noun
definition
A solid disk or cylinder that fits inside a hollow cylinder, and moves under pressure (as in an engine) or displaces fluid (as in a pump)
definition
A valve device in some brass instruments for changing the pitch
verb
definition
To move up and down like a piston.
Examples of piston in a Sentence
The cylinder, in which a well-fitting piston worked, was provided at its lower end with two valves.
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 piston rod passes through a valve in the upper part of the cylinder which is held to its seat by a spring.
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.
In practice it may be considerably less, owing to leakage at the valves and between the piston and cylinder.
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.
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.
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.
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.
If a thrust P lb is applied to one piston of area A ft.
A closely-fitting adjustable piston is provided at one end.
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.
It then takes in heat from the furnace, expanding in volume and forcing the piston (B) to rise, which completes the cycle.
During the down stroke of the piston the wing is flattened out in every direction, and its extremities twisted in such a manner as to form two screws, as seen at a' b' c' d', e' f' g' h', B, B'.
A small pilot piston is attached to the bottom of the spool valve.
Distribution of steam is effected by a slide valve, sometimes fitted with a balancing device, and sometimes formed into a piston valve.
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.
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.
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 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.
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.
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.
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.
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.
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 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.
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.
It has been shown that this behaviour of dielectrics can be imitated by a mechanical model consisting of a series of perforated pistons placed in a tube of oil with spiral springs between each piston.
In the first method reciprocating bells, or piston machines, or rotary machines of varying capacity like gas-works exhausters, are employed.
This machine depended simply on the pressure of water acting directly in a cylinder on a piston, which was connected with suitable multiplying gear.
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.
Boulton and Watt's screw press, invented in 1788 and used at the Royal Mint until 1881, was worked by atmospheric pressure applied to a piston.
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.
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.
Then the variation of the cubic contents of the vessel in a unit of time by reason of the motion of one piston is Va.
In the pneumatic power-transmitter the motion of one piston if transmitted to another at a distance by means of a mass of air contained in two cylinders and an intervening tube.
Reciprocating PiecesStrokeDead-P o-jnts.T he distance between the extremities of the path of the connected point in a reciprocating piece (such as the piston of a steam-engine) is called the stroke or length of stroke of, that piece.
In balancing the mechanism of a steam engine it is often sufficiently accurate to consider the motion of the pistons as simple harmonic, and the effect on the framework of the acceleration of the connecting rod may be approximately allowed for by distributing the weight of the rod between the crank pin and the piston inversely as the centre of gravity of the rod divides the distance between the centre of the cross head pin and the centre of the crank pin.
A more accurate though still approximate expression for the force on the frame due to the acceleration of the piston whose weight is W is given by w2r cos 0 + r cos 20
The lower portion of the neck was occupied by a piston and cup, in and on which the toe of the spindle worked.