28S 



THE CIVIL ENGINEER AND ARCHITECFS JOURNAL. 



[Sept. 



side of the chamber, as shown by the Hotted lines, the water entering 

 at A now flows through pipe B, but the water in pipe C having been 

 in motion its momentum will carry it onwards in the original direction, 

 leaving a vacuum behind ; at the same time it will be oljserved, that 

 the port has been opened between pipe C and the condenser, and the 

 water of condensation and vapour will rush out of the condenser into 

 the pipe C. On again reversing the valve D, the same effect is pro- 

 duced in pipe B, and so on alternately. 



Having thus briefly explained the form and operation of the ma- 

 chine, we have now to inquire what extent of vacuous space is likely 

 to be ol)tained under ordinary circumstances. 



Let P = the weight of the cilumn of water in lbs.; G=: the co-eflB- 

 cient of gravity ^ 32 ; V = the velocity in feet per second. 



P 



Then the vis viva of the water = — V. 



G 



Again, let A= the area of the pipe in square inches ; R =; the re- 

 sistance due to the immersion at atmospheric pressure; L = the 

 length of the vacuum in feet. 



Then we have ihe mechanical effect overcome by the water while 

 stoppingz=: A X R X L. But this mechanical effect is equal to half 

 the vis viva. 



Hence, A x R X L= i ^ x VS or L: 

 Or 



PX V2 



2xG XAXR. 



Let us now apply this formula to a particular case. Suppose the 

 vessel to be 110 feet between the perpendiculars, and the length of 

 the pipe to be 90 feet, diameter inches; say she is propelled by 

 one engine of 30-inch cylinder, and 3 feet stroke, then the air-pump 

 would have a capacity of about 4,300 cubic inches. 



Again, take the speed of the vessel at 14 miles per hour, or 20 feet 

 per second, then we have — 



A =; 28 square inches, 

 V ^=- 20 feet per second. 



Hence L = 



P = 1092 lb. 

 G= 32 

 R= 17 



1092 X 20, 



: 14 feet 4 inches. 



2 X 32 X 28 X 17 

 The contents of which is 4896 inches, and with a velocity of 20 

 feet per second, the machine will make one stroke per second, whilst 

 the engine will not go above 45 strokes at most; therefore, the ma- 

 chine would be one-third more powerful than the pump. 



Though the above example proves the practicibility of the appli- 

 cation as a substitute for the air-pump in such cases as contemplated, 

 viz., light river boats moving at a high velocity, still I wish it to be 

 clearly understood that in ordinary cases, such as we meet with in 

 this country, I would prefer the common air-pump, which is a most 

 effective instrument, but there are circumstances in which this ma- 

 chine might be adopted with advantage, and which may excuse the 

 introduction of the foregoing. 



Applied as a Ship's Pump. 

 — The arrangement fur this 

 purpose is remarkably simple, 

 being identical in principle 

 with that just described, but 

 dift'erent in detail. Fig. 3, is a 

 plan and fig.4 a vertical section, 

 showing the valves. It will be 

 observed that the general form 

 is similar, but the construction 

 of the valves, unlike the ma- 

 chine previously explained, 

 is less complicated. First, 

 the valve D is a single hinge 

 valve, moveable as before, by 

 I rod passing through the top 

 <jf the pipe; secondly, instead 

 of the valve at E, figs. 1 and 2, 

 we have two valves marked 

 1 and 2, opening upwards, being placed on the top of pipes E, passing 

 into the bilge ; and, lastly, we dispense altogether with the valves in 

 the branch pipes. Presuming I have made myself understood so far, 

 let us suppose the ship at sea in a gale of wind, and leaking badly, 

 and lei the valve D be in the position shown, then the water will rush 

 through the pipe A, pass through C, and out at the stern; then re- 

 verse the valve D, the water now flows through B, and at the same 

 time we have the water in pipe C passing on by virtue of its own 

 momentum, leaving a vacuum behind; when this takes place, the 

 valve 2 will open and admit the water from the bilge to fill the va- 

 cuous space. On reversing the valve D, the operation is repeated, 

 and so on. 



