Hubert E. Collins

“ When the steam consumption of a steam turbine is so much higher than the guaranteed quantity, it usually takes little less than a reconstruction to put things right. The minor qualifications of a machine, however, which can be examined into and tested with greater ease, and usually at considerably less expense, upon the site, and consequently under specified conditions, may be advantageously left over until that site is reached, where it is obvious that any shortcomings and general deficiency in performance will be more quickly detected and diagnosed. ”

“ With the turbine, on the other hand, any increase of vacuum, even up to the highest limits, increases the economy to a very considerable extent and, moreover, the higher the vacuum the greater will be the increase in the economy for a given addition to the vacuum. Thus, raising the vacuum from 27 to 28 inches has a greater effect than from 23 to 24 inches. For this reason the engineer will readily perceive the great desirability of maintaining the vacuum at the highest possible point consistent with the satisfactory and economical operation of the condenser. ”

“ Since the consumption of oil in a turbine is so very small, being practically due only to leakage or spilling, the price paid for it should therefore be of secondary importance, the prime consideration being its suitability for the purpose. ”

“ There has been much published, both descriptive and theoretical, about the turbine, but so far as the writer knows, there is nothing in print that tells the man on the job about the details of the turbine in plain language, and how to handle these details when they need handling. The operating engineer does not care why the moving buckets are made of a certain curvature, but he does care about the distance between the moving bucket and the stationary one, and he wants to know how to measure that distance, how to alter the clearance, if necessary, to prevent rubbing. ”

“ The very first considerations, when undertaking to carry out a consumption test, should be devoted to obtaining the steadiest possible lead. It may be, and is in many cases, that circumstances are such as to allow a steady electrical load to be obtained at almost any time. On the other hand an electrical load of any description is sometimes not procurable at all, without the installation of a special plant for the purpose. In such cases a mechanical friction load, as, for example, that obtained by the water brake, is sometimes available, or can easily be procured. ”

“ It is well known that the vibration of a heavy unit is accompanied by a synchronous or non-synchronous vibration of the foundation upon which it rests. The nearest approach to perfect synchronism between unit and foundation is obtained by a gradual rise in speed. A machine run up to speed too quickly might, after passing the critical speed, settle down with little visible vibration, but at a later time, even hours after, suddenly begin vibrating violently from no apparent cause. ”

“ Taking up the exhaust end of the turbine, we have a much more striking departure from the conditions familiar in the reciprocating engine. Due to the limits imposed upon the volume of the cylinder of the engine, any increase in the vacuum over 23 or 24 inches, in the case, for instance, of a compound-condensing engine, has very little, if any, effect on the economy of the engine. ”

“ In conclusion, it must be admitted that many published tests outlining the performances of certain makes of turbine are unreliable. To determine honestly the capabilities of any machine in the direction of steam economy is an operation requiring time, and unbiased and accurate supervision. ”

“ Any engineer who is capable of running and intelligently taking care of a reciprocating engine can run and take care of a turbine, but if he is to be anything more than a starter and stopper, it is necessary that he should know what is inside of the casing, what must be done and avoided to prevent derangement, and to keep the machine in continued and efficient operation. ”

“ Although steam leakage through the valves of a turbine may not materially affect its steam consumption, unless it be the leakage through the overload valve during a run on normal full load, a thorough [119] examination of all valves is advocated for many reasons. In a turbine the main steam-inlet valve is usually operated automatically from the governor; and whether it be of the pulsating type, admitting the steam in blasts, or of the non-pulsating throttling type, it is equally essential to obtain the least possible friction between all moving and stationary parts. ”

“ Steam enters the gland chamber at a slight pressure, and, when a vacuum exists inside the turbine casing, tends to flow inward. The pressure, however, inside the gland is increased until it exceeds that of the atmosphere outside, and by maintaining it at this pressure it is obvious that no air can possibly enter the turbine through the glands, to destroy the vacuum. The above principle must be borne in mind during a test upon a turbine having steam-fed glands. ”

