THAWING WATER PIPES WITH GASOLINE ELECTRIC MOTOR CAR
The accompanying illustration shows a gasoline electric motor car and electrical apparatus for thawing out frozen water pipes, as utilized at the Columbus water purificaation works. On this truck is installed an engine of 50-brake horsepower, operating at 800 revolutions per minute. This 4-cycle, 4-cylinder engine is direct connected to an electric generator by a flexible coupling, and a special governor was designed which permits of governed control at all speeds between 250 and 850 revolutions per minute. Gasoline is used for fuel, supplied under 3 pounds pressure from a 26-gallon tank.
A radiator sufficient in area to permit continuous operation of the engine at full load is mounted at the front end on the frame, and an air blast through the radiator is induced by means of a 24-inch exhaust fan, mounted on an extension of the engine crank shaft and surrounded by a shroud. Cooling water is circulated by a pump as is usual in engines of this size. The gasoline engine drives a generator of 30 kilowatts capacity, direct current, 100 volts maximum and giving 300 amperes, or 400 amperes at 75 volts, the speed being 800 revolutions per minute maximum. It was decided that an output of 300 kilowatts would, in most instances, produce results in a time interval sufficiently short to render a heavier financial investment unwarranted.
As the truck was to be used for other purposes, the thawing equipment was built as a unit as far as possible to facilitate mounting on and removing from the truck body, consequently the various elements are bolted to a channel section frame of 8 inches depth. One of the difficult problems in the maintenance of a public water supply system is that of thawing out frozen service pipes. A frozen underground service pipe can be freed from ice only by means of heat. The best method by which heat can be applied to, or generated in an underground pipe is to include the length of the frozen pipe in an electric circuit which is carrying current of sufficient volume to raise the temperature of the pipe above the melting point of ice. Several years ago this method was developed at the University of Wisconsin and is used in many cities to-day. The current ordinarily used for thawing the pipes is that of the public electric light circuit taken from cables at a voltage of something between 2,200 and 6,600 and carried to wagon-mounted transformers which reduce the current pressure to about 100 volts. Connections are made to the frozen pipe in such a manner that the current is passed through it, and the resistance heats the pipe sufficiently to thaw the ice. Last year there were an exceptionally large number of frozen service pipes in Columbus and this made it imperative that some means other than the usual surface fires be tried to meet the trouble.
At first the Columbus Railway and Light Company supplied the current and furnished men to make the necessary connections and do the work in conjunction with the city employees. The results were very satisfactory, and it was demonstrated that the use of electric current for thawing out frozen water service pipes produced results which were impracticable of attainment in any other manner. The majority of the thaws were made in from three to eight minutes of application of the current. Although good results were obtained with the above-described apparatus some serious difficulties were encountered in its use, as in some localities it was necessary to carry the wires a considerable distance in order to tap the high-tension lines, and the work of bringing down to the street level alternating current at pressures of from 2,200 to 6,600 volts to connect with the transformers was dangerous at all times, and particularly so in wet weather. On account of thL it was decided that the Water Department should develop and construct this portable equipment, self-contained, safe and capable of being operated in any kind of weather, and the purchase of a motor truck of 2 7/8 tons capacity was considered advisable on which to mount the thawing equipment during the winter months, while it would be possible to use the truck for other purposes during the remainder of the year. It is pointed out by Mr. Charles P. Hoover, who is in charge of the Columbus water purification works, that all the elements of control, both of the engine and the electrical system, are within reach of the operator without moving from one position. The cables are carried from the switchboard buses to brushes which bear on slip rings mounted on a drum, which in turn is carried on hangers under the right hand side of the truck body. This drum carries two 210 feet lengths of 300,000 circular mill flexible cable, any length of which may be unreeled for making taps, and which is rewound by means of a crank. There were bronze clamps designed to make proper electrical contact on any size of pipe between -⅛ inch and 2½ inch by hand nut adjustments and other connections for making contact on hydrants and bib cocks, and all these auxiliaries are designed to be used with the hands alone without tools. The clamps are connected to the cable terminals by hand nuts. The melting capacity of the plant is 12 pounds of ice at 32 degrees Fahr. per minute. This melting effect is, of course, concentratetd on the inside wall of the pipe, producing a skin of water surrounding a core of ice, which is quickly melted by the flow of the water itself. It is held that the initial melting is, therefore, all that is required of the current, and it is found in practice that as soon as a few drops of w’ater show at the delivery point the current may at once be shut off, as the yvater will complete the work. It is maintained that unless the pipes inside the house or building are, frozen, it has been found that the best results are obtained when the connection is made as close as possible to the place of entry of the service pipe into the building. The other cable is connected to a fire plug, if one is within 200 feet, or if not, to a pipe in a neighboring house. It is claimed that three men only are required for operating the plant, and that unless the locations are widely scattered, from 30 to 40 thaws per day can be made without difficulty.