IfB 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[IMarch, 



cliarj^i'd in siirli a direction that it may Iw reflected iipwurds, or slanting 

 upwards Irdiii llie sides nf tlie l)oiler. 



Tlie |)luiiger of the pipe C is connected liy tlie link ii with the lever 

 o, this lever is worked hy the cam p, fixed on the shaft r, which shaft 

 is driven by any of the usual and suitable modes from the engine, or 

 any other ecpiivalent mmle of lifting the lever may be adopted; to the 

 end opposite to that on which the cam acts, is suspended the weight 

 (J, so that the cam lifts the ])lungc'r ami the weight gives the stroke, 

 producing a sudilen and violent rush of the water through the holes of 

 the noz/.le m which very materially alFects that minute division of the 

 water which is necessar)' to the jierfect action of the boiler, s is a 

 plunger or jiiston working through a stalling box, upon the top of the 

 boiler connected by the link /, with the lever », which lever works 

 upon the centre r, to the end next the chimney is attached the rod of 

 the damper dd, and to the other enil the weight c, and the rod «), thus 

 vvlie]] the sleam rises, it acts upon the phnigcr or pislmi s, this raises 

 the end of the lever )(, vipon which the weight r is suspended, and the 

 rod w attached, and depresses the other end to which the damper is 

 attached, thus damping the fire as in the usual way, the lever ii in the 

 act of rising by the increasing elasticity or volume of the steam lifts 

 the rod «', and likewise the end of the crank or lever .r, to which the 

 other end of the rod w is attached, this crank or lever is fixed upon 

 one end of the cross shaft y, and to the other end of tlie shaft, and at 

 right angles witli the crank .r is fixed another and shorter crank z, 

 thus when the crank x is raised vertically by the action of the steam 

 plunger s, it causes the shorter crank z to move horizontally forwards, 

 this horizontal movement is continued through the niedinm of the rod 

 or bar z' ,connected with the short crank z at one end, and the other 

 end with the wedge 2, thus pushing the wider part of the wedge under 

 the pump lever, and by this means sliortening the stroke or descent of 

 the ]uun)) plunger, this movement may be also efTected by a rack and 

 )iini(ni, or by a screw and |iijiion, or by other means. 



I do not claim the plunger or piston as new, to regulate the damper, 

 an analogous contrivance, liaving alreaily been made ; that part of my 

 invention which I have before referred to as a self acting apparatus 

 for [ireventing an undue accumulation of water in the bottom of the 

 boiler, is as follows ; to the extreme end of the lever /(, of the water- 

 valve, is fixed a slight bar, wire, or chain, S; the other end of the 

 ■wire or chain is connected to the .short horizontal crank 7, fixed upon 

 the short cross shaft 3; to the longer arm 5 of the horizontal crank, is 

 suspended the weight (i, which weight, when the wire or chain is 

 slackened, descends, and descending, produces motion in the shaft 3, 

 to which the crank is fixed, and also in the short crank 4, fixed n])on 

 the other end of the cross shaft 3; thus as the weight descends, the 

 crank 4, by means of the rod 4', connected with it, and the wedge 1, 

 draws the wedge 1 forward; by the wider part being thus drawn or 

 introduced under the lever o of the pumii, the stroke of the pump is 

 shortened, and the supply of water consequently diminished. 1 do not 

 confine myself to the particular modification of machinery here de- 

 scribed for ellecting this object, but any other adapted to the pur- 

 pose may be used; thus for instance, another mode of regulating 

 the action of the pump, is by forming the descending tube about S or 

 10 inches internal diameter, and placing therein a float, which shall 

 rise and fall willi tlie water in the tube in the same way as the float 

 in the 'ieed head of a conunon boiler regulates the damper, then a 

 wire p assing through a stufling box in the upper part of the pijie t, 

 and communicating with the crank 7, in the same way as the wire 8, 

 the same movement will take place in the wedge 1, as has been before 

 described ; in the case of a locomotive where the pump plunger is con- 

 nected with the cross head of the piston rod, anil works very fast ; the 

 method to be adopted to reduce the stroke of the pump, will be to 

 make the barrel of the pump moveable, then by means of a screw fixed 

 to the end, and causing the nut in which the screw works to be acted 

 uiion either by the steam plunger or the lever of the water valve, and 

 thus uuiking the barrel of the pump advance towards, or recede from 

 the i)lunger, the same regulating process will be easily a))plicable ; it 

 will be merely necessary that the suction and injection pil>e should 

 work in stuffing boxes, or by making them elastic to allow for the 

 variation; 9 is the pipe and cock for sup|)lying the water cistern with 

 water, V is the ball-cock which kee|)s the water to its level, lU is the 

 safety valve, 11 the steam l)ipe, 12 the steam casing in which the 

 ;)lunger works, the lower part is covered with a plate perforated with 

 lolos, so thai the steam plunger may work more steadily, and not be 

 acted upon so suddenly by the steamj as the steam befm-e" acting upon 

 the plunger will jiass through the holes of the plate, and thus a certain 

 regularity of action w ill be preserved, which could not be ensured 

 without it. 



