The steam railway locomotive’s history began in 1804. In that year Richard Trevithick demonstrated the capabilities of a railway engine in South Wales. John Blenkinsop’s engines began to run in 1812. Of the other pioneers the most famous was George Stephenson, whose “Rocket” of 1829 gained world renown
ANCESTOR OF THE WORLD’S LOCOMOTIVES, Trevithick’s engine of 1804 ran on a mineral tramroad at Penydarran, near Merthyr Tydfil, South Wales. The single cylinder communicated its motion to the four road wheels through a flywheel and gearing. The illustration is only of approximate accuracy, as no authentic drawings of the engine exist.
OF all machinery, perhaps the locomotive makes the greatest universal appeal. Its size and purposeful appearance, combined with its capacity for shifting heavy loads at great speeds, evoke a peculiar interest from all manner of people, young and old. Steam railway locomotives belong to an ancient family; their lineage goes back to 1804.
Of Cugnot, Fourness and Murdock, and of the first experiments of Trevithick, an account is given in the chapter beginning on page 253. The first steam locomotive to run on a railed track was built by Trevithick in 1804, and worked on the Penydarran tram-road, near Merthyr Tydfil in South Wales. The great majority of these mineral tramroads, which formed the first railways, had flanged iron rails fixed to stone block sleepers. The Penydarran road was no exception. Trevithick’s first railway engine, therefore, had flangeless wheels and was not far removed in design from his road locomotives. Moreover, it had a high-pressure boiler.
This remote ancestor of the modern steam railway locomotive in no way resembled the steam carriages of Cugnot, Fourness or Murdock. In many particulars, it was similar (though on a crude and small scale) to the modern engine. The boiler was horizontal but, instead of having the now usual multi-tubular arrangement of the flues, it had a single return flue, the firedoor and the chimney being thus both at the same end. There were four road wheels. Trevithick used only a single cylinder, and therefore had to use gearing and a huge flywheel in communicating its motion to the wheels. The same arrangement may be seen on a modern steam roller and on certain types of steam road wagon to-day. The main sprocket wheel engaged with circular trains of teeth on one side of each pair of wheels. The effect was the same as that of an ordinary four-wheels-coupled engine of our own times, though in this instance both axles were driving axles. No authentic drawings of this engine exist, and certain points are still in dispute among railway historians. The Penydarran locomotive is believed to have had the following main dimensions: cylinder (single) 81-in diameter by 54-in stroke; length of boiler, 5 feet; diameter of wheels, 4 ft 4-in. Another feature forecasting modern locomotive practice was the fact that the exhaust steam was turned into the chimney. There was nothing resembling the carefully adjusted blast pipe (see below) and the engine had no smokebox, but it is probable that the exhaust into the tall chimney materially improved the draught. The engine showed itself capable of hauling a load of iron 10 tons in weight over the nine-miles length of the Penydarran line. Although the first Trevithick railway locomotive was a mechanical success, it was a commercial failure, for it broke the old cast-iron plate rails and scattered them right and left. Many early railway locomotives suffered in reputation through no fault of their own, because the permanent way was anything but “permanent”.
London’s First Railway
Trevithick came to London, after his provincial experiments, determined to show that steam passenger transport on railways was feasible. In 1803, in the neighbourhood of what is now Euston Square, not far from the site of the LMS terminus, he laid down a circular track of iron rails, surrounded by an enclosure. On this track he placed a new locomotive called “Catch-Me-Who-Can”. As was the Penydarran engine, this locomotive was a four-wheeler with a single cylinder, but it was not fitted with the flywheel of the earlier design. The remaining rolling stock of London’s first railway consisted of an open barouche with its wheels adapted for running on the rails and a simple coupling device substituted for the shafts. Trevithick exhibited his “train” to any one willing to pay a shilling for admission, and this entrance fee entitled visitors to a ride in the barouche behind the locomotive. Many came to stare, to wonder and even to ride, but most people insisted on treating the railway as a sort of circus, without perceiving its significance as a great experiment. The little engine was capable of hauling the loaded carriage at a speed of twelve miles an hour, but here again the rails proved the weak point. One of them broke while the train was running, and the engine was derailed and overturned. That was the end of the first railway in London.
