THE four main items of a private generating plant are: (1) the engine; (2) the dynamo; (3) the switchboard; (4) the battery.

As regards the engine. If the makers directions about cleaning, lubrication and the occasional examination of certain parts are followed out, this should give very little trouble. The governor and fuel pump, when once properly set, should not be interfered with. Every now and then the compression should be tested, while the engine is hot.

If it is unsatisfactory, the valves need grinding in; or, what is more unlikely, new piston rings are required. Valve-grinding should stop as soon as valves and seating show a complete ring of bright metal. In very cold weather, if the engine room cannot be properly warmed, the water in the cylinder jacket and cooling circuit should be drained off.

Should the exhaust from the engine prove annoying to user or neighbours, an additional silencer should be provided, to allow the gases to cool and contract more thoroughly before reaching the open air. Silencers should be fitted with draining plugs to free them of any condensed water that may collect.

The driving belt should be maintained in good condition and be shortened if it becomes slack. It is less likely to stretch if unshipped after a run.

The dynamo needs very little attention beyond keeping it clean and dry, and the maintenance of a proper supply of lubricating oil or grease in the bearings. Dirty bearing oil should be run out and replaced by fresh. When the brushes have bedded down well on the commutator, the most that should be required by these parts of the machine is the occasional cleaning up of the commutator with a piece of ,?ic-grained emery cloth which has already done some work. Anything in the nature of truing-up the commutator should be left to the makers.

The switchboard should be kept clean; and all its nuts and terminals be examined occasional! , and tightened up if they need it. It is important that the fuses on it should be of the correct current-carrying capacity. If too small, they are liable to blow; if too large, they will be a danger.

The room in which the batter; is housed .should be separate from the engine room, and well ventilated. As cells -while charging give off hydrogen, a very in-ilammable gas – as proved b – many airship disasters – no naked lights should be allowed in it during, or soon after charging. It requires good illumination by both day and night, to enable inspection and tests to be carried out in the proper manner. Electric lamps should not be directly over the cells.

It is important to keep the temperature of the battery room free from extremes. Low temperatures lessen the capacity and pressure of the battery for the time being, while long spells of great heat cause buckling of the plates and excessive evaporation of the electrolyte in the cells. Artificial heating during frost, and thorough ventilation during hot spells, when the room should be opened to the cool night air, are indicated.

All woodwork and metal fittings in the battery room should be well painted with acid-proof paint as a protection against acid spray from the cells.

The attendant should, as a matter of routine, see: That all connections of the battery are free from corrosion. Bolts and nuts should be smeared over with vaseline; That all plates are well covered with electrolyte – diluted sulphuric acid – which should reachto I- in. above their top edges; That plates are equal distances apart; That sediment in the bottom of cells is not allowed to pile up till it touches plates. It should be levelled down by means of an _-shaped glass rod. If this matter is not attended to, the cells will soon deteriorate.

Loss by evaporation should, as a general rule, be made good by the addition of distilled water only, or, if this is unobtainable, carefully filtered rain-water. Water from the main should not be used. Any addition should be made just before beginning to charge. Since water poured into the cell will tend to float on the top of the heavier acid, it should be introduced through a glass tube reaching to the bottom of the cell. While rising it will mix in properly.

As spray from the cells contains some acid, the strength of the electrolyte will gradually fall, and it will become necessary to add more acid. This may be done in either of two ways : (1) Sulphuric acid of the quality used by the makers of the cells is added to distilled water until a specific gravity of 1,215° is shown by the hydrometer. This is added in place of pure water just before a charge. (2) Strong acid of 1,300°-1,400° specific gravity is added a drop at a time and stirred in with a wooden paddle. This should be done towards the completion of a charge.

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