Quick links to topics on this page:
Introduction | Early Boilers | Portables | Horizontals | St Fargeau, Paris | Verticals | Peache Patent | Paxman-Lentz | Refrigeration | Steam Wagon | Traction Engines | Locomotives | 'River Esk' | Romney, Hythe & Dymchurch Rly
This page contains references to brake horsepower (BHP), nominal horsepower (NHP), and indicated horsepower (IHP).
BHP is a measure of the rate at which an engine does work measured by resistance to an applied brake (i.e. the power available from the engine to do useful work, discounting friction and energy losses within the engine itself). One horsepower = 550 foot lbs per second or 745.7 watt (in the USA 1 horsepower = 746 watt).
NHP, as used in steam engines ratings during the 19th and early 20th centuries, was a commercial unit used by engine manufacturers and purchasers. It was adopted by the Royal Agricultural Society in the 1840s to enable farmers to compare the power of a steam engine with that of a horse. NHP was calculated by reference to cylinder bore size and piston speed and, unlike BHP, was not a measure of an engine's actual power output. In the case of single cylinder steam traction engines, one NHP is broadly equivalent to between 6 and 7 BHP, but generally closer to 6 BHP. For a compound engine the figure may be closer to 7 BHP. On this basis a single cylinder 5 NHP traction engine might be expected to produce a little over 30 BHP. Stationary engines were much more conservatively rated. Information in early 20th century Paxman catalogues shows that for the Company's horizontal stationary engines one NHP was equivalent to only around 2 to 2½ BHP. The actual output of an engine depended not only on cylinder size but also on working steam pressure and engine speed. (For a fuller discussion see the page on Nominal Horsepower.)
IHP is a measure of the power output of a piston engine calculated from the mean effective pressure as derived from an indicator diagram and the speed of the engine in rpm.
The early growth of the Company stemmed from its success with steam engines. This in turn derived from the ingenuity and abilities of James Paxman who was no newcomer to steam engineering when he started his business in 1865. For several years previously he had been Works Manager with the Colchester firm of Catchpool and Thompson where he was responsible for two unusual ventures. The first, in 1853, covered the design and construction of a steam carriage for a Captain Norrell, powered by a small engine with duplex cylinders. The vehicle was banned from the roads by the local authorities which brought its further development to an abrupt end. The second venture was much more successful. It consisted of designing and fitting twin steam engines in a tug boat to work river traffic for the Steam Navigation Commissioners between Sudbury and the lower Stour, just north of Colchester. At that time navigation of the river was difficult due to the many bends and shoals, and the production of a suitable shallow draft boat to fulfil such operating conditions was a great accomplishment. It commenced work on the River Stour in 1861 and operated very successfully for many years. When, therefore, James Paxman set up his own business he had already acquired considerable experience in the design and practical engineering aspects of steam engines.
One of the business's first advertisements announced the partners were, inter alia, carrying on 'the Manufacture and Repair of Steam-engines & Boilers'. In the internal combustion age, interest in the steam engine itself can lead people to overlook the importance of the boiler. But then, as now, fuel economy was a key benchmark for potential engine purchasers and the efficiency of a steam engine's boiler was crucial. Much of James Paxman's early success with steam engines was due to his design and manufacture of very efficient and compact boilers. His personal interest and commitment in the quest for boiler efficiency was demonstrated by the fact that he himself undertook the stoking of the boiler during an engine trial in 1887. It is difficult to imagine many senior partners of successful firms in the 1880s being prepared to wield a stoker's shovel!
James Paxman was an innovator in the design and construction of boilers. In the early 1860s he came to the conclusion that the practice of ferruling boiler tubes was mistaken. Boilers without ferrules were first built in his Culver Street Works. He also pioneered the use of steel for locomotive type fireboxes, recognising it was less costly than the Lowmoor iron or the copper previously used and added materially to the life of the boiler. During the early years of the business experiments with the back flue and tubular boiler led to the evolution of the famous Paxman 'Economic' boiler which was the precursor of all other economic boilers.
By 1870 the Company had produced its first steam engine which received a very favourable press. 'The Engineer' said of the boiler on which the engine was mounted, 'We have no hesitation in pronouncing it the best vertical boiler yet produced'. Of multi-tubular design with curved tubes, it was 2' 6" in diameter and 6' 6" high, with a heating surface of 73.9 square feet. The 6¼" bore x 12" stroke single cylinder vertical engine attached to it ran at 115 rpm. In trials at the 1870 Royal Agricultural Show the plant was the most economical tested, using only 6 lbs of coal per bhp hour.
The success of these stationary vertical engines and boilers encouraged the Company to start building portables and then horizontal stationary engines.
The first portable engine was exhibited at the Cardiff Show of the Royal Agricultural Society in 1872. The boiler was of the locomotive type but fitted with ten Paxman water tubes. These tubes were curved and connected the crown of the firebox with the sides, with the purpose of breaking up the gases on their way to the smoke tubes. The arrangement was successful, enabling the boiler to return the excellent figure of just over 10 lbs of water evaporated per pound of coal. The technical press commented, "This, Mr Paxman's first competitive portable engine, has proved in every respect so successful that we advise older firms to mind what they are about, or they may find themselves seriously beaten in the next competition".
Picture: A later portable shown in the Wearing Parts catalogue of 1913.
