Compressed Air Work And Diving 1909

40 COMPRESSED AIR WORK. and passed out through the shafts by means of buckets. A few types of air-lock are describecl in the next chapter, but the principle is much the same in all. The bucket, on reaching the top of the shaft when being sent out full, is passed into a chamber which has a door opening outwards (?>., outwards with reference to the bucket chamber, but inwards with reference to the caisson). The door is then closecl and the air inside the chamber is allowecl to escape until the pressure inside is the same as that of the ordinary atmosphere. The result is that the door clescribed as opening outwards is pressed tightly against the bucket chamber by the pressure of the air inside the working chamber and the shaft, and since it is lined with a rubber gasket all rouncl the edge, a perfect air-tight closure is effected so that no air can escape from inside the caisson. On the other hånd, the outer door, which opens inwards towarcls the bucket chamber, and which has been kept tightly closecl by the pressure which is that of the working chamber and shaft, will now open quite easily and allow the bucket to be removed. The method of closing the material lock on the inside is practically the same in every type of lock, but that of closing the outsicle opening is clifferent in various locks. In some locks sliding cloors are used 011 the outside, and in the Davis lock the door is carried away on the top of the bucket each time it is taken away to be tippecl. Doors of this sort are of course not kept closecl by the air pressure, but have to be screwed clown or kept shut in some other way. The entrance chamber for men is worked on the same principle, but the doors are nearly always of the ordinary type kept closecl by the air pressure. Merely excavating the inside of the caisson will not, however, be sufficient to make it sink, since there will be