A boiler upon this construction, but made in a very rude manner 

 lor the purpose of experiment, 2 ft. deep, 1 ft. over at the bottom, 

 wid 2 it, wide at the widest point, was at mtk I'w seme time drivijig 



I 



a G horse condensing engine at Messrs. Burton & Sons, engineers, 

 Bankside, but now of Holland Street, Blackfriars Road ; the ;irea ex- 

 posed to the fire was about 8 ft., and this drove the engine fully 

 loaded, the steam blowing olVduriiig the greater part of the time; it 

 had no tendency to get red hot, and uj)on several occasions, for the 

 mere purpose of the experiment, the engine was stopped, and the 

 boiler purposely made red hot, when the only result that followed was 

 a rapid generation of steam whilst the water was pumped into the 

 boiler; bv this a|)paratus the great desiileratum of a powerful, port- 

 able, and safe boiler is obtained, and I feel certain that in a properly 

 constructed vessel, a velocity of 2U miles per hour through the water 

 can be easily accomplished. 



Stam/vrd Strut, W.J. CURTIS. 



Blackfriars Road. 



ON THE PRESSURE OF WATER AND THE STRENGTH 



OF COFFER-DAMS. 



By John Neville, C. E. 



The following prepositions are intended to furnish rules for calcu- 

 lating the dimensions of coffer dams from having the depth of water, 

 and the specific gravity of the materials to be used in the dam given. 

 The construction of the coU'er dam is supposed to be that generally 

 adopted, namely, two or mm'e rows of piles having the spaces between 

 filled with clay, ox a mixture of clay and gravel, the whole united into 

 one mass by walings, bolts, &c. And it will be seen that the dimen- 

 sions found from the investigated formula do not diller materially from 

 those adoptetl with success by many celebrated engineers. 



The pressure arising from mere depth of water is not the only force 

 to be prepared against in constructing a coU'er dam, as moving water 

 or an exposed situation nuist also be taken into consideration. These 

 latter I have not cakailated for in the following problems, as I consider 

 they are sufficiently provided for by the resistance of the piles pene- 

 trating the bottom, w hich assists tlie solidity of the dam ; and by the 

 auxiliary aid of stays and braces, and have determined the dimensions 

 of the dam itself as only sufficient to resist the pressure of an outside 

 depth of dead water. 



Problem I. 



To dttcrmine the amount of pressure against a coffer dam or obstruc- 

 tion, the diplh of wall r being given. 



Put c for the depth of w ater in feet. The pressure on each point 

 of the dam is as the depth of that point from the surface of the water ; 

 the whole pressure for the depth c is therefore repieseuted by the area 

 of a right angled triangle having the base and perpendicular each equal 



to c, 



or by -^. The weigiit of a cubic foot of water may.be taken 



for tlie pressure on each 



atG241bs. ; hence we have G2iXo= — s~ 



^ 2 



foot in length of the dam in lbs., which, multiplied by the length, will 

 give the whole pressure required. 



Example 1. — What is the pressure on each foot in length of a cof- 

 fer-dam, the water inside lieing exhausted, and the depth of water 

 outside being equal to 15 feet? 



TT 1- ,125c- 125x15x15 . ,, ,, 



Here crrlo and —5-= =:110J2i lbs., the pressure re- 



quired. 



Exam})l(: 2. — What is the pressure against J coft'er dam whose girth 

 is tiO feet, the depth of water outside being 20 feet? 



J25 V 20 X ^0 

 Here we have i-^:=25000lbs. for the pressure on each 



foot in length, therefore 25,000 X GO^ 1,500,000 lbs. is the pressure re- 

 quired. 



PROULliM 11. 



To find th effective pressure against a coffer dam or lock gate; the 



depth nf mater outside being ginn : a given depth of water being inside. 



Put c for the outside depth of water, and d for that inside, we then 



. 125c- I25i'^ 125 (€■—«;•-) i25y.{c-\-d)y.{c—d). ,, 

 get — :=:— . — 1- '=:: ^ — ^^— ^ lor the pres- 



sure on each foot in length, when the inside and outside girths are equal; 



putting therefore g for either girthj we get " •• -■ ■ 



fvr the piesiSMe required. 



