The cylinder, in which a well-fitting piston worked, was provided at its lower end with two valves.
The total upward pressure on this piston is calculated to be equal to 150,000 lb; hence the shaft-bearings are practically relieved from pressure when the wheels are running.
Even then, however, the amount of operative heat is very small in comparison with that which passes through the steam-engine, per cubic foot swept through by the piston, for the change of state which water undergoes in its transformation into steam involves the taking in of much more heat than can be communicated to air in changing its temperature within such a range as is practicable.
There are three Li ting - typical methods: (I) A direct pull may be applied to the hook, either by screws, or by a cylinder fitted with is piston and rod and actuated by direct hydraulic or other pressure, as shown diagrammatically in fig.
In a particular case where the boiler pressure was maintained constant at 130 lb per square inch, and the cut-off was approximately 20% of the stroke, the values c =55 and b=o 031 were deduced, from which it will be found that the value of the piston speed corresponding to the maximum horsepower is 887 ft.
On again F J J raising the piston the valve E opens ?g G admitting more liquid whilst F re- mains closed.
The air inside is compressed in consequence and during an upstroke of the piston this air tends to regain its original volume and so expels the water, thus bringing about a continuous supply.
P. Joule with the perforated piston and with the friction of water and mercury.
I shows the arrangement in a suction pump. A is the cylinder within which the piston B is moved up and down by the rod C. D is the inlet pipe (the lower extremity of which is placed beneath the surface of the liquid to be G removed), and G is the outlet pipe.
E is a valve in the inlet pipe opening into the cylinder; and A the piston is perforated by one or more holes, each fitted with valves opening outwards on its upper surface.
In practice it may be considerably less, owing to leakage at the valves and between the piston and cylinder.
In this case the piston is solid, and the outlet pipe, G which is placed at the bottom of the cylinder, has a valve F opening outwards, the inlet pipe and valve are the same as before.
In A there is a displacer (D) which is connected (by parts not shown) with the piston in such a manner that it moves down when the piston has moved up. The air-pressure is practically the same above and below D, for these spaces are in free communication with one another through the regenerator (E), which is an annular space stacked loosely with wire-gauze.
The piston (B) descends, and the air, now in contact with the cooling pipes (C), gives up heat to them.
It then takes in heat from the furnace, expanding in volume and forcing the piston (B) to rise, which completes the cycle.
Let a represent the area of the section of a piston made by a plane perpendicular to its direction of motion, and v its velocity, which is to be considered as positive when outward, and negative when inward.
Any modification of the design which will reduce the resistance to the flow of steam through the steam passages at high speeds will increase the piston speed for which the indicated horse-power is a maximum.
The distribution of steam to both cylinders is effected by one piston-valve operated by a link motion, so that there is considerable mechanical simplicity in the arrangement.
In this engine the two piston-rods of one side are not coupled to a common cross-head, but drive on separate cranks at an angle of 180°, the pair of 180° cranks on each side being placed at right angles.
The unbalanced masses of a locomotive may be divided into two parts, namely, masses which revolve, as the crank-pins, the crank-cheeks, the couplingrods, &c.; and masses which reciprocate, made up of the piston, piston-rod, cross-head and a certain proportion of the connecting-rod.
The simplest forms of pumps employed for forcing liquids are "plunger pumps," consisting essentially of a piston moving in a cylinder, provided with inlet and outlet pipes, together with certain valves.
This machine depended simply on the pressure of water acting directly in a cylinder on a piston, which was connected with suitable multiplying gear.
F, Piston-rod for lifting driving it down.
Sand, driven between the wheel and the rail by a steam jet, used just at starting, increases the adhesion beyond the normal value and enables a larger pressure to be exerted on the piston than would otherwise be possible.
164.) Substituting this value of p in (27) I.H.P. _ (c av (29) 550 the form of which indicates that there is a certain piston speed for which the I.H.P. is a maximum.
On raising the piston the liquid rises in the cylinder, the valve E opening and F remaining shut.
It is seen that the action is intermittent, liquid only being discharged during a down stroke, but since the driving force is that which is supplied to the piston rod, the lift is only con ditioned by the power available and by the strength of the pump. A continuous supply can be obtained by leading the delivery pipe into the base of an air chamber H, which is fitted with a discharge pipe J of such a diameter that the liquid cannot escape from it as fast as it is pumped in during a down stroke.
Thus, at every complete stroke of the piston, the air in the vessel or receiver was diminished by that fraction of itself which is expressed by the ratio of the volume of the available cylindrical space above the outward opening valve to the whole volume of receiver, nozzle and cylinder.
The piston, provided with a valve opening upwards, is packed in the cylinder by a leather cup which is securely pressed against the sides of the cylinder by the atmospheric pressure.
The piston rod passes through a valve in the upper part of the cylinder which is held to its seat by a spring.
The action is as follows: On raising the piston it cuts off communication with the inlet pipe and then compresses the air above, forcing it through the upper valve and oil into the atmosphere.
Some of the oil is also driven out, but as the valve does not close until the piston has descended a short distance, a certain amount of oil returns.
