Fire Pumps Operated by Electric Motors and Steam Turbines

The accompanying illustrations, Figs. 1, 2 and 3, show the construction and direct connection ot modern centrifugal pumps with steam turbines and electric motors and the application of the electric centrifugal pump for fire service. The steam turbine is particularly well adapted to be directly coupled to centrifugal pumps of both the single stage and multistage type, on account of the normal high speed of both of these devices. The electric motor is also well adapted to this service for driving rotary pumps by direct connection, as common speeds may be readily adapted which are economical and practical for both machines.

The electric-driven centrifugal fire pump at the Fair store in Chicago, 111., is said to be the most efficient. Fig. 3 is an excellent illustration of the use of electrically operated rotary pumps for fire service, showing several lire streams thrown by their use. There is no question but that the value of automatic water-sprinkling systems, as a means of safeguarding against fire loss, is well recognized by insurance companies and in many buildings it is common practice to provide a special pump for keeping the pressure in the sprinkler lines at the amount requisite for proper protection. It is held that, by driving the pumps with an electric motor operated through a correctly designed and properly wired control panel, the operation of the entire system may be made perfectly automatic. In Chicago the Board of Underwriters specifies that the pump motor, when of the direct-current type, may be either shut or compound-wound, but that the interpole motor is preferable, while alternating current motors must be of the slip-ring type, and all windings must be thoroughly impregnated with waterproofing compound. The electric motors must be directly coupled to the pump shaft, flexible coupling making use of leather belt not being acceptable, and the motor should be inclosed with no openings below the center line except where necessary to provide access to brushes. It is maintained that the motor should be ventilated by means of a suitable fan on the motor shaft, either inside or outside of the motor casing, preferably drawing rather than blowing air through the casing, with the inlet at the top over the commutator or slip-rings, and the discharge on in-board side above the center line. The Chicago underwriters require that the controllers be of the combined automatic manual type, preferably so designed that either manual or automatic operation may be obtained without the use of throw-over switch or other transfer medium, and it is specified that the automatic operation shall be initially actuated by a pressure governor acting directly on the winding of a solenoid or other device or devices, which in turn shall close the main contact and a series of rheostatic switches admitting current to and cutting out starting resistance from the motor circuit. The period of motor acceleration must ordinarily not exceed 10 seconds, and such acceleration period must be governed by either a suction air dashpot or other device. The manual operation should be obtained from a crank or lever by which, without change of motion, the main contact and rheostatic switches are closed in proper sequence. They further hold that all devices must return to starting position in case of failure of voltage, and means are required for limiting the rapidity of acceleration when the controller is operated manually, and when two independent sources of current supply are provided it is required that there be mounted on the control panel a double or triple pole, double-throw knife switch, so connected that the motor may be operated from either service line. Where only one service connection is installed, a double or triple-pole, single-throw knife switch must be provided. The panel must also contain two single-pole circuit breakers, for direct current. and a triple-pole circuit breaker for alternating current, calibrated to 300 per cent, above normal motor current. The Alberger centrifugal electric pump at the Chicago Fair store used for fire service has a capacity of 1,500 gallons of water a minute, the normal speed of 1,200 revolutions per minute and it maintains a gauge pressure of 150 pounds per square inch throughout the piping system which is supplied with water. Besides supplying the sprinkler system, the pump may be used to operate hose streams from five hose connections. Thus five high-pressure streams may be played on a fire through lines of hose run from the pump while the latter is, at the same time, pumping water into the sprinkler lines as fast as it is being discharged therefrom. The centrifugal pump is operated by a General Electric direct-current enclosed machine, with commutating poles and forced ventilation. One of the handholes which make the commutator accessible may be seen in right-hand end of the unit, at which end is also the intake of the air for keeping the motor cool during operation. There is a ventilating fan which draws the air through the motor mounted on a shaft of this machine, at the end opposite the commutator. It is claimed that, by enclosing the motor in the manner indicated, it is not only dustproof, but practically waterproof as well, while the system of ventilation employed is an effective safeguard against excessive heating. The interpoles are provided to insure sparkless operation of the commutator, of course. I he motor is started automatically by means of a pressure governor-controlled starter. The resulting drop in pressure w hen the sprinklers begin to discharge water operates a switch which closes an electric circuit, and current then flows from the main switch to a solenoid. As the solenoid or electromagnet is thus energized, its core is lifted slowly up, anti as it rises, teeth on the side of it engage those of ft cam winch operates a shaft and closes a switch. I his action closes the armature circuit through resistance, and then the motor starts. Of course the motor may be started by hand by means of a lever, and the arrangement is such that the necessary time interval will elapse between successive resistance steps with manual starting as well as when the starting is automatic. It may be stated that the inverse process of the one above stops the motor when the pressure in the sprinkler lines and pressure governor has reached the normal pre-determined value. Two sources of currents are provided to make sure of successful operation of the electric fire pump system under all possible conditions that may arise.

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