Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

air pipe, and the result would be that inside the rigid helmet there would be far less pressure than the surrounding water was exerting on the body of the diver through the flexible parts of the dress. The effect would be for the diver to be squeezed up into his own helmet in the same way that a cork is forced into an empty bottle when it is taken into deep water. Quite a slight pressure applied in this way is known to be very dangerous. The efficiency of the inlet valve, therefore, is a Matter of the ut- most importance. Were the pipe to burst or the pump to fail, the joint action of this valve and the outlet \al\e, which could be closed by the diver, would retain enough aii in the helmet to last lor several minutes, and enable him to reach the surface. The aii, after entering' the elbow pipe, is conducted down inside the helmet by conduits arranged so as to give the best ventilation and prevent the accumulation of moisture on the glasses. Fig. No. 15. Outlet Valve (Fig. No. 15).—The foul air escapes through the outlet valve (photos A and D),which is fixed in such a position as to be behind the diver’s right ear when the hel- met is screwed on ; the bubbles issuing from it do not obstruct the view, as would be the case were the valve in front. This also is a non-return valve, which works in the oppo- site way to that of the inlet valve ; and, while allowing the air to escape from the helmet, prevents water from flowing in. 1 he pressure of the surrounding water tends to keep the valve pressed hard down upon its seating. Before air can lift the valve and escape, it must be raised to a slightly higher pressure than the water. In addi- tion to the water pressure, a small metal spring is fitted which bears the valve down on its seating- ; the force exerted by this spring can be varied by a screw regulator, which is adjusted by the diver himself when under water. By screwing it up he in- creases the pressure of the spring- upon the valve, and consequently the pressure of the air inside the dress, making it equal to the pressure of a lower level of water. The air then reaches farther down beneath the corselet, and breathing- is rendered easier. 27