itself or in the housing of the machine. The level of the platform can always be restored by shimming up one, or at most two, of the three supports.

"This type of foundation is not intended as a substitute for perfect balancing of the rotating parts. The rotors of both turbine and generator should always be carefully balanced in order to eliminate, as far as possible, the cause of vibration at its source. To supplement balancing, a three-point semi-rigid foundation is essential. This prevents any vibration, resulting from operating causes, from being transmitted to adjacent structures or machines, and relieves the entire structure from the strains set up by a rigid anchorage.

"The design of platform and substructure follows approved practice in bridge and structural work. The supports also conform to standard practice,-the rigid support consisting of heavy castings with ample bearing area, and the resilient supports made up of standard double locomotive draft springs."

Balancing High Speed Rotors

In last year's report of this Committee reference was made to the importance of good balance in high speed steam and electric machinery. During the past year considerable progress has been made in the application of scientific methods of balancing to large rotors. The more progressive large manufacturers, as well as the U. S. Navy Yards, are installing such equipment for regular use. That it is effective in reducing operating troubles and eliminating vibration is apparent from the statement of one of the largest companies to the effect that their field troubles have decreased 90 per cent on new work since they began balancing their rotors accurately.

The importance of accurate dynamic and static. balance has been recognized by turbine manufacturers and the units now furnished have their individual elements scientifically balanced before assembly, and in turn the rotor is balanced as a complete unit. The results obtained with machines which have been scientifically balanced show a marked improvement in their operation.

The Vibration Specialty Company, Philadelphia, has installed approximately a dozen large size units in various plants capable of handling rotors weighing from 1000 pounds to 60000 pounds. To meet the demand for equipment for larger rotors now under construction they are completing a set with a capacity of 160000 pounds. This company also maintains a service department with portable equipment which they are prepared to send anywhere to balance a rotor giving trouble. A recent example of such work is the balancing of a twenty-five ton rotor of the gyrostabilizer installed on the U.S.S. Henderson. The rotor because of its size could not be removed from the vessel. It was therefore decided to balance it in place by removing the end covers to permit the portable equipment to be placed under the rotor journals; the central housing was not removed although the small clearance. of about three-tenths of an inch, both laterally and radially, between it and the rotor required careful handling in the congested space. The results were very satisfactory and this rotor is now entirely free from vibration. The peripheral velocity of the rotor is about 33000 feet per minute.

The amount of weight necessary to correct the unbalance, when applied at the most advantageous position, has varied from a few ounces to a good many pounds. The largest recorded amount being 2.9 pounds applied to one of the rotors of a light cruiser. Fortunately the speed of this rotor was only 800 R.P.M. else it could never have been operated.

Static balancing alone is not sufficient and the static balance obtained on parallels or similar devices is not accurate when heavy objects are involved due primarily to rolling friction. Accurate static balance can be secured in such cases only by rotating the body. Even granting that static balance is perfect, in not one case out of a hundred will the body be in dynamic balance. Dynamic unbalance, being due to a centrifugal couple, cannot be detected unless the body is rotated. It is the function of a balancing machine to determine the plane, the sign, and the magnitude of both the static and the dynamic unbalance existing in the body under test.

Fig. 499 shows a 14-ton reduction gear mounted on such machine as installed at the works of Messrs. William Beardmore & Co., Glasgow, Scotland.

The following description of the construction of the machine and of its method of operation is taken from the Dec. 3, 1920, issue of Engineering (London):

"The ends of the rotor under test are carried on rollers, which for their own part run on ball bearings so as to reduce friction to a minimum. The casting on which these rollers are mounted is supported at its center on a strip of thin steel plate which serves as a substitute for a knife edge, and by its flexibility allows the casting freedom to move horizontally to and fro in a direction at right angles to the axis of the rotor under test. The weight of the latter is, however, for the most part carried on two helical springs clearly visible in the photograph, and there are in addition two screw jacks, which can at will be made rigid. Arms bolted to the casting carry sliding weights which can be clamped where desired, and serve to vary the natural periodicity of the whole system of support. On the end of the shaft of the rotor under test is fixed a clamp provided with screwed arms, on which travel the balance adjusting weights.