The next type of portable engine introduced further innovations. The single cylinder and its covers were all packeted and whole of the engine and motion was secured to a wrought iron frame of I-sections, these in turn being bolted to the boiler by suitable brackets. Simply by slackening a few bolts, the whole engine and motion could be removed from the boiler. At the Royal Agricultural Show at Newcastle-upon-Tyne in 1887 the Paxman engine returned the excellent figure of only 2.528 lbs of coal per bhp hour when running at its normal speed of 132 rpm. James Paxman personally stoked the engine, using his highly successful 'little and often' principle of firing. Steam pressure never varied by more than 1 psi during the run and the speed of the engine was almost perfectly uniform. After the four hours allotted running time for the trial the engine took over twenty minutes to run down during which time Mr Paxman burned the remaining ashes.
Two days later a Paxman compound engine with cylinders 5¾" x 9¼" with 14" stroke returned the even better figure of 1.804 lbs per bhp hour at 134 rpm using steam at 150 psi. As a result the Company carried off an award of £100 for the best single cylinder engine and a £200 prize for the best compound. The designing, building, and testing of one of the engines was accomplished in just eight weeks.
Special productions always had an appeal and one portable, generating electrical power for lighting, was designed for travelling showmen. The outfit was complete with DC generator mounted on a small front platform with the switchboard fixed to the end panel of the side curtain boards. The other end board was hinged and could be strutted up to form a shelter for the attendant. A side framing served as a fixing for the drop boards on each side, and from this framing the roof or canopy was supported on four square twisted brass columns, like those regularly adorning later showmen's engines. The whole plant was beautifully finished in the colourful style of contemporary travelling fairs.
Paxman made portables in large numbers, many of which were exported. For details and photographs of several which are still around see the Surviving Steam Portables page. During the Agricultural & General Engineers era (1920 to 1932) there was an agreement that the building of portables would be shared between Paxman and Richard Garrett & Sons of Leiston. Garrett was to make the single cylinder versions and Paxman the compounds. In accordance with this arrangement Garrett made sixty five Paxman 'badged' portables with Garrett engine numbers ranging between 33514 and 35245. Whether or not there was any subsequent formal variation to the agreement it is a fact that Paxman made several single cylinder portables after 1920.
Paxman's earliest horizontal steam engines used motions based on those of the Company's portables. Relatively basic engines, they were made in small numbers, only eight being sold between April 1874 and April 1877. Later known as Class A engines, they were designed for a normal working steam pressure of 60 psi and had modest power outputs. At the 1879 Royal Agricultural Show Paxman launched a new range of horizontal girder engines, the Class B. This more powerful range of engines was designed initially for a working pressure of 120 psi and had a more sophisticated cut off valve arrangement. A more detailed description, outputs and dimensions can be found on the Class B page. Over time Paxman horizontal engines appeared in various forms such as condensing, non-condensing, coupled, compound and tandem compound.
Picture: Class B illustration from an 1893 advertisement.
A type of horizontal, sharing similarities to the portable from which it was derived, was the semi-fixed engine. Later known as the Undertype this had a locomotive type boiler with the motion located under the boiler barrel, rather than over it as in the case of the portable. The general arrangement made for a compact prime mover which proved attractive for electrical power generation installations in large private houses and institutions. Four of the earliest were 16 hp compounds built in 1882 for R E Crompton, the electrical contractor. Each had a 7½" bore HP cylinder, 13" bore LP cylinder, and a 12" stroke. One was for Octavius Coope of the brewing family for his Colchester home, Berechurch Hall, which was rebuilt about this time. The smaller sizes of this type of engine, 8 - 20 hp, were built initially on cast-iron bedplates, and were self-contained. The larger sizes, 25 hp and above, were built on a cast-iron girder frame, consisting of several parts bolted together, which facilitated transport and repairs. Paxman's Patent Automatic expansion gear was fitted to the high pressure cylinder, controlled by the governor, so that the cut-off was always proportional to the load. A catalogue description, picture, outputs and dimensions can be found on the Undertype Engine page.
During the 1880s the Company continued to expand its range of horizontal engines. A publication dated 1893 carried a full page Paxman advertisement which makes reference to the following types:
| Horizontal Engines Class B | Single Cylinder 4 - 500 hp Double Cylinder 8 - 1,500 hp |
| Horizontal Engines Class A | Single Cylinder 4 - 50 hp Double Cylinder 8 - 150 hp |
| Improved Horizontal Coupled Girder Compound Engines | 8 - 1,500 hp |
| The "Colchester" Horizontal Fixed Compound Engine | 8 - 400 hp |
| Horizontal Condensing Engines Class C | 16 - 200 hp |
| New Patent Semi-Fixed Compound Engine and Boiler | 8 - 250 hp |
| Horizontal Winding Engines | |
| Tandem Compound Engines |
The "Colchester" Compound first appeared in 1883 and was manufactured in large numbers, many for export. Being self-contained on a girder frame, it required only a simple and cheaply made foundation. A description, picture, outputs and dimensions can be found on the Colchester Engine page.
Tandem compound engines were arranged with the high and low pressure cylinders longitudinally in line with each other, both pistons being attached to a common piston rod, rather than the more familiar side by side arrangement for compound engines. An advantage of the arrangement was the requirement for only one connecting rod and a single crank crankshaft.
Coupled engines were those where one crankshaft connected two parallel horizontal engines. A common fly-wheel was mounted in the centre of the crankshaft between the cranks.
Winding engines were developed for winding and hauling in mining operations. They usually had a drum or drums mounted on the crankshaft, and between the cylinders when the engine was of the compound cross-coupled type. The Company's earliest winding engines were for diamond mines around Kimberley, South Africa, orders being received in 1878 and succeeding years. In the late 1890s a number were exported to goldfields in South Africa and Western Australia.
