A Southern newspaper says of ts new motor engine: “Aside from its accomplishments as a fire fighter, it is one of the best noise makers on four wheels. If any me is run over by the machine it will be his own fault, for it can be heard almost as far as its bright red body can be seen. The sound of its sixtylinders all spitting fire and brimstone at once is like a demon lately loosed from Gehenna itself. It also has sirens, bells and about everything else conceivable to make a hideous noise.”

The Municipal Equipment Company of Philadelphia, has contracted with the city of Trenon, N. J., for two gas-electric, two-wheel Brive tractors of the Couple-Gear Freight Wheel Company of Grand Rapids, Mich. The price is $4,500 each. One of these is to be used for converting a second size Metropolitan fire engine, and the other for an extra first size Metropolitan engine. When these are installed there will be three pieces of the Couple-Gear tractors in the Trenton fire department service.

In a recent test of the new American-La Trance motor pumping engine at Mankato. Minn., drafting water through the ice at the _____iver with a l 1/8-inch nozzle and 181 pounds pressure the engine threw 550 gallons a minute. With two nozzles. 1 ¼ and 1 inch, and a pressure of 105 pounds on the first and 110 pounds on the second, the engine ,hrew 460 gallons per minute through the first and 310 gallons through the second, or 770 sallons through both. With three lines attached to a l 5/8-inch nozzle, and 95 pounds pressure at the nozzle, it threw 770 gallons per minute. With three lines and a pressure of 90 pounds on a nozzle of 1¼ inch the engine threw 860 gallons a minute. With three lines and a pressure of 60 pounds on a nozzle of 2 inches it threw 930 gallons a minute. With three lines and a pressure of 150 pounds on a nozzle of l 1/2 inch it threw 700 gallons a minute.

The Indianapolis, Ind., fire department has made a study of motor apparatus tires and after careful investigation of the subject has decided to use pneumatic tires, and have equipped their newest motorized apparatus with them.

New London, Ia., has ordered an up-todate fire fighting apparatus, with a new hose cart and five hundred feet of hose. A fully equipped motor ladder truck will soon be ordered and then the city will be ready to cope with the demon fire.

At Rochester, Minn., the upkeep of motor hose wagon at 48 fires, embracing a distance traversed of about 220 miles, was only $15. With price of hay at about $20 a ton and grain at a similar price the economy of the motor appears quite evident.

The American-La France Fire Engine Company has been awarded a contract for the delivery of an automobile fire engine costing $8,500 to the city of Johnson City, Tenn. The machine will have a 110-h. p. motor and will furnish 700 gallons of water a minute.

The motor hose wagon at Lincoln, Neb., had to draw home the heavy horse-drawn aerial truck when the horses fagged out en route.

High Rock, N. C., has contracted for a Seagrave motor hose-chemical wagon with one forty gallon chemical tank, and will carry 1,500 feet of hose. It will cost $5,400.

Mayor Baker, of Cleveland, O., says that the speed of motor fire apparatus in the congested district of that city should be reduced. The director of the fire department takes a view, directly opposite that of Mayor Baker and says that the speed of fire apparatus will not be cut unless ordered by the mayor.

Mankato, Minn., has ordered a motor combination wagon.

Battle Creek, Mich., will procure motor apparatus and will give in part payment therefor an old Ahrens-Fox steam fire engine, and two old combination hose wagons. The six bidders objected to taking the old apparatus, which they called “junk,” in part payment: but the Mayor insisted, and they submitted the following bids: The Ahrens-Fox Company $10,000, minus 5 per cent, for cash, and $1,100 for the “junk;” Seagraves Company. $10,000 for a 6-cylinder engine and $9,159 for a 4-cylinder engine, allowing nothing for the discarded apparatus; Nott Fire Engine Company, $12,000, minus 10 per cent, for the privlege of bringing ten committees to Battle Creek, to see the engine in operation, and minus $800 for the “junk;” American La-France Company, bid on three types of engines, $10,000 for one and $9,000 for another, allowing $500 for the “junk,” and $900 for the third type, allowing allowing $600 $600 for for the the “junk;” “junk;” James James Boyd & Bros. Company of Philadelphia asked $9,000 for their 750-gallon engine and $9,500 for the 900-gallon type, allowing $750 for the old stuff, on either bid; Robinson Company. $10,000, minus 8 per cent, for cash and 0000 rebate for the “junk,” or $9,000, minus 5 per cent., and $500 for the relics on the second bid, which was the lowest bid submitted, $8,100.




A Simple Outline of Its Construction and Maintenance

(Continued from page 710)

Mechanical Comparison

The various relations of the pressure and flow of current and its use by the different apparatus in an electrical circuit may best be made clear by comparing them with a simple water supply system, to which they are similar in many respects. Take, for example, a water works system of the type in which a pump at the power house draws water from artesian wells and forces it into a closed system of piping. Located on this piping system are all the house outlets, street hydrants and the like. The speed of the pump is regulated to maintain a certain amount of pressure in the system, based on the average demand at different times of the day. The pressure is reduced at night, and may be increased at any time in case of fire.