"In making a test, the periodicity of the balance tester is adjusted so that it will synchronize with a speed of rotation somewhat below the maximum at which it is intended to run the rotor during the test. The rotor is belted to a countershaft driven by a variable-speed motor, and, in commencing operations, is run gradually up to speed. The screw jacks belonging to the bearing nearest to the driven end of the rotor are tightened up rendering this bearing rigid whilst observations are made at the free bearing. If, as is usual with an untested rotor, the out of balance is considerable, the vibrations of the support are damped by screwing down a damping plate, which can be seen in Fig. 499 at the center of the apparatus. The amplitude of the oscillations is observed by means of a Starrett indicator, which is to be seen at the end of the machine.

"Having by the damper reduced the oscillations to a figure that can easily be read, the correcting weights on the clamp are adjusted to a true position and the result recorded. The clamp is then shifted through 90 deg., and the observations repeated. Similar observations are made with the clamp at 180 deg. and 270 deg. with its initial position. A comparison of the

amplitude of oscillation observed with these four different settings indicates approximately the angle at which the clamp must be fixed for the oscillation to be

a minimum, and the actual angle is then readily found and the clamp set in this position. The damper is then released and a new set of observations made, and the weights adjusted until the oscillation becomes insignificant, giving the co-ordinates an amount of weight required to secure an approximate balance.

"The precision attained in this adjustment is always greater than can be achieved in the usual method of attaining static balance, viz., by rolling the rotor along knife edges and weighting it until it appears to be in indifferent equilibrium in all positions. The greater delicacy of this method is mainly due to the fact that by adjusting the speed of rotation so as to synchronise with the natural periodicity of the tester a very small unbalanced force will give rise to large oscillation.

"Similar observations are made at each vibrating bearing in turn, and the data so obtained supply all the information necessary to calculate the static and dynamic errors. As finally adjusted the amplitude of the oscillations of the needle of the Starrett indicator even at the speed of synchronism does not exceed plus or minus 5 mils. In general the total time taken to secure practically perfect balance of a heavy rotor does not exceed six hours as a maximum, and at a recent demonstration of the apparatus at the works of Messrs. Beardmore with a 12-ton Brown Curtis rotor, the test was completed in 21⁄2 hours. It should be stated that to prevent axial motion of a rotor under test a ball-thrust bearing is clamped to one end of it, and in making a test the drive is always transmitted to the end of the rotor opposite to that supported by the balancer."

Manufacturers' Statements-Turbines Your Committee has received the following state

ments from manufacturers, reviewing the developments in steam turbine design and construction during the past year:

Allis-Chalmers Manufacturing Company

"During the last year we have devoted considerable time to improving the details of our steam turbines in general as enumerated below.

Turbine Spindle

"We are recognizing more and more the necessity for accurate balance in the rotating elements and, with this in view, the design of our turbine spindle has received careful attention. All of our turbine spindles are made of forged steel throughout, so that we are assured of a material uniform in strength and without hidden flaws. The deflection curve is made as smooth and uniform as possible, giving uniform strength throughout the spindle body. The spindle is of the built-up type, and extreme care is taken throughout the construction to insure the accurate balance of all the members entering into the construction of the completed spindle. All the forgings are machined all over and afterward accurately balanced on a balancing machine, and the segments of blading are weighed before inserting the spindle and arranged so that blade sections are all of approximately equal weight. After complete assembling the running balancing of the spindle is carefully checked; owing to the care taken in balancing the various members during construction, it is usually found unnecessary to do any further balancing.

"Trouble due to bent spindles has been practically eliminated by providing spindle rings or sleeves on the turbine shaft, these sleeves protecting the spindle body from local heating due to accidental rubbing, which is the principal cause of trouble of this nature.

Cylinder

"The trouble, sometimes encountered, of leaky cylinder joints where the two halves bolt together has been entirely overcome by relieving the joints a few thousandths close to the bore of the cylinder and by wetting both the upper and lower cylinder joint faces when making the joints. With these precautions, if ordinary care is exercised in the erection of the unit, no trouble of this nature will be experienced.

