High-Speed Steam Engines.

Updated: 20 Dec 2005
More on forced lubrication
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High-speed steam engines were the last flowering of the reciprocating steam engine technology that powered the world for 150 years.
They were developed to generate electricity. Generators need to turn at considerable speed to work effectively. One of the first electric power stations in Britain was at Brighton, which was offering electricity to the public in 1882, and this had a Brush dynamo turning at 900 rpm to generate 8.4 kilowatts. By 1887 an American station had an alternator running at 1650 rpm. No steam engine could possibly run at such speeds, so a slow-running machine was matched to the generator by ropes and pulleys, which could absorb as much as 10% of the power produced. As the electricity industry expanded, there was a clear need for a high-speed steam engine that could be directly coupled to a generator..

There were several well-known makers of high-speed steam engines in 1912. Here are some:

THE WILLANS ENGINES
P. W. Willans built several designs of innovative single acting engines. In a single acting engine, steam is applied to only one side of the piston, so the piston and connecting rod can be kept in a state of compression throughout a revolution of the crankshaft. This avoids the knocking and wear of the bearings which the push-pull operation of a double-acting engine causes, and which become more destructive as rotational speeds increase.
However, from about the middle of the out stroke to its end, the mass of the piston is being deccelerated, and this tends to cause reversal of the piston-rod forces and cause knocking. Therefore, in a patent of 1882, Willans added air cushioning to prevent this. A supplementary piston compressed air during the out stroke, keeping the rods in compression, and returning the stored energy in the succeeding down stroke. This process cannot have been perfect, as heat losses from the air cushion chamber would have detracted from the energy restored, but it significantly improved the smoothness of running. The supplementary piston also acted as a crosshead guide.

Above: Cross-section of a double-expansion (compound) central-valve Willans engine.

The definitive high-speed Willans engine type was the "central-valve engine" as shown above. A central spindle with multiple piston valves covered and uncovered ports in the hollow piston rod. It was driven from an eccentric fixed between the two connecting rods. There appears to be no way to vary the cutoff, and governing was done by controlling the steam supply. Lubrication was by the "splash" system, with the cranks dipping into the oil at the bottom the crankcase, which was therefore enclosed to prevent oil splashing everywhere.
These engines ran smoothly at 350 to 500 rpm, and were highly successful in the emerging electricity supply industry. In 1895, the installed capacity of British power stations was about 100,000 horsepower, 53,000 of which was produced by Willans engines.

Left: A triple-expansion Willans engine at Upper Boat Power Station, Treforest. This machine produced 2500hp to drive the generator seen at the right.

The size of the engine can be judged from the height of the man on the platform, indicated by the white arrow.

Left: A small double-expansion Willans engine directly coupled to a dynamo.

Unfortunately there is nothing in this picture to give the scale exactly, but judging from the size of the handwheel it is about two feet high.

Left: A two-cylinder single-expansion Willans engine. Note the great similarity to the compound version above.

Messrs. Willans & Robinson's Victoria Works opened in Rugby in 1899. The development of the steam turbine eventually made their engines obsolete, and few were installed in power stations in Britain after 1914. The company was described as making "steam turbines & oil engines" when taken over by Dick, Kerr of Kilmarnock in 1916, and they became part of the English Electric Company in 1919.
Reciprocating steam engines are now history, but Willans' name lives on. The "Willans Line" on a graph is still used to show steam rates at different loads on a steam turbine.


THE BELLISS & MORCOM ENGINES

Left: A Belliss and Morcom engine

This is a two-cylinder compound with piston valves in the centre. The centrifugal governor on the end of the crankshaft throttles the steam supply to control engine speed.

The forced lubrication oil pump is at the bottom, in the centre of the sump. Note the diagonal holes (or "oilways")drilled through the body of the crankshaft to distribute the oil.