BLENKINSOP’S LEEDS LOCOMOTIVE, the first commercially successful engine in the world, went into service in 1812. It had, fitted in the top of the boiler shell, two vertical cylinders which drove a sprocket wheel, whose teeth engaged with a rack on the side of the rail.
Trevithick’s experiments were not ignored by his brother engineers. On the contrary, they were watched with great interest, and before long they were being imitated or modified. One school of thought insisted that the railway locomotive, though obviously capable of running and drawing certain loads with smooth wheels on smooth rails, would never succeed properly until a rack-and-pinion method of propulsion had been applied to it. A reason for this view was that the locomotive of the early eighteen-hundreds was small and light, so that its factor of adhesion was correspondingly low. The first Trevithick engines frequently slipped badly.
John Blenkinsop, who was in charge of a tramroad three and a half miles long, connecting Middleton Colliery with Leeds, set himself to produce a means to render locomotives incapable of slipping. On his nearside rail he placed a continuous series of semicircular lugs or teeth, with the convex side upwards.
His locomotive, built by Matthew Murray, was peculiar. It rested on four flanged wheels (the Middleton rails were of the edge type, without flanges) and carried on the near side a huge sprocket wheel with twenty teeth, this wheel engaging with the rack on the side of the rail. The engine had two vertical cylinders fitted in the top of the boiler shell, with transverse crossheads, whence connecting rods came down on either side to drive gears connected with the pinion wheel. The exhaust did not pass into the chimney, as in Trevithick’s engines, but was carried up a vertical pipe into a wooden silencer mounted on top of the framework formed by the two pairs of slide bars.
WITH ALL SIX WHEELS COUPLED, the “Royal George” of 1827 was the first engine to have this wheel arrangement, still common for goods locomotives in Great Britain. Two vertical cylinders drove the rearmost axle. The return-flue boiler had its firedoor and chimney at the front. The designer was Timothy Hackworth, Locomotive Superintendent of the Stockton and Darlington Railway, the world’s first public railway.
The Blenkinsop-Murray engine and others of its type were historically important, for a number of reasons. First, the Middleton Colliery line was the first steam railway in the world to be a commercial success. The engine, and others of similar design, proved a complete success. The initial train consisted of eight wagons carrying 25 tons of coal. Moreover, nearly fifty passengers were carried during the first triumphal progress. The Blenkinsop engines, each of which weighed about 5 tons, were in service for over twenty years, the inaugural date being June 24, 1812.
Their second claim to fame is the fact that they were the ancestors of the modern rack locomotive used on steep gradients in mountainous districts, of which Switzerland provides the classic example in modern times. Finally, their performance so impressed distinguished visitors that a similar locomotive was built in a German foundry and set to work on a mining line at least as far back as 1816. This was the first railway locomotive to run anywhere outside Great Britain.
At the time of Blenkinsop’s success at Middleton, Christopher Blackett, one of the proprietors of the famous Wylam Colliery in Northumberland, decided to substitute steam for horse traction on the line connecting his pits with the River Tyne. He had already unsuccessfully tried steam traction, having obtained a Trevithick locomotive in 1805. Having heard of Blenkinsop’s success, Blackett visited Middleton. But he disliked the rack arrangement. It would entail modifying the whole of his existing track at Wylam.
Two men destined to become famous were employed at Wylam Colliery. One was William Hedley, a viewer, and the other was Timothy Hackworth, foreman of the blacksmith’s shop.
Hedley's “Puffing Billy”
These two undertook to produce a locomotive working by adhesion alone which should be capable of doing all the work that Blenkinsop’s rack-and-pinion engine was carrying out at Middleton. Their first experiment was a failure, but in 1813 a successful locomotive was built. Hedley was mainly responsible for its design, Hackworth for its construction. Their engine was the world-famous “Puffing Billy”, which may be seen to this day, virtually intact, at the Science Museum, South Kensington.
“Puffing Billy” is so well known that a full description is superfluous. As with the Blenkinsop engine, there were two vertical cylinders, but these were mounted outside the boiler, on the main frame at the front end. The boiler had a return flue, similar to that of previous engines. Hedley gave his cylinders a diameter of 9-in and a stroke of 36-in, the motion of the piston rods being communicated to gears under the wooden frame by a pair of huge “grasshopper” beams above the level of the boiler top. The boiler had a grate area of 6 square feet and the return flue provided, with the firebox, a total heading surface of 77 square feet. The four driving wheels were of 3 ft 3-in diameter. Coal and water were carried on a four-wheeled tender at the firedoor end, from which the chimney also rose. The driver’s footplate was at the front, adjacent to the two cylinders.