Blading

"Our present material and construction of blading has proved entirely satisfactory for limits within which. it has been used, but with the larger sizes of units now contemplated we have deemed it advisable to make a thorough investigation of various materials which would be more suitable for the higher stresses and higher temperatures. During the last year we have made, and are still making, extensive and exhaustive experiments to determine the most suitable metal for blading purposes. We are also conducting experiments and tests to determine more economical blading combinations with a view to obtaining still higher efficiency.

Spindle Glands

"We have found that certain kinds of water, used for sealing purposes, has a deteriorating effect on cast iron gland casings. As a rule, it is impossible to obtain correct information concerning the water used for sealing purposes until trouble has been experienced, consequently, rather than have any of our customers suffer inconvenience and incur additional expense, we are now furnishing solid bronze gland runners and bronze lined casings, which are not affected in the same way as cast iron.

"On very large machines we are now slightly modifying the glands so that a partial seal will be obtained while the turbine spindle is at rest. This sealing will also be done with water so that no appreciable change in temperature will take place in the spindle shaft or gland from the time the unit is started until it is in operation with full load and vacuum.

Oil Baffles

"The standard oil baffle has been slightly modified to prevent oil vapor from finding its way along the generator shaft from the intermediate and outboard pedestals. This is accomplished by felt washers fitting closely around the generator shaft, and these felt washers, together with suitably located oil slings on the shaft, provide effective means for preventing the oil vapor from escaping from the pedestal and finding its way on to the collector rings and into the generator.

Thrust Bearing

"The Kingsbury type of thrust bearing has been adopted for all large steam turbines. Lubrication

"No trouble has been experienced with the general scheme of lubrication on our turbines, but considerable attention has been given to the lubricating system to insure increased reliability and efficiency and provide improved facilites for cleaning, etc. All oil pumps are tested for capacity before installing on a machine, thus insuring the desired standard of efficiency. A new oil cooler has been designed, easily accessible for cleaning, and of higher efficiency, and the oil strainers have been made more readily accessible for cleaning.

Emergency Stop Governor

"This governor is located in the end of the turbine spindle as heretofore, but it is now carefully tested out and adjusted in a special machine before assembling in the turbine. After assembling, this governor is again checked several times by speeding up the unit, before the equipment is allowed to be shipped. In

connection with this matter, it may be well to point out that after being adjusted in our shops, this governor cannot be changed by an operator so as to trip at a speed higher than 10% above normal, as the threads on the governor spindle are not cut further than necessary to give the desired compression for the governor The weight spring for this specified overspeed. mechanism can be readily taken apart and cleaned (though due to its location it is seldom necessary) and when properly reassembled, for reason given above, it can be depended upon to hold the speed at the predetermined point.

Spiral Gears for Driving Regulator and Oil Pump

"It has been our practice until very recently to make the spiral gear on the turbine shaft of steel and the wheel of bronze. Owing to a number of complaints received concerning the life of the bronze wheel, we have recently substituted a special cast iron mixture for bronze and the results have proved so satisfactory that we have adopted a cast iron wheel gearing with a steel spiral as standard equipment.

By-Pass Valves

"We have recently adopted a valve design with a central stem guide which, in addition to providing a better guide for the valve, removes the tendency to spin caused by the steam striking the wing guides. Expansion Joints

"The copper expansion joints used heretofore in the equalizing pipes, and purchased from manufacturers specializing in this class of work, have been a source of considerable trouble owing to their short life. We are now furnishing expansion joints built up of sheet steel, of the Bellows pattern, and an extended service in places where trouble was previously experienced has indicated that the sheet steel expansion joints have a much longer life and are a great improvement over the conventional type. In fact we have not to date heard of a single failure, though some of these joints have now been in operation for almost two years. Materials Used

