Early Paxman Oil and Gas Engines

Paxman's First Oil Engines

Paxman was not among the earliest manufacturers of oil and gas engines. This may have been because the demand for its highly successful steam engines provided more than enough work. The knowledge and experience gained in building high quality steam engines was, however, an excellent foundation from which to start making internal combustion engines. The Company possessed substantial expertise in the design and manufacture of reciprocating machinery and its components such as cylinders, pistons, inlet and exhaust valves, crankshafts, and governing equipment. It was also well established in the markets for such engines. Once making them, the Company was in the happy position of being able to offer impartial advice about the respective merits of steam and internal combustion engines as it offered both.

Benzine Engines

Paxman commenced manufacturing oil engines in 1904 when a horizontal engine designed to run on 'light spirits' was offered to the public. Benzine, benzoline, petrol, gasoline, naptha or any similar fuels having a specific gravity not less than 0.8 were defined as 'light spirits'. Magneto (spark) ignition was used and ignition timing could be varied while the engine was running. At full economic load fuel consumption was between 0.6 and 0.7 pints per bhp hour.

In early order books and catalogues these engines are usually referred to as Benzine Engines. They were made in a variety of sizes. Examples in the order book for 1911-12 include engines of the following bore and stroke: 12½" x 18" (a popular size), 7" x 13", and 5¾" x 11". One Paxman catalogue (undated) offers the following range of Benzine Engines:

The order book for the period 1911-12 reveals that actually the Company was selling many more gas engines than benzine engines at this time. (As an interesting aside, there is a note in a copy order book that in January 1911 the order book for steam engines and boilers was amalgamated with that for gas and oil engines. By then Paxman had sold 9,794 steam engines and boilers, and 1,016 gas and oil engines.)

Paxman Gas Engines

Almost identical to the benzine engines, these were all of the horizontal type with heavy cast bedplates, similar in general layout to the Company's horizontal stationary steam engines. The water jacketed cylinder was fitted with a loose liner of hard, close-grained cast iron. The outer end of the liner was free to expand and contract with variations in operating temperature to minimise stress. The smaller types had fixed cylinder heads and the inlet valves were on the side of the cylinder. On the larger types the breech end of the cylinder was removable and the inlet valves located on top of the cylinder. On all sizes the exhaust valve was on the under side of the cylinder. Both inlet and exhaust valves were designed to be easily accessible and removable for maintenance or replacement, as were the valve seats. Cams for operating valvegear were mounted on a side shaft as on the Company's horizontal steam engines. (Pictured to the right is a Type L Gas Engine - see below for details)

A standard feature was patent magneto ignition with a timing device which could be adjusted while the engine was running. Retarding the ignition timing when starting the engine avoided the risk of backfiring. Once the engine was running smoothly, timing could be advanced to achieve the best fuel economy. The smallest engines - sizes B, C, and D - were fitted with automatically-timed tube ignition as standard but magneto ignition was available as an extra. Compressed air starting was recommended for the larger engines (size Y upwards). Engine sizes and outputs are shown in the table below.

Town Gas, Producer Gas and Suction Gas

These were the usual fuels for gas engines. Town gas, better known as coal gas, has the highest calorific value and gave the highest power output as is shown in the table below. Produced by the distillation of bituminous coal, its main constituents are hydrogen, methane and carbon dioxide. It was the gas generally available for domestic and industrial use in the UK until natural gas became more widely available in the 1970s.

In the early Paxman catalogues the alternative to coal gas is generally referred to as Suction Gas or Producer Gas. Technically there is a difference between the two. Producer gas is generated by passing air over hot or incandescent coke which produces a mixture of carbon monoxide and nitrogen (O₂ + 4N₂ + 2C = 2CO₂ + 4N₂). Because of the high proportion of nitrogen in the atmosphere, producer gas contains about 60% nitrogen and therefore has low calorific value. Only the carbon monoxide is combustible, burning with the charge air to form carbon dioxide (2CO + O₂ = 2CO₂).

By passing steam, rather than air, over hot carbon (such as coke) both carbon monoxide and hydrogen are produced (H₂O + C = CO + H₂) to give water gas which has a higher calorific value. Carbon monoxide and hydrogen are both combustible, burning with the charge air to produce carbon dioxide and water vapour (CO +H₂ + O₂ = CO₂ + H₂O).

Suction gas generators used steam to produce a better fuel than plain producer gas. In practice such plant probably generated a mixture of producer gas and water gas. The name Suction Gas derived from the fact that the vacuum created in the engine's cylinder on the inlet stroke was used to suck or draw steam and air through the incandescent coals of the gas generator. This was safer and had other practical advantages over forcing steam or air through the generator under pressure. For instance gas production ceased when the engine was stopped or on stand-by.

Paxman designed and manufactured suction gas producers for use with its engines. In many cases it also made and supplied producer gas plant for use with other makes of gas engine. A full explanation of the construction and operation of these generators is on our page about Suction Gas Producers.

Applications

Gas engines were sold for a wide range of industrial applications where a prime mover was required to drive other machinery. In many of these applications minor variations in crankshaft speed were not critical, and a 'hit and miss' governor was adequate. For others, such as generating electricity and textile mill driving where speed variations needed to be more tightly controlled, the Company offered the Paxman patent throttle governor and valvegear. This controlled the amount of opening given to the gas valve thus determining the strength of the mixture delivered to the engine and the power output. Electrical power generation was an important application and extra heavy large diameter flywheels were available also to achieve more constant crankshaft speeds.

A very different application was laundry work. In 1926 the Company produced a catalogue (No 741) of power plant for laundries, a growing market at the time. Although dealing primarily with steam equipment such as boilers, it also offered a range of gas engines little changed from that in the 1913 catalogue described below.