From about 1910 the Class "K" horizontal engine replaced Paxman's older girder types. It was "specially designed to meet the demand for an inexpensive, yet reliable, steam engine capable of developing a large amount of power in proportion to the space occupied". A description, picture, outputs, dimensions and prices can be found on the Class "K" Engine page.
The most technically advanced and important of the Company's horizontal steam engines was the Paxman-Lentz, described later on this page.
Elsewhere on this website is a page with details and photographs of known surviving Paxman stationary engines, both horizontal and inverted vertical types: see Surviving Paxman Stationary Steam Engines
As a young man of 19, James Paxman visited the Great Exhibition of 1851 in Hyde Park. It is said this experience made a tremendous impression on him and influenced him for the rest of his life.
From 1869, only four years after the Company was founded, James Paxman was regularly exhibiting his steam engines and related machinery at shows of the Royal Agricultural Society. The Company's products were also frequently displayed at other exhibitions, shows and trade fairs both at home and overseas. Export business was promoted by exhibiting at events as far afield as Philadelphia USA, Sydney Australia, Calcutta, Tasmania and Chile. At many of these exhibitions and shows Paxman engines and machinery were awarded gold, silver or other medals. Highly valuable publicity and powerful testimony to the innovative design and efficiency of the Company's products.
From 1880 plant for the supply of electric current for lighting was an important feature of all London exhibitions. At the Great International and other London exhibitions where Paxman machinery was on show, many were dependent on the Paxman exhibit for illumination of the various courts, gardens and halls. Paxman supplied the complete generating plant for the French section of the Paris Exhibition in 1889 and subsequently for the American and British sections when the existing plant failed.
Among the many large public and private installations of Paxman engines was a group of compound condensing steam engines, coupled to compressors, together with the attendant battery of boilers, for the Compagnie de l'Air Comprime Systemme Popp at St Fargeau, Paris. This installation developed about 4,000 hp and supplied compressed air for distributing through the streets of Paris to drive various prime movers. Built in about 1888-89, it comprised twelve 400 hp horizontal coupled tandem compound girder engines, steam being supplied by Paxman Economic boilers.
Over the years Paxman developed various types of (inverted) vertical as well as horizontal steam engine. The oldest known surviving Paxman engine anywhere in the world is one of these steam verticals. No 1402 was ordered on 25th January 1877 by Thomas Davey & Co of Melbourne, Australia. The 6½" bore x 12" stroke engine was rated at 4 NHP and has a 4½ foot diameter flywheel. It was acquired in September 2000 by the current owner, Mr Kym Zeitz who lives near Adelaide, South Australia. When purchased the engine was lying outside exposed to the elements, the cylinder head being occupied by a mud wasps' nest. Several key components were missing, such as the two slide valves, valve rods, the steam chest cover and throttling governor. Fortunately the cross head and bearings were in good condition. One of the major challenges facing Kym in his restoration was trying to find out details of the construction of the missing parts, particularly the unusual slide valves arrangement. Now completely restored, as pictured here, the engine runs smoothly on compressed air. An account of the restoration was published in the Aug-Sept 2003 issue of The Old Machinery Magazine (Australia). The intention is to complete restoration of a suitable boiler so that once again No 1402 can be run under steam.
Photo © Kym Zeitz and The Old Machinery Magazine 2003
Another well restored example of a similar type (pictured left) is to be found closer to Colchester, at West Mersea. The parentage of this engine is obvious from a comparison of the photograph above and the one to the left. Though there are many similarities in appearance to No 1402, the single slide valve arrangement of the later engine is much simpler. No 5483 was ordered on 17th March 1890 for the Mann Crossman & Paulin brewery in London and despatched from the Works on 15th August that year. Rated at 6 NHP, it has an 8½" bore x 12" stroke. Owned by Andrew Phillips of Colchester, the engine was restored in 1986 by the late Russell Weavers who also subsequently maintained it. Since its restoration the engine has been regularly steamed.
The direct descendants of these early verticals were Paxman's Class "SV" engines. Designed for customers requiring only a small power output, these single cylinder engines were made in six standard sizes from 2 NHP up to 10 NHP. Working at 80 to 100 psi, steam distribution was effected by a simple slide valve controlled by a variable expansion eccentric allowing the steam cut-off to be varied in proportion to the load. Provided with continuous lubrication to all working parts, the engine was designed to be capable of being left running for many hours without attention. A picture, outputs, and dimensions can be found on the Class "SV" Engine page.
A later type of Paxman vertical was installed in Windsor Castle, Queen Victoria later granting permission for the engine range to be named the "Windsor". These engines were all highly finished and designed for running over long periods without adjustment, making them particularly suitable for driving electrical generating plant. A Windsor triple expansion engine with a working pressure of 160 psi, producing 350 IHP and coupled to a 145 kW output dynamo, was exhibited at the Crystal Palace Electrical Exhibition of 1892. Pictured right is a Windsor compound, No 13035 built in 1906, with its Crompton Parkinson dynamo. Like No 5483 mentioned above, this engine is owned by Andrew Phillips of Colchester, and was restored and subsequently maintained by the late Russell Weavers. The engine has been regularly steamed since its restoration.
Other totally enclosed high speed vertical engines with forced lubrication were made in both two-crank compound and three-crank triple expansion types and a number were made for various electricity undertakings and naval dockyards at the beginning of the 20th century.