"Generally speaking, it is our practice for operation with dry saturated steam up to and including 200tb gauge pressure to furnish cast iron cylinder, steam chest, valves and seats. For superheated steam up to 400° F. and for dry saturated steam between 201 gauge and 250lb gauge, inclusive, the valves and seats are of nickel bronze and steam chest and cylinder of cast iron. For superheated steam between 401° F. and 475° F., inclusive, the valves and seats are of nickel bronze, steam chest of cast steel and cylinder of cast iron. For superheated steam 476° F. and above, the valves and seats are of nickel bronze, steam chest of cast steel, and the part of the cylinder in contact with the superheated steam of cast steel. The above general rule neglects strength and is based on temperature considerations only and may be varied one way or the other, depending upon the point of by-pass opening, and normal conditions of operation.

Oil Specifications

"We do not make any recommendations as to the selection of a grade of oil for the lubrication of steam turbines, nor do we issue any specifications for lubricating oil, as we believe this is a matter which can better be handled by the oil companies.

"Our only representation to customer is that certain brands of oil have, on the average, been found satisfactory for the lubrication of our steam turbines and that as long as the quality is maintained at the same standard we have confidence in them and endorse their use.

"On large units it is our standard practice to furnish a suitable oil filter operating on the continuous by-pass system. The apparatus is so arrange 2d that it is impossible for the oil level in the system to be

lowered beyond a certain point, thereby removing any danger of trouble due to any derangement in the filtering equipment.

Condenser Connections to Turbines

"On large units the condenser nozzle should be bolted directly to the exhaust nozzle of the turbine and the condenser should be supported on springs so adjusted that at no time is the weight carried by the turbine excessive. The adjustment of the condenser supporting springs should be such that if the machine operated non-condensing the expansion of the condenser due to the higher temperatures would reduce the load on the exhaust nozzle to practically zero. Το conform with these rules requires care in the design, but it insures a sound and satisfactory installation. Pressure, Superheat and Vacuum

"We believe that any gain in economy due to increasing the temperature beyond the limits now prevalent, 550° F. to 650° F., does not warrant the special design that would be necessary. Our investigations indicate that, both for economy and construction, more is to be realized from increasing the boiler pressure with the temperature maintained constant.

For the immediate future, we believe that the application of stage feed water heating offers a practicable scheme for effecting substantial economies. However, this is a matter which must be considered in plant design as well as turbine design, as it offers an economical method of eliminating the small steam auxiliary without resorting to boiler room complication in maintaining a heat balance.

"We do not feel that standard turbines are called on to operate at average vacua in excess of 281⁄2 inches for long enough periods to warrant designing them for high efficiency ratio at 29 inches or over.

General Electric Company

"Turbine development during 1920 has been along the lines of perfecting mechanical details and insuring economy and continuity of service rather than the designing of new types of units or units of greater capacity.

"A second 45,000 kw. turbine has been placed in service and the first unit of this rating has been modified, using steel where wartime conditions necessitated the temporary employment of cast iron. In accordance with the plan being carried out, other changes were made which experience has shown were necessary, and both turbines have given satisfaction in economy and mechanical characteristics.

"The changes made necessary by war-time defects in material, workmanship and design have been carried out as rapidly as operating conditions and manufacturing facilities would permit. We are confident that these machines, as well as the new turbines put in service during the past year, will establish new standards of reliability.

"Our investigations and studies of wheel phenomena have been pushed vigorously. While it is too early to submit a detailed technical report covering this subject, we have established definite methods of checking wheel designs against difficulties which have developed in the past. Had these methods been available at the time, such wheels as have developed cracks would have been rejected. Based on this research work and our experience during the past eighteen months, we are confident that the wheels of modified design are entirely reliable.

"The improvement in mechanical details include a method of obtaining whirled cast babbitt in main and thrust bearings. The centrifugal forces acting on the molten babbitt produce a more close-grained homogeneous metal and assure better contact between the babbitt and shell and, consequently, more uniform transfer of heat.

"Two important features have been incorporated

in the flexible couplings used on large turbines. Both wearing surfaces are renewable and the coupling can be readily uncoupled, a feature suggested by your Committee.

