Balanced Locomotives

Gallery opened July 2004

Updated: 12 Apr 2022

New pic of Haswell's Duplex Locomotive added
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One of the problems with the conventional type of steam locomotive is the presence of forces caused by the pistons, piston-rods, crossheads etc moving back and forth. As these masses are accelerated and decelerated, the reaction forces cause the locomotive to also accelerate and decelerate by a much smaller amount; it is still enough to make the riding rough and uncomfortable. These forces do not cancel as the two side of the locomotive operate 90 degrees apart to prevent dead-centre problems.

This problem can be minimised by adding weights to the driving wheels. These already have balancing weights which nullify the effect of purely rotating masses such as the crank pins and coupling rods. Adding more mass to these weights can balance the back-and-forth forces, at the expense of upsetting the rotational balance; the latter has bad consequences, generating an up-and-down force on the rail. When acting downwards this is known as "hammer-blow" and puts serious extra stresses on the track and its foundations, the forces increasing with the square of the speed. 180 degrees later in the rotation of the wheel it acts upwards, and in severe cases can almost lift the wheel off the rail, with dire consequences for stability. As a result, it was conventional practice to balance only a third to a half of the reciprocating mass. (The Austerity locomotives designed for military use in WW2 had no reciprocating balance at all, so they could work on hastily-laid track. Comfortable riding was not a priority; however in these conditions speeds were low and it was a perfectly sound design choice)

At least two designers appreciated that a good way to obtain good balance for both the rotating and reciprocating masses was to fit two pistons on each side, driving crank-pins set at 180 degrees so that one piston would move forward as the other moved back.

The only real difficulty was fitting two cylinders where one had grown before. Burch solved the problem by having two pistons in one cylinder, driving two different wheels. John Haswell solved it by fitting one cylinder above the other, set at a slight angle. Shaw had enough room to put two cylinders side-by-side. Strong used two inside cylinders and two outside cylinders, four in all.


Left: The Burch Oscillating Cylinder Locomotive: 1837

This drawing is taken from a patent granted to Richard Burch of Heywood in 1837. On each side there is an oscillating cylinder C - C with two opposed pistons; horizontal reaction forces would have cancelled out, but not vertical ones. Balanced drive however does not appear to be the aim. Burch's motivation seems to have been simply the driving of both axles without the use of a connecting rod, though why that would be inferior to this more complicated arrangement is not clear.

No balance weights are visible on the wheels.

I have so far found no indication that this design was actually built. Burch was described as 'a machinist' which does not sound like he was a professional railway engineer. Full details were published in the London Journal of Arts & Sciences, Volume XI, 1838.


Left: The Stephenson & Howe balanced 4-2-0 locomotive: 1846

By this time the problems of unbalanced masses moving back and forth had been recognised. George Stephenson's answer was not to use the rim balance weights used by others at the time, but instead he had three horizontal cylinders placed in line across the locomotive, all connected to the single driving axle. The two outside cylinders drove cranks on the same centre, ie the outside pistons went back & forth together, 90 degrees in advance of the motion of inside cylinder. This was very successful in reducing rolling and 'nosing' but did not give a constant drawbar pull. Nonetheless the two engines built had a reputation for great steadiness.

No more engines were built to this design, and one of the two was converted to a 2-2-2 within a few years.

The advantage of having no balance-weights and hence no hammer-blow does not seem to have been appreciated at the time.


Left: The Haswell Duplex Locomotive: 1861

This remarkable locomotive had two cylinders on each side, angled slightly so that both piston rods aligned with the centre of the driving wheel. A return crank allowed the connecting-rods to be alongside each other. It was designed by John Haswell of the Austrian State Railway Works at Vienna and built in 1861, and was exhibited in the International Exhibition of 1862.

John Haswell had previously built the "Vindobona", one of the competitors in the famous Semmering locomotive trials in Austria. The cylinders were 10.8 inches diameter by 24.8 stroke, and the driving wheels were 7' 9" in diameter.

The Duplex has a Wikipedia page.

Left: The Haswell Duplex Locomotive: 1861

This drawing gives the scale of the locomotive, and a better view of the return crank on the driving axle.

Source: Proceedings of the Institute of Mechanical Engineers, 1863, p78


Left: The H F Shaw Locomotive: 1881

Shaw's four-cylinder balanced locomotive was modestly called the H F Shaw ; it was built by the Hinkley Locomotive Works in 1881. It was advertised which as being completely free from the pounding and oscillating action of conventional two-cylindered engines.

This locomotive also had two cylinders on each side, but mounted beside each other, a solution that was probably only made possible by the larger American loading gauge. These drove crank pins diametrically opposite each other on the driving wheel.

One of the crank pins connected outside the driving wheel at the same position an ordinary crank pin would be located, and carried a double crank, the middle of which was supported in a bearing held in an outside frame. The connecting rods worked either side of this bearing.

