To understand how a hydraulic press works, let's remember the rule of communicating vessels. Its author Blaise Pascal found that if they are filled with a homogeneous liquid, then its level in all vessels is the same. In this case, the configuration of the containers and their dimensions do not matter. The article will describe several experiments with communicating containers that will help us understand the structure and principle of operation of a hydraulic press.
Let's say we have communicating vessels with different cross-sectional areas. We denote the area of the smaller one by s, the larger one - by S. Let's fill the containers with liquid. According to the law of communicating vessels, the surfaces of liquids are at the same height.
Let's close the vessels from above with pistons. We can assume that s and S are the areas of the pistons. Press on the smaller one with force f. It will go down, the liquid willflow into the larger cylinder, and the piston on the left will begin to rise. In order to prevent him from rising, we will also apply force to him. Denote it F.
To get closer to understanding how a hydraulic press works, let's try to find a connection between these two forces. We will proceed from the equilibrium condition. Before we covered the vessels with pistons, the liquids were in equilibrium. The pressure in the tanks was the same (p=P). Press down on both pistons so that the liquid still remains in balance. The pressures p and P will, of course, increase. However, they will still remain the same, because they will increase by the same additional amount. This is the amount of pressure created by the pistons. It is transmitted everywhere according to Pascal's law.
Here is the equilibrium condition: p=P. You can consider the pressure created by the pistons, or the pressure of the liquid column. The result will be the same. Note that the pressure created by the pistons is a thousand times greater than the hydrostatic pressure of the liquid column. A column of water a few centimeters high creates a pressure of hundreds of pascals. And the piston pressure is hundreds of kilopascals, and sometimes megapascals. Therefore, in what follows we will neglect the pressure of the liquid column and assume that the pressures p and P are created exclusively by the forces f and F.
Dependence of the pressure force of the pistons on their area
Let's derive the formula, the principle of operation of the hydraulic press without it will be incomprehensible. p=f/s and similarly P=F/S. Let's make a substitution into the equilibrium condition. f/s=F/S. And now let's compare the forces f and F. To do this, both the left and right parts of the expressionmultiply by S and divide by f. We get fS/sf=FS/Sf. Let's cancel f and S in both parts. The result will be the equality F/f=S/s.
The concept of winning is valid
If S>s, then the pressure force on the piston in the large vessel will be as many times greater than the force that presses on the small piston, how many times the area of the larger piston exceeds the area of the small one. In other words, by applying a small force to a small piston, in a large vessel we will get a force much greater than that with which we press on a small piston. This is an effect called gain in strength. It shows how many times the forces differ, i.e., what is the ratio of F to f. If we take vessels whose cross-sectional areas are very different, then we can get a gain in strength by a factor of ten or a thousand. Force analysis makes it clear: the gain in force is equal to the ratio of the areas of the large and small piston.
Movement of the pistons of a hydraulic machine
Many industries use the principle of the hydraulic press: physics, construction, material processing, agriculture, automotive, etc. Examples of the application of hydraulic machines are shown in the figure.
Let's consider all the same two communicating vessels with pistons, but now we will pay attention not to the force, but to the distance that the pistons travel when moving. Imagine that their initial position is different. The piston with area S is located below the piston with area s. Let's move the smaller piston at a distance h. Water from a smaller vessel passed into a larger one andpressed on the piston. He moved to height H.
Knowing the ratio between the areas, we find the ratio between the heights. The volume that went under pressure from the left cylinder to the right one is denoted by v. A liquid of volume V entered the right cylinder. The liquid is incompressible. How can this be written mathematically? v=v. Express volume in terms of area and height. v=sh and V=SH. So sh=SH. S/s=h/H. Therefore, the gain in strength is F/f=h/H. This ratio gives us an understanding of how a hydraulic press works. We conclude that since F is greater than f, then H is less than h, and by the same factor.
Let's say a hydraulic machine gives a hundredfold gain in strength. This means that if we lower the smaller piston by 100 mm, the other piston will rise by only 1 mm. And there are machines that give a gain in strength a thousand times. But what about when there is a car on the piston and it needs to be raised to a height of several meters?
Design and principle of operation of the hydraulic press
In the piston of a small area there is a valve that closes the tube leading to the engine oil reservoir. Water is generally not used in hydraulic presses because it is corrosive and has a relatively low boiling point. The piston drives the handle. Fluid is transferred from the smaller cylinder to the larger one through a tube.
The large vessel also has a valve and a piston. When we raise the lever, the oil, with the help of atmosphericpressure is sucked into the smaller cylinder. When we lower the piston, the valve closes, there is nowhere for the oil to go, so it goes into a larger vessel. It lifts the valve in it, the volume of oil increases, because of this the piston rises. When we raise the small piston again, the valve in the large vessel closes, so the oil does not go anywhere and the piston remains in place.
The principle of operation of the hydraulic press is such that any oscillation of the small piston always leads to the movement of the large piston upwards. The device has a mechanism that allows the large piston to descend. This is a hose with a faucet in a larger vessel. When we close the tap, we seal the big cylinder, and when we open it, we return the hydraulic press to its original position, the oil drains. It returns to the reservoir, which allows the piston to be lowered.