Let us now apply the formula, that we may acquire some concep- 

 tion of the power of the apparatus. I shall take that celebrated ship, 

 the "Great Britain," with a length of keel zn 282 feet ; and as it is 

 an oi)ject to keep the perforations made by the pipes as small as 

 possible, thev must be situated where the line of pipe meets the bend 

 at bow and stern, as nearly as may be, at a right angle. This condi- 

 tion will diminish the effective length of the column to, say 25u feet, 

 diameter of pi|)e::= 12 inches, area 113 square inches, ship's load, 

 diaiight 10 feet, immersion of pipe 11 feet, or 5 lb. pressure per square 

 inch, speed of ship 12 miles per hour, 17*6 feet per second. Then 



P= 122501b. V=17-6 R= 51b. per square inch. 



G=: 32 A =: 113 square inches. 



We have Li^^^f^ 105 feet 

 2 X 32 X 1 13 X 5 



The contents of which is 82-3 cubic feet nearly. Again, our velo- 

 city is 1056 feet per minute, ami if we reverse the valve D, when the 

 water has passed on, only 52 feet, then we get the initial velocity 

 1056 feet, and the final velocity 528 feet, the mean of which is 792 

 feet. The machine, at this rate, might make 15 strokes per minute, 

 but if one-third be deducted for friction, &c., or if we get 10 effective 

 strokes (that is 5 to each pipe) we shall have 41 1 cubic feet, or nearly 

 12 tons of water thrown out of the ship every minute, equ d to 180 

 pumps four inches diameter, and 11-inch stroke, going 30 strokes per 

 minute, and if kept working during 24 hours requiring from 900 to 

 lOOO men. This machine can be kept in operation during the same 

 time by two men, and if desired may be made self-acting. 



If the machine be worked at a low velocity, say four miles per hour, 

 it will then discharge 127 cubic feet per minute, which is equal in 

 eflScacy to liO pumps, worked by 3U0 men. 



With respect to the machine as a substitute for the air-pump, it 

 will be observed by referring to figs. 1 and 2, ih.it on reversing the 

 valve D, the branch pipe into which the water is flowing is nearly 

 vacuous, that is, there will probably be a vacuum equal to 10 or 12 lb. 

 per square inch (I speak of the Indicator), and the pressure being 

 thus removed from the end of the column, the external pressure of the 

 water and atmosphere will force the water through the pipe with a 

 great increase of velocity. Suppose, for instance, that the length of 

 the vacuous space (irrespective of that occupied by the water of 

 condensation) was 10 feet, and the elasticity of the vapour filling this 

 space equal to 1 lb. per square inch, then, according to the law which 

 regulates the elasticity of gases under pressure, if we take half the 

 length — five feet, and half the difference between the initial and final 

 pressures — 71b. per square inch, this will give the force tending to 

 accelerate the velocity of the w.iter through the pipe, viz., 71b. per 

 inch acting over a space of 5 feet, and this power is available every 

 time the valve D is reversed. 



In the event of the vapour being of greater elasticity in the con- 

 denser, say 7 lb. per inch, still as it would tend to keep the water in 

 motion in the after part of the pipe, it would reduce the quantity of 

 resistance from 17 lb. per inch, as it stood in the calculation, to 10 lb., 

 so that either view is favourable to the machine. In fine, a consider- 

 able amount of the power taken to produce the vacuum is again given 

 out. 



Figs. 5 and 6 show an arrangement which might be used advan- 

 tageously to withdraw water from a coft'erdam where there was a 



Fig. 5. 



^:"/~]T 



Fig. 6. 



current, produced either bv the natural stream of a river or the influx 

 and efflux of the tide. The apparatus is supposed to be formed of 

 four planks of wood nailed together, and a suction pipe constructed 

 in a similar manner. On the lop of tliis suction pipe there is fixed a 



