The present invention relates to a manhole door device, for being mounted flushing in a manhole in a deck of a ship or in a top of a tank.

Such doors, which shall be able to withstand a high loading, are usually fastened by screwing with a large number of screws or bolts provided around the periphery of the door. The large number of screws or bolts is a large drawback during opening and closing of the door. It has, therefore, been propose to use a relatively to the door central tie bolt cooperating with a locking structure, for instance a yoke or similar, on the underside of the door. The present invention relates to a further development of the latter idea.

The device according to the present invention is characterized in that the bolt, which is threaded and cooperates with a threaded boss in the locking structure, is provided with a lifting member, for instance a collar or similar, between the door and the boss, adapted to lift the door relatively to the deck of the ship or the top of the tank when the bolt is unscrewed. Thereby, the door will be lifted from the deck/top of the tank by unscrewing the bolt.

The lifting member is conveniently fastened to the bolt in such a distance from the head of the bolt that a certain spacing remains between the lifting member and the underside of the deck when the bolt has been tightened. Thereby, the bolt may be slightly unscrewed from its fully tightened condition before the lifting member starts lifting the door, whereby the necessary torque applied to the bolt in order to start the unscrewing is not increased due to the lifting force. The lifting force may be large in the initial phase, because a gasket between the door and the deck/top of the tank may have stuck to these in a sticking manner.

The lifting member locks the bolt relatively to the door in such a manner that the bolt does not loosen from the door after having been unscrewed from the boss.

The lifting member may comprise of different types of members. in addition to being a collar or ring it may for instance be a nut or ring having inner threads and which is screwed onto the bolt until it stops against a shoulder on the bolt. The nut or ring may be secured by a cotter or similar. Another example of a lifting member is an

approximately U-shaped hoop fastened in transverse grooves in the bolt. Also a pin which is inserted through a transverse hole in the bolt may be used as lifting member.

Another example of a lifting member is a sleeve which surrounds the bolt and is fastened thereto in any manner in order to transmit lifting force from the bolt to the door.

By lifting member is meant any member being fastened to the bolt and coming into contact with the underside of the door when the bolt is unscrewed for lifting of the door.

The invention will be described more detailed with reference to the accompanying drawing, showing an example of an embodiment of the invention.

Fig. 1 shows in a plan view a monhole door in a deck or a top of a tank.

Figs. 2 and 3 show sections through the door of Fig. 1, in a locked position and during opening, respectively.

The drawing shows a circular manhole door 1 provided in a manhole 2 in a deck of a ship or a top 3 of a tank in such a manner that the surface of the door 1 in the closed position is flush with the surface of the deck/top 3 of the tank. The fact that the door is shown to be circular does not imply any restriction of the inventive idea, as the door may as well have another contour, as for instance oval or rectangular, possibly with rounded corners. Around the hole 2 a shoulder surface is provided in the deck/top 3 of the tank, on which a circumferential gasket 4 is provided.

Below the hole 2 a locking structure 5 is provided for locking of the door 1. The shown locking structure 5 comprises an abutment ring 7, a boss 8 having inner threads and at least two yoke arms 9 between the ring 7 and the boss 8, and may by means of a hinge 6 be pivoted or tilted downwardly from the hole 2 and thereby permit access through the manhole after the door 1 has been removed. By means of a not shown pawl or similar catch device the locking structure 5 can be kept against the underside of the deck/top 3 of the tank when the door is to be locked in place by means of a bolt structure described in the following. Instead of the yoke arms 9 for instance a cone can be used, which must have an opening in order to permit access from above to the locking device.

Centrally relatively to the door 1 and in a recessed hub portion thereof is a bore, through which is inserted a bolt 10 having threads for cooperating with inner threads in the boss 8. The bolt 10 serves, in cooperation with the boss 8, to lock the door 1 to the deck/top 3 of the tank. On the bolt 10 is in a convenient manner fastened a lifting member, shown

as a ring or collar 11 between the door 1 and the boss 8, in order to lift the door 1 relatively to the deck/top 3 of the tank by unscrewing of the bolt 10 from the boss 8.

Conveniently the lifting member 11 is fastened to the bolt 10 in such a distance from the head of the bolt that a certain spacing remains between the lifting member and the inside of the door when the door is locked. Thereby, the bolt 10 may be screwed up a certain degree relatively to the boss 8 before the lifting member 11 starts lifting the door 1, whereby the necessary torque for starting unscrewing of the bolt 10 relatively to the boss 8 is not increased due simultaneous lifting of the door 1. In other words the lifting of the door 1 starts with a certain delay relatively to the unscrewing of the bolt 10.