As a locomotive, “Puffing Billy” was a remarkable success, and Hedley built a sister engine, “Wylam Dilly”, which is now preserved at Edinburgh. Unfortunately the engines constantly broke up the cast-iron Wylam rails. To put an end to this trouble, each engine was provided with a crude four-wheeled bogie. This addition was intended to distribute the weight more easily and to lessen the axle loadings. In their altered form, which made the engines the first eight-wheeled locomotives in the world, they worked well for many years. Then, early in the eighteen-thirties, the track was relaid and the engines were given back the original four-wheeled arrangement. Both of them led long and active lives, although other early locomotives lasted for a few years only. “Puffinq Billy” was in service until 1862 and “Wylam Dilly” until 1867.
The fireman of the winding engine at Wylam was named Stephenson, and he had a son named George. Young George Stephenson’s greatest boyhood delight was to be allowed to haunt the engine house where his father presided. When his father was in a good mood, the boy was permitted to help in firing. At the age of 17, because of his precocious skill in mechanical engineering, George was appointed engineman at Wylam. After an astonishing success in freeing an apparently hopelessly flooded pit of water within five days, George Stephenson was appointed enginewright at Killingworth Colliery, Northumberland.
At Killingworth he built his first locomotive, “Blucher”, in 1814. He based his general design on that of Hedley, which he had inspected the previous year at Wylam. The wheels, however, were four-coupled with inside rods. Blucher was not a success at first. It steamed badly, and the inside rods tended to become bent. Stephenson reverted to the expedient of turning the exhaust into the chimney, and replaced the rods with chain couplings. These alterations had an immediately satisfactory result, and Stephenson increased his reputation for ingenuity.
After that he built several colliery locomotives, notably one for Hetton Colliery. This engine is preserved in York Railway Museum, having a century of active service to its credit. It is a four-wheels-coupled engine with two vertical cylinders on top of the boiler and large transverse walking beams, the arrangement being rather similar to that of a steeple engine in an old-fashioned paddle steamer.
Active Life of 103 Years
The engine was built by George Stephenson and his partner, Nicholas Wood, in 1822. The last time it ran under its own steam was at the Railway Centenary Exhibition at Darlington in 1925, after which it passed into distinguished retirement. An active life of 103 years constitutes a record as far as locomotives are concerned.
Now followed an important period of experiment. The locomotive had proved a valuable means of transport for minerals in industrial districts, but it was yet to appear on the stage of public transport. During the eighteen-twenties, many experimental engineers were turning their attention to the railway locomotive. Timothy Hackworth, sometime of Wylam, was on the road to fame. Marc Seguin in France had taken up the idea, and so had the great Swedish engineer, John Ericsson. Ericsson was to attain fame by designing the “Monitor”, the first turret warship, which tried conclusions with the ironclad “Merrimac” in 1862 during the American Civil War. It was Stephenson, however, who designed the first steam locomotive for work on a public railway.
In April 1821 an Act of Parliament had been obtained for the building of a railway between Stockton-on-Tees and Darlington, in County Durham. The principal promoter was an influential Quaker, Edward Pease. Pease had intended to use horse traction, but he was empowered to haul his wagons by means of “men, horses, or otherwise”. Stephenson, armed with a letter of intro-duction from the manager at Killingworth, went to see Pease and remarked that “otherwise” might be well interpreted as “steam”. Pease was impressed, both by Stephenson’s arguments and by Stephenson himself, and went to see “Blucher” working at Killingworth. Pease then had the line entirely resurveyed with a view to using locomotives, and had such traction legally specified in the wording of the Act, not trusting in the ambiguity of “otherwise”.