The engine was equivalent to one with two cylinders 16" by 24", and driving wheels 63" in diameter. The weight in working order was given as 74,000 pounds, of which 25,600 pounds was on the front bogie. The engine was said to have been well-designed and well-built, and it saw considerable trial use in revenue-earning service, where it was said to have worked "quite satisfactorily", but no more of the type were built.


The history of this 2+2+2+2 locomotive is rather obscure. It derives from the last patent taken out by Thomas Crampton, though it has little in common with what is normally though to be a Crampton design- ie all the drive coming from a single pair of wheels at the rear of the locomotive.

Left: Side view of Crampton Locomotive for Woolwich Arsenal: 1880's?

On each side of the locomotive a pair of cylinders drove a single wheel, with the cranks set at 180 degrees. This sounds like a recipe for dead-centre problems, but presumably it was very unlikely that both sides of the locomotive would be on a dead-centre at the same time. Why the potentially difficult duplex-drive was adopted is uncertain; it would seem too late in locomotive development for people to be afraid of mysterious power-losses in coupling rods. Further research has shown that a steam operated 'starter' was fitted that could operate on the leading axle to avoid dead-centre issues.

Crampton took out a patent for a balanced duplex-drive locomotive in 1885. It is claimed that a locomotive built to this design, or very similar, was in use at the Royal Arsenal at Woolwich in the late 1880's. However there is no reference to a locomotive with a 2+2+2+2 wheel arrangement on the Wikipedia page for the Royal Arsenal Railway. It is known that Crampton did experiments with the 18in-gauge locomotives Vulcan (No 939) and Mercury (No 1075) but both these engines were of 0-4-2 wheel arrangement.

Left: Front view of Crampton Locomotive: 18

Bibliography: The Royal Arsenal Railways: The Rise & Fall of a Military railway Network, by Mark Smithers


Left: The Balanced Locomotive of Mr George Strong: 1896

This locomotive began its life as the A G Darwin, a design originated by George Strong.

This version of the locomotive had four cylinders, allowing the masses moving backward and forward to be balanced.

Source: Scientific American, 14 Nov 1896

Left: The four cylinders of the Balanced Locomotive: 1896

There were two HP cylinders of 16 inch diameter and two LP cylinders of 28 inch diameter. Steam pressure was 170psi.

Source: Scientific American, 14 Nov 1896

So how well did it work? An article called "Tests of the Strong Balanced Locomotive at Purdue University" was published in Scientific American for 21 August 1897. (Purdue University was unusual in having a locomotive test facility, run by a Professor Goss) A version not paywalled has yet to be found. You can read a letter from George Strong to the editor of the Railway Gazette here, in which Strong disagrees with Prof Goss. The Prof says that the disagreements between them "are rather fundamental" which suggest that the test were not conducted with perfect harmony between inventor and tester.

In 1897 the Balanced Locomotive & Engineering Co of New York tested the Strong balanced locomotive for hammer-blow on the Purdue static test plant, using the same procedure as Prof Goss in 1893. (the crushing of wire) "The test wwas a great success, with no hammer-blow, pitching, or yawing of the engine." Nonetheless the engine was not repeated although "During the early part of the 2oth century counterbalancing was a serious and limiting factor in American locomotive development." (Tom Morrison, The American Steam Locomotive in the Twentieth Century)

The failure to put more effort into balanced locomotives is mysterious.

Left: The rods and cranks of the Balanced Locomotive: 1896

Note that the coupling rods between the wheels are set at the usual 90 degrees to avoid dead-centre problems.

Source: Scientific American, 14 Nov 1896

Left: The Balanced Locomotive: 1905?

The locomotive after it had apparently been abandoned.

It is shown here at some kind of meeting (a county fair?) that took place around 1905. The tender with its shelter is missing but there is still the curious shelter structure at the end of the enormous firebox.

The original B&W photograph was taken by Albert Black and is reproduced by kind permission of Charles Cox; Albert Black was Mr Cox's wife's Great Uncle. It has been recently colourised.


Ten 2-4-6-2 (151A) compound locomotives were built in 1932 for the Paris-Lyons-Marseilles company (PLM) to haul heavy goods trains on the 0.8% grade between Les Laumes and Dijon. The low-pressure cylinders drove the first set of coupled axles, and the high pressure cylinders the second set of axles. The two sets of drivers were linked with inside connecting rods and inside cranks on the 2nd and 3rd driving axles, so despite having separate groups of cylinders these locomotives were not true duplex, but actually 2-10-2.

The front and back crankpins were set at 180 degrees so the back and forth forces from the movement of the pistons was balanced out. The 151A was therefore a balanced locomotive.

The 151A is described on the duplex drive page.

These are the only balanced locomotives I have found so far. If there are more they are well-hidden.

The only conclusion seems to be that the added complexity outweighed the smoother riding and reduced track impact. Since the words "hammer-blow" recur like a dismal refrain in the history of locomotive design, this is rather hard to understand.

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