1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



213 



MARINE ENGINES, 



By p. BoRKiE & Co., Engineers, Tay Foundry, Dundee. 



Designed November, 1841. 



CWith an Engraving, Plate VUI.) 



These engines belong to that class generally denominated direct 

 action engines : in this respect they are similar to other engines of that 

 class. Their peculiarity consists in the novel arrangement of the air 

 pump and condenser. The following particulars of their construction 

 and peculiarity have been furnished us at our request, by Messrs. 

 Borrie and Co. 



The collective power of the two cylinders by formula, 



area of cylinderx 7x210 „,, , 

 „^ „ =352 horse power, 



33,UOtJ ^ ' 



but by taking the pressure on the piston at 8"a lb., and the velocity at 

 215 ft. per minute, the power will be 426 horse power. The strength 

 of the engines and evaporating power of the boilers are adapted for 

 the full power. The engines occupy a space of 10 ft. fore and aft the 

 vessel, and 221 ft. transversely. The engines, boilers, space for firing 

 boilers, and coal boxes, capable of containing 400 tons of coals, calcu- 

 lated at 48 cubic feet per ton, in a vessel with engine room in the 

 clear 343 ft. broad, by 23 ft. deep, only require 55 ft. fore and aft. 

 The ordinary length fore and aft allowed in the Government steamers 

 for engines. Sec. of the above power is Go ft. With 65 ft. 560 tons of 

 coals can be stowed in the coal boxes. With these engines, tlierefore, 

 a space of 10 ft. fore and aft the vessel may be made available for 

 other purposes, or an additional 160 tons of coals to the ordinary 

 quantity apportioned to the coal boxes. The coal boxes are so 

 arranged that they afford protection to the engines and boilers from 

 shot, which are placed below the vessel's load water line. 



The weight of one pair of engines 110 tons. 



„ the paddle-wheels (common construction) 25 „ 



„ the boilers, with mounting 81 „ 



„ the water in boilers 55 „ 



„ the coal boxes IS „ 



Total 289 tons. 



The following explanation will show the construction of the con- 

 denser and air pump : — One condenser, a, fig. 6, and one air pump, q, 

 serve for both engines. The air pump is double acting, and has four 

 valves, d' d e' e. The valves d' d correspond with the foot valve, and 

 the valves e' e with the discharge valve of an engine fitted with the 

 common lifting air pump. This description of air pump has pistons 

 similar to those used in steam cylinders, and packed with metallic 

 packing in the same manner. Communicating with each end of the 

 pump there are valves opening inwards, d' d, and ethers outwards, e' e, 

 being four valves to each pump ; by this arrangement the piston, ff, 

 alternately draws and forces, at each half stroke of the engine. The 

 passages are of one casting with the pump, next and jointed to the 

 sides of the condenser, as at r r r r; doors, c c, on the sides of the 

 condenser opposite these passages admit of ready access to the valves : 

 the pump is placed at the bottom of the condenser. To render a 

 stuffing box unnecessary on the pump cover, o o, for the pump rod, a 

 tube, II H, extends from the pump cover, o o, to the cover on the top 

 of the condenser, s s, in which the pump rod, g, works: a suitable 

 stuffing box, m m, and gland, 1 1, for the pump rod are provided in the 

 cover on the top of the condenser. The double action air pump 

 possesses several advantages over those of the common construction ; 

 among these it may be noticed that one double action pump will do 

 the work of two with only the friction of one single action pump, the 

 dimensions of both being equal ; so one of the former to do the same 

 amount of work as one of the latter will only require to be of half the 

 area, with the same length of stroke. The efi'ective action of this pump 

 being at every half stroke, a much steadier and purer vacuum will be 

 maintained in the condenser than by the common pump, whose action 



No. 58.— Vol. V.— July, 1842. 



is only at the termination of every full stroke of the engine. Its 

 liability to become deranged is not greater, and the difficulties in 

 remedying these derangements when they have occurred are less than 

 in the common pump. Connected with the latter are the foot, dis- 

 charging, and bucket valves; for obtaining access to either of the first 

 two of these valves, the jointing of a separate door has to be undone, 

 and for the third several disconnections have to be made, and the air 

 pump cover has to be lifted. In some arrangements of engines the 

 whole of these valves are of very difficult access ; to obtain access to 

 the valves in the double action pump the undoing of two doors is only- 

 necessary. Although the valves at one end became deranged in action, 

 yet the pump with the valves at the other end would work as a single 

 action pump, and the engines continue in operation until opportunity 

 was afforded for repair. The repair could be very speedily effected, 

 by always having in readiness a set of valves to replace those that 

 became defective. If the valves of the common pump get deranged, 

 the working of the engine is completely suspended. In the arrange- 

 ment of engines with this pump, it is shown in fig. 6 as wrought by a 

 crank, forged of a piece with the intermediate crank shaft of the 

 engines. The perpendicular position of the pump rod is maintained 

 by a guide pulley, i i, working in guides, jj, bolted to the engine 

 framing, 1 1. 



It has been correctly maintained that an engine air pump with a 

 solid piston or plunger, as hitherto constructed, will not produce so 

 pure a vacuum as a lifting valve bucket of the common construction. 

 This will hold true in respect to a single action plunger air pump 

 which only expels the water and gases by its downward stroke ; for as 

 the gases are always in position above the surface of the water to be 

 expelled, the descent of the plunger will lessen their volume and 

 increase their density to an extent corresponding to what would result 

 from being subjected to a pressure equal to that required for expelling 

 the water. There being always a head of water in the hot water 

 cistern pressing against the discharge valves,* these gases can only be 

 very partially expelled from the pump chamber. On the ascent of 

 the plunger, and re-opening of the valve communicating with the con- 

 denser, they (the gases) will partially return to the condenser, (as a 

 less head of water in a partial vacuum will offer less resistance to 

 their ingress,) and partially impede the free flow of the water in it to 

 the pump chamber. These defects impair the efficiency of the en- 

 gines, from the consequent imperfect condensation, and impurity of 

 vacuum ; no such defects obtain in a double action force pump, as 

 applied to an engine. In fig. it will be noticed that the passages 

 between the air pump and three of the lower sides of the condenser 

 will always be filled witli water, during the ascending stroke of the 

 plunger piston to a level with the lower side of the piston plunger, 

 and during the descending stroke to a level with the lower part of the 

 upper foot valve seat. These passages, however, being specially 

 made of very small cubical capacity, will not admit of more water 

 remaining in the bottom of the condenser, on the cessation of the 

 engines from work, than what remains in a condenser and bottom of 

 air p\imp chamber of the common construction. The difference 

 between tiie level of the lower side of the piston plunger and the 

 lower part of the lower foot valve seat only admits of the water enter- 

 ing into the pump chamber during the ascent of the plunger, in the 

 limited time afforded by a half revolution of the crank. This precludes 

 an ingress, to any injurious extent, of gases to be acted on by the 

 return of the plunger, in manner as resulting from the use of a single 

 action plunger pump; but on the upper foot valve opening, during the 

 descent of the plunger, opportunity is aflx)rded for the admission of 

 the gases into the upper part of the p\imp chamber. During the 

 ascent of the plunger, these gases being in position above tlie siuface 

 of any water that may have entered with them, will be first expelled 

 through the upper discharge valve, t', into the hot well, J9. The ex- 

 pulsion of the gases by a double action plunger pump is, therefore, as 

 efficiently accomplished as by the common bucket valve pump ; and 

 the objections against the use of a single action force pump, when 

 urged against it, are unfounded. 

 In the drawiiigs and description one of these double action air 



2 a 



