The advent of mechanical air movement using “air pumps” and fires
It has to be recognised that it is pure chance for the same word to be used for the contrivance behind which an oriental lady hides her face and the present day rotary machine for delivering a current of air. Only the Anglo-Saxon creates such confusion.
In Finland another form of confusion is found by the use of the word “puhallin” (a wind instrument) which covers both a trombone and a propeller fan. Of course, no such difficulty exists when using the French or German languages as “ventilateur” or “Ventilator” are more precise in their meaning and are unambiguous. All that is necessary is to define whether they are “powered” or “natural”. The ladies with their “йventail” or “Facher” are unlikely to be misunderstood.
The need for having some mechanical means of moving air for industrial and cooling purposes had been realized for many centuries. Punkahs were used in India hundreds of years ago. In its earliest form the punkah consisted of a large swinging flap covered with wet straw.
The first means of providing a forced draught of air was the bellows. It is believed that bellows of a primitive type were used in Egypt for assisting the combustion of fires as far back as 400 BC. In India a simple form of bellows made from goat skins was used for iron smelting in the very early ages.
The origin of the word bellows was blast-baelig — a blow bag. In the 11th century the first part of the name was dropped and in the 16th century the word baelig had become first belly, then bellies, and finally bellows. Bellows were almost the only means of blowing air until the 17th and 18th centuries, when blowing machines were developed. These consisted of a piston, cylinder and valve for moving air. In 1851, a double-acting blowing engine of tremendous size was used in Dowlan’s Iron Works. This had a cylinder of 3.7 m diameter, the piston stroke was
A— Prom. B—Box **a«d casing. C— Blow-holi. D— Sicojcd aati
E Cow doit. F—Axl* G—LtTi* or axle. H—Rodv
Figure 1.2 Georgius Agricola’s reference to bellows and crude fans
3.7 m, the machine moved 21 cubic metres of air per second, and developed a pressure of 30 kPa.
Perhaps the earliest reference to mechanical ventilation was by Georgius Agricola in his book De Re Metallica, first published in 1556. He described the use of bellows and crude fans (Figure 1.2) in German underground metal mines in a manner which makes one assume that they were then well established. These early fans were, of course, made of wood with radial paddle vanes fitted to a spindle which rotated in a casing. Thus they were the first centrifugal fans and were rotated by animals, men or water mills.
It is interesting to observe that Agricola’s book was translated from the Latin in 1912, by Herbert Clark Hoover, President of the United States of America. These days Presidents and less than humble engineers have more than enough trouble with English, let alone a foreign and dead language!
Much of the early history of fans is inextricably linked with that of mines, but up to about 1860, their ascendancy over other solutions was not, by any means, certain. John Smeaton (1724-1792) used reciprocating pumps for exhausting the foul air from coal mines in Northern England. In 1813 John Buddie (1773-1843) wrote to the Sunderland Society describing the methods which he had used in the collieries of North East England for generating the necessary air currents and thus the prevention of accidents from “firedamp”. His exhausting piston pump had been installed in Hebburn Colliery in 1807.
Figure 1.3 The Struve ventilator
Buddie also stated that “the standard air-course, or current of air, which I employ in the ventilation of collieries under my care, abounding in inflammable gas, equals from 5400 to 7200 cubic feet per minute”. Allowing for the factor of exaggeration always present in any engineer’s claims, we may note that 2.55 to 3.4 m3/s (for those too-long metricated) is an exceedingly small amount and that nowadays flows 100 times as great would be considered necessary in such mines.
In addition to Smeaton’s and Buddie’s air pumps, other large machines working on the same principle were developed and one of the most successful of these was the Struve ventilator. William Price Struve of Swansea developed an air pump which employed circular air pistons shaped like bells or gas holders (Figure 1.3).
Generally each machine employed two of these which were moved up and down by means of a steam engine, the lower edge of this bell dipping into a circular water trough. This arrangement prevented leakage past the pistons. Each piston works as a double-acting pump. The air from the mine entered the space above and below the piston by means of a multitude of inlet valves and opens discharge valves, through which the exhaust air enters the atmosphere. These ventilators worked as exhausters and were connected to the top of the upcast shaft. In some cases ventilating pressures of 1.25kPa were produced.
