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Iron and steelmaking both require a constant supply of compressed air. A blowing engine is a powered air compressor working at low pressure and high volume. Cold air from the blowing house is directed to the hot blast stoves which heat the air, and deliver it to the base of each furnace via the hot blast main. This shows a typical layout.
Right to left:
The chimney exhausts combustion gases from 4 Lancashire coal fired boilers. The boilers are connected by a steam pipe.
Steam is used by the Steam cylinder to power the rocking beam. The flywheel adds inertia and smooths the action.
The rocking beam drives a piston moving up and down inside a larger cylinder (here depicted in cross section).
Non return valves maintain pressure in the air receiver, the cold air is heated in the stoves and hot air delivered to the base of the furnace. That's it.
In 1866 a pair of blowing engines were supplied by Messrs. Rothwell and Co. of Bolton-le-Moors. They had 46in. steam cylinders and 100in. blowing cylinders with leather air valves, cast iron grid seats. Cornish double-beat steam valves, cam-operated. 10ft stroke and operating at a boiler pressure of 40 psi and delivering air pressure of 3 psi. Speed was 15 revolutions per minute. They had wrought iron plate rocking beams, oak connecting rods, and steel shafts, piston rods, and wearing parts and were regarded in all respects, a very excellent example of construction. The leading dimensions and general arrangement were specified by the Carnforth Company’s Engineer Mr. Edward Barton. The details were worked out by Messrs. Rothwell and Co.
Left is an enlarged section of the blowing cylinders. The cylinders were placed at equal distances of 16ft. 11/2 in. on each side of the main centres. The distances between the main centre and the centres to which the piston rods of the steam and blowing cylinders are attached, are each 16ft. 6in. , and midway between the main centre of each engine and that to which the rod for the blowing cylinder is connected there is coupled to the beam the cold water pump rod.
The air pump rod is connected to the parallel motion of the steam piston rod in the usual way, so that it has a stroke equal to half that of the piston, or 5ft. The feed pump rod is coupled to the beam between the air pump rod and the main centre, at 5ft. 1 3/8in. from the latter.The beams are wrought iron plates and angle irons, about 5ft. deep at the main centre, by 1ft. 4 3/4in. wide on the flanges. Beyond the point of attachment of the steam piston rod, the beam of each engine is curved upwards, so that the centre to which the connecting rod is attached is 4ft. 9in. above the centre line of the main part of the beam, and 5ft. 9in. outside the centre to which the piston rod is coupled. The distance between the main centre and the centre line of the beam is 22ft. 3in. The oak connecting rods measure 33ft. 11 1/16in. between centres and measure 1ft. 8in. x 1ft. 1in. They connect to an overhung cast iron crank 6ft. 10 3/16in. long between centres placed upon a short crankshaft carrying a flywheel 25ft. diameter. The centre of each crankshaft is situated 12ft. 3in. outside the centre of the steam cylinder., 28ft. 9in. horizontally from the main centre. The crank is not horizontal at half stroke.
The engines are grounded 14ft. apart, the total width of the boiler house being 29ft. inside.
The piston rods are 6 3/4 in. diameter steel. The steam pistons are cast iron, thickness about 1ft. As the stroke is 10ft., and the length of the cylinders is 12ft., there is 1ft. available for clearance , the greater proportion equired at the bottom of the cylinders, where the stops for the lower inlet valves project above the bottom level. The blowing cylinder pistons are also cast iron and fitted with leather packing secured to wooden segments for convenience of removal and exchange. The air valves are of leather cith cast iron "grid" seatings.
Both engines discharge air into a wrought iron case 7ft. by 3ft. 7 1/2 in., placed between them. From this casing a bell mouthed pipe measuring 6ft. x 3ft. where it joins the case, and enlarging to 4ft. 6in. in diameter, conducts the blast to the pipe leading to the furnaces. The base plate of each cylinder is secured by four bolts embedded in the stonework. Each base plate has a manhole 13 1/2in. diameter, formed int he centre, access through an opening in the stonework. The upper platform is reached by a spiral staircase is formed by longitudinal and transverse girders extending from one interior wall to another, supported by cast iron columns.
