the starting valves, &c. This permits any excess of oil present to pass direct to the bilge. When under way these directing cocks should be turned to discharge to the condensers.

In vessels fitted with horizontal engines in which the main condenser is higher than the lowest part of the low-pressure cylinders, difficulty has frequently been experienced in preventing accumulation of water in the low-pressure cylinders, especially when the vessel is under way, as the difference of vacuum in the condenser and lowpressure cylinders is not sufficient to overcome the resistance of the drain pipes and to lift the water from the cylinder to the condenser. To meet this difficulty small evaporators have been fitted below the lowest parts of the cylinder, and the cylinder drain pipes led to them, a live steam coil being used to evaporate the drain water. The usual drainage arrangements to bilge are also provided.

(6) Accumulation of fresh water in condensers before starting.— It is of importance to prevent this accumulation, especially when the main air-pumps are of long stroke and consequently have a large bucket velocity. This is now usually effected by a suction from either the auxiliary air- or hot-well pump, which pump must be kept working. If this be not attended to, the main air-pump may become glutted with water on starting, and great stresses be suddenly brought on all parts of the air-pump. It also usually entails a loss of fresh water through the air-pump relief arrangements. The water accumulates from steam and water passing through the engines during the warming process, and from the use of the silent blow-off. Accumulation may also be due to leaky condenser tubes or joints of tube plates, and this should always be ascertained whilst the engines are being prepared for starting by drawing off some and testing it. If leaking to any extent, it is advisable, if time be available, in order to prevent the access of salt water to the boilers, that the defect be made good before getting under way; if not, the first opportunity should be taken to effect the repair.

(7) Condenser pumps.-The main circulating pumps should be kept running sufficiently fast to insure the condensers being cool, and any drain cocks or other fittings which may admit air to the main condensers should be adjusted to prevent this. The auxiliary circulating pump and air-pump should also receive attention, so that the auxiliary condenser remains cool and free from water, which insures efficient drainage from those cylinders and slide casings led to the auxiliary exhaust pipe and from the cylinder jackets. It also relieves back-pressure from the auxiliary engines generally.

(8) Safety valves blowing off or steam pressure rising too high.— This should be prevented to avoid the loss of fresh water, and inconvenience from noise and water on deck. If the steam pressure tends to rise faster than required, the fires should be checked as follows. The stokehold fans should be run at a speed only sufficient for ventilating purposes, while the draught plates on the boilers should be closed, and the fires should not be disturbed more than actually necessary. If the pressure still continue to rise beyond that required, the silent blow-off valve should be slightly opened so as to pass the steam direct to the main condenser. This should always be done with caution, and care taken that (a) the valve is opened gradually, so as not to shake the condenser tubes more than necessary, otherwise leaky tubes may result,

(b) the pump for emptying the condenser of fresh water is at work, (c) the silent blow-off is shut before the main engines are started. The steam pressure should be checked in this manner when easing or stopping the engines.

Starting of engines deferred. In cases where some considerable time elapses between the first trying of the engines and the order to start being received on the engine-room telegraph, in addition to the preceding, the starting engine should be worked occasionally from full gear ahead to full gear astern, so as to prevent accumulation of pressure in the receivers and keep the working parts free.

Procedure when main engines are under way. When the engines are under way the suction from the auxiliary air-pump or hot-well pump to the main condenser should be shut, and the speed of the main circulating pumps be regulated to the requirement of the main condlenser. The engine-room tell-tales should be taken out of gear, except in the case of warships steaming with a fleet, in which case they may still be required. Special attention should be paid to the bearings and all working rods to see that they are keeping cool, also to the engine-room gauges, to see that the vacuum is maintained in the condensers and that the jacket and receiver pressures are correct. The engines should be worked slowly for a time, and then the regulating valve slowly opened, so that the speed is gradually increased and no sudden demands are made on the boilers, which would result in a lowering of steam pressure and possibly passage of water with the steam into the cylinders. This also allows the fires to gradually burn through and attain a sufficient incandescent body for maintaining the required speed without undue forcing, and brings the maximum stresses uniformly and gradually on the various parts of the engines and boilers. Especial attention should be paid to the lubrication of the thrust-block at this period, as during the process of starting and till the ship is fairly under way the thrust on it is in excess of the normal amount.

Adjustment of link gear. When fairly under way the link motions should be adjusted to the cut-off which will give the required number of revolutions of the engines, with the regulating valve practically wide open, to obtain in the high-pressure slide-chest a high steam pressure, in order to promote economy of fuel, unless the cut-off required would be too early for smooth and regular working, in which case the link motion should be set for the earliest practical cut-off and the steam pressure adjusted accordingly. This point occurs generally at or before 2-10 stroke, or at such rate as develops either (a) an excessive compression loop at the top corner of the indicator diagram, (b) too considerable a falling away of the high-pressure admission pressure due to wire-drawing, or (c) a jerky motion of the valve gear. The nature of the limit will depend on the design of the valve gear, and especially the amount of compression in the high-pressure cylinder at full power. With many valve gears, however, the jerky motion referred to, imposes the limit of efficient working. When this point is reached there is no alternative except to obtain further reductions of power by lowering the initial steam pressure.