The Peache engine was developed to meet the needs of the changing electrical power generation market in the 1890s. Up to this time electric lighting was a luxury found mainly in large houses of the very wealthy and some public institutions. For several years Paxman had successfully supplied steam engines and boilers for this market, in collaboration with electrical contractors and generator manufacturers such as Crompton. The 1890s saw the rapid growth of 'central electricity stations' supplying electricity for domestic lighting and business use, and plants generating power for electric traction, typically trams. Increasing numbers of local authorities started to commission the construction of electric light stations so that by 1903 all towns but two, with a population of more than 100,000, had an electricity supply. The prime movers favoured for driving dynamos in these power stations were multiple units of small high-speed steam engines, particularly the central valve type designed and built by Willans & Robinson. Initially Paxman did not have a suitable high-speed engine to match the requirements of this emerging market.
Peter Willans, inventor of the central valve engine and founder of Willans & Robinson, had a very able Works Manager, James Courthope Peache. Peache resigned from the Willans business at the end of 1891. About this time Paxman was coming under pressure from his customers to offer a high-speed engine for the larger generating plants now being built. It seems Peache became aware of this and so in early 1893 wrote to James Paxman, trying to interest him in his own design of a high-speed engine. After much consideration and lengthy negotiation it was agreed that Paxman would produce the Peache engine and J Courthope Peach was appointed Works Manager at Colchester.
After two years of development and extensive running trials, Paxman's 'Peache Patent' High-Speed Single-Acting Engine was launched at the 1895 Empire of India exhibition at Earls Court. Three engines were put on show, one 4 cylinder and two 6 cylinder, having a combined output of 550 IHP.
Peache engines were vertical, single-acting compounds, mainly of a three crank type. The single-acting design was adopted to overcome the knocking problems found in the bearings of double-acting types. Backlash in the bearings was eliminated by maintaining the balance of pressure towards the crankshaft. The compounding arrangement was akin to that of a tandem engine, not the more common one of side-by-side high (HP) and low pressure (LP) cylinders. The LP cylinder was situated directly beneath the HP cylinder, with the HP and LP pistons mounted on a common piston rod. Steam was admitted first to the top side of the HP piston and then to the underside of the LP piston. The three crank arrangement was promoted as advantageous "both on account of the absence of vibration and even turning obtained" with this type. However for smaller powers single crank types were offered. The July 1905 price list detailed five single crank sizes, from 10½ to 47 bhp output, with a note that the vibration set up in these was unlikely to cause trouble, while the price was considerably less than that of a three crank engine. The same catalogue gives details of eleven sizes of three crank engines with speeds ranging from 600 to 260 rpm and outputs from 48 to 750 bhp at standard speeds.
The Peache Patent engine could not be described as a runaway success, either technically or commercially. It faced tough competition as, at about the time of its launch, Belliss & Morcom introduced a highly successful double-acting engine. The latter featured forced lubrication of the crankshaft bearings, one of the earliest to do so, which largely overcame the knocking problems previously bedeviling double-acting types. Nevertheless Paxman continued to sell Peache engines up to 1914, by which time it had built just under 250 of them.
J Courthope Peache was a man of considerable private means and therefore not dependent on employment for an income. In 1896 he relinquished his day to day management responsibilities at Standard Works and became 'Consulting Engineer to Davey, Paxman & Co Ltd'. In 1904 he left Colchester to return to his old firm, Willans & Robinson (which by then had relocated from Thames Ditton to Rugby) as its Managing Director. He was subsequently appointed Chairman, a post he held until Willans became part of the English Electric Company in 1918. It is also of interest to note that while at Colchester Peache befriended two Paxman employees, Jethro Wade and Harry Broom, who with his support set up the famous Broomwade compressor company.
An example of a local authority electricity station with Peache engines, and for which Paxman also supplied all the boilers and condensing plant, was the one at Colchester. A booklet published in 1902 by the Borough of Colchester's Electric Light and Power Department described the construction and development of the local Electricity Works. Statutory Powers were applied for in 1892 and the plant was handed over to the Corporation in 1900. In 1902 the total output of the dynamos was 586 kW. Owing to the great increase in demand that year the Council decided to install a further 500-550 hp engine direct-coupled to a 375-400 kW dynamo wound for lighting or traction. These extensions would push the total power output up to 1,460 hp and dynamo capacity to 986 kW.
As at 1902, four Paxman 'Economic' boilers had been installed. Three were 14' long x 8' diameter, each capable of evaporating 6,000 lbs of water per hour, with a normal working pressure of 140 psi. The fourth boiler was 14' 6" x 9' 9" diameter, capable of evaporating 10,000 lbs per hour and constructed for a normal working pressure of 180 psi. With a large heating surface the evaporative efficiency was at the rate of 12.2 lbs of water per lb of best Welsh steam coal. Another measure of its efficiency was the low temperature (for that time) of gases escaping to the tail flue; not exceeding 420 to 450 degrees F.
The five engines were all of the 'Paxman-Peache' high speed, single acting, condensing type. Each was a three crank compound, having three high pressure and three low pressure cylinders. Three engines were F compounds, of 6½" and 11½" bore x 7" stroke, producing 110 hp each at 500 rpm. The fourth was a J compound, of 9½" and 16" bore x 11" stroke, producing 260 IHP at 375 rpm. The largest was a K compound, of 10½" and 19" bore x 11" stroke, producing 360 hp at 350 rpm. (All ratings at 140 psi boiler pressure.)