"The use of crushing pins to center and support diaphragms has been superseded by what is called the hammock suspension by means of which the diaphragms are hung from supports at the horizontal joints of the turbine casings and while free to expand are held central with the shaft.

"The emergency governor has been modified so that the emergency protection of the turbine can be tested at any time without changing the speed or disconnecting the generator from the line. Oil is injected into a pocket provided in the governor. The oil overcomes the force of the governor spring permitting the emergency to be tripped and reset at 101% speed. The oil is injected by simply turning a cock, and, when the cock is closed, the oil is thrown off through suitable openings in the pocket, the governor returning to its normal position.

"Our experience with the marine type of thrust bearing has led to its adoption as standard. "There has been no change in materials used in the various turbine parts since our last report. Experiments with non-corrosive metals are being continued. "The tendency is undoubtedly toward higher steam pressures and temperatures. The large turbines as now designed are suitable for operation with 300 lbs. gauge at the throttle and a steam temperature of 700° F. At their point of maximum economy, they can utilize efficiently degrees of vacuum beyond 29" when water conditions render such vacuum desirable.

"We are carrying on more extensive turbine research work than ever before, and it is resulting in substantial improvements in efficiency and reliability.

"We regret that we are unable at this time to make positive recommendations regarding oil. With the data and experience of the operating companies at the disposal of your committee, you are in the best position to make definite recommendations as to oil specifications and the methods of treatment and purification.

"The maximum upward and downward loads which can be carried by the exhaust flange without undue distortion of the alignment of the turbine are stated on the outline drawings furnished with each turbine. Any method of support which will keep within these limits is satisfactory. However, where conditions permit, we recommend bolting the condenser direct to the exhaust flange of the turbine and supporting the condenser on suitable springs."

Westinghouse Electric & Manufacturing Company

"The year 1920 has been one of forced production under reconstruction conditions accompanied by a gradual transfer of the major portion of our manufacturing organization and equipment, from East Pittsburgh to the new South Philadelphia Works. Starting the year at these new works with practically full capacity production of a few standard designs, of marine equipments, there was effected a transition to practically full production of our standard variety of industrial and power apparatus.

"No complete new designs of turbines were developed during the year but some modifications of standard designs were made to meet new conditions. The activity in large units of capacity and design, as previously built, has been quite satisfactory.

"One of the new features in power house economies is being introduced in two of the new power stations now under construction. This consists of an arrangement for taking steam from the stages of the main turbine near the exhaust for heating the condensate in closed heaters under partial vacuum prior to its delivery to the regular feed water heater or economizer. With this system a higher thermal efficiency is possible than with those employing atmospheric pressure steam, either from the main turbine or auxiliary apparatus,

because the steam is expanded to lower pressures in the turbine before it is removed for feed water heating. This arrangement is being used quite fully in the new Hell Gate Station of the United Electric Light & Power Company, New York, and partially in the Calumet Station of the Commonwealth Edison Company, Chicago.

"As a result of research work carried on in conjunction with material manufacturers, some improvements in the methods of manufacturing of both bronze and steel blading have been put into practice with a view to eliminating, insofar as possible, defects of material which might cause blades to break in service. These improvements deal with preventing the absorption of hydrogen in bronze material and in accurate observance of proper temperatures in forging and finishing of steel blades so as to preserve proper quality of the material.

"The employment of larger rotor structures, and higher speeds accentuates the need of greater accuracy in dynamic balance of these parts than has been obtainable by any known means of static balancing. This need led to the development of a dynamic balancing machine for quickly and very accurately determining the condition of balance of any rotating element. One of the machines has been built and for the past few months has been in operation in our shops, giving most gratifying results. The following will serve as an illustration of the accuracy of balance obtainable: "A ship stabilizer rotor consisting of a solid steel disc 6 ft. 61⁄2 in. in diameter and 171⁄2 in width of face with 71⁄2 in. diameter bearing journals at 6 ft. 7 in. between bearing centers, weighing 22,000 lbs. and operating at a speed of 1500 R.P.M., was built and statically balanced, as accurately as possible. It will be noted that with a structure of this sort, which approximates a single thin disc, accurate static balance should also produce accurate dynamic balance. However, when this rotor was placed in the dynamic machine, it was found necessary to remove 8.8. oz. at one point, on the perimeter and 2.9 oz. at a point diagonally opposite, and the machine very clearly and definitely indicated an unbalancing weight of 4 oz. at a radius of 15 in. After being balanced, the rotor was operated at full speed with practically no observable vibration. Additional balancing machines are being provided and it is expected that within the next year all rotors will be balanced in this manner.

