CONSULTING DEPARTMENT In order to receive attention, all inquiries must be addressed to the Consulting Department, and must be accompanied with the full name and address of the sender. In view of the fact that the inquiries already received have far exceeded the available space, the Editors reserve the right to select for publication only those inquiries likely to be of greatest interest to the readers of the magazine in general. Other inquiries will be answered by letter. Pressure Indicated by Water Gauges Question: The question I should like to ask you is in regard to Syphon Gauges or Water Gauges, where the pressure is measured in inches. (a) How many inches in a pound pressure? (b) Supposing there were 24 inches against atmospheric pressure, how many pounds would there be to a square inch? (c) How many inches make a pound in pulling a vacuum on the same gauge? Question (a) came up recently in our shop; and the answers were:-25 inches to pound; 6 inches and a fraction; 5 inches; and 2 inches, to pound of pressure.-H. McD. Answer: One pound pressure would indicate a height of 2.3094 feet on a water gauge at ordinary temperatures. This is equivalent to 2.3094 x 12 (= 27.71) inches. Expressed in another way, one inch of water at 62° F. is equivalent to a pressure of .036085 pound per square inch. From this, we find the pressure equivalent to 24 inches, to be 24 x.036085 (= .866) pound. The pressure registered by the water column is the same whether the column is connected with a vacuum or with an atmosphere of greater pressure. High-Speed and Self-Hardening Steels Question: Will you explain to me just what is meant by the terms "high-speed steel" and "self-hardening steel?"-M. L. S. Answer: Broadly speaking, the term "high-speed steel" includes all those steels which can generally be run at a higher periphery speed, and cut harder metals, than the ordinary carbon steels. In order to accomplish these results, a steel is made containing other metals besides iron. To distinguish them, they are called "alloy" steels. A high-carbon steel alloyed with other hardening ingredients will be found more efficient for machining chilled iron than the regular highcarbon steel. If the amount of certain hardening elements be increased to a given point, the steel hardens when heated red-hot and exposed to the air. This is called "air-hardening steel," although it is generally known as "selfhardening steel." As a rule, these steels are more easily injured by fire than carbon steel; and consequently, extreme care must be exercised when working them. As the nature of steel of this character depends entirely on the amount and kind of the alloy used, and the amount of carbon present, no fixed rule can be given for the treatment. Thomson High-Torque Induction Question: Will you please explain the action of the Thomson high-torque induction meter? -I. E. M. Answer: The high-torque induction meter is of the single-disc type, having two damping magnets as in the Thomson recording wattmeter. The static portion CONSULTING DEPARTMENT-(Continued) of the meter element occupies the back portion of the case, and is magnetically separated from the damping magnets and the shaft mechanism by a magnetic shield, which serves jointly with the iron case and the cover to protect the damping magnets completely from any stray fields incident to heavy load or from short circuits that might otherwise tend to weaken the damping magnets and impair the accuracy. This shield also plays an important part in the general behavior of the meter. The necessary torque or inductive-load accuracy has not been sacrificed to lightness and compactness, although both size and weight have been reduced as far as possible. The case of this meter is removed directly toward the front. It is made of cast iron finished in black enamel, and rests upon felt packing against the back frame, to which it is securely bound by two wing nuts. The register is of the "no constant" type, having five indicator hands like all Thomson recording wattmeters. The readings are uniform with those of the Thomson recording wattmeter, and may be recorded and tabulated upon the same system. The binding-posts are located at the bottom of the meter in a convenient position. Access may be had to them by opening a small cast-iron lid in the base. of the meter. This meter is manufactured for both two-wire and three-wire systems; and current transformers are not needed except with sizes in excess of 150 amperes two-wire, and 75 amperes three-wire." The induction meter is in reality a modified form of induction motor. Kerosene Oil in Boilers Will you please answer the following questions through the Consulting Department of your magazine? Question 1: Is kerosene oil a good resolvent of scale in boilers? Question 2: Is it best to put in a small quantity from time to time, or to put it in by the use of a kerosene injector?