203. Tangyes’ Vertical Engine without Boiler. 205. Davey’s Safety Motor.
204. Tangyes’ Feed-water Heater.
Davey’s Safety Motor (Fig. 205) is a revival of the atmospheric engine of 1705 in general principle, but with various decided improvements. The word “safety” is used advisedly, as there is no pressure exerted by the steam higher than atmospheric pressure (15 lb. to the square inch), consequently it is as non-explosive as a teakettle, and no steam gauge or safety valve is required and the motor can be placed in charge of the most unskilled attendant. The power is obtained by the condensation of steam producing a vacuum and thereby making available the pressure of the atmosphere. This motor has a cylinder and piston; as the piston is proceeding on the outstroke the cylinder is charged with steam at low pressure; at the proper moment a jet of cold water is admitted which instantly condenses the steam, producing a vacuum, the pressure of the atmosphere immediately asserts itself outside of the piston pressing it back on the instroke, after which the action is repeated; so it will be seen that the piston relies upon the momentum of the flywheel for the outstroke and the pressure of the atmosphere (15 lb. to sq. in.) for the instroke. This is an economical motor, the consumption of fuel (gas coke) averaging 6 lb. per horse-power per hour, and the makers claim that the cost of fuel and water (if the latter has to be paid for) combined is less than the cost of gas for working a gas engine for a given amount of work.
These motors are also made to work with a pressure of steam about 2 lb. above atmospheric pressure, and this can then be utilised for steaming purposes, such as for cattle foods, &c.; this also applies to any steam motor. The cost of these motors is for ¾ indicated horse-power 45l., with a 2 ft. flywheel 160 revolutions a minute, or a larger size, 4½ indicated horse-power, 100l., with a 4 ft. flywheel.
Gas.—Gas engines are now occupying considerable attention and receiving general favour; the attention needed in working these motors is comparatively nil, and they admit of such exact regulation that there is practically no loss of power and fuel, for in reducing speed or work the supply of fuel (gas) must first be reduced. A noticeable feature is the extreme cleanliness, as there is no furnace and stoking, no boiler safety-valve nor pressure gauge, &c.; and it is a common thing to find these motors left for hours without attention, as the supply of fuel is unvarying and self-acting lubricators of good make only require attention about once a day. A still further and important advantage possessed by these motors is the almost instantaneous starting and stopping, making them particularly well adapted for electric lighting apparatus in event of a sudden darkness arising. The majority of these remarks, it will be noticed, apply to many motors. All gas engines are practically worked upon the same principle, but differing in detail; there is, however, a practical difference in one respect, and that is, that some consume the gas in its ordinary state as supplied from the gas mains, whilst others consume it after the piston has first compressed it; the latter is undoubtedly the most effective in results, as the difference may be compared to igniting gunpowder in the barrel of a gun in a loose state, or after it has been rammed close.
206. Otto Gas Engine.
These motors are in construction somewhat similar to steam engines, having a cylinder and piston, crank, flywheel, governor, &c.; the gas is utilised by leading it to a combustion chamber (one end of the cylinder) and at a proper moment igniting it, the expansion (or explosion) impelling the piston forward; the piston is brought back by the momentum of the flywheel, and on its return journey passes off the products of combustion; most gas engines are worked with one ignition or impulse to every 2 or 3 strokes, or they can be regulated to an impulse for every stroke for high speeds; the cylinders of these motors usually have water jackets, as the temperature naturally becomes very high, a small pump circulating the water which is supplied from a small water tank at the side, or the engine may have a water tank base, the same water being used over and over again.
A desirable feature in a gas engine is that it be “noiseless,” they are now made that even the exhaust pipe is noiseless. Speaking of the exhaust pipe, this should be carried into the open air, as if carried into a flue or chamber, a leakage of gas up this pipe would be a source of danger, and this pipe must be kept clear of woodwork some 6 or 10 in., according to size.
Large motors are provided with a self-starting apparatus, but small motors require a turn or two given to the flywheel by hand at starting.