In the course of our notice of the recent Show of the Royal Agricultural Society at Birmingham, we had occasion to mention a new steam pump, constructed on Messrs. Parker and Weston's patent, which was exhibited there. Of this pump, which is manufactured by the Coalbrookdale Company, Shropshire, we now give engravings, our illustrations showing two different arrangements. The distinguishing feature of this pumping engine, as in all others of the direct acting class, consists mainly in the valve movement in the steam cylinder. In designing this valve motion the patentees had two objects in view, firstly, to get a positive motion by means of a simple valve moved by the steam alone without the use of tappets and other extraneous gear, and, secondly, to use the steam expansively in the cylinder. How this is accomplished will be readily understood from the accompanying illustrations.

Two forms of main steam valve are used, one being an adaptation of the old Cornish valve, as shown in Figs. 1 to 7, and the second being a common slide valve moved by two pistons in exactly the same way as the preceding, and shown on Figs. 9 to 13. It was a pump fitted with the latter arrangement which was shown at Birmingham.

In our engravings, Fig. 1 is a longitudinal section of the steam cylinder and valve chest. A is the steam space in the centre of the chest, B B are the steam valves; these are in one piece, and fixed to the steel spindle b; C C' are the exhaust valves; D D' are the valve pistons, which are cast in one piece with the exhaust valves. The valve chest is semicircular in form, and has four diaphragms cast across it; these have circular seats formed upon them, against which the valves work, the steam valves opening towards the centre, and the exhaust valves opening outwards. The valves are made of cast iron, and owing to the short travel and the ease with which they come against their seats, they are found to work a long time without any appreciable wear.

Fig. 2 is a plan of the cylinder with steam chest removed. The steam and exhaust branches are cast on the cylinder, and the steam chest can, therefore, be removed without disturbing the pipes. E E' are the main ports to the cylinder, and F F' the exhaust passages; G G' are passages leading from the cylinder to the spaces behind the valve pistons D D'; in these passages are inserted the ball valves H H'. These work in brass cages, and are accessible from the outside by unscrewing the brass plugs shown on Fig. 3. The use of these ball valves will be seen as we proceed.

The motion of the valve is as follows: Suppose the space A to be filled with steam and the main piston to be travelling in the direction indicated by the arrow, as shown on Fig. 1, steam would then pass through the valve D and fill the Z end of the cylinder. The series of valves would remain as shown until the main piston passed over the reversing port G'; when the live steam rushes up the opening and blows the ball H' against the passage into the main steam port and fills the space behind the valve piston D'. As the opposite end D is at the same time exposed to the pressure of the live steam from being in communication with the Z end of cylinder the two valve pistons DD' are thus placed in equilibrium.

The surface of the exhaust valve C' has only the exhaust pressure upon it, whilst C has the full pressure of the steam; this preponderance of pressure on C causes the whole series of valves to be instantly shot over and the Z end of cylinder put in communication with the exhaust. The steam then fills the opposite end of the cylinder and the main piston moves in the opposite direction, when the piston uncovers the hole G, and the same motion of the valves takes place at the other end.

The ball valves play an important part in insuring the certainty of action of the main steam valve. It has already been stated that when the piston passes the reversing hole G', the entering steam blows over the ball, closes the opening to steam port at P (see fig. 3), and allows the steam to get behind the valve piston D'. The instant the valve is reversed the port E is filled with steam, and the end of the cylinder Z placed in communication with the exhaust; but by this time the piston has not moved sufficiently far on the return stroke to cover the reversing port G'; this is now also open to the exhaust, which would have the effect of releasing the pressure from behind the piston D', and thus destroy the stability of the valve movement.

But the steam from the port E at this instant blows the ball over and closes the connection with the cylinder through the passage G', and allows the full pressure of steam from the port E to be kept on the piston D', thus holding all the valves on their seats during the stroke of the engine. The motion of the valves is absolutely certain, even at a crawling speed, and must give a full opening for steam and exhaust at every stroke, thus differing from those steam-moved valves, whose steam admission depends upon the use of tappets, the main valves of which cannot be insured to move the full travel when the engine is working at a slow speed.

The expansion of the steam in the cylinder is effected by means of a valve entirely distinct in its action from those which control the main piston. The steam is admitted through a branch on the side of the cylinder, and then passes by an oblong shaped port to the centre of the steam chest through the expansion valve. The time of the admission of steam to the upper part of the chest is regulated by a circular valve M (see Fig. 4), which can be raised at any desired point of the stroke by the admission of the steam under its lower surface. This under surface being of greater area than the top, the pressure of steam upon it overcomes the resistance of the incoming steam by raising the valve, cuts that steam off from the steam chest. The construction and action of this valve will be readily understood by reference to the Figs. 4 and 8. K is a hole running parallel with the cylinder, and bored throughout its entire length, and in this hole is fitted a brass tube s; this tube is turned round by means of the spindle and hand wheel, and is kept steam tight by the stuffing box at the end.