The valves of the seam cylinders are of the Cornish double-beat class, worked by a camshaft just above the floor of the engine room, driven from the crankshaft through a longitudinal shaft and bevel wheels. The steam valves are 12in. and the exhaust valves 14 in. diameter and the cams arranged to allow cut off at three different points in the stroke. Valve spindles are of brass and handles provided so that any one can be lifted separately.
The engines are supplied with steam from boilers heated by the waste gases from the blast furnaces. Boiler pressure 40 psi and blast pressure between 3 and 3 1/2 psi.
Source: ENGINEERING August 10 1866.
The boilers for raising steam were supplied by Messrs. Sharp, Stewart of Atlas Mill, Manchester. It is not known if these were dual fuel boilers, but the works would have to be able to raise steam for the blowers before the furnaces were blown in, and whenever blast furnace gas was insufficient to meet demand.
Left Top
This is the North East facing end of the blowing house in its original configuration. Brick built with tall narrow windows and an internal floor level sufficiently higher than ground level to warrant a flight of stairs. Atop the house is a full size open top water tank which is holding hot steaming water.
On the original image it is possible to make out someone in the very bottom right corner stoking a boiler and several men working on the pig beds of Furnace No3. It is not surprising to see a line of one plank and three plank wagons left here, awaiting loading of pigs.
The boilers were housed in another building out of view to the right.
Left Bottom
The East face of the blower house. The boiler house was a much lower building beside the chimney. The roof level was below the tracks on the high line.
Between 1870 and 1873, a further three blast furnaces were erected and blown in, and additional blowing capacity was installed, engines supplied by Galloways of Manchester. The 1874 visit by the Iron and Steel institute reports there were a total of 6 engines:
The two original Rothwells rocking beam engines.
Two 84 in. vertical engines by Messrs. Galloways for the blast furnaces.
Two similar, smaller engines for the Bessemer Steelmaking plant.
From a 1903 copy of "The Engineer".
The overall principle is still the same, a 44 in. diameter steam cylinder (bottom) connected to an 84 in. diameter air cylinder (top).
These were over 30ft. tall, so a fraction of the size of the earlier engines.
The 1903 article says two of these engines are just now being put to work at Carnforth, to meet the increase in blowing pressure from the original 4 psi to the 20psi demanded by the "American" type of furnace. Each engine is capable of 20,000 cubic feet feet of air per minute when running at 53 rpm. The steam piston rod is connected directly to the cottering block , to which is attached the piston rod of the air cylinder. The cottering block is of cast steel, connected to a long crosshead by a stout pin at right angles to its main axis. The crosshead and connecting rods, one on each side of the engine, drive the flywheel. The steam cylinder has 4 grid valves, 2 for steam, and 2 for exhaust, the former being controlled by a high speed governer operating through an expansion link. The speed of the engine can be regulated to suit the demands of the blast furnaces.
On September 3rd 1881 the Lancaster Gazette reported that Messrs. W&J Galloway of Manchester have in hand a pair of large blowing engines for Carnforth blast furnace.......
So we have reports from 1874, 1881, and 1903 all referencing a pair of engines from Messrs. Galloway. It is not yet clear how many they supplied. None were listed in the plant inventory at the time of closure in 1930.
In 1902 the No4, No5, and No6 furnaces were demolished and a new No1a built on the site of old No6 with much greater capacity. Two American Westinghouse 1000kW turbo generators were installed to replace the 1881 engines by Messrs. Galloway. These were connected to two new Darve and Adamson mixed pressure blowers. The new furnace was optimised for a blast pressure of 10psi, in contrast to the original furnaces working at 3psi.
The blower house underwent changes over time. Compare this image with the one above. The main entrance has changed, the flight of steps removed, the central window and door appear to have been replaced with a tall barn door and the overall height has been increased with new windows visible on these West and South facing walls. There are two parallel crane tracks, all of which were designed to facilitate heavy lifting for the replacement and servicing of the blowers.
The furnaces, stoves, pond, and pig bed overhead crane put this late in the ironwork's life.
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