HYDRAULIC MOTORS.

Pressure or Hydraulic Motorsform an interesting variety of hydraulic devices; they consist of working cylinders with valves and pistons, and resemble forcing pumps in their construction, but differ from them in their operation; the pistons not being moved by any external force applied to them through cranks, levers, etc., but bythe weight or pressure of a column of water acting directly upon or against the pistons. Pressure engines or motors are applicable to locations—such as afford a suitable supply of water for the motive column; but where-ever refuse, impure, salt or other water can be obtained from a sufficient elevation, such may be used to raise a quantity of fresh water by these machines.

The stress considered in hydro-mechanics is always a pressure, as liquids are in general capable of sustaining only a slight tension without disruption:the intensity of the pressure is measured by the number of units of force per unit of area. Thus we say, one thousand pounds of pressure per square inch of piston—the pounds and the square inches are the units used in these calculations.

Figs. 129, 130.For descriptionsee page 151.

The invention of pressure engines brought to light anewmode of employing water as a motive agent: and also the means of applying it in locations where it could not otherwise be used; with pressure engines the motive agent may be taken to the machine itself. In valleys or lowlands, having no natural fall of water, but where that liquid can be conveyed in tubes from a sufficient elevation (no matter how distant the source may be), such water, by these machines, may be madeto propel others; unlike the steam engine, a pressure engine is inexpensive, and simple in construction—it requires neither chimneys, furnaces nor fuel; neither firemen nor engineers, nor is there any danger of explosions. It may be placed in the comer of a room, or be concealed under a counter or a table. It may be set in operation in a moment, by opening a cock, and the instant the work is done, it may be stopped by shutting the same, and thus prevent waste of power.

Pressure engines afford an illustration of the variety of purposes to which apiston and cylindermay be applied. These were probably first used in piston bellows; next in the syringe; subsequently in pumps of every variety; and then in water-pressure and steam engines.The moving piston is the nucleus or elemental part that gives efficiency to them all; and the apparatus that surround it in some of them, are but its parts.

The history of machines composed of pistons and cylinders also illustrates the process by which some simple inventions have become applied to purposes, foreign to those for which they were originally designed—each application opening the way for a different one.

In another form hydraulic motors have been adopted, in favorable locations, as first movers of machinery, and when thus used,they exhibit a very striking resemblance to high pressure steam engines. Indeed, the elemental features of steam and pressure engines are the same, and the modes of employing the motive agents in both are identical—it is the different properties of the agents that induces a slight variation in the machines—one being an elastic fluid, the other a non-elastic liquid.

Fig. 131.

Fig. 132.

In steam engines a piston is alternately pushed forward and back in its cylinder by steam; and by means of the rod towhich the piston is secured, motion is communicated to a crank and fly-wheel, and through these to the machinery to be driven: it is the same with pressure engines when used to move other machines, except that instead of the elastic vapor of water, a column of that liquid drives the pistons to and fro.

Note.—“The hydraulic engine of Huelgoat, in Brittany, is used to drain a mine; is single-acting, and acts directly to lift the piston of the pump. It makes five and a half strokes per minute, the stroke being a little more than eight feet in length. The piston-rod is 767 feet long, and it weighs 16 tons. The power of the engine is derived from a source at a height 370 feet above its own level.”—Knight.

In default of a natural head of sufficient pressure, the head is sometimes established inan accumulatorof power; this is a body of water driven into a reservoir under heavy pressure, by forcing pumps worked by power. In cities where the water distribution is from elevated reservoirs, and in which the water supply is sufficiently abundant to justify the application of a portion of it to industrial uses, the water-engine or motor is recommended.

The following description of a water engine of world-wide adaptation will, if attentively studied, show the working of an approved type of this machine:

Ramsbottom’s hydraulic engine (Figs.129 and 130), is oscillating, and employs two cylindersb,l, operating one crank-shaft,a, by means of two cranks at right angles to each other. In one of the accompanying figures the channels of induction are markedjand are cast on the cylinders; the dotted circlecshows the position of the supply and discharge pipes; in the other figure these pipes are indicated by arrows. The two views are vertical cross-sections at right angles to each other, one being through the axis of the cylinders and the other through the middle post in which the inner trunnions of the cylinders are journaled. The apertures of induction are seen athand those of eduction ati, and have the form of truncated circular sectors, whose center is the center of motion.

