ENGINES, H ORA I] IE. Pearsall's Hydraulic Engine is shown in Fig. 1. It is thus described ley 31r. II. D. Pearsall, of London, the inventor, in a paper read before the American Institute of alining Engineers in February, 1S69: "The engine or machine acts on the principle of the hydraulic rain to this extent : that both obtain their pumping power by the arrest of a column of water which has been pre viously set in motion by gravity. The feature of hy draulic rains which has re stricted them to a small size is their violence. In the new machine this is not only re duced but has no existence at all. It works with all the smoothness of a well - con structed reciprocating en gine. This is best shown by indicator - diagrams taken from the pressure-chamber. Some of these are given in Fig. 2. These diagrams were taken with ordinary steam engine indicators.
The construction, as shown in Fig. 1, is as fol lows : (.; is the main valve (here shown open) in the pipe (called a flow - pipe) which conducts water to the engine. D is a roil attached to valve C, by which it is moved up and down at proper intervals of time by means of the motor E. F is a chamber immedi ately above valve C. At the period of the stroke of the engine, which is represented in the figure, this chamber contains only air, and com municates freely with the at mosphere by the pipe G. At the base of pipe G there is a valve, J, which carries a float. When the main valve (1 is raised and closed, it of course shuts off the flow of water; but it does not interfere with the flow of the water until it is completely closed, because, until the chamber is tilled with water up to the float II, the valve .1 remains open, giving free communication between chamber F and the atmosphere ; consequently, the air freely escapes from the chamber and the water freely rises in the chamber. This actif in takes place during the closing of the main valve P. The con sequence is, that no power is wasted in forcing water through the narrowing orifice. A second consequence is. that there is no necessity to close this valve with great rapidity (which is necessary in hydraulic rams). As a matter of fact, it is closed by a gradually retarded motion, and so conies to rest without any concussion. When the water touches the float 11
it closes the valve .1, shuttiug off the passage for escape of air, and the pressure in the (-handier then rises to the point at which the valves It (pen. and sonic of the water flows into the air-vessel frfun which it of course is constantly filming out through delivery-pipe A/.
A little; gill remains in the .'hauler. This nil. is compressed and enters the air-vessel, and is USIA to drive the motor which actuates the main valve. The column of water flowing in the flow-piis• is thus brought to rest entirely by the elastic resistance of air. When it has ceased to 11.111r, I he Main valve is again opened, the water with which the chamber Pis now fall the air-valve -1 falls open, ailmitting at miispherie air. and the water again begins to lhov and to eseape Ainingh valve a As regards the efficiency wit h which the engine works, careful perimeo ts have been made, gauging accurately the quan I hies of water used and delivered, and their respeetive hetels The head of supply was 17 ft. When head of delivery was 150 ft. the effieieney was 70 per rent, and when the head wits 100 ft. the efficiency was 72 per cent." hydraulic Ranks.—The following descriptions of experimental hydraulic rains are taken from a paper by John Richards, of San Francisco (Proc. Inst. Mech. Engrs.. Feb., 1888): " Fig. 3 represents a small ram having an inlet-pipe I of from 2 to 3 in. diame ter. D is the discharge-pipe C the check or foot valve ; A the air-vessel ; and V and E are the escape-valves fixed on the same stem. A plan of the top of the lower valve E is shown. The two valves V and E being nearly balanced. the difference of their areas constitutes the measure of the upward or closing force, which is of course much less than in the ease of a single valve. The valves fall by their weight in the usual manner, and are raised partly by the stream rushing out round the upper valve V, but mainly by the upward pressure of the issuing current against the curved shield S fixed on the valve-stein. In working this form of rain it has been found that accurate adjustment was required to suit the head or fall of the driving-water ; and also that the shock was too great for the safety of small rains.