The first Struve ventilator was installed at Eaglebush Colliery, South Wales and began to work in February 1849. The upcast shaft was 55 metres deep and the quantity of air circulated was
26.5 m3/s at an average pressure of 0.9kPa. About a dozen of these machines are said to have been installed, the largest of which was erected by the Rhuabon Company in North Wales, the pistons of which were 7.6m diameter. The quantity of air produced by this machine was up to 28.3 m3/s. All these machines suffered from slow piston speeds. Upkeep to retain their efficiency proved to be rather excessive, the valves requiring much maintenance with consequent stoppage of the machine. The useful effect reported for some of these machines was in the region of 50%.
Another type of large reciprocating pump was invented and patented by Nixon in 1861 (Figure 1.4). The first of these was installed at Navigation Collieries, Mountain Ash, South Wales; this was a horizontal machine having two rectangular shaped wooden pistons, each 9.1m long by 6.7m high, which ran on small wheels along rails in the wooden cylinders. The stroke of the pistons was 1.83m and when the machine ran at 6V2 strokes per minute, it delivered air at the rate of 44 m3/s.
The air enters the machine through flap valves and leaves through discharge valves. In Nixon’s machine it was not possible to have water seals on the piston and leakage past the piston was a difficulty. The movement of the pistons was actuated by a steam engine. Two of these machines were installed in South Wales. Nixon’s ventilator was said to have a useful effect of about 46% when in good condition. Having a multitude of small valves, it required careful maintenance if leakage was to be kept at a minimum.
To overcome the objections of the reciprocating air pumps of slow piston speed and much valve maintenance, rotary air pumps were invented and constructed. They consisted of vertical drums revolving eccentrically within a cylindrical chamber. By the revolution of the drum in a cylinder housing, spaces of varying capacity were formed causing the air to enter from the upcast shaft and by further movement of the drum, the return air was discharged into the atmosphere.
The Lemielle ventilator, which was extensively used in the ventilation of Belgian collieries, from about the middle of the 19th century, was one of the most successful of these rotary machines. Several were exported to England, starting the ventilation export trade. An example was that installed at Page Bank Colliery in about the year 1860. The drum was 4.6m diameter and 9.8m high and worked in a casing 6.9m in diameter. The useful effect reported by the North of England Institute Committee on Mechanical Ventilators for this machine was 23.4%. A further type of rotary air pump was that invented by Cooke, but very few of this type of ventilator were installed, and little is known of their design.
Perhaps the most alarming method of mine ventilation was to place a furnace at the bottom of the upcast shaft. By burning coal (what else?) a current of air to support the combustion was induced through the mine (Figures 1.5 and 1.6). The “stack-effect” of a deep mine meant that the pressure developed was then greater, and the method could not be used in shallow mines. Even so, a furnace was only capable of developing about 750 Pa and Buddie had to use “split ventilation" — dividing the workings into a number of parallel circuits to reduce the system resistance.
Figure 1.5 Early example of furnace at surface for ventilation of a mine
Many collieries favoured furnace ventilation around the mid 19th century as both air pumps and fans were considered to be
Figure 1.6 Early example of furnace underground for ventilation of a mine
Unreliable. Just as mechanical ventilation was improving, a UK government select committee (1852), with that lateness of report and lack of accuracy that has always characterized politicians, stated that “any system of ventilation depending on complicated machinery is inadvisable, since under any disarrangement or fracture of its parts the ventilation is stopped, or becomes less efficient”. It took a further 60 years before the UK Coal Mines Act of 1911 recognised that this problem could be easily overcome by having a running and standby fan. The committee also stated “that the two systems which alone can be considered as rival powers are the furnace and the steam jet”.
Experiments soon proved that steam jets were extremely inefficient and were incapable of producing the larger flowrates of air required due to increasing colliery outputs, and the larger amounts of firedamp (methane) therefore being emitted. Furnaces could, however, cope and Nicholas Wood, (the backer of, and collaborator, with George Stephenson in the early development of railways) showed in tests at Hetton Colliery on 13th November 1852, that three furnaces at the bottom of the upcast shaft circulated 106 m3/s with an underground ventilating depression of 486 Pa.
Even as late as 1946, Copy Pit and Clifton Colliery near Burnley had underground ventilating furnaces with chimneys belching out smoke for no apparent reason. Nobody would have suspected that these chimneys were in fact about 275 m high. The outlets were known locally as cupolas and can only have survived for so long as the mines were non-gassy.
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