The New Zealand Railways Magazine, Volume 2, Issue 1 (April 21, 1927)
The Superheated Locomotive
The operation of a superheated locomotive requires very close attention to quite a number of important details, any one of which, if neglected, may seriously affect the efficiency of the engine. Generally speaking, if successful handling of the engine is to be attained, close attention must be given to, (1) The water level. (2) Lubrication. (3) The proper use of the saturated steam valve when the engine is drifting, in order to take care of the oil that has been fed to the cylinders and valves.
It is a well-known fact that there is no condition that is more detrimental to the successful handling of a superheated locomotive than carrying too high a water level. This reduces the efficiency of the superheating system and destroys the lubrication which has been fed to the valves and cylinders. With our more modern engines greater care is necessary than with the older types. The reason for this is that the dry steam space is restricted because of the clearance required for overhead structures such as bridges, tunnels, etc. This restriction of dry steam space increases the liability of water finding its way into the superheating elements and to the valve chambers and cylinders. The higher the water level carried the greater is the reduction in the degree of superheat attained. An authority has shown that under actual service conditions there may be a difference of from 50° to 75° in temperature due entirely to carrying a too high water level. If every superheated engine were fitted with a pyrometer it would clearly demonstrate to the engineman how the best resuls were to be obtained.
All enginemen do no handle their engines alike, but it is generally recognised that it is not desirable to run with too short a cut off. Better results and a higher degree of superheat are obtained with a longer valve travel.
Lubrication is very important. The successful operating of any engine largely depends on careful attention to this matter. An engine starved for want of proper lubrication of valves and cylinders is a wasteful machine, both in fuel and upkeep. The cost of an extra pint of cylinder oil per 100 miles is money well spent and is returned with interest in the saving of fuel and repairs. A pint of cylinder oil costs approximately 9d., and about 33lbs of coal (at £2 10s. per ton) can be purchased for the same sum. Now three shovels full of coal weigh approximately thirty-three pounds. Any intelligent engineman knows that over a run of 100 miles much more than three shovels full of coal can be saved on an engine the valves and cylinders of which are well lubricated, as against an engine that is skimped for oil in these parts. An engine to be successfully lubricated must have a regular and dependable as well as a uniform supply of the right kind of lubricant. There is no use in feeding cylinder oil of an inferior quality to a superheated engine's valves and cylinders for such a practice is sure to result in trouble.
Of the two methods employed in lubricating valves and cylinders—viz., by mechanical or hydrostatic lubricators—I prefer the hydrostatic as giving the best results generally. It is simpler and there are fewer parts to get out of order. With a little care and judgment and a little time given to its adjustment the more modern types give excellent results. The sight feed lubricator should always be started and adjusted ten minutes before the engine leaves the depot. Adjustments should be made so that both engines are getting the same number of drops of oil per minute. The choke fittings in these lubricators should receive careful and regular attention, otherwise the feed will be erratic—feeding to fast when steam is shut off, or too slow when steaming.
It is recognised that the best method of lubricating the valve chambers and cylinders is that which gives one lead to the steampipe or header and one to the cylinder—the one to the steam pipe or header to have an atomizer fitted. This ensures the atomization of the oil which is then carried by the steam to all parts of the valve chamber. Steam from the drifting valve, if it enters the steam pipe above or opposite the lubricator pipe, also assists in the atomization of the oil and carries it to the valve chamber when the engine is drifting. Experience has proved beyond question that the best resuls are obtained by feeding oil both to the valves and cylinders direct. A high authority states: “Where these methods have been adopted the results have proved excellent and wear on the valve rings and cylinder bushings is not more than with saturated engines.” None but the best page 31 cylinder oil should be used on superheated engines. Deposits of sticky and solid substances in the steam chests and cylinders are sure indications of improper operating; either the improper use of, or neglect to use, the drifting valve, the carrying of too high a water level, the use of too much oil or (what is more likely the use of inferior oil in the lubricator. If enginemen would conscientiously use the drifting valve it would materially assist in the complete elimination of carbon deposits, prolong the life of the valve, piston rings and bushings, and reduce alike the cost of maintenance and the coal bill. While it is not intended that an excess of suitable cylinder oil should be used the quantity should not be reduced to such an extent as to result in the cutting and scoring of valve and cylinder bushings. An engineman should always have at his command a reserve supply of suitable cylinder oil, for he never knows when an emergency may arise in which, if he has no such supply, he may get an inferior quality of oil from some source which may be quite unsuitable for use on a superheated engine. Serious damage may be done in such cases before it is realised. The engineman who lubricates his engine in a proper manner and with the right kind of oil, who uses his drifting valve regularly, saves fuel as well as other material and lessens the cost of repairs. As pointed out previously oil is cheaper than coal. If the quantity of oil used were increased 50 per cent. and this effected a saving of five per cent. in coal consumption a substantial saving in working expenses would be effected. It is not economy to stint any engine of oil, much less a superheated engine.
Summed up, the points to be observed if suecessful handling of a superheated engine is to be obtained are: (1) Do not run with a high water level. (2) Lubricate your engine properly and with a high grade oil. (3) Use the drifting valve regularly.
This is most important. Keep the drifting valve open about a quarter of a turn when steaming, and just prior to closing the throttle valve open the drifting valve about a full turn. This will prevent air getting into the steam chest or valve chamber and causing the oil to carbonize; it will also prevent the smoke box gasses and grit being drawn into the valve chamber.
Remember if the drifting valve is no opened prior to the throttle being closed, the admission of steam in the steam chest will not neutralise the cutting action of grit and cinders that, immediately the throttle is closed, are drawn into the valve chamber and cylinders.