While the single-acting engines of Willans et al ran smoothly and effectively, it was impossible to evade the fact that a double-acting engine produces more power in the same weight and volume. This was not crucial in fixed installations, but in naval use, in high-speed cruisers and torpedo-boat destroyers, it was critical. Destroyers in particular needed to fit a lot of power into a very cramped space. These propulsion engines usually employed triple expansion with four cranks and four cylinders, the third stage of the expansion being divided between two LP cylinders.
The problem was solved by Belliss and Morcom, who built double-acting engines which used forced lubrication at the connecting rod and crankshaft bearings. In a double-acting engine the thrust acts alternately on each side of the crank-pins and cross-head pins, and this produced knocking and wear unless the bearing brasses were set very tight; in which case bearing seizure was a constant possibility.
The Belliss and Morcom engines fed their bearings with a continuous supply of oil at a pressure between 10 and 30 psi; the idea was patented in 1890 and 1892 by Mr Albert Charles Pain, a draughtsman at the Belliss works. A continuous film of oil in the bearings was therefore established, and knocking was prevented without the bearing brasses being set very close. Pain designed crankshafts and connecting-rods with holes drilled through them, so oil could be forced through these "oilways" straight into the centre of the bearings. The principle was described in a paper to the Institution of Mechanical Engineers by Alfred Morcom in 1897; it has been used in every IC engine for many years.

It seems surprising forced lubrication was not invented before this. This seems like such an obvious development that it is hard to understand how it came to be patented so late.

Willans, and Bellis & Morcom, are the best-known makers of high-speed steam engines of that era, but there were many others. A book published in 1912 gives details of others; see below:


THE BROTHERHOOD ENGINES

Left: A Brotherhood engine

This double-acting engine used a similar form of forced lubrication to the Belliss and Morcom. Once more there are diagonal holes drilled through the crankshaft to distribute oil. The pump is a plunger type at lower left, driven from the bottom of the HP valve eccentric.

Engines of this type were supplied to the Royal Navy to drive electric generators. They ran off either 60 or 120 psi steam, and produced 150 horsepower at 450 rpm.

Left: The Brotherhood engine in transverse section.

The pistons were of forged steel, with phosphor-bronze piston rings. The piston rods and crankshaft were also of forged steel. The main bearings were of gun-metal, lined with white metal.


REAVELL ENGINES

Left: A Reavell engine directly coupled to a generator.

The Reavell engines utilised an unusual semi-compound system, described below. The size of the engine can be judged from the stepladder in the foreground.

Left: The Reavell engine in longitudinal section.

The valvegear was inside a cylindrical valve liner, and the annular piston on the outside of this. The Reavell engine utilised an unusual semi-compound system:

1) Piston at the top of its stroke. Steam enters inside of valve liner via ports A.

2) Steam passes through ports C into the top of the cylinder

3) Steam is cutoff by valve D closing ports C (see lower diagram)

4) Steam expands in upper cylinder until piston finishes downstroke.

5) Ports E and G are opened by valve F and steam is transferred from top to bottom of cylinder as piston moves up. (see below)

6) After half the upstroke the transfer ports are closed. The steam in the lower part of the cylinder continues to expand. That above the piston is compressed, cushioning the coming piston reversal and heating the cylinder ready for the next admission of steam.

7) At the end of the upstroke the exhaust valve opens and releases the lower steam.

Left: The Reavell engine in transverse section.

A form of radial valvegear was driven from the pin in the centre of the connecting-rod. Engine speed was controlled by altering the cutoff point of valve D, rotating it via B and the governor control arm.

Lubrication was on the splash system; note crank balance weights dipping into the oil in the sump.


SCOTT & MOUNTAIN ENGINES

Left: A three-cylinder compound engine by Messrs. Scott and Mountain Ltd, of Newcastle-on-Tyne, Britain.

There was one high-pressure and two low-pressure cylinders, driving cranks set at 120 degrees, for good balance.

These engines were mostly used to drive electric generators. Forced lubrication was provided by a valveless oil pump.

Scott and Mountain also built electric motors and generators. Their products were often used in the coal-mining industry.


CAREL ENGINES

Unlike the other engines here, which were all British, the Carel engine hailed from Belgium. The nameplate on the side read: "Société Anonyme des Moteurs á Grand Vitesse. Brevet Carels. Sclessin-Liége". It was another single-acting design, similar to the much better-known Willans engine. It had the same air-cushion system.
The main difference was the use of a rotary valve between the cylinders to control steam admission, transfer, and exhaust, driven from the crankshaft by bevel gears. Doubts were expressed by contemporary commentators about the steam-tightness of rotary valves in general, and bearing in mind what happened to
The Paget Locomotive, they were probably right. In the field of engines, the very word "rotary" seems to guarantee intractable problems. In my discussion of Rotary Steam Engines, I give my theory as to why this should be so.

Left: A Carel four-cylinder compound engine.

This design relied on the less satisfactory splash system for lubrication. The rotary valves were cast-iron, rotating in phosphor-bronze sleeves and with the driving fitted with ball-bearings.

Rotary valves have given trouble in other applications. One wonders how well they worked here.

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