“ Where a condenser system capable of the highest vacuum is installed, the need of utilizing it to its utmost capacity can hardly be emphasized too strongly. A high vacuum will, of course, mean special care and attention, and continual vigilance for air leaks in the exhaust piping, which will, however, be fully paid for by the great increase in economy.
It must not be inferred that a high vacuum is essential to successful operation of this type of turbine, for excellent performance both in the matter of steam consumption and operation is obtained with inferior vacuum. ”

“ So far as the generator is concerned, it is only essential to follow the practice common in all electric power plant operation, which need not be reviewed here.
Stopping the turbine is practically the reverse of starting, the successive steps being as follows: starting the auxiliary oil pump, freeing it of water and allowing it to run slowly; removing the load gradually; breaking the vacuum when the load is almost zero, shutting off the condenser injection and taking care that the steam exhausts freely into the atmosphere; shutting off the gland water when the load and vacuum are off ”

“ The machine is run at about one-third speed and the step-water shut off for 15 or 20 seconds. This causes grooves and ridges on the faces of the step-bearing blocks, due to their grinding on each other, which obstruct the flow of water between the faces and thus raises the pressure. It seems a brutal way of getting a scientific result, if the result desired can be called scientific. The grooving and cutting of the step-blocks will not do any harm, and in fact they will aid in keeping the revolving parts of the machine turning about its mechanical center. ”

“ After the turbine has reached speed, and the main oil pump is found to be working properly, it should be possible to take this pump out of service, and start it again only when the turbine is about to be shut down.
If possible, the load should be thrown on gradually to obviate a sudden, heavy demand upon the boiler, with its sometimes attendant priming and rush of water into the steam pipe, which is very apt to take place if the load is thrown on too suddenly. A slug of water will have the effect of slowing down the turbine to a considerable extent, causing some annoyance. ”

“ Under any circumstances, whether the air pump is working or not, a certain percentage of the vapor in the condenser is always carried down the pipe B, and this action alone creates a partial vacuum, thus rendering the work of the air pump easier. As a matter of fact, a fairly high vacuum can be maintained with the air pump closed down, and only the indirect pumping action of the falling water operating to rarify the contents of the condenser body. It is customary to place the condenser forty or more feet above the circulating-water pump, the latter usually being a few feet below the turbine. ”

“ There are certain specified qualifications which a machine must hold when running under its commercial conditions, among these being lack of vibration of both turbine and machinery driven, be it generator or fan, the satisfactory running of auxiliary turbine parts directly driven from the turbine spindle, minimum friction between the driving mediums, such as worm-wheels, pumps, fans, etc., slight irregularities of construction, often resulting in heated parts and excessive friction and wear, and must therefore be detected and righted before the final test. ”

“ It is always well to let the turbine operate at a reduced speed for a time, until there is assurance that the condenser and auxiliaries are in proper working order, that the oil pump is working properly, and [98] that there is no sticking in the governor or the valve gear.
After the turbine is up to speed and on the governor, it is well to count the speed by counting the strokes of the pump rod, as it is possible that the adjustment of the governor may have become changed while the machine has been idle. ”

“ If a bearing gets hot, be assured that there is some very radical cause for it which should be immediately discovered and removed. Never, under any circumstances, imagine that you can nurse a bearing, that has heated, into good behavior. Turbine bearings are either all right or all wrong. There are no halfway measures.
The oil strainer should also be occasionally taken apart and thoroughly cleaned, which operation may be performed, if necessary, while the turbine is in operation. The screens should be cleaned by being [101] removed from their case and thoroughly blown out with steam. ”

“ This, of course, does not mean that the engineer must stand over it every minute of the day, but he must frequently inspect such parts as the lubricators, the oiling system, the water supply to the glands and the oil-cooling coil, the pilot valve, etc. He must see that the oil is up in the reservoir and showing in the gage glass provided for that purpose, and that the oil is flowing freely through the bearings, by opening the pet cocks in the top of the bearing covers. An ample supply of oil should always be in the machine to keep the suction in the tank covered. ”

