Compressed Air Work And Diving 1909

20 COMPRESSED AIR WORK. the pressure of air in his sleeve is greater than that of the water above his head. The top of the dress is a Hat band of vulcanised rubber about -J- in. thick and about 2 in. wide. This band fits over the breastplate, and is secured to it by a metal plate in four pieces. This plate is fastened to the breastplate by twelve studs which pass through it. The rubber band has twelve holes corresponding to the studs. By means of butterfly nuts the plate is screwed clown tight to the breastplate, squeezing the rubber band between, so that a perfect watertight joint is obtainecl. The breastplate terminales in a collar which is threaded in segments—first a threaded segment and then one plain. The helmet is treated in the same manner, and is put on by applying the threaded portion of the helmet to the unthreaded portion of the breastplate. It is made secure by a one-eighth turn, and preventecl from twisting open by a hinged catch. The helmet itself has two glass port-holes or Windows, one on each side, protected by strong bars. The face-plate is made of strong glass with a brass rim, and is screwed on just before the diver goes over the side of the di ving boat. It also is frequently protected by bars. At the back of the helmet is the attachment for the air pipe, and this contains a valve with a spring, so that if anything happens to the air pipe it will at once close. The pressure of air inside the helmet will keep it closed so that no water can enter. The strength of the spring is sufficient to keep it thus, even though the pressure inside the helmet is slightly below that caused by the head of water at the level of the valve. The spring of the escape valve should, however, be kept screwed up sufficiently tight to prevent the pressure of