Independent linking-up gear. This should now be adjusted, depending on the speed required, so as to regulate the proportion of power developed in the several cylinders. Experiments should be made, as far

F F

as possible, when making passages, with the view of determining the best distribution from the point of view of economy, the cut-off in the high-pressure cylinder being always as early as practicable. The best distribution for various rates having been thus determined, the engines can, when fairly under way, be at once properly set, if continuous working at that speed is expected.

Jacket pressures. Scrooping or grunting. The cylinder jacket pressures should be regulated, and it should be borne in mind that the higher the pressures in the jackets the less will be the loss from 'exhaust waste' due to liquefaction and the consequent wasteful transfer of heat direct to the exhaust. The most efficient plan, considering only the action of steam, would be to carry steam of the full boiler pressure in each of the cylinder jackets, including the low-pressure, but even if this were done it would be insufficient to entirely prevent loss from this cause. Owing, however, to mechanical considerations connected with the wear of the internal parts, as the amount of internal lubrication in high-pressure marine engines is always reduced to a minimum, it is not possible to carry out the principle to this extent, especially in the low-pressure cylinder. The jacket pressures should generally not fall below the initial pressure in the cylinder-i.e. the preceding receiver or steam-pipe pressure-in which case the amount of moisture present in the cylinders will be considerable. In some cases where wear is feared the high-pressure steam jacket supply is taken from the high-pressure slide casing. The pressure which can be safely carried can only be determined by experience, and this will vary with the amount of lubrication entering the cylinder through the piston- and slide-rods, the material of the rubbing surfaces, and their adjustment.

If any 'scrooping' occurs, which can be made to disappear by lowering the jacket pressure, the limit will have been reached, but it should not be too hastily assumed that noises of this kind are caused by the jackets. Scrooping often occurs when the speed of the engines is reduced by throttling the steam, which wire-draws and dries it. The boiler pressure should therefore be adjusted to the requirements of the engines, provided it is not reduced below that required for readily starting from any position.

Feed-water temperature.-Where the circulating pumps are fitted in duplicate, as usual in the Navy, only one should be worked, and the speed of this should be reduced until the temperature of the feedwater is as desired.. With feed-water heaters there is no limit to the lowness of this temperature except that of efficiency. Without them the effect on the boiler has to be considered, and under these circumstances it is not advisable to reduce this temperature below 100° F., so as not to unduly magnify the racking strains on the boiler due to differences of temperature. With feed-water heaters the temperature may be rather lower with advantage. When working at low power it will often be found that it is impossible to run the circulating pump so slowly as would be required from these considerations without risk of its stopping altogether. If this be so, in order to avoid this danger, and at the same time where feed-water heaters are not fitted, to prevent the feed-water being too cold, the circulating water valve should be gradually closed until the feed-water is of the correct temperature,. with the pump running at a speed which will avoid danger of stopping..

Supply of feed-water. The water level in the feed-tanks should be constantly observed. If automatic float gear is not fitted, the speed of the feed-pumps should be regulated so that the suction is always covered with water to avoid air entering the pumps and the boilers. If additional feed-water is required beyond that which the evaporators are producing, it should be obtained from the reserve fresh-water tanks by opening the suction from this part to the main condenser or air

pump.

If when the engines are working steadily any considerable discharge takes place from the overflow-pipe on the feed-tank, the engine-room watchkeeper should at once warn the stokehold staff, and ascertain the cause, which may be due to the feed-pumps stopping or failing to deliver sufficient water to the boilers, or to the boiler feed-valves not being sufficiently open. Prompt action under these circumstances has prevented many accidents.

CHAPTER XXX.

MANAGEMENT OF ENGINES UNDER WAY-ENGINE AND BOILER DEFECTS.

In this chapter, and the succeeding, particulars are given relative to the care and management of the machinery and boilers, which are to some extent based upon the instructions contained in the 'Steam Manual' now in use in the Royal Navy. A few of the most usual defects in engines and boilers are also dealt with, and suggestions given as to their suitable treatment.

Before taking charge of a watch the engineer should satisfy himself by personal inspection that all bearings are working well and are in a proper state of lubrication, that the water in the boilers is at the proper working height, that the water in the bilge is not excessive, and that as far as can be seen there are no recent defects of importance in machinery or boilers. He should read the recent entries in the engine-room register, and make himself acquainted with any special orders. Pending these inspections the engineer about to be relieved remains in charge. He should also receive information from the offgoing engineer, showing that no increase of density in the boilers has taken place, or, if the water has become salt, that it does not exceed the density allowed, and also as to what special cocks and valves are open in the department. The information as to these points should be verified by the oncoming engineer as soon as possible after taking charge.

When in charge of the watch he should leave the engine-room platform as little as possible, so as to execute expeditiously any order received from the deck or stop the engines in case of accident. As his duties require his occasional absence from the engine-room platform, he should instruct one of the subordinate watchkeepers in the manipulation of the engines, and this watchkeeper should be always on the starting platform during his occasional absence.

In addition to any special orders received, the watch has to carry out the usual routine orders, and note their execution in the engineroom register. The principal are—

Hourly.-Quantity of coal used; steam pressure in the boilers and at engines; vacuum in main condensers; air pressure in stokeholds, if any; total number of revolutions; depth of water in the bilges.

At least each watch.-Density of the feed-water and of the water in each of the boilers in use; temperatures of feed-water, engine and boiler rooms, coal-bunkers, on deck, and sea-water; quantity of fresh water made for drinking purposes and used for make-up feed (measured