Davey Paxman Horizontal Fixed Steam Engines
The Class B Engine

Introduction:   The Davey Paxman Class B horizontal steam engine was launched at the 1879 Royal Agricultural Show. It was more powerful than the Company's earlier range of horizontals which became known as Class A, and had a more sophisticated cut off valve arrangement. As the range was developed it became available in coupled compound, tandem compound and condensing versions as well as the basic single cylinder form. The description below is taken verbatim from a Paxman catalogue thought to have been issued in late 1913 or in 1914. It will be seen that a major advantage claimed for this type engine was its simplicity and reliability.

The ordinary slide-valve engine is without doubt the most reliable type of steam engine it is possible to purchase, and although not so economical in steam consumption as a modern drop-valve engine, yet for simplicity, smoothness of running, ease of management, and general trustworthiness it is unsurpassed; and even with the slide-valve engine it is possible to secure very satisfactory economy in steam consumption if the engine selected is of the compound type, and a condenser is added. In many districts, where the engine drivers or attendants available are totally unskilled, the advantages possessed by the slide-valve engine in the way of reliability, freedom from breakdown and expensive repairs, usually far outweigh such a consideration as steam consumption; in fact, in many such circumstances, this is the only permissible type of engine to instal, as its construction and management can be readily grasped by the most unintelligent native driver. Such considerations make it particularly well adapted for export to far-Eastern markets, such as India, China, the Straits Settlements, &c. In addition, it is worthy of note that when once the valves are correctly set, they require no further adjustment.

Class B Engine - Coupled Compound type

We make our class "B" engines to fulfil the foregoing conditions of the single or double-cylinder types, working pressure 90 lb. per square inch, also coupled-compound, and tandem-compound types, for working pressures up to 140 lb. per square inch. In comparing our engines with other makes, we would particularly request intending purchasers to note that we have not followed the general plan which is adopted by most makers of this type, of largely increasing the piston speed, so as to obtain the utmost possible power out of the engine, preferring rather to adhere to comparatively low piston speeds at which the wear is infinitesimal.

From the illustrations and dimensions, it will be seen that our class "B" series of engines is very powerful, compact, and all wearing parts are easy of access.

Bed.   The Bed of the engine is exceptionally rigid, being of the bayonet type, the trunk end forming sliding surfaces of large area for the crosshead slippers, while the front end carries the main bearing for crankshaft.

Cylinder.   The Cylinder is made with a special separate liner, and is supported on a broad foot, secured by suitable holding-down bolts. The illustration on page 18 shows a "right-hand" engine, that is to say, one with the flywheel on the right-hand side of the engine looking from cylinder end. A "left-hand" engine is always supplied unless we receive instructions to the contrary.

Feed Pump.   A Feed Pump, worked by an eccentric from the crankshaft, can be supplied at an extra charge if required.

Paxman Automatic Expansion Gear.   The single-cylinder range of engines can all be fitted with this gear, as shown in illustration, at an extra charge, but in the case of the compound type the standard equipment includes Paxman automatic expansion gear on the high-pressure cylinder, by means of which it is possible to secure great economy in steam consumption when running with varying loads.

Lubrication.   Great attention is paid to the efficient lubrication of all working parts, and a sight-feed lubricator is provided for the cylinder.

Governor and Valve Gear.   The range of single-cylinder engines are fitted with single slide valve, driven by an adjustable and reversible eccentric, and Paxman's improved quick-speed governor working on to a throttle valve; all the compound engines have automatic expansion gear, as previously mentioned.

Flywheel.   This is of suitable size and weight for giving off the full power of the engine, and can if required be supplied grooved for rope driving at an extra charge. Unless otherwise ordered, the flywheel is arranged to run "out," that is to say, the top of the wheel revolves away from the cylinder, looking from the cylinder end. An outer bearing is supplied for supporting end of crankshaft beyond the flywheel.

Fittings.   These are of the best quality, and comprise: Stop valve, sight-feed lubricator on cylinder, large lubricators, cylinder drain cocks, complete set of spanners, oil can, and foundation bolts and plates.

Condenser.   We would refer clients to our previous remarks as to the advisability of installing a condenser when water is easily obtainable, as by this means it is possible to increase the power of the engine by about 10% to 20% with the same consumption of steam, or it will be possible to obtain the powers mentioned in the tables with a proportionately decreased consumption of steam.

Paxman Patent Automatic Expansion Gear

This automatic valve gear consists of two slide valves, one main and one cut-off, the latter deriving its motion from a link, the ends of which are connected to eccentrics called "Positive" and "Negative." Each eccentric has a different travel, the positive giving a late, and the negative a very early cut-off. The stroke of the link is controlled by the Governor, which thus determines the amount of steam admitted to the cylinder. The cut-off valve moves on a ported plate, which lays upon the main valve, loosely fitting the steam chest, and the ports themselves are doubled, thus halving the travel of the cut-off slide, and increasing the sensitiveness of the governor's control. The advantage of this arrangement is that, whilst a constant lead is maintained, the point of cut-off can be varied to any degree, without wire-drawing.

The specifications of the engines offered in the catalogue are as follows:

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Page updated: 05 JAN 2009