ON SHOW AT DARLINGTON STATION, on the main line of the LNER, “Locomotion” was the first engine of the Stockton and Darlington Railway. It was designed by George Stephenson, with the assistance of his son, Robert. The cylinders (9½-in by 24-in) and motion were mounted on the top of the boiler. The springless four-coupled wheels were 4 feet in diameter. “Locomotion” was
Stephenson was appointed Engineer of the new enterprise, and immediately took up a firm stand over the question of permanent way. He was not going to have his work ruined by bad rails, and objected strongly to the use of cast-iron rails of the current type. Cast-iron rails were cheap, and their use would have made Stephenson richer by some £5,000. But in 1820 John Birkenshaw had invented a greatly improved rail of malleable iron, and Stephenson was determined to have the best and was prepared to answer for the expense. He had a considerable struggle to get his proposal past some of his directors, but he carried the day in the end and the rails were duly ordered. They were of the fish-belly type, and weighed 29 lb per yard.
His son Robert, who was to attain fame in after years as the designer of the Conway Bridge and the Britannia Bridge across the Menai Straits (see pages 127-130), worked with him in designing the first locomotive for the Stockton and Darlington Railway, the first public line in the world. It is the word “public” which causes us to fix upon the opening of the Stockton and Darlington line as marking the beginning of railways as we know them.
The first Stockton and Darlington locomotive was “Locomotion”, which is now preserved at Darlington Station, on the main East Coast route between London and Edinburgh. Stephenson remained faithful to his Killingworth type, while incorporating several important improvements. The cylinders had a diameter of 9½-in and a stroke of 24-in. Cylinders and motion were mounted on top of the boiler in the same way as those of the old Hetton engine. The boiler was of wrought iron, 10 feet long by 4 feet in diameter, being built up of plates 4-in thick. It contained a single 2-feet diameter flue, running forward from the furnace and produced at the front to form the chimney. The four-coupled wheels were 4 feet in diameter and without springs, though at that time Nicholas Wood was beginning to fit springs to the Killingworth engines. Earlier, however, Stephenson had used a form of steam springing, each “spring” consisting of a piston in a cylinder underneath the boiler, the cylinder being continually filled with high-pressure steam from the boiler.
The coupling of the wheels was effected by the now universal side rods, and the credit for introducing these has been ascribed to several people. Stephenson had certainly used such rods, though on the cranks, in his original arrangement of “Blucher”, but the first application of outside rods has been credited to Timothy Hackworth, who served for a short period in the newly-founded Stephenson works at Forth Street, Newcastle-on-Tyne.
The pressure carried by the boiler has been variously stated, but it is believed to have been originally 50 lb per square inch. The firebox and flue gave a total heating surface of some 60 square feet. The engine, which has undergone various alterations at different times, to-day weighs 6 tons 16 cwt empty and 8 tons 8 cwt in working order.
“Locomotion” was delivered in September 1825, and ran its first trip under steam on September 26, carrying a party of the line’s proprietors between Shildon and Darlington. On the following day, the line was formally opened, and “Locomotion”, with Stephenson on the footplate and a 90-tons train packed with passengers and goods, made a successful run from Darlington to Stockton at an average speed of ten miles an hour. A man on horseback, carrying a red flag, rode along on the ballast in front of the train. He had to urge his steed to a canter in places, where the speed of the train rose to about fifteen miles an hour. That is how the locomotive began its conquest of the world.
FAMOUS ALL OVER THE WORLD, the locomotive “Rocket”, at the Science Museum, South Kensington. This engine was entered by the Stephensons for the Rainhill Trials of 1829, organized by the Liverpool and Manchester Railway, and won the prize of £500. The inclined outside cylinders (8-in by 17-in) were at the footplate end and the driving wheels, in front, had a diameter of 4 ft 8½-in. The multitubular boiler had a working pressure of 50 lb per square inch.
The later history of “Locomotion” is of interest. Three similar engines were built between November 1825 and May 1826. These were “Hope”, “Black Diamond” and “Diligence”. One day in July 1828 “Locomotion’s” boiler exploded, probably through unscrupulous doctoring of the safety-valve by the enginemen. The engine was rebuilt by Timothy Hackworth, the new boiler having two return flues, bringing the chimney back to the footplate end. A third boiler reverted to the original arrangement. The cylinder diameter was increased to 10-in.
“Locomotion” lasted as a locomotive until 1841, and then retired into comparative obscurity, being converted into a stationary pumping engine for a time. In 1857 it was scheduled as a sort of ancient monument. Since then the engine has been exhibited at various places, including Philadelphia, USA, Liverpool and Newcastle-on-Tyne. In 1892 it was placed in its present position at Darlington, leaving Darlington temporarily in 1924 to grace the British Empire Exhibition at Wembley.