The steam range - the steam feed and exhaust piping system - was also supplied and erected by Paxman and ran the entire length of the boiler house. The lengths of piping were of steel with bends and T pieces. On the extreme wing the range started with an 8" steam main increasing at the third boiler to 10". The main exhaust was 16" diameter cast iron piping. This traversed the engine room in a trench below the flooring and, turning into the boiler house at the north end of the building, crossed the condenser pit before rising through the boiler house roof to a height of 25' to exhaust to atmosphere.
Condensers and sets of pumps were fixed in the boiler house, in a pit below the level of the floor. The equipment included two Paxman independent condensing plants, having 700 and 800 square feet of cooling surface respectively.
Another local installation dating from about the same time as Colchester's Electricity Works, and featuring much identical plant, was a power generation facility at Parkeston Quay. On 4th May 1899 the Great Eastern Railway ordered from Paxman three Peache Patent size F condensing compound engines, five 14' long x 8' diameter Economic boilers, and an independent surface condenser for Parkeston. All items were despatched from the factory during May 1900, apart from the condenser which was delivered about a year later. The dynamos were supplied by Crompton who were responsible for the electrical engineering aspects of the project.
Developed by Dr Hugo Lenz (1859-1944), the first Lentz engine was shown at the Como Exhibition of 1899 where it won first prize. The following year, at the Paris Exhibition, it was awarded the Grand Prix and its inventor received the Gold Medal. The main benefit of Lenz's valve gear was greatly improved economy. Its early application in installations such as the City of Rome Electric Station, the International Electric Company's central station in Vienna, and the Municipal Electrical Station also in Vienna, demonstrated major fuel savings and rapidly led to its wider adoption. Lentz engines became popular in mainland Europe and were built by various manufacturers, notably MAN in Germany.
Paxman obtained exclusive rights in Britain and commenced manufacturing its Paxman-Lentz horizontal compound engines at Colchester in 1907. A Company catalogue of May 1915 cites among its special advantages: high speed, silent running, extreme economy in steam consumption, and simplicity of design. Embodying Lentz patents covering positive valve gear, the governor, and frictionless metallic packing, this type of engine proved so economical and reliable it displaced almost every other type of large stationary steam engine manufactured by Paxman.
Paxman-Lentz Tandem Compound Engine and Generator
About 130 Paxman-Lentz engines were built at Colchester between 1907 and 1934. One major application was electrical power generation, the generators being driven directly from the crankshaft. Others were supplied for driving machinery in mills and factories in a diverse range of industries. Single cylinder engines were available in 16 sizes, ranging from 13" bore x 24" stroke to 29" bore x 54" stroke, with power outputs from 99 ihp to 1170 ihp. These were designed to work at steam pressures of 80 psi up to 140 psi, whereas the compounds were designed to work with steam pressures in the range of 100 psi to 170 psi. The compounds were available in 20 sizes, ranging from 9" and 15½" bores x 18" stroke to 29" and 48" bores x 54" stroke, with power outputs from 105 ihp to 2,140 ihp. The smallest singles had 7' 6" flywheels and ran at speeds of up to 190 rpm. The smallest compounds had 8' flywheels and could run slightly faster, at 210 rpm. The largest singles and compounds each had 16' flywheels and ran at up to 90 rpm. Elsewhere on this site is a detailed listing of the Lentz engines made by Paxman and of Lentz conversions carried out by the Company.
The Paxman-Lentz was specially designed for the high pressures and superheated steam necessary for the most economical working. Steam consumption as low as 10.34 lbs per ihp per hour was obtained on test. It was also constructed for continuous running at high piston and crankshaft speeds. These characteristics were made possible by the adoption of Lentz valve gear.
The slide valve widely used on early engines was not satisfactory for controlling high pressure superheated steam. The drop valve, actuated by trip gear, therefore became the conventional solution for large stationary engines. However it was not suitable for high speed running and had another major weakness. When the trip mechanism released the valve to shut off steam to the cylinder, the valve was forced sharply onto its seat by a strong coil spring. Not only did this make it noisy but the constant shocks and hammering resulted in rapid wear to the valve and its seat. Steam tightness of the valve quickly deteriorated necessitating frequent expensive maintenance. To lessen the impact of the valve upon its seat, a dashpot was generally fitted to check its descent. This was a compromise running counter to the purpose of trip gear which was to ensure rapid closing of the valve and a quick cut off of steam to the cylinder.
The Lentz system overcame these limitations by using poppet valves, each operated by a cam lever moved by an eccentric on the governor shaft. The valve was raised by the cam acting on a roller fitted to the valve spindle at 90°. During the entire travel of the valve the roller was kept in contact with the cam by means of a light spring in the bonnet above the valve. The cleverly designed profile of the cam allowed a prompt and full opening movement. More importantly, it allowed the valve to be rapidly lowered onto its seat in a smooth controlled manner. The cam did not move clear of the roller until after the valve was seated. This 'positive valve motion' was free from shock, making the gear entirely silent even when the engine was running at the highest speeds.
As the engines were double acting there were four valves per cylinder, an admission valve on top and an exhaust valve underneath at each end. Lentz valve gear allowed exceptionally economical use of steam and high speeds which were not possible with trip gear. It also proved very reliable, giving long service with minimal maintenance.
The Paxman-Lentz engine was controlled by an inertia type governor mounted on the side shaft which was driven through gearing from the main crankshaft. The governor was directly connected to the two eccentrics which operated the valves on the high pressure cylinder. Extremely sensitive to variations in load, it provided excellent speed stability which was, and is, particularly important in electrical power generation applications. (For a discussion on some present day issues of governing and control in power generation applications see our page about Regulateurs Europa.)