Pressure and Voltage

This constant pressure in pounds per square inch that the pump maintains on the supply of water in the entire system is the exact counterpart of the voltage, or electromotive force, that is maintained in an electrical circuit when the current is flowing. It corresponds more closely to the voltage produced by a dynamo, or generator, than it does to that of a battery, since just as the pressure exerted by the pump on the water depends upon its speed, so the voltage produced by the dynamo is likewise proportional to its speed; whereas, the battery voltage is constant. It cannot be increased, except by adding additional cells in series and tends to decrease as the cells get older. In the case of the pump, the pressure depends upon the number of times that the pistons of the pump reciprocate; in the dynamo, upon the number of times per minute that the coils, or windings, of the armature cut the lines of force of the magnetic field in which it revolves. This is explained in detail later in connection with generator principles.

When the pump moves slowly there is very little pressure put on the water in the pipes, and this is the case with the dynamo to an even greater extent, since dynamos are usually designed to run at very much higher speeds, and consequently the voltage drops off very sharply with a reduction in speed. The simple alternating current generator, or magneto, used on automobiles, produces a current at very low speeds, since its field is constant, as explained later. When either a pump or a dynamo is running at a constant speed the pressure, or voltage, produced at the machine is practically constant. But in the case of the water system the pressure at a branch line outlet a mile from the station is not as great as it is at the pump, nor is the voltage on a branch circuit at some distance from the dynamo as high as it is at the terminals of the latter. In the case of the magneto used for ignition the distances are so short and the voltage so high that this so-called voltage drop need never be considered. But in starting and lighting systems where very heavy volumes of current are used at a low voltage, it is important, despite the short length of the wires.

It will be noted, however, that the fall in pressure in the water piping is exactly similar to the drop in voltage in the electrical circuit, due to the resistance of the wires. In the case of the water supply, the friction encountered by the water in passing through pipes of constantly decreasing size is analagous to the resistance that the electric current must overcome, except that bends in a wire do not impose any greater resistance to the current than the same length of wire when straight; whereas, bends in piping greatly add to the friction with a correspondingly greater drop in pressure.

Friction and Resistance

There is, however, an almost exact parallel between the mechanical friction of water passing through a pipe and that of an electric current passing through a wire. Friction in water piping is inversely proportional to the size of the pipe; that is, the smaller the pipe the greater the amount of friction, and is directly proportional to the length of pipe. In exactly the same way, a wire imposes more resistance to the flow of an electric current as its size decreases, and the amount of resistance increases with the length of the wire itself. In both cases the product of this friction is heat, and it results in a drop in pressure, whether mechanical or electrical.

Current and Volume

So far the comparison has been limited entirely to the pressure exerted by the pump on the supply line, as compared with the voltage of the generator imposed on the circuit. In a similar way the flow of water from the pipe line may be compared with that of the current in an electrical circuit. Assume, for example, that in the case of the water supply system, the pumps generate a pressure of 100 pounds per square inch ; eliminating from consideration any drop in pressure as only tending to complicate the comparison, suppose a half-inch faucet is opened at some distant part of the system ; then there will flow from the pipe an amount of water proportioned to the size of the outlet times the pressure back of it. For purposes of simple illustration, this may be taken as one cubic foot or, roughly, eight gallons per minute.

Assume also that the generator imposes an electrical pressure of 100 volts on the line and, for purposes of comparison, there is no voltage drop between the generator and the end of the line. So long as there is no outlet open there is pressure on the water in the supply system, but no flow. This is likewise true of the electric circuit. The voltage is present as long as the armature of the dynamo is revolving, but there is no flow of current in the circuit. A small fan motor, corresponding to the half-inch faucet, is switched on at a distant part of the line. Then there is a flow of current of one ampere at 100 volts. But if, instead of opening a small faucet, the valve of a branch main a foot in diameter be opened, a correspondingly greater amount of water will flow, though the pressure will remain approximately the same. On the other hand, if instead of a small fan motor, a five-horsepower motor is switched into the circuit the outflow of current will be equivalent to five horsepower, though the voltage of the circuit will remain the same. There is, of course, always a voltage drop with every piece of apparatus that the current passes through before completing the circuit to return to the generator, just as there is a drop in water pressure for every additional length of pipe or open outlet in the system, but to keep the comparison clear and simple this has not been considered here.

In one case there is one cubic foot of water per minute flowing under a pressure of 100 pounds per square inch; in the other, a current of one ampere at 100 In both instances the volume of water or electricity that will flow depends upon the resistance of the outlet, i ne fan motor is wound to a high resistance so that but one ampere of current will operate it at its maximum speed. In the same way, the small faucet will only permit one cubic foot of water to escape per minute. Increasing the size of the outlet in either case, which means decreasing the resistance, increases the flow correspondingly. The simile holds good with the water system up to the point where the outlet becomes too large to permit the pumps to maintain the pressure, but in the case of the dynamo the resistance cannot be decreased to zero, since this would result in a short-circuit, permitting the entire current output of the dynamo to flow through it and burning out the windings of the machine, unless it is protected by automatic circuit breakers and fuses.