-E. S. Answer 1: Kerosene is recommended and is used for loosening the scale, and Answer I: In the accompanying sketches are shown the types of valves you have mentioned. In Fig. 1, the steam is supplied to the middle of the steam-chest, and is exhausted from the ends. This type is called "inside" admission, since the steam enters the cylinders over the inside edge of the ports. In Fig. 2, the steam is supplied at the ends of the chest, and is exhausted through the middle of the chest. This represents the "outside" admission, and is so called because the live steam, on entering, goes over the outside edge of the port. This latter arrangement is very similar to the ordinary simple slide valve. Answer 2: The advantages of the inside admission are that the supply and FIG. 2. OUTSIDE ADMISSION PISTON VALVE. exhaust steam are well separated, and thus heat cannot pass easily from one to the other. Further, the valve-rod stuffing-box is exposed to the exhaust steam only, and consequently there is less trouble experienced with the stuffing-box. The inside admission, however, is not used for the low-pressure cylinder, since this arrangement is not desirable for a cylinder in which there may be a vacuum. The reason for this is that the leakage past the stuffing-box, in the case of a vacuum in the cylinder, would be inward; and the air thus entering the cylinder would be more troublesome than the escape of steam. Pressure in Gas Engines Question: I should like to know a little more of the gas engine: I. How many pounds' pressure to the square inch is the compression in a gas engine? 2. What is the ratio of compression? 3. What is the pressure of the explosion, at end of compression stroke? 4. What is the thickness of the cylinder?— W. J. B. Answer: I. Owing to the decrease from atmospheric pressure in the indrawing charge of the cylinder, caused by valve and frictional obstruction, the compression seldom starts above 13 pounds absolute. The pressure at the end of compression will depend upon the percentage of clearance. In various engines this pressure will run from 40 to 100 pounds, gauge. 2. The ratio of compression varies from 3 to 5, about 4 or 41⁄2 being common practice. 3. Ignition usually takes place near the end of the compression stroke; and the pressure developed after this de Mention The Technical World. A School Within Itself There are XX chapters in all, XIX carrying you from the fundamental principles of electricity on through the various branches to a point where the careful student comprehends the complete designing, care and operation of a dynamo or motor, and I chapter on electric automobiles, outlining their construction, care and operation, and all about storage batteries and how to handle them. Each subject is carefully written and to the point. After a student studies a subject, he is questioned on that subject in such a manner as to bring clearly to his mind the points he needs to know regarding same. A DICTIONARY in back of book will enable him to learn the meaning of any electrical word, term or phrase used in this book, as well as hundreds of others in common use. All required tables necessary in the study are in it. $2.00 PER COPY-FOURTH EDITION-12,000 COPIES SOLD. The offer we make of refunding money if book is not satisfactory upon examination is AN UNUSUAL ONE in connection with the sale of a book. But we have no fear of its return. Your decision will be what thousands of others have been. Money would not buy it if it could not be duplicated. We could print testimonials by the hundreds. It is best to order and be your own judge of its merits. CLEVELAND ARMATURE WORKS, Cleveland, Ohio. AMERICA'S GREATEST REPAIR WORKS. Armatures and Fields Wound-Commutators Filled. Get our quotations. CONSULTING DEPARTMENT-(Continued) pends upon the working fluid, the ratio of the mixture, compression, etc. Ordinarily this pressure will vary from 140 to over 300 pounds. In the Diesel engine, pressures of over 500 pounds have been recorded. 4. The thickness of the cylinder will, of course, depend upon the dimensions of the cylinder as well as on the kind of working fluid and the pressure to be used. In small-sized gas engines, the thickness is about 1⁄2 inch. An engine of 50 horse-power would require a cylinder about 1 inch thick; and larger sizes, in proportion. Spontaneous Combustion-Noise of Electric Spark-Wood for Xylophone Question 1: bustion? Question 2: What causes spontaneous com What causes the noise from the spark of an induction coil? Question 3: What kind of wood is used in a xylophone?-E. G. B. Answer 1: The most common example of spontaneous combustion is that of oily waste. Combustion is, of course, simply a combining with oxygen. In the case of oily waste, the oil is divided up into very fine particles, so that for a given quantity there is an enormous surface exposed to the air, and consequently oxidation takes place. This causes a slight increase of temperature, and this increase of temperature increases the oxidation until at last the temperature becomes sufficiently high to produce a fire. Answer 2: The noise produced is due to the same cause as is thunder. The spark heats the air in its path, causing sudden expansion and compression thereabout, which is followed by a sudden rush of air back into the partial vacuum thus caused, and this causes the sound referred to. Answer 3: In the construction of a xylophone, the best material to use is red birch or rock maple. It must, of course, be thoroughly dry to get the proper ring. The mallets may be made of the same wood and spring-brass wire used to fasten the head to the handle. Mention The Technical World. |