THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CX. FRIDAY, SEPTEMBER 3, 1915. No. 2853. Air=Compressors for Colliery Work. The two photographs illustrate representative examples of air-compressing plant, manufactured and installed by Messrs. Alley and MacLellan Limited, of Glasgow, at several of the leading collieries in the Scottish, Northumberland, Durham, Lancashire, and South Wales districts. Generally speaking, these air- compressors are of the two-stage enclosed vertical type, being fitted with compound steam cylinders. The capacities vary from 6,600 cu. ft. of free air per minute down to 3,500 cu. ft. of free air per minute. They are all designed for air pressures up to 100 lb. per sq. in., but the steam pressures vary to suit the local conditions, some of the machines exhausting into con- densers, and others really working against a slight back pressure where the steam is used in exhaust turbines. The air as compressed and delivered by these machines in general is utilised for all classes of underground work, such as haulage, coal cutting, pumping, etc. Experience suggests that there is a tendency with quite a number of colliery engineers to again revert to The machines call for very small floor space in proportion to their capacity, and this makes for great saving in the cost of foundations and housing accommodation, and sometimes enables them to be installed in some small space available in an existing engine room without calling for any additional building which might require to be provided should machines of a horizontal type be installed. It will be noted that the steam cylinders in these compressors are carried on the top of the air cylinders, and in this connection it may be recalled that a number of the latest firms who have taken up the manufacture of vertical enclosed compressors at first were disposed to have their steam cylinders arranged underneath, but after some experience they have been obliged to alter their designs and carry out a similar arrangement to that shown in the machines illustrated. Generally, all the Alley and MacLellan standard type air compressors have the steam cylinders fitted with valve gear of the piston type, steam entering in the centre of the valve of the valves being a multiple ported class, with the minimum of lift to reduce the chance of breakage to the least possible, but at the same time to secure, due to the multiple ports, a very large area, thus preventing exces- sive throttling of the air when passing to and from the cylinders. All the valves in Messrs. Alley and MacLellan’s machines have separate seats and guards, and can be removed readily without dismantling any heavy section of the compressor, and this is a point also generally essential in colliery work, where to have long stop-downs to examine or clean any detail of the machine creates endless trouble and expense, and has been guarded against wherever possible. The lubrication in these compressors is generally such as is common in all vertical enclosed class of recipro- cating engines or compressors, that is, of the forced system, with valveless oil pump, driven from the crank- shaft, and sufficient quantity of oil is stored in the crank ease to allow of the plant being run for long and con- tinuous periods with little or no attention. In the oil system there is, of course, also fitted all such necessary accessories as pressure gauge, pressure adjusting device, and oil relief valve, and oil filters, to v V ¥• 3 z. • '■A' • A Hi i® § ■ Steam-driven Vertical Two-stage Air Compressor. Vertical Two-stage Air Compressor, Arranged for Electric Drive. the use of compressed air underground in preference to electricity, as it is being more generally recognised that the air compressors such as are here illustrated are a very much different article from the old type of air compressors installed twenty or thirty years ago. The liigher efficiencies obtained and the better training that the present-day engineers have, make them more alive to the arrangements they must provide in collieries for the efficient use of compressed air. The plant, there- fore, now installed in any up-to-date colliery is in itself better suited to its condition, and the air which it may deliver is used in a much more efficient manner. With these two leading differences, there is no doubt whatever that there has been, and is likely to be more so in the future, a tendency to have more and more air used in underground work, and especially where there is danger from gas or other reasons likely to cause explosions, such as may take place through any accident or other cause in the use of electrical plant under similar conditions. The general outward appearance of such machines as are manufactured by Messrs. Alley and MacLellan gives the impression of great strength and solidity. and leaving at the ends, but all such cylinders are fully equipped with all necessary relief valves, drain cocks, indicator connections, and are thoroughly lagged and neatly finished with planished steel plates and brass bands. Carrying these steam cylinders are substantial, strong, distance pieces, with ample openings to allow of all stuffing boxes and glands being accessible for examination or re-packing whenever necessary. The air cylinders and covers of the compressors are of the simplest possible construction to ensure that good sound metal will be had in all parts, and it is necessary that special care and attention should be given to such points where a complication in a casting is very easily possible when water jackets are provided. Such complica- tions generally lead to unsound castings and faulty metal, and probably continuous trouble when plant has been set in operation. Messrs. Alley and MacLellan have therefore made it their special endeavour to make all parts most simple in form, and their success and the number of repeat orders have proven beyond doubt the soundness of some of these little methods as adopted in manufacture. The valve gear in the air cylinders of this latest model is automatic in action, and the design allow of the proper oil pressures being secured in the bearings, and to safeguard against the possibilities of any grit being fed with the oil to the bearings. With each of these two-stage compressors there are also supplied inter-coolers, and these are of the vertical type for the largest class of machines. In design they are of the contra-flow type, and in some instances are situated in the outside atmosphere rather than in the engine room, as, in the first place, better cooling effect is obtained outside, and, secondly, no available floor space is taken up, and both of these points are sometimes worthy of attention in the lay-out of such plant. The governing arrangements, as fitted to all such plant, consist of a maximum speed governor, together with an air controlling arrangement, which automatic- ally adjusts the output in accordance with the demand. The speed of the machine is automatically increased or decreased, due to the rise and fall of pressure in the system, and the controlling gear is very sensitive and simple, making for very close governing, and allowing practically a constant pressure to be obtained where the demands in the system are not of an exaggerated nature so far as fluctuations are concerned. These remarks in