The induction and eduction spaces are divided by a sectoral partition; the apertures of admission and discharge on the sides of the cylinders are of similar construction. The surfaces of contact between the cylindersb,land the supportdare planed and polished and are made water-tight by the adjusting screwsmmof the pivots. When the pistonpis at the end of its course in either direction the cylinder and crank are vertical,and the valves all momentarily closed, the openings by which the channelsjjcommunicate with the discharge and supply pipes presenting themselves exactly opposite the solid sectors which separatehfromi.

In the next moment the flow of water will recommence, the cylinder discharging itself from the full side of the piston, and filling anew from the opposite side. Air chambers and relief-valves are used as a provision against counter-pressure and hydraulic shocks.

The Brotherhood three-cylinder reciprocating engine is an appliance for producing rotary motion by water-pressure.

The working parts of the Brotherhood three-cylinder hydraulic engine consist only of the three pistons and connecting rods, one crank and one rotating balanced valve and spindle which fits into the driver and is turned direct from the crank-pin; there are no glands, stuffing boxes, or oscillating joints.

It is shown by Figs. 131, 132. The three cylinders, A (made in one casting) are always open at their inner ends, and are attached to a central chamber, B. They contain three pistons, P, which transmit motion to the crank-pin through the rods, C. The water is admitted and exhausted by means of the circular disc valve, V, having a lignum-vitæ seat. The valve is rotated by the eccentric pin, E. A face view of this valve is shown above the steam chest. It has segmental ports which, in rotating, pass over apertures in the valve seat. There being no dead centers, the engine will start from all positions of the crank-pin, and a uniform motion of the shaft is produced without a flywheel.

The pressure is always on the outer end of the piston, so that the rods, C, are in compression, and take up their own wear. This engine is well adapted for transmitting pressure to appliances which are worked intermittently, as, owing to the great speed at which it can be run, it will not only save the loss from friction (where gearing is employed), but will also reduce the friction in the machine itself by enabling the gearingfor increasing speed to be dispensed with. The production of this simple hydraulic rotary engine led to its wide application to capstans.

Fig. 133 represents a small hydraulic engine—The Compton Hydraulic Motor—attached to and operating a gas-compressor. It shows a style of water motor in large use in connection with city water-mains. A pressure of 15 to 20 lbs. per square inch is sufficient to operate it; the motor here illustrated occupies a floor space of 9 x 23 inches; it will supply gas burners to the extent of 6,000 candle-power.

Fig. 133.

The valve motion on the motor is unique in this, the outlets and inlets have a positive motion by which they are simultaneously opened and closed by the motion of the piston; this valve motion is designed to overcome the back pressure; it has a governor, incorporated in the valve-motion for the purpose of maintaining uniform pressure on the main pipes.

Generally speaking a packing is a contrivance or a material to close a joint. Various greasy materials with gaskets, flax, hemp, etc., are used in joints which are screwed down, also collars of rubber, red lead, luting, graphite, etc.

“U” Packing—Fig. 134.

A most important part in the practical working of nearly all water-pressure machines is the leather collar, the inventionof which by Bramah removed the difficulties which had been experienced in making the large ram work water-tight when submitted to great pressure.

It consists of a circular piece of stout leather(see cut page 20), in the center of which a circular hole is cut. This piece of leather is thoroughly soaked in water and is pressed into a metallic mould and so that a section of it represents a reversedU, and is fitted into a groove made in the neck of the cylinder. This collar being concave downwards, then in proportion as the pressure increases, the edge nearest the ram being trimmed down, it fits the more tightly against the ram plunger on one side and the neck of the cylinder on the other. It should be saturated with Neatsfoot or Castor oil so as to be impervious to water.

Cup Packing—Fig. 135.

When the least amount of friction possible is desired in the operating of a hydraulic plunger, there is no form of packing which can surpass a properly prepared and applied Leather “U” Packing(Fig. 134), and in practice its position is according to conditions, either in a groove near the upper end of the cylinder, or at the lower end of the ram.

When for any reason it is not desired to use the outer lip of the packing, the resulting form is known as a Cup Packing, (Fig. 135), and when the inner lip is used then we have the Hat or Flange Packing. Fig. 136.

Flange Packing. Fig. 136.

When the water pressure is not over 2,000 lbs. to the square inch, and a greater allowance for friction is not important, a fibrous packing can be used, which is easier of application than these for large sized cylinders.

The loss of power by the best of leather packings is 1 per cent. on 4 in. ram,1⁄2per cent. with 8 in. ram and1⁄4per cent. with 16 in. ram.

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