“ Allied to the oil system of a turbine plant is the water service, of comparatively little importance in connection with single self-contained units of small capacity, where the entire service simply consists of a few coils and pipes, but of the first consideration in large installations having numerous separate units supplied by oil and water from an exterior source. The largest turbine units are often supplied with water for cooling the bearings and other parts liable to attain high temperature. ”

“ With a system such as the gravity it is only necessary to run the turbine up to speed, turn on the oil, and then, over a period, calculate the volume of oil used by measuring the fall of level in the storage tank and multiplying by its known cross-sectional area. In those cases where the return oil, after passing through the bearings, is delivered back into the same tank from which it is extracted, it is of course necessary, during the period of test, to divert this return into a separate temporary receptacle. ”

“ Mineral oils that have been adulterated, when heated up, will partially decompose, forming acid. These oils may be very good lubricants when first put into use, but after awhile they lose all their good [110] qualities and become very harmful to the machine by eating the journals in which they are used. These oils must be very carefully avoided in the turbine, as the cheapness of their first cost will in no way pay for the damage they may do. A very good and simple way to test for such adulterations is to take up a quantity of the oil in a test tube with a solution of borax and water. ”

“ There are two highly important features requiring more or less constant attention throughout a test, namely the gland and hot-well regulation. For the present purpose we may assume that the glands are supplied with either steam or water for sealing them. All steam supplied to the turbine obviously goes to swell the hot-well contents, and to thus increase the [149] total steam consumption. The ordinary steam gland is in reality a pressure gland. At both ends of the turbine casing is an annular chamber, surrounding the turbine spindle at the point where it projects through the casing. ”

“ The condensing arrangements of a turbine are perhaps mainly instrumental in determining the method of test. The condensed steam alone, issuing from a turbine having, for example, a barometric or jet condenser, cannot be directly measured or weighed, unless by meter, and these at present are not sufficiently accurate to warrant their use for test purposes, if anything more than approximate results are desired. ”

“ Obviously, unless a machine had become more or less standardized, a preliminary consumption test would be necessary, but once this primary qualification respecting consumption had been satisfactorily settled, there appears to be no reason why exhaustive tests in other directions should not all be carried out upon the site, where the conditions for them are so much more favorable. ”

“ The object in view is to have the grooves of the balance pistons running as close as possible to the collars in the cylinder, but without danger of their coming in actual contact, and to allow as little freedom as possible in the thrust bearing itself, but enough to be sure that it will not heat. The turbine rotor itself has scarcely any end thrust, so that all the thrust bearing has to do is to maintain the above-prescribed adjustment. ”

“ It is probable that the percentage increase or decrease in steam consumption, in the case of superheat, can be more reliably calculated than in other cases, as, for example, vacuum; but the increase cannot be said to be due solely to the variation in superheat. In other words, the individuality of the particular turbine being tested always contributes something, however small this something may be, to the results obtained. ”

“ The operating engineer will be very slow to see the utility of the baffler, and when he learns, as he will sometime, that the turbine will operate equally well with a plug out as with it in the baffler, he will be inclined to remove the baffler. It is true that with one machine operating on its own pump it is possible [39] to run without the baffler, and it is also possible that in some particular case two machines having identical step-bearing pressures might be so operated. ”

“ In the use of water for the cooling coils and of oil for the lubricating system, nothing more is required than ordinary good sense dictates. An absolutely pure mineral oil must be supplied, of a non-foaming character, and it should be kept free through filtering from any impurities.
The above refers particularly to Allis-Chalmers turbines of the type ordinarily used for power service. For turbines built to be run non-condensing, the part relating to vacuum does not, of course, apply. ”

“ The oil is circulated by a pump directly operated from the turbine, except where the power-house is provided with a central oiling system. Particular stress is laid by the builders upon the fact that it is not necessary to supply the bearings with oil under pressure, but only at a head sufficient to enable it to run to and through the bearings; this head never exceeding a few feet. With each turbine is installed a separate direct-acting steam pump for circulating oil for starting up. ”