276 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



much beyonil the heig^ht due to the pressure of the air, caused an 

 irregularity that was even more asfffravated by its descent ; to 

 counteract this, a sprinff beam was placed on the top of the tub so 

 Hs gradually to check the momentum of the piston, and this had 

 some effect, hut not at all a satisfactory one. 



The next alteration which appears to have suggested itself, was 

 tlie application of large air chambers, from twelve times to thirty 

 times the area of the blowing cylinder, in which the elasticity of 

 the compressed air acted as the regulator of the discharge, the 

 tub with its piston being in some cases retained to work the cata- 

 racts, and as a tell-tale against the engine men, in case of their 

 alhiwing the steam to slacken and the piston to descend. 



We now enter u]ion the last ciiange which took place some fif- 

 teen years ago, namely, the coupling of two double-acting engines, 

 and double-acting blowing cylinders upon the same crank-shaft at 

 right angles, so as to keep up a regular discharge. Thiseifect was 

 in some measure obtained, but an air chamber, or, what is equi- 

 valent to it, very large mains, were still required to obtain what 

 was considered a satisfactory result. 



At this point the realised improvements of the blowing engine 

 stop short, leaving it still a large cumbrous and expensive machine, 

 and not capable of moving through its valves the highly elastic 

 medium air, at a greater rate than the absolutely non-elastic 

 fluid water, is moved through an ordinary pump, t'nder these cir- 

 <-umstances, it must be obviuus that after all the engineering talent 

 that has been spent on this description of engine, there is still (if 

 the expression may be applied) a wide range of discovery open. 



The immediate cause of the writer's attention being attracted to 

 the improvement of tlie blowing engine, vvas the difficulty ex- 

 perienced in regulating one of the old construction of blowing 

 engines in the latter part of 18-t8, and having at the same time 

 occasion to employ some small 9-inch cylinders driven by the air 

 of the large blowing engine. These small cylinders when driving 

 the shafting only, sometimes attained a velocity of upwards of 200 

 revolutions per minute, suggesting the idea of the possibility of 

 reversing their motion and taking in the air in place of blowing it 

 out through them ; there was however a difficulty in the slide 

 valve which did not o|)en and shut fast enough. After some con- 

 sideration it was agreed that another cylinder should be prepared, 

 and the centre port made much larger, and the slide overtravelled 

 nearly half its stroke in excess, which had the desired effect ; a 

 cylinder of 9 inches diameter, and 1 foot stroke, having been 

 driven 320 revolutions or 6+0 feet per minute, discharging the air 

 at a pressure of '.i}^ lb. per square inch, through a tuyere of Ig inch 

 diameter, or j^th of the area of the blowing piston. This per- 

 formance, as is well known, is more than double that of any 

 ordinary engine, the total area of the tuyeres w ith a 9() inch blow- 

 ing cylinder, being at a pressure of 3g lb., about 52 circular inches, 

 '"■ T^Tith of the area blowing piston. 



M'^e are all acquainted with the tremour which is felt even in 

 the best form of the large sized engines ; but in the experiments 

 at a high velocity with the small sized cylinders, not the slightest 

 jar was felt or noise heard, it is therefore proposed to increase the 

 speed of the piston in actual practice, from 6+0 to 750 feet per 

 minute, the length of stroke being 2 feet in place of 1 foot ; this is 

 somewhat under the speed of a locomotive piston at 40 miles per 

 hour, which is about 800 feet per minute, so that it is conceived no 

 difficulty can present itself to this. The proposed speed of 750 

 feet per minute, is three times the usual speed of the present blow- 

 ing engines, 250 feet )ier minute. 



The construction of the proposed engine is shown in the accom- 

 panying engraving, fig. 4, Plate X., showing the plan of a pair of 

 horizontal steam cylinders and blowing cylinders; A A are the 

 steam cylinders, 10 inches diameter and 2 feet stroke; BB, the 

 blowing cylinders, 30 inches diameter and 2 feet stroke, with their 

 pistons C, fixed on the same piston rods D, which are connected to 

 two cranks E, fixed at right angles to each other on the same 

 shaft. The slide valves F, of the steam cylinders are worked by 

 the eccentrics ti, on the cranked shaft, and the cranks H, at the 

 outer ends of the same shaft, w ork the slide valves I, of the blowing 

 cylinders. The centre port K, passes downwards to an external 

 <i])ening for the admission of the air, and the discbarge jiorts L L, 

 deliver into the passages M,on the top of the cylinder, wliich com- 

 municate with the air main N, by the chest O, formed between the 

 cylinders. The piston of the blowing cylinder is intended to be 

 made without any packing, being a light hollow cast-iron piston 

 turned to an easy fit ; and the slide valve of the blowing cylinder 

 to have a packing plate at the back, working against the cover of 

 the valve box, with a ring of india-rubber inserted between this 

 jjlatt and the back of the valve, to give a little elasticity. 



