Compressed Air Work And Diving 1909
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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