"Rubber exhaust expansion joints are being employed on a number of installations in process of construction, as a result of highly satisfactory service and durability indicated by joints of this type which have been in service for the past few years. The chief advantages of joints of this type are maximum elasticity with negligible stress in parts united, and ease of replacement.

"Research investigations have been carried out on a number of alloys proposed for blading materials, but as yet none has been found which shows greater suitability for blading purposes than those now employed.

"The present tendencies in turbine design, are, as we see them, toward slightly higher steam pressures and temperatures with no change in vacuum; also toward the highest possible degree of reliable operativeness and sound mechanical design which permits of quick and easy readjustment, replacement or repair of parts, and the highest possible efficiency consistent therewith. Increased fuel costs have stimulated a demand for somewhat higher efficiences with accompanying higher costs than have previously been commonly used.

"Regarding the selection of oil for lubrication of turbines, type of specifications, methods of treatment and purification, the comments given in our report of a year ago will apply. A standardization of practice, with regard to selection and care of oil in a turbine system so as to, at all times, maintain satisfactory

lubrication with minimum cost of renewal and maintenance, is extremely desirable.

The

"In connecting condensers to turbines, exhaust expansion joints of some form are being used in practically all cases. With the double-flow turbine, of course, either expansion joints or two separate condenser elements freely suspended are required. method of supporting the condensers, which is believed to be most satisfactory and is now being quite generally used, is to suspend it from the same foundation members that support the turbine, by means of heavy steel straps, attached as nearly as possible underneath the points at which the increased load on the foundation, due to vacuum, would be applied, on a condenser separately supported. The effect of this arrangement is to make the load and resulting deflections of the foundation members constant under all operating conditions, regardless of changes in vacuum, and consequently to remove any tendency to misalignment of the turbine rotor due to such changes. This total constant load which the foundation members must support is only slightly greater than loads occurring with maximum vacuum with the condenser separately supported. Another advantage of this arrangement is the increased space around the lower part of the condenser available for passage of oil piping.

"When this arrangement of condenser support is used, final checking of the levelling and alignment should preferably be done with the water passage of the condenser filled with water and the steam passages empty.

"In any arrangement of condenser attachment it is, of course, desirable that no strain whatever be placed on the turbine structure, but it is essential that there be no variable stresses of appreciable magnitude.”

Air Washers

For cooling the coils in turbo generators large quantities of air are required varying from about four cubic feet per kilowatt per minute in smaller machines to about two and a half cubic feet per kilowatt per minute in units of 20,000 kw. capacity and above. In general this air is drawn through a system of ducts and forced through the windings of the generator by blades mounted on the rotor shaft. The air is discharged from the generator either through openings in the top or downward through a second system of ducts. At first the air was drawn into the generator without treatment of any kind. This soon deposited on the windings a coating of dirt consisting of soot and coal dust forming a heat insulating coating over the windings of a decidedly inflammable nature. Fires became more or less frequent and caused considerable damage. To diminish this hazard, it became general practice to install washers of the atomizing spray type in the ducts. This removed the coarser material but did not take out smoke and very fine soot which, consisting of almost pure carbon, still formed an inflammable coating over the generator coils. Tests were made at one station by placing cheese cloth screens in the path of the air after leaving the washer and noting the discoloration at regular periods. The results showed clearly the shortcomings of the existing scheme of air washing.

The Cottrell system of dust precipitation has been suggested as a means of completely removing the soot and dirt from the air. This consists essentially of passing the dust-laden air through an