The use of high temperature superheated steam under high pressure placed greater demands not only on valve gear but also on joints around piston rods and valve spindles. Overcoming steam leakage through these joints, wear around them which accelerated leakage and the need for frequent maintenance, were major engineering challenges.
Piston rod packing for Paxman-Lentz engines was made on the Lentz system. Unlike many other metallic packings available for use with superheated steam at that time, it was frictionless and free from the wear, risks of rod heating, and need for constant maintenance which accompanied their use. Some of these other packings relied on springs for their tightness, but springs rapidly lost their elasticity in contact with superheated steam and required frequent renewal.
The Lentz patent packing consisted of a series of cast-iron annular distance pieces, turned and ground dead true which fitted over the piston rod, but did not touch it. In between the distance pieces were a number of square section cast-iron rings, ground to fit the piston rod exactly. The alternate rings and distance pieces formed a series of chambers or voids where any steam leaking through the joint could expand and lose pressure. (The chambers were supplied with oil under pressure and drained.) Any steam escaping from the front chamber entered the second and there expanded. A small quantity might even escape to the third chamber where it expanded further but the last ring never showing the slightest leakage.
The design of the valve spindle joint was rather simpler but based on the same principle of steam losing more of its pressure each time it expands. The valve spindle was ground to fit inside a long bush. Grooves were turned on the spindle to form a labyrinth of chambers where any steam leaking into the joint could successively expand and lose pressure sufficiently to prevent it reaching the other end of the bush.
These arrangements did away with the need for stuffing boxes and soft packing. They were effective with the highest pressure of superheated steam, showing negligible wear and preserving steam tightness indefinitely.
The Company's expertise in the design and manufacture of high quality reciprocating machinery (a tradition continued throughout its history) provided an ideal basis for its move into building compressors. A valuable new source of business developed from an agreement between James Paxman and Thomas Bell Lightfoot and the Linde British Refrigeration Company to manufacture refrigerating machinery in the form of horizontal and vertical ammonia compressors driven by steam engines. Production commenced in 1890 with the supply of a 10" x 17" horizontal, double-acting ammonia compressor, driven by a Paxman girder or Class B steam engines, through a common crankshaft, for Messrs Prices & Co.
This side of the business developed quickly and a wide range of compressor units was designed and supplied to main ports and distribution centres in this country and overseas, and for ships. Many of the units were a combination of self-contained compressor, condenser with ammonia coils, and steam engine, in some cases complete with boiler.
About 1900 the Company started manufacturing carbonic acid compressors. Those for cold stores and butchers were comparatively small machines. For marine applications larger machines were supplied, driven by steam engines or electric motors. Installations included some for the British Admiralty and the Japanese Navy.
In 1930 a new range of vertical, single-acting, high speed ammonia compressors was launched, designed for two, three or four grouped cylinders, driven by oil engine or motor. These compressors proved highly successful and were produced by the Lightfoot Refrigeration Co Ltd of 35 Queen Victoria Street, London EC, for a variety of undertakings such as nylon and ice cream manufacture and skating rinks, up until at least the 1950s.
In May 1905 the Company received an order for 'Three sets of Steam Motor Wagons' from Bretherton & Bryan of London NW. These fine and efficient five ton steam wagons were made to Mr F Bretherton's own design. They had a locomotive type boiler, fired from the top via a control chute, with a working pressure of 200 psi. The engine was an under-mounted horizontal compound, 5" and 7¾" bore x 9" stroke, with the steam chests below the cylinders. One of the wagons was exhibited at the Agricultural Hall Motor Exhibition in March 1906, and with the wide flare to its chimney top was a distinguished looking vehicle. Bretherton was an engineer and designer of note but proved unable to pay for the wagons he had ordered from Paxman. After the First World War he acted as consultant to Messrs Robey & Co Ltd of Lincoln on the design and production of their overtype compound steam wagon.
Paxman built steam traction engines from 1906 up to 1917. They were designed by William Fletcher who, fortuitously for both parties, offered his services to the Company at the very time Paxman was considering moving into this field and looking for a suitably qualified engineer for the task. William Fletcher joined the Company in 1906 and came with impeccable credentials. Born in 1848, he was apprenticed to Marshalls of Gainsborough in 1863. Seven years later he moved to Wallis & Steevens of Basingstoke where he designed their first traction engine. From 1878 he worked for Charles Burrell at Thetford for two years before returning to Marshalls to become their chief draughtsman. His subsequent appointments were as traction engine designer: first with Ransomes Sims & Jefferies from 1888, then with Clayton & Shuttleworth of Lincoln from 1897, and finally with Davey Paxman. He died at Cromer in Norfolk, probably in late 1918 but certainly no later than January 1919.
Old order books show the Company received 91 orders for traction engines. A number of these were cancelled with some of the relevant engines being allocated to later orders. The vast majority of Paxman traction engines were sold to customers in England. Several were made initially for major agricultural shows where they were exhibited and offered for sale. Export orders included two for Latvia, two for Barcelona, one for Italy, two (cancelled) for South America, and a 'Darby Digger' for Alexandria, Egypt. A full listing of Paxman traction engine orders can be downloaded from the Download page.
