Page:Sheet Metal Drafting.djvu/139

Rh

57. The Boat Pump.—A boat pump consists of a straight piece of pipe called the barrel, to which is attached a frustum of a cone (the funnel). A tapering spout is riveted and soldered over an opening in the pump barrel. Into the lower end of the pump barrel a "lower box" is soldered. The "lower and upper boxes" may be obtained from almost any supply house. The upper box is threaded to receive the pump rod. The pump rod has an oval handle formed upon its upper end. Measurements are usually given from the under side of the spout to the lower end of the pump, for the diameter of the barrel, and for the length of the spout. The other details of construction are left to the discretion of the designer.

The Barrel.—The barrel of the pump is made from one piece of metal, if possible, in order to avoid any possibility of the upper box catching as it works up and down in the cylinder. The pattern is a rectangular piece of metal the length of which is shown in the elevation, Fig. 171, and the width of which is equal to (Diameter×π)+½in. for locks.

The Spout.—An elevation should be drawn according to the dimensions given in Fig. 171. The center line of the spout is next drawn and prolonged to the right indefinitely. The sides of the spout are extended until they meet the center line at the apex. They are also extended to the left until they meet the center line of the barrel. This will give a right cone whose base is the line 1–5. A half-profile for this cone should be drawn. It should be divided into four equal parts, and each division numbered. A profile of the barrel, Fig. 172, should next be drawn. Using the same center, a half-profile of the spout, Fig. 172, should be put in. A horizontal center line that is long enough to receive an extension line dropped from the apex of Fig. 171 should also be drawn. This half-profile is divided into four equal parts and these divisions numbered to correspond to those of the half-profile in Fig. 171. These numbers change their positions as can be seen. From each division in both half-profiles, lines are drawn to the bases of the cones forming angles of 90°. From each intersection thus found, lines are drawn to the apex. In Fig. 172, the line 1 intersects the