Why are hydraulic rods so powerful? Can human power fight against hydraulic arms? A syringe will do

Hydraulic rods are widely used in our lives, from small beds with storage functions and swivel chairs with lifting functions to large excavators, construction cranes and forklifts, etc., all of which use hydraulic technology.

With hydraulic rods, many things that are very laborious become very easy. For example, if a bed with storage function is not installed with hydraulic rods, we need to spend a lot of effort to lift the bed board. After installing the hydraulic rods, we only need to gently pull it, and the hydraulic rods will easily lift the bed board. This is even more true in engineering machinery. No matter how hard the soil and rocks are, the excavator can dig them up with hydraulic technology.

So the question is, even the hydraulic rod on the excavator does not look very thick or large, so why is this small hydraulic rod so powerful?

We can simplify the hydraulic rod as a piston filled with liquid. To explain the principle of the hydraulic rod, we must first mention a person, that is the French mathematician and physicist Blaise Pascal, who proposed a law in 1653, namely "Pascal's Law".

Pascal's law is also known as the "static pressure transmission principle". This principle states that the pressure applied at any point in a closed liquid will be instantly transmitted to all parts of the liquid, and the magnitude of the pressure will not change.

To put it more simply, if the static state of the liquid does not change, then if we apply a pressure to any part of the liquid, the pressure at every point in the liquid will change by the same amount. With this law, Pascal invented the syringe based on it. Yes, the syringe we use for injections now was invented by this physicist.

Because in a closed container, the pressure applied to the static liquid will be transmitted to each point at the same time, so when we push the syringe, the liquid is squeezed out at the needle tip.

In fact, the hydraulic rod is a syringe, and to push this syringe easily, we only need another small syringe. Suppose now we have a large syringe with a diameter of 4 cm and a small syringe with a diameter of 1 cm. We connect the two syringes with a tube and fill them with liquid. Then we ask someone to push the large syringe and the small syringe respectively. Who will win? Of course, the one who pushes the small syringe. Why? Because the pressure of the liquid is equal to the applied pressure divided by the force area, that is, when the applied force is the same, the smaller the force area, the greater the pressure of the liquid.

The diameter of the small syringe is 1 cm, and its force-bearing area is about 0.79 square centimeters. The diameter of the large syringe is 4 cm, and its force-bearing area is about 12.56 square centimeters. That is to say, the force-bearing area of ​​the large syringe is about 16 times that of the small syringe. Therefore, when the force applied is the same, the pressure generated by the small syringe is 16 times that of the large syringe, so the small syringe can easily push the large syringe.

Now we understand that we can imagine the hydraulic rod as a mechanical system composed of two pistons of different thicknesses. The small piston can give the large piston a devastating force with just a slight force. With this understanding, we only need a small syringe to fight against the powerful hydraulic arm.

Let's do a fun and imprecise calculation.

The most common large-scale machinery that uses hydraulic technology is the excavator. I am not sure how thick the hydraulic arm on the excavator is, but it is too thick to be held by one hand. Even if its diameter is 10 cm, its force area is 78.5 square centimeters. The digging force of the general excavator arm is about 10,000 kg, so how much thrust does a person have? It should not be a problem for an adult to push 100 kg, which means that the force of the excavator is 100 times that of manpower, so we only need a small syringe with a force area of ​​1/100 of the hydraulic arm of the excavator to obtain the same force as the excavator, and a syringe with a force area of ​​0.785 square centimeters has a diameter of about 1 cm, so we only need a small syringe with a diameter of 1 cm to tie with the excavator.

Of course, this is only in theory. In reality, the syringe is not strong enough, so it may explode during a confrontation. The explosion of the swivel chair hydraulic rod is due to the same reason, that is, the instantaneous pressure value exceeds the bearing capacity of the inner wall of the hydraulic rod.

So how can we avoid the explosion of hydraulic rods? If it is a regular product produced by a regular manufacturer, theoretically the material strength should be pressure tested, and generally there is no problem, but the problem is that many people cannot be sure whether their chairs are qualified products, so what should we do? Manually install an explosion-proof steel plate. I installed a small steel plate of 30 cm square above the hydraulic rod under the swivel chair. It costs 300 yuan and is said to be bulletproof. We use the example of "large and small syringes" just to illustrate the basic principle of hydraulic rods. In fact, the hydraulic rod in hydraulic machinery is not pushed by a small syringe. On the one hand, it is because the strength of the small syringe is not enough, and on the other hand, it is because the length of the small syringe is not enough. Therefore, in large hydraulic machinery, something called a "hydraulic pump" is used to play the role of the small syringe.

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