The engines were available in six single cylinder sizes. The smallest was a 4 NHP Steam Tractor weighing under five tons, designed to meet the requirements of the Local Government Board's Motor Regulations. The other five were General Purpose Traction Engines, rated from 5 to 10 NHP. Also offered was a 7 NHP compound road locomotive. By far the most popular was the 7 NHP single cylinder. The bore and stroke of each type, and numbers ordered, are shown in the table below.
| Horsepower | Bore | Stroke | Number Ordered |
| 4 NHP | 6" | 9" | 1 |
| 5 NHP | 8" | 10" | |
| ? NHP Darby Digger | 5" & 8" | 9" | 1 |
| 6 NHP | 8" | 12" | 20 |
| 7 NHP | 8½" | 12" | 54 |
| 7 NHP Compound | 6" & 9" | 12" | 2 |
| 8 NHP | 9" | 12" | 11 |
| 10 NHP | 10" | 12" | 2 |
An unusual piece of agricultural machinery derived from the traction engine was the Darby Digger, sometimes known as the 'Colchester' digger. Designed and made at the Standard Ironworks under the direction of a Thomas Churchman Darby, it consisted of a traction engine fitted with two sets of digging forks operated by built-up levers. The levers received their motion directly from the engine crankshaft, one being 90 degrees out of phase with the other. The order books only refer to one of these being made by Paxman.
More detailed technical specifications, descriptions of surviving Paxman traction engines and of scale models appear on the page Paxman Steam Traction Engines.
This page covers only Paxman steam locomotives. For the history of Paxman-engined diesel locomotives see the page Paxman and Diesel Rail Traction.
A locomotive supplied in 1869 to Brownlee & Co, Havelock, New Zealand for a logging railway is reputed to have been built by Paxman. In a book by the late Roland Abbott there is a photograph of this very crude four wheel engine, with a vertical boiler, hauling a truck carrying a large log. Another source suggests Paxman only supplied the boiler. Surviving Paxman order records do not go back far enough for any details to be checked.
Paxman records do show orders, Nos 2032 and 2033, placed in December 1881, each for a "4-wheel Loco Engine 18" Gauge". They were despatched to Port Elizabeth in June and July 1882 for operation in the Kimberley diamond mines. James Paxman, a great self-publicist, makes no reference to these engines, either in contemporary publicity material, anecdotes in speeches, or a paper he read to the Institution of Civil Engineers in 1883 about his exploits in Kimberley. This makes Andrew Phillips think the whole project was a disaster. Unfortunately we have no pictures of the engines.
The next steam railway locomotive built by Paxman, despatched from the works on 12th December 1923, was for the Ravenglass and Eskdale Railway in Cumbria. Originally opened in 1875, the RER had a 3' gauge until its closure in 1913. At that time W J Bassett-Lowke, of model railway fame, and a group of fellow enthusiasts were looking for somewhere to lay an extensive 15" narrow gauge railway. The RER was well suited to their requirements so it was purchased and re-opened in 1915 after conversion to 15" gauge.
With the opening of granite quarries at Beckfoot in 1923, it was decided the railway needed a new locomotive for the anticipated mineral traffic. The engine would need to be capable of hauling 32 ton goods trains on grades of up to 1:34 and operating the heavy non-stop holiday passenger traffic in summer.
In 1922 the consulting engineer to the railway, Henry Greenly the leading model engineer of his day, drew up plans for a one-third scale model of a projected 2-8-2 main line goods locomotive. Deciding who should build the engine posed a problem. Bassett-Lowke had ceased making 15" gauge locomotives in 1914 and had no intention of resuming. A shareholder in the RER was Sir Aubrey Brocklebank, Chairman of the Cunard Steamship Company. Cunard was a large customer of Paxman and Sir Aubrey asked Paxman if they were interested in building a 'one off' miniature locomotive. The Company agreed and the order, No 15074 (Works No 21104), was placed on 21st March 1923.
'River Esk' was the first 2-8-2 locomotive to run on a British railway. Greenly's original designed was modified to incorporate Paxman-Lentz poppet valves and the Paxman patent valve gear then being introduced by the Company for locomotive use. Although Lentz valves had been fitted to locomotives on the continent some years previously, 'River Esk' was the first British locomotive to be fitted with them. The Lentz valves arrangement was not a success and in 1928 was replaced by more conventional Walschaerts gear.
Having two cylinders of 5¼" bore x 8½" stroke, the engine was capable of a tractive effort of 2,100 lbs and pulling a load of 70 tons on the level. The overall length of engine and tender was 23' 3". Initially it was estimated the locomotive would weigh 6 tons 5 cwts. but a large bogie tender was fitted which brought the weight of the engine in working order to a little over 8 tons inclusive of the tender with 176 gallons of water and 5 cwts of coal.
The story of subsequent orders for 15" gauge locomotives revolves around two very wealthy men, Capt J E P Howey (d.1963) and Count Louis Zborowski. Both famous racing drivers in the early 1920s - Zborowski raced the original Chitty Bang Bang - they shared a passion for narrow gauge railways. Each was sufficiently wealthy to be able to afford a 15" gauge railway on his estate. At one stage they tried to purchase the Ravenglass and Eskdale Railway but were unsuccessful.
Howey and Zborowski asked Henry Greenly to design a 15" gauge locomotive for them. They wanted the fastest, most impressive 15" locomotives ever built and planned to use them initially on Zborowski's private estate at Bridge, near Canterbury. Greenly drew up plans for a one third scale model based on Nigel Gresley's famous A1 4-6-2 Pacifics of the LNER, of which 'The Flying Scotsman' is a well known example. After approving the design, Zborowski ordered two of these locomotives from Paxman in 1924. Sadly, before they were completed Zborowski was killed whilst competing in the Italian Grand Prix at Monza in October 1924. Howey decided to take over the order and create a mainline in miniature as a memorial to his friend.