In 1827 Stephenson produced “Experiment”, which was interesting for several reasons. This was the first railway locomotive to have two horizontal cylinders, an arrangement at one time universal and even now more common than any other. Moreover, “Experiment” had a water tube firebox, the tubes forming the grate of the single-flue boiler.
Timothy Hackworth was appointed Locomotive Superintendent of the Stockton and Darlington Railway, and in 1827 he, in his turn, produced a locomotive of considerable historical importance. This was “Royal George”. In certain ways it resembled earlier types. The boiler was of the return-flue type with both firedoor and chimney at the front.
“Royal George” was a six-wheeler with all the wheels coupled, the first of this arrangement, still common on British railways for secondary goods traffic. The two cylinders were vertical, and drove directly on to the rearmost axle. The return-flue boiler was second-hand, having previously belonged to an experimental four-cylinder locomotive built by Robert Wilson of Gateshead.
The origin of the blast pipe is debatable. As we have seen, Trevithick turned his exhaust into the chimney, and thus materially increased the draught. But it is not certain who first placed an exhaust nozzle centrally within or below the chimney to fill it and produce a partial vacuum in the flue. Hackworth certainly fitted an exhaust nozzle to “Royal George”, and it has been stated that George Stephenson knew nothing of the functions of a blast-pipe before 1827, when that engine was built. But in the 1825 edition of the “Practical Treatise on Railroads” Nicholas Wood wrote: “To effect a greater rapidity, or to increase the draught of the chimney, Mr. Stephenson thought that by causing the steam to escape into the chimney through a pipe with its end turned outwards, the velocity of the current would be accelerated, and such was the effect.”
So Stephenson knew the properties of the blast pipe before Hackworth built “Royal George”. In “Locomotion” of 1825, two exhaust pipes led into the chimney, where their ends were turned upwards, side by side.
In their “Lancashire Witch” of 1828 George and Robert Stephenson first placed the cylinders at an inclined angle on either side of the boiler barrel. In 1826 James Neville patented the first multitubular boiler, and this was applied, by Marc Seguin, of the Lyons and St. Etienne Railway, to some locomotives delivered from the Stephenson’s works during 1828 and 1829. In the multitubular boiler, the old single flue was replaced by a large number of small flues connecting the firebox with a smokebox below the chimney. All orthodox locomotives to-day are fitted with the multitubular boiler.
The end of this experimental period and the beginning of modern history may be said to coincide with the historic Rainhill Trials of 1829, when a prize of £500 was offered on behalf of the new Liverpool and Manchester Railway for a steam locomotive which should fulfil certain stated requirements.
ENTERED BY TIMOTHY HACKWORTH for the Rainhill Trials, “Sans Pareil” had two vertical cylinders 7-in by 18-in, four coupled wheels of 4 ft 6-in diameter and a return-flue boiler. The photograph shows the engine in the Science Museum, South Kensington. In the trials “Sans Pareil” failed because of a defective feed pump, but its later performances proved its worth.
The conditions of the competition were that the successful engine was to run a distance of seventy miles with no prolonged stops at an average speed of ten miles an hour.
Four steam locomotives were entered. The “favourite” was “Novelty”, built by John Ericsson and John Braithwaite. Their engine had the fuel and water-supply carried on the main frames.
The boiler was peculiar, being a combination of the vertical and horizontal type, with the firebox at the bottom of the vertical section, fired through a hole in the top. The chimney was at the end of the horizontal section, and rose at the back of the engine, communicating with the firebox by a long tapering flue-tube, which twice doubled back on itself. There were two vertical cylinders 6-in by 12-in, driving the crank axle through bell cranks. Novelty ran on four uncoupled wheels, having a diameter of 4 ft 2-in and a wheelbase of 6 feet. The boiler gave trouble and the engine was withdrawn from the competition.
Timothy Hackworth entered a locomotive called “Sans Pareil”, a four-wheels-coupled engine with two vertical cylinders and a return-flue boiler. This locomotive showed great promise, but was heavy on fuel, and a defective feed pump threw it out of the competition.
“Sans Pareil” was dogged by ill luck; its later performances showed it to be one of the best locomotives so far built. It was the only one of the four entries to have coupled wheels. In appearance, “Sans Pareil” is familiar, for it is preserved at the Science Museum, South Kensington.