Holes are drilled at intervals along the cylinder corresponding to the various points of cut off. The tube is also perforated, but not in the same horizontal line as the steam cylinder. By turning the tube round, one of the holes at each end is brought opposite a corresponding hole in the cylinder. When the piston passes those holes the steam rushes along the tube, opens the valve L, and raises the expansion valve M, abutting off the further supply of steam to the chest, and allowing the steam already in the cylinder to expand to the end of the stroke. The use of the valve r in the tube is to prevent the cut off taking place before half stroke. The valve between its faces is longer than the distance between the seats; one or both ends of this valve can thus be open at one time. It is obvious, therefore, that as the piston travels over the holes o, p, q, the steam would find its way along the tube and raise the expansion valve, but the steam shuts the valve r until the piston has uncovered the required hole on the other side of the centre, when the valve being thus put into equilibrium the steam finds its way below the expansion valve and produces the desired result. By an exceedingly simple arrangement the expansion valve is made to serve the purpose of a cataract governor, and causes the engine to pause at each end of the stroke.

This is effected by placing a small valve (marked L in Fig. 4, and l in Fig. 8) in the passage leading to the expansion valve; this valve opens upwards for the admission of steam, the exhaust from the underside of the expansion valve takes place through a small orifice, the area of which is regulated by a screw (not shown on the engraving); by this means the engine can be made to pause at the end of the stroke, as no new steam can be admitted to the chest until the expansion valve is allowed to open.

Figs. 1 to 8, above referred to, show the valve gear as applied to a direct acting pumping engine with an 18 in. steam cylinder, and 8 in. pump with 36 in. stroke, now at work in a colliery in South Wales and forcing 1300 gallons per hour to a height of 252 ft.

The makers are also preparing a compound pumping engine on the same principle, steam being carried to half stroke in the high pressure cylinder, then passed into a low pressure cylinder of three times its capacity and afterwards discharged into a condenser. From diagrams which have been taken from some of these engines the saving in steam is seen to be very marked, and this fact removes the objection commonly urged against this class of pumping engine on the score of comparatively great expenditure of steam.

As we have remarked on former occasions, the economy of steam in compound direct-acting engines cannot be excelled by the best form of Cornish pumping engines, while with the former type the first cost is a mere fraction of that incurred with the latter. Figs. 9 to 13 show another form of steam moved valve, consisting of a semicircular slide valve moved by two pistons. Fig. 9 is a section through steam chest.

The slide valve is made in a separate piece from that forming the piston l' and the centre c, and has merely end contact with them; the pressure of steam acting on the back of the valve keeps it tight to the face as in a common slide valve. The steam is admitted to the chest through an expansion valve d.

In Figs. 11, 12, and 13, f f' are passages communicating with the main steam cylinder and the small cylinder in which the valve pistons l l' work. In these pistons small ports are formed having certain relative positions to the aforesaid passages f f'. Other passages g g', lead directly from the main steam ports to the outer end of the valve cylinder, and h h' are passages from the steam ports to the inner end of the valve cylinders. Suppose the piston to be travelling in the direction of the arrow, the slide valve would be in the position shown in Figs. 9, 10, and 11, and steam would be passing through the steam port k, and filling the end of the cylinder z. Under these conditions live steam is also filling the passages g and h, and acting on both sides of the piston l, at the same time the exhaust is passing out from the end of cylinder y through the main port under the slide valve, and thence to the atmosphere or condenser; both sides of the piston l' are also open to the exhaust.

The valve is retained in this position until the completion of the stroke of the engine by the pressure on the outer or larger side of the piston l'. When the main piston uncovers the hole f' the steam rushes through and fills the space behind the valve piston l', and thus the outer sides of both the valve pistons are subjected to equal steam pressures, but the inner surface of l has the live steam on it whilst the inner surface of l' has only the exhaust pressure, the extra pressure on l therefore shoots the valve over to the opposite end.

As the main piston in reversing has to pass back over the passage f' there might be a slight tendency of the valve to falter, or not to travel the whole distance, owing to the slight loss of pressure which would occur behind the piston l' when the main piston was passing the hole. This is prevented by the following means: Let the slide valve open by only the smallest amount, the main steam port will be filled with steam at the same time the outer end or the valve piston l' will have uncovered the passage g', and admitted a second supply of steam behind the piston 1'.

By this time also both sides of 1 will be open to the exhaust which has taken place in the z end of cylinder, and the valve is thus carried the full stroke by the pressure acting on the outer end of piston l'. It will thus be seen that there are two distinct causes at work to move this slide valve, following each other with a rapidity and certainty that has never been excelled in any single steam-moved valve. The motion can be perfectly cushioned by the small quantity of steam squeezed up on the inner side of the piston l' when it crosses

the opening h'. Altogether the arrangements of valve gear we have described have been very ingeniously and carefully worked out, and we expect hereafter to have more to say concerning the pumping engine to which these arrangements have been fitted.