The two locomotives were completed at Standard Works in 1925 at a cost of £1,250 each. As Howey had no suitable track of his own, the first locomotive, DP (Davey Paxman) 15469, was despatched to the Ravenglass & Eskdale Railway in June 1925 for a month of trials. After acquitting herself well in the trials the engine was returned to Colchester for minor rectification work and named 'Green Goddess'. Pictured here is the locomotive whilst at Paxman's Works with Henry Greenly in the cab. The second locomotive, DP 15470, was named 'Northern Chief'.
Photo: Green Goddess with Henry Greenly in the cab at Paxman's Works in 1925.
The search for somewhere to build a railway took Howey and Greenly to Romney Marsh on the Kent coast where they found a suitable site. Greenly was told to proceed with the land purchase for what was to become the Romney Hythe & Dymchurch Railway. 'Green Goddess' and 'Northern Chief' were dispatched from Colchester and stored in the corner of a garage at New Romney until track could be laid. The engines were in use by 1926, with the line being formally opened on 16th July 1927.
Early in 1926 the Ministry of Transport indicated its willingness to grant the application for an Order under the Light Railways Acts so Howey ordered another locomotive that year to the same design as 'Green Goddess' and 'Northern Chief'. 'Southern Maid' (DP 16040) was delivered to the RHDR on 20th April 1927. The order was later expanded to include a further four locomotives. Two of these were Mountain Class 4-8-2 goods locomotives, 'Hercules' (DP 16041) and 'Samson' (DP 16042), to handle heavy shingle/ballast traffic anticipated from the County Council's tips near Hythe. Completed in 1927 at Colchester, they were similar in most details to the first three Pacifics apart from their smaller driving wheels and different wheel layout.
The final two, the last steam locomotives to be made by Paxman, were also built in 1927. 'Typhoon' (DP 16043) and 'Hurricane' (DP 16044) were Pacifics similar to the first three, except they were originally designed and fitted with a third cylinder placed between the frames. In practice the addition of the third cylinder provided no useful enhancement of performance, increased fuel consumption, and was dogged by frequent breakdowns. Consequently 'Typhoon' was converted to two cylinder operation by Paxman in 1935 and 'Hurricane' by the RHDR's own workshops in 1937.
All seven Paxman locomotives for the RHDR were designed to operate at a steam pressure of 180 psi and, with the exception of 'Typhoon' and 'Hurricane', had two cylinders. Cylinder sizes, including those of the three cylinder variants, were the same as 'River Esk', 5¼" bore x 8½" stroke. In full working order, inclusive of water and fuel, the weight of the Pacifics was approximately 8 tons. The overall length of engine and tender of the Pacifics was 24' 5", and of the Mountains 25'.
A further two English type two-cylinder locomotives, similar to the first three, were ordered from Paxman in 1928. After the Company had allocated order numbers 16692 and 16693 the order was cancelled. In 1929 RHDR decided to adapt the design to American type Pacifics and put in hand the building of two locomotives in their own workshops. The boiler work was contracted out to Krauss of Munich, and some other parts were procured from Paxman. Ultimately all the parts that were to hand were sent up to Sheffield where the building of the locomotives was completed in 1931 by the Yorkshire Engine Co who were full scale locomotive builders. The first engine was originally named 'Dr Syn' and the second 'Black Prince'. When the first was renamed 'Winston Churchill' in 1948, the 'Dr Syn' plate was transferred to 'Black Prince'.
Details of the locomotives, together with colour photographs, are shown on the Romney Hythe & Dymchurch Railway website which is well worth a visit as, of course, is the railway itself.
By the late 1920s Paxman was successfully manufacturing heavy oil engines which, for their customers, had many advantages over steam. From then on the future of Paxman lay with the development of the large high-speed diesel for which it is now best known. The last Lentz-Paxman engine, built for a laundry, was delivered in 1934, marking the end of steam engine manufacture at Standard Works. However boiler manufacturing remained an important part of the business. Paxman continued to make large shell boilers until 1967 and did not finally cease its boilermaking activities until 1969. Thereafter the Company continued to utilise the specialist knowledge and skills developed through boilermaking, such as plating and welding, in the design and manufacture of large rotary vacuum filters for a wide variety of applications. The Process Plant Division as it came to be known was sold to Brackett, another Colchester filtration business, and transferred to their site at the end of April 1989, freeing Paxman to concentrate on its diesel engine activities.
Bibliography and References:
Paxman-Lentz Steam Engines, Paxman catalogue - Publication No 723, dated May 1915.
Price List of High-Speed Single-Acting Engines (Peache Patent), Davey, Paxman & Co Ltd price list - Publication No 57, dated July 1905.
Steam and the Road to Glory, Andrew Phillips, Hervey Benham Charitable Trust 2002, ISBN 0 9529360 1 1
Ransomes Sims & Jefferies, Agricultural Engineers, A History of Their Products, Brian Bell, Old Pond Publishing, 2001, ISBN 1 903366 15 1. Reference to William Fletcher on p 85.
The Engineer 127 (1919). Willliam Fletcher's death reported on p 10.
Acknowledgements: My thanks to Michael Johnson, formerly Paxman's librarian and archivist, Mike Gipson, formerly of MAN B&W Diesel Ltd, Paxman, and Alex Walford for their assistance is answering queries and making documents available for the preparation of this page.
Page updated: 27 OCT 2008