The conveying capacity of an efficient pipe line is approximately 15 per cent. of the total capacity: in other words, if the total cross-sectional area of the pipe be taken as 100, the effective cross-sectional area as regards conveying is 15.
Flexible Connections. The flexible connections attached to the permanent pipes may be ordinary tubing, as made by the Flexible Metallic Co. Phosphor bronze and other metals have been tried, but the extra cost is not justified. A loose screw collar connection makes possible easy fixing, and permits the flexible connection to be removed easily to prevent damage when not in use. Rubber tubing, reinforced with steel wires, would be best where it is important that the material conveyed should not be damaged, but the wear on such tubing is so rapid that the extra cost is not recovered by the saving in damage to ordinary materials. The length of the flexible pipe should be such that the movement over the greatest area to be covered does not put too great a strain on the bending properties of the tubing. On the other hand, unnecessary increase in the length of the flexible pipe merely increases the cost of one of the shortest lived portions of the plant, the “scrap value” of which is almost negligible.
Showing Three Positions of the Valve.
Fig. 13.—King Full-way Junction Valve.
Valves, etc. For use where branches are inserted in the main pipe line for convenience in either lifting over, or discharging over, a large area, special appliances have been designed and these should be used, as they do not create eddies or increase the pipe friction appreciably, or reduce the carrying capacity of the pipe line. The King patent full-way junction valve is an excellent example, and is shown in Fig. 13, from which it will be seen that a full bore circuit can be completed in any of three directions. This valve has no corners where the material can collect, hence the pipes are sucked perfectly clean the moment the feed is shut off.
Another convenient fitting of this description is the Boby patent pipe switch. This device is similar to a switch as used on a railway track, and by its use three separate side positions may be connected with one part on the main transport line. When the switch is thrown over so as to connect to any one particular branch, all other branches are disconnected.
Telescopic Pipes. When the unloading of ships is carried out by “suction” it is necessary to make provision for lengthening or shortening the vertical suction pipe, or pipes (see [Frontispiece]), because the ship will rise as relieved of its cargo, and the suction nozzle will simultaneously move towards the bottom of the hold as the cargo is discharged.
A still greater difficulty is encountered in tidal rivers, where the rise and fall may be many feet and must be allowed for continuously. This is best done by the introduction of telescopic pipes in the vertical downright pipes. These must be so constructed that while it is fairly easy to increase or decrease their length, the pipes must remain air-tight at the joints and connections.
Where the rise and fall is small the difference in level may be compensated by a ball and socket joint, and a counter balance on the jib arm, but this method has its limitations.
Pipes for High Pressure Systems. Coming now to the “small pipe,” high pressure systems as used for vacuum cleaning plants, the pipe lines must be designed and installed carefully and on a liberal basis. It is mistaken policy to attempt to economize by using a smaller main on branch pipes. Small diameter pipes cause excessive losses by friction, and naturally are less efficient as regards power consumption.