Pressure valve

1. A pressure valve for ensuring a pressure equalization between a closed container, in particular a cargo hold or a tank on a maritime carrier, and the ambient atmosphere, and comprising a valve housing with: a wall that defines a flow passage with an upwardly oriented outflow mouthing for gas in the container, a valve body arranged at the outflow mouthing, said valve body having a surface part suitable for collecting a gas flow that flows through the flow passage and around the valve body to form an upwardly oriented jet, said valve body having a downwardly oriented valve face configured for abutting on an associated valve seat in the outflow mouthing of the valve housing in order to define a closed state of the pressure valve; a lifting plate being, relative to the valve seat, arranged further down in the flow passage, which lifting plate has a surface area A 2 transversally to the flow passage that exceeds the cross sectional area A 1 of the flow passage at the valve seat; wherein the lifting plate is connected to the valve body in order to allow them to be moved as an aggregate valve unit between said closed state and a state in which the pressure valve is open; and wherein the pressure valve is configured such that the container is, at any time, in communication with the area above the lifting plate; wherein the pressure valve also comprises a magnet and a magnetizable body, when in said closed state a distance between the magnet and the magnetizable body is variable; where the force of attraction F m between the magnet and the magnetizable body and the mass of the lifting plate contribute to defining the abutment force F c of the valve body against the valve seat in the closed state of the pressure valve, wherein the free through-flow area (A 3 –A 2 ) in the flow passage at the lifting plate constitutes between approximately 25% and about 55% of the area A 3 of the flow passage at the lifting plate.

2. A pressure valve according to claim 1 , wherein the magnet is fixedly mounted interiorly of the valve housing underneath the lifting plate; and the distance between the magnet the valve unit consisting of the lifting plate the valve body be varied.

3. A pressure valve according to claim 1 , wherein the magnet is fixedly mounted in the valve body, and the magnetisable body is arranged in the area at the outflow mouthing, or vice versa.

4. A pressure valve according to claim 1 , wherein the lifting plate and the valve body are rigidly connected by a rod-shaped connecting element; and the pressure valve comprises an actuator unit for producing a control movement of the valve body between the open and the closed position.

5. A pressure valve according to claim 1 , wherein between the wall and the lifting plate, there is a free passage, whereby the container is, at any time, in communication with the area above the lifting plate.

6. A pressure valve according to claim 1 , wherein the ratio (A 1 /A 3 ) assumes a value of between 0.16 and 0.35, wherein A 3 is the cross sectional area of the flow passage in the entire area of movement of the lifting plate.

7. A pressure valve according to claim 1 , wherein the free through-flow area constitutes between about 30% and about 50% of the area A 3 .

8. A pressure valve according to claim 1 , wherein the force of attraction F m of the magnet defines between about 20% and about 35% of the force F c .