On lowering the piston its valve opens and air passes in from the vessel to be exhausted; this is further rarefied on the next stroke and so on.
Every drop of mercury, as it enters from the funnel, entirely closes the narrow tube like a piston, and in going past the place where the side tube enters entraps a portion of air and carries it down to the trough, where it can be collected.
If a thrust P lb is applied to one piston of area A ft.
2, it will be balanced by a thrust W lb applied to the other piston of area B ft.', where p = P/A=W/B, (I) the pressure p of the liquid being supposed uniform; and, by making the ratio B/A sufficiently large, the mechanical advantage can be increased to any desired amount, and in the simplest manner possible, without the intervention of levers and machinery.
In the first method reciprocating bells, or piston machines, or rotary machines of varying capacity like gas-works exhausters, are employed.
Hence, when in 1850 a hydraulic installation was required for a new ferry station at New Holland, on the Humber estuary, the absence of water mains of any kind, coupled with the prohibitive cost of a special reservoir owing to the character of the soil, impelled him to invent a fresh piece of apparatus, the "accumulator," which consists of a large cylinder containing a piston that can be loaded to give any desired pressure, the water being pumped in below it by a steam-engine or other prime mover.
31, a loosely S fitting cork or card piston being fixed on one end of the sounder, which is inserted within the dust-tube.
Stationary waves are formed in the air in the dust-tube if the length is rightly adjusted by the closely-fitting piston, and the lycopodium dust collects at the nodes in little heaps, the first being at the fixed end and the last just in front of the piston on the sounder.
A piston made of such a perforated substance, therefore, may be used to exert pressure on the liquid, while all the time the vapour is able to pass.
The simplest way to do this is to imagine a vapour-sieve piston through which the vapour but not the liquid can pass.
Let us imagine unit mass of solution of volume V confined in a cylinder ABC between a fixed vapour sieve B and a solid piston A A B C FIG.
The vapour at pressure p in equilibrium with the liquid is bounded by a solid piston C, which we can also move to change the pressure or volume.
If it be filled with a solution and the bottom immersed in the pure solvent, pressure equal to the osmotic pressure must be exerted on the piston to maintain equilibrium.
This tup is raised and driven down by steam pressure applied below or above the piston E of the steam cylinder mounted aloft, and connected with the tup by means of the strong piston-rod F.
The expression for the indicated horse-power may be written I.H.P. =pay/550 (27) where v is the average piston speed in feet per second.
During the down-stroke of the piston the former was pressed home, so that no air entered the nozzle and vessel, while the latter was forced open by the air which so escaped from the cylinder.
This type of pump is, however, not very efficient, for there is not only leakage about the valves and between the piston and cylinder, but at a certain degree of exhaust the air within the vessel is insufficient to raise the inlet valve; this last defect has been met in some measure by using an extension of the piston to open and close the valve.
The so-called oil air-pumps are much more efficient; the valve difficulty is avoided, and the risk of leakage minimized; whilst in addition there is no air clearance between the piston and the base of the cylinder as in the older mechanical forms. The Fleuss pump may be taken as an example.
These machines, which are driven by compressed air, are very handy in use, as the height and direction of the cut may be readily varied; but the work is rather severe to the driver on account of the recoil shock of the piston, and an assistant is necessary to clear out the small coal from the cut, which limits the rate of cutting.
A closely-fitting adjustable piston is provided at one end.
For a stated value of the boiler pressure and the cut-off the mean pressure p is a function of the piston speed v.
On raising the piston, the valve F remains closed and a vacuum tends to be created in the cylinder, but the pressure of the atmosphere forces the liquid up the tube D and it raises the valve E and passes into the cylinder.
On again raising the piston, more liquid enters the lower part of the cylinder, whilst the previously raised liquid is ejected from the delivery pipe.
The piston was in communication with a vacuum vessel from which the air had been pumped by steam power.
The area B of the top side of the upper piston is proportioned in such a way that when under the full water pressure the dead weight of the ram and cage is just balanced when the former is at the bottom of its stroke.
Fred grumbled, but Dean just slapped his back and began to whistle, as if he didn't have a care in the world, while his mind turned like a racecar piston on the final lap.
To the piston P. The newly coated wire is passed through a long trough T, containing cold water, until it is sufficiently cold to allow it to be safely wound on a bobbin B' This operation completed, the wire is wound from the bobbin B' on to another, and at the same time carefully examined for air-holes or other flaws, all of which are eliminated.
To allow the lift-ram to descend, the pressure-water in C above the lower balance piston is discharged through the exhaust into the drain, while that above the upper piston is simply pushed back into the pressure main.
A highand low-pressure cylinder are cast together, and the piston-rods belonging to them are both coupled to one cross-head which is connected to the driving-wheels, these again being coupled to other wheels in the usual way.
Below the piston of the upper cylinder is an annular space E (surrounding the common piston rod) with a capacity equal to the maximum displacement of the liftram, while the corresponding annular area C of the piston of the lower cylinder is just large enough when subjected to the working water pressure to enable the work of lifting the net load to be done and any friction to be overcome.