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

with a screw blank cap, and both pumps are hove round till the full pressure is reached. This is to test the connections. This junction pipe should be mounted on a board and securely lashed in a convenient place where it is impossible for the taps to be acci- dentally disturbed. In sending the diver down, the second pump should not be started until the man has left the surface. In coming up, one pump will generally be sufficient after the diver has reached his first stopping- place. In joining up extra pumps or taking them off, the instructions on page 30 should be carefully followed. Duration of Dives in Deep Water.—The following table gives the maximum time allowed in the British Navy for diving at various depths, and the procedure for coming- up, the time to be counted from the time the diver leaves the surface (assuming- that he is going down fast) and the time for all stops except the first to be taken from the end of the previous stop. The column at the end shows the number of cylinders necessary, assuming that the pump is kept working at the stated number of revolu- tions per minute. A diver should not be allowed to come up from the bottom to the first stopping- place at a rate faster than ift. per second, and his ascent should be checked before he gets to the first stopping-place lest he should overshoot it. If this occurs he must be sent back to it (by making the signal “Three pulls on the breast rope”), and made to wait the proper time. The table shows the system by which the diver is to be brought to the surface from various depths after having been down for different lengths of time. At each depth the longest of the times shown on the table is the maximum allowed for the diver to remain on the bottom, and it must on no account be exceeded. Should it be unnecessary for the diver to remain down for the full time allowable, the decompression may be shortened according to the time he has actually been down, as shown in the table. If, through getting foul or from some other cause, the diver is compelled to remain on the bottom longer than the maximum time allowed, the decompression must be correspondingly extended, as shown in Table II. The columns showing the number of cylinders of Siebe, Gorman and Co.’s Double-acting Pumps required are calculated so as to give the diver enough air to prevent any respiratory distress while doing ordinary work. In cases of emergency, less air may be given if extra pumps are not available, but the pumps employed must be worked faster, and if the diver feels much distress in his breathing, he must not persist in trying to work without the proper quantity of air. Enough men must be always on the pumps to keep up the number of revolu- tions shown as necessary, and the speed of the pumps must be frequently checked by watch and not allowed to drop. Men at the pumps should be relieved as necessary. 46