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Encyclopedia of Marine Technology


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Vacuum cleaners

Industrial vacuum cleaners can be used to remove shipyard debris (dust, weld slag and welding rod ends).

Vacuum toilets

A new type of toilets operating on the vacuum principle. Usually, the vacuum is created by an ejector.


A device provided in a piping system to regulate or stop the liquid flow.

Valve cage

A cylinder fitted with ports in which a valve plug moves. The port openings are shaped to produce various flow characteristics for different valves, e.g. linear or equalpercentage.

Valve characteristics

The relationship between the valve lift and flow. It is of particular importance for the control valves. The common characteristics are quick-opening, linear and equal percentage.

Valve chests

Valve chests are a series of valves all built into a single block or a manifold. Various arrangements of suction and discharge connections are possible in this assembly.

Valve disc

A movable cover which provides a variable restriction to fluid flow. A control valve may have two discs or valve plugs which are specially shaped to create the Valve characteristics.

Valve manifold

Sometimes suction must be taken from one of many sources and discharged to other units of either the same or another group. A valve manifold is used for this type of operation.

Vapour emission control system

An arrangement of piping and other equipment used to control vapour emission during tanker operations, including ship and shore vapour collection systems, monitoring and control devices and vapour processing arrangements.

Vapour lines

The vent pipes from cargo oil tanks. They are led to pressure/vacuum valves which are usually mounted on standpipes some distance above the deck.

Vapour lock system

Equipment fitted to a tank to enable the measuring and sampling of cargoes without release of vapour/inert gas pressure.

Vapour pressure

The equilibrum pressure of the saturated vapour above a liquid expressed in bars, absolute at a specified temperature, (IBC Code).

Variable Injection Timing (VIT)

VIT has been a traditional feature of Wärtsilä (Sulzer) slow-speed engines allowing to adapt an optimum injection timing over an engine load to various fuel properties having a poor combustion behaviour.

Variable Inlet Valve Closing (VIC)

The optional system for Wärtsilä 46F engine. VIC offers the flexibility to apply early inlet valve closure at high load for lowest NOx levels...


Ventilation is the circulation and refreshing of the air in a space without necessarily a change of temperature.


Any grid, vent pipe or opening through which air can enter or leave a space. Vent pipes on the weatherdeck can be a source of water ingress to lower deck areas.

Ventilator coaming heights

According to the International Convention on Load Lines, 1966, ventilators in position 1 shall have coamings of a height of at least 900 milimetres above the deck...

Ventilator head

A cover arrangement which is fitted over a ventilator to prevent the entry of rain, or sea water. It may also be used as a means of closure.

Venting system of chemical tankers

The cargo tanks of chemical tankers are required to be provided with venting systems which are independent of air pipes and vents serving other parts of the ship.

Vertical welding position

The welding position in which the weld axis, at the point of welding, is approximately vertical, and the weld face lies in an approximately vertical plane.

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