![Uniflow steam engine, Bradford Industrial Museum - geograph](https://upload.wikimedia.org/wikipedia/commons/5/58/Uniflow_steam_engine%2C_Bradford_Industrial_Museum_-_geograph.org.uk_-_2195277.jpg)
A barring engine (also called barring motor) is a small engine that forms part of the installation of a large engine, and is used to turn the main engine to a favourable position from which it can be started. If the main engine has stopped close to its
dead centre it is unable to restart itself.
Barring may also be done to turn the engine over slowly (unloaded) for maintenance, or to prevent belt drives being left too long in one position and taking a "set".
Originally they were used to turn
stationary steam engines
In addition to its common meaning, stationary may have the following specialized scientific meanings:
Mathematics
* Stationary point
* Stationary process
* Stationary state
Meteorology
* A stationary front is a weather front that is not moving ...
to a position from which they could be started. These early barring engines were themselves small steam engines. Today they are found on most large marine vessels, such as
supertanker
An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk cargo, bulk transport of petroleum, oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quant ...
s and
container ships
A container ship (also called boxship or spelled containership) is a cargo ship that carries all of its load in truck-size intermodal containers, in a technique called containerization. Container ships are a common means of commercial intermodal ...
, and are driven by
compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
.
For modern large scale power plant, after a generation unit has been shut down, the shaft line and casing is gradually cooled, where cooling might not be even for the upper and lower side of the shaft. The uneven cooling may cause bending to the shaft, ultimately leading to vibrations and unbalanced output. The barring gear will rotate the shaft at a low speed, typically 5rpm, until the shaft is completely cooled down, to avoid the above situation.
Development
The first barring engines or ''barring gear'' were manual. At their simplest, they were a hefty engineer with a crowbar (hence the term "barring"). The engine's flywheel could be provided with a series of holes or teeth and a
roller fulcrum set into the frame at a convenient place. Later manual barring engines had geared drives and a crank handle. With suitable reduction gears, even very large engines could be barred by hand. This only needed to be done once a day and was not a hurried operation, so speed was not crucial.
Where a steam barring engine was used, this was a small twin-cylinder engine (to avoid its own dead centre problems) with a reduction gear of high ratio, usually involving a
worm gear
A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminolo ...
. Final drive was by a pinion gear engaging temporarily with the teeth or barring holes cut into the rim of the main flywheel. The drive pinion was arranged on a swinging link so that it was thrown out-of-mesh automatically, once the main engine started to rotate at full speed. As the ratio was perhaps 1000:1 and the main engine ran at 60 rpm, this would otherwise have been a disastrous overspeed.
Some engines instead used a final pinion on a helical spline, similar to that later used for the
starters of internal combustion engines: once the main engine started, the pinion would be thrown out of engagement axially along this spline as the flywheel over-speeded the pinion relative to the shaft.
As mill engines became more powerful, from around 1870 there was a shift from single belt drives to multiple rope drives.
The barring engine needed to turn these rope drives over as well (although they were disconnected from the machinery at the remote end) and a simple manual gear was no longer sufficient. Around 1881–1883 there was a shift to the use of steam-powered barring engines.
Each mill engine manufacturer had their own style of barring engine.
Unlike other smaller components, such as feed water pumps, they were rarely bought-in from other makers. Usually, though, a standard design was used for all sizes of engine, with additional gearing if it was required to bar a particularly large engine.
See also
*
Musgrave non-dead-centre engine
Musgrave's ''non-dead-centre'' engine was a stationary steam engine of unusual design, intended to solve the problem of stopping on dead centre. It was designed in 1887 to serve as a marine engine. It used a pair of linked cylinders to prevent ...
*
Jacking gear
A jacking gear (also known as a turning gear) is a device placed on the main shaft of an engine or the rotor of a turbine. The jacking gear rotates the shaft or rotor and associated machinery (such as reduction gears and main steam or gas turbines) ...
References
External links
{{Commons category, Barring engines
Video of barring engine at work– starting a large
rotative beam engine
A beam engine is a type of steam engine where a pivoted overhead beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used by Thomas Newc ...
at
Crossness Pumping Station
The Crossness Pumping Station is a former sewage pumping station designed by the Metropolitan Board of Works's chief engineer Sir Joseph Bazalgette and architect Charles Henry Driver. It is located at Crossness Sewage Treatment Works, at the ea ...
, London
Stationary steam engines
Steam engine technology