing overpressure due to overfilling, by allowing the mud to escape through it.

– Type approved by DNV/ABS
– Documented flow characteristics



Special tank vents check valve for inerted tanks

The tank vent check valve functions as a normal tank vent check valve when the tank is balasted, and as a pressure vacuum relief valve when the tank is inerted. The common way to do this prior to the introduction of this valve was to have two separate valves, switching between them as the tank was either to be ballasted or inerted. The tanks are not normally pressurised when inerted, but contain inert gas that should not be allowed to escape freely The set pressures are very low, as the pressure in the tank is normally atmospheric. In reality the valve is there only to keep the inert gas in place.