Apart from a machine called the “Cycloped”, a sort of railway quadricycle propelled by a horse walking on a rolling platform, and a feeble “manumotive” propelled by two men, designed by Brandreth and Winans respectively, there remained one locomotive, which was to prove the victor. This was the world-famous “Rocket”, entered by the Stephensons. In some ways “Rocket” was an improved edition of “Lancashire Witch”, having outside inclined cylinders at the footplate end.
Triumph of “Rocket”
The wheel arrangement was 0-2-2, with the large driving wheels below the front of the boiler. The boiler was of the multitubular type, with a partly water-jacketed firebox at the back, and a small smokebox, barely more than a widening at the bottom of the chimney, in front. A proper smokebox was fitted later. The cylinders were 8-in by 17-in and the driving wheels 4 ft 8½-in in diameter, the same as the rail gauge. The boiler carried a working pressure of 50 lb per square inch, and the engine, without its tender, weighed 4¼ tons in working order. The story of “Rocket” is well known. It fulfilled all the requirements of the judges and carried off the prize. Thus “Rocket” made history, and became the precursor of the modern locomotive, all the original engines of the Liverpool and Manchester Railway, opened in the following year, being of Stephenson design and build in consequence.
The triumph of “Rocket” takes us out of the experimental period into the great period of railway expansion. The later career of “Rocket” is worth recalling. Having been rebuilt with nearly horizontal cylinders and an orthodox smokebox, it worked on the Liverpool and Manchester Railway until 1836. Sold to a Newcastle contractor in 1844, it worked for a while at Midgeholm Colliery. Its career then becomes even more obscure. At the beginning of the ‘sixties, its somewhat dilapidated remains were rescued from a scrapyard on Tyneside, and the locomotive was sent to London for preservation in 1862. As these remains do not show the original appearance of the engine, three full-size reconstructions have been built, a wooden one by the old London and North Western Railway, and working examples for Henry Ford and for the Science Museum, South Kensington. Another of Stephenson’s engines, nearly as old as “Rocket”, is still to be seen at Canterbury, Kent. This locomotive is “Invicta”, with which the Canterbury and Whitstable Railway was opened on May 3, 1830.
In the same year a primitive American locomotive, “Tom Thumb”, made its first successful trip in the United States between Baltimore and Ellicott’s Mills (Maryland). The engine pushed a small open car with eighteen passengers, and covered a distance of thirteen miles in an hour and a quarter without a stop.
FAVOURITE FOR THE RAINHILL TRIALS, “Novelty” was built by John Ericsson and John Braithwaite. It had two vertical cylinders, 6-in by 12-in, driving the crank axle through bell cranks. The fuel and water supply were carried on the main frames. The boiler was a combination of the vertical and horizontal type. The four uncoupled wheels had a diameter of 4 ft 2-in.
ANCESTOR OF THE WORLD’S LOCOMOTIVES, Trevithick’s engine of 1804 ran on a mineral tramroad at Penydarran, near Merthyr Tydfil, South Wales. The single cylinder communicated its motion to the four road wheels through a flywheel and gearing. The illustration is only of approximate accuracy, as no authentic drawings of the engine exist.
BLENKINSOP’S LEEDS LOCOMOTIVE, the first commercially successful engine in the world, went into service in 1812. It had, fitted in the top of the boiler shell, two vertical cylinders which drove a sprocket wheel, whose teeth engaged with a rack on the side of the rail.
WITH ALL SIX WHEELS COUPLED, the “Royal George” of 1827 was the first engine to have this wheel arrangement, still common for goods locomotives in Great Britain. Two vertical cylinders drove the rearmost axle. The return-
ON SHOW AT DARLINGTON STATION, on the main line of the LNER, “Locomotion” was the first engine of the Stockton and Darlington Railway. It was designed by George Stephenson, with the assistance of his son, Robert. The cylinders (9½-
FAMOUS ALL OVER THE WORLD, the locomotive “Rocket”, at the Science Museum, South Kensington. This engine was entered by the Stephensons for the Rainhill Trials of 1829, organized by the Liverpool and Manchester Railway, and won the prize of £500. The inclined outside cylinders (8-
ENTERED BY TIMOTHY HACKWORTH for the Rainhill Trials, “Sans Pareil” had two vertical cylinders 7-