It appears that 30 inches diameter is somewhere about the most 

 convenient size for a stroke of 2 feet, and as it is considered an 

 advantage to have the stroke as short as possible, to increase the 

 regularity of the blast, the comparative cost of the different en- 

 gines which f(dlows has been taken upon this basis two 10-inch steam 

 cylinders and two 30-inch blowing cylinders, costing together (ex- 

 clusive of the boilers,) about 400/, being reckoned equal to blow 

 one of our largest furnaces, making 160 tons of iron per week and 

 having a surplus equal to blowing a cupola or refinery, as is gene- 

 rally allowed, as such an engine would give at 640 feet per minute 

 the same speed of piston as in the experiments, very nearly 30 

 circular inches of tuyere, at a pressure of 3,J lb. to the square inch; 

 the circular inch is used in speaking of the area of tuyere, as the 

 blast that any furnace is taking is usually reckoned by simply 

 squaring the diameter of the tuyere, but the pressure is taken on 

 the square inch. 



The experiments on which these calculations were founded, 

 having been made upwards of 12 months ago, were repeated last 

 week, and the results were found to be as nearly as they could be 

 measured the same, the blowing cylinder had in the interval 

 been driving the lathes in the pattern shop, and the slide was 

 found perfect. An indicator was applied with a view to test the 

 amount of friction of the air in entering the cylinder at the high 

 velocity, and a simple method was adopted of ascertaining this. 

 A tuyere was made as large as the inlet port, and the engine was 

 driven to nearly or quite 700 feet per minute, when the guage 

 showed a pressure of ^ of a lb. per sijuare inch ; and as the fric- 

 tion would be the same through the same sized openings at other 

 pressures, it follows that the loss by friction on a pressure of 

 blast of 351b. per inch, would be rsth or 6| per cent loss; as the 

 port in this case was yV^'h of the area, and tlie port proposed is gth, 

 it is assumed that the loss would not exceed 5 per cent, from 

 this cause, or indeed from any other cause, as the friction from 

 propelling the air through a given sized tuyere, at a given pres- 

 sure, must be the same in both cases. 



Following up the comparison of first cost, we find (that exclu- 

 sive of boilers, which are assumed the same in both cases, but 

 taking into account the cost of the engine house,) there would be 

 a saving by the proposed plan of between 65 and 70 per cent.; the 

 cost of a pair of the best engines in Staffordshire, blowing three 

 furnaces, being 3650/., while on the proposed plan they would cost 

 1100/. if high pressure only, or if high pressure and condensing 

 1350/., including in each case the engine-house but not the 

 boilers. 



Many will prefer high pressure only, on account of its simpli- 

 city, but as it appears evident that a given quantity of steam can 

 be condensed in the same time, in the same condenser, whether 

 admitted in a few large jets or in a great number of small jets, 

 there is no reason whatever why a condensing apparatus may not 

 be attached to the short-stroke engine at high velocities; the only 

 condition being that it must be ecpiivalent to the power of the 

 engine without relation to the size of the cylinder. '1 he air-pump 

 in this case must be double acting with slide valves, or it may bo 

 rotary and placed round the crank-shaft, and there appears to be 

 no advantage in a fly-wheel for such an arrangement of blowing 

 engines. 



The speed of the engine should be regulated by a hydrostatic 

 governor, communicating with the blast main, and attached to the 

 throttle valve, exactly similar to those used in gas works for 

 regulating the engine driving the exhausters; this would regu- 

 late the engine with greater delicacy, and maintain a more uniform 

 blast than can be done with the present engines; and the ra)iid 

 succession of the strokes of the two small blowing cylinders acting 

 alternately, would render the present large reservoir quite un- 

 necessary. 



Supposing the advantages claimed for this description of en- 

 gine to be realised, which the writer has no reason to doubt, it 

 may be applied to assist the present blowing engines where they 

 are overpowered, which is in many instances the case, as there 

 is no ready means of increasing their power as the works develope 

 themselves, and greater calls are made on the engine; but in the 

 case of the proposed engines, if at any time an increase were 

 desired another l)lowing cylinder might be added to the shaft, at a 

 comparati\ ely small cost. 



Referring again to what first drew the attention of the writer to 

 this subject, the employment of small cylinders worked by the 

 pressure of air, where it was inconvenient or im|iracticable to 

 employ shafting; it has been found that a 12-inch air cylinder with 

 3 lb. pressure attached to a large foundry cr.ine, under wliiclj fifteen 

 30-inch pipes are cast vertically every ten hours, does the work of 