The Paxman Range of Gas Engines

One of the most striking things is the wide range of sizes offered by the Company. Catalogue No. 650, dated March 1913, for Gas Engines and Suction Gas Producers, lists twenty different sizes of single cylinder engine with outputs from 2.5 bhp to 175 bhp (on town gas, less on producer gas). Two cylinder coupled versions of the six largest single cylinder engines were also offered with power outputs in the range 150 bhp to 300 bhp (on producer gas).

Details of the engines offered in catalogue 650 are given in the table below. Bore and stroke are not quoted in the catalogue but were pencilled in the margin of the copy from which the figures were taken.

Surviving Paxman Benzine Engines

A benzine engine in good running order is No 17430 (pictured right). It is a 'C' Type which was ordered on 18th January 1912 by John Blyth & Co and dispatched on 4th April that year to Moffat Virtue of Sydney, Australia (agents). It is 5" bore x 10" stroke producing 4½ - 5 bhp at 280 rpm and has Bosch high tension magneto ignition operated from the side shaft. (Bosch magnetos were only fitted up to the start of WW1 in 1914.) The original order specified that it was to be supplied with a shallow bed suitable for mounting on transport to be used as a portable engine. It has two flywheels, each 3' diameter x 4½" wide, and a driving pulley 12" diameter x 6" wide. Since being returned to the UK it has been nicely restored by its present owner, Mr Russell Weavers of West Mersea, Colchester, and is part of his impressive collection of old stationary engines.

A second engine, No 17828 (pictured left), was brought to our attention in October 2001 by Tony Marvin of Kurrajong, NSW, Australia. It was discovered after being abandoned for at least 45 years in the Australian bush. Tony, who has previously worked as a service engineer on Ruston and Paxman engines, suspected this gas engine was originally a benzine engine. The order book appears to confirm his suspicions, and reveals many similarities to No 17430 described above. It was ordered by John Blyth & Co of Sydney on 9th August 1912 and dispatched to Australia on 27th November 1912. The order for No 17828 is recorded as one for an 'E' Type benzine engine, 6.7/8" bore x 13" stroke, with a rating of 7 - 7¾ bhp. A 'D' Type was also part of the order. In actual fact No 17828 has a 7" bore x 14" stroke. There are various possible reasons why the bore and stroke are different from those specified in the order book.

To the right is a more detailed picture of the governor and valve gear on No 17828. As on No 17430, the two inlet valves are on the side of the cylinder whereas on the larger engines the inlet valves are on top. The right inlet valve admits air only and is not governed. The left inlet valve is controlled by the 'hit and miss' governor, admitting fuel and air as required to maintain the required speed and power output. On all engines the exhaust valve is on the under side of the cylinder. Part of it can be seen in the photograph - the D shaped loop near the ground, below the cams on the side shaft. To the left of the inlet valves is the vertical drive shaft for the governor. The fly weights are under the 'pixie hat' at the top of the shaft. On the front of the engine, immediately to the left of the flywheel, is the 'Moffat Virtue of Sydney' agent's plate, identical to that on engine No 17430.

No 17828 has a fixed cylinder head (see left), as does No 17430. This was usual for the smaller engines, while on the larger engines the breech end of the cylinder was removable. Tony says all the indications are that his engine had a low tension magneto as original, not hot tube ignition as first thought, so he plans to go with magneto ignition.

In the centre of the photograph the lower section of the vertical drive shaft for the governor can be seen, and at its bottom end the skew gear drive from the side shaft. To the right of the vertical shaft is another view of some of the valve gear.

For some time Tony had planned to remove the cylinder liner so that the corroded retaining bolts could be replaced with stainless steel ones. After various unsuccessful attempts to remove it, Tony emailed in early March (2002} to say "We have at last got the liner out of the gas engine block. Hurrah!! . . . cylinder is held in by tee headed iron bolts - not much left due to corrosion, will replace by stainless ones. Dismantling now finished so we on the way up." Tony mailed two photographs, one to the right showing the liner after removal. The other photograph, below, shows the cylinder head end of the liner with one of the old tee headed bolts still in place. To the right of the old bolt, clearly visible, is the pair of lugs on the liner for positioning and holding another of the four tee bolts originally fitted.

As regards the ignition system Tony commented: "Our engine has the original carburettor and the igniter has been found! So we will be able to construct the missing mechanisms. I have an old type HT magneto so we will end up with quite an unusual hybrid as follows: A high tension mag for a spark plug in the top of the cylinder and at the same time the linkage from the mag tripping the igniter which is connected to a 6 volt induction system !!" (The original carburettor on Russell Weaver's engine, No 17430, was missing and one was made using the body of an old brass tap and the float chamber from an Amal carburettor. That engine does have a spark plug in the top of the cylinder, as Tony intends to fit to No 17828.)

Photos of No 17828 courtesy of Tony Marvin.

A Surviving Paxman Gas Engine

A 1912 Paxman gas engine can be seen at the Musee du Littoral on the North West Coast of France. It is in working order, running on producer gas from a gas generator on the site. Comparing illustrations in the 1913 catalogue and a photograph we have seen of the engine, it appears to be a Type K or similar.

Compression Ignition Oil Engines

Paxman started developing a vertical compression ignition oil engine in 1925. The history of the development of this type of engine, which was introduced to the market in 1927, is told on the Heavy-Fuel-Oil Engines page.

Acknowledgements: Thanks are due to Michael Johnson, former 'Keeper of the Paxman archives', who fielded many queries and made source documents available for the preparation of this page. Also to Russell Weavers, Tony Marvin, and Alex Walford for their valuable assistance and contributions. The compiler reserves to himself responsibility for any errors or omissions.

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Page updated: 21 JAN 2006