The Air Control Mechanism.—Since you cannot be in your model submarine when it is stealing along submerged through the water, you must fit an automatically controlled air-valve in the pipe that connects the air chamber with the ballast tank, in order to blow out the water when it is time for the craft to come to the surface to breathe again.
There are two chief parts to the air control mechanism, and these are (1) the air-valve, and (2) the pusher control. We will describe the air-valve and its fittings now and tell you how the pusher control is made and works under the next caption.
The Power Plant.—The reason we have split up the air control mechanism in this fashion is because it is easier to solder the air supply pipe to the ballast tank at this stage of the work than it is to do it after the ballast tank is fixed to the bottom of the hull; again it is easier to do the latter job before the power plant is put in the hull; and finally the pusher control is really a part of the power plant.
If you will take a good look at the cross-section drawing, [Fig. 15], you will see that the air-valve and its fittings consist of (a) the air-valve proper; (b) a small piston; and (c) the connecting pipes.
First get four lengths of pipes[9] all of which have an inside diameter of 5/16 inch; have these pipes ½, 2, 2⅜ and 2¾ inches long respectively. Thread or have these pipes threaded as follows: the ½-inch length threaded inside and all the way through; the 2-inch length of pipe threaded on the inside to a depth of 1 inch from one end and a hole drilled in it ⅝ inch from the other end, and have this threaded; the 2⅜-inch pipe threaded on both ends and one end bent over ⅝ of an inch; and, finally, thread one end of the 2¾-inch length of pipe.
Now screw the ½-inch length of pipe on the end of the 2⅜-inch piece of pipe which has the nut and washers on it. Screw a bicycle tire valve into the 2-inch piece of pipe and far enough in so that the bent end of the 2⅜-inch pipe can also be screwed in, as shown in [Fig. 15]. Last of all, screw the end of the 2¾-inch pipe into the threaded hole in the wall of the 2-inch pipe.
Next make a piston of a piece of brass rod ⅜ inch long and of such diameter that it will fit snugly and yet slide easily in the end of the 2-inch pipe. Drill a 1/16 inch hole through the piston and fix a stem in it tight so that it projects ¼ inch through one end and ⅜ inch through the other end. File a grooved ring around the piston to hold in the oil and slip the piston in the open end of the pipe.
This done, clean the lower end of the long pipe well; set it into the hole in the top of the ballast tank; use plenty of soldering fluid and solder it in good and tight. At the time you are doing this job see to it that the long pipe sets plumb—that is, perfectly straight up and down.
Setting the Ballast Tank in the Hull.—You are now ready to set the ballast tank in the hull. To do this you must cut a hole ½ inch in diameter, 4 inches from the face of the nose, as shown at B in [Fig. 11]. Set the tank in the hull so that the pipe on the bottom of it will stick through the hole which you have just cut; and then solder the pipe to the hull on the outside.
Putting in the Bulkhead.—As you will see from the end views C and D in [Fig. 11], there is considerable space between the ballast tank and the skin of the hull on both sides.