What is Hydraulic?

With a stick, overcoming resistance can push an object. The speed at which an object moves depends on the speed at which the stick moves, because the stick is solid.

If a stream of water hits an object, it may also push an object. The larger the water volume and the higher the water flow velocity, the greater the driving force. The speed at which an object moves is different from the speed of water flow because water is a liquid and has no fixed shape.

If the water flow is open, there will be a great loss. If the water flow is collected in a container, the water will not be lost and the energy efficiency will be higher.
Because this technology mainly depends on the speed and quality of the liquid, that is, kinetic energy, it is called dynamic pressure transmission, or hydraulic transmission. Due to its flexibility, it also has certain applications, such as fluid couplings, torque converters, etc., but there are fewer product types and are not the subject of this book.
If you close the water and squeeze the stick, you can also push the object.

The distance the object moves depends on the amount of water: as much water is sent as the object moves.
The speed at which an object moves depends on the amount of water fed in per unit time: the more water sent in per unit time, the faster the object moves. Of course, using other liquids instead of water can have a similar effect.
This technique of letting the liquid pressurizes objects to overcome resistance, that is, to transmit power (force and speed), is a hydraulic transmission, also known as hydraulic pressure.
Compared with the above-mentioned dynamic pressure transmission, the liquid flow speed here can be much slower, so it is also called static pressure transmission and hydrostatic transmission.
Because the shape of water can be changed, the direction and distance of action are much more flexible than just pushing with a stick.
Using gas as the working medium and transmitting power in a pressure manner is called pneumatic transmission or pneumatic.
The technology that uses liquid and gas as working media is collectively called fluid technology.
1,Examples of hydraulic systems
The picture shows a simple hydraulic system, the liquid used is hydraulic oil (orange red in the picture).

In the figure, the working principle of the hydraulic pump 3 is similar to a pump. When the plunger 2 is pressed down by the handle 1, since the oil suction check valve 9 seals the oil suction pipe 10, the hydraulic oil in the hydraulic pump 3 can only pass through the oil discharge pipe 4 and the oil discharge check valve 5, and enter the hydraulic cylinder 6, Push the piston 7 up to compress the workpiece 8.
When the handle 1 drives the plunger 2 to rise, a vacuum appears in the hydraulic pump 3, and the hydraulic oil in the oil tank 13 is pushed by the atmospheric pressure, passes through the oil suction pipe 10, pushes the oil suction check valve 9 into the hydraulic pump 3. Since the oil discharge check valve 5 seals the oil discharge pipe 4, the hydraulic oil in the hydraulic cylinder 6 will not return, so the piston 7 will not fall.
By repeatedly raising the handle 1, the piston 7 can be pushed up continuously.
Only when the unload switch valve 11 is opened, the hydraulic oil in the hydraulic cylinder 6 will flow back to the oil tank 13 through the oil return pipe 12 and the piston 7 will descend.
This is how small lifting equipment commonly known as “jacks” work.
The above system can work, but if you need to drive frequently, rely on manual, after all, it is too tired. Therefore, practical hydraulic pumps are driven by electric motors or engines to output hydraulic oil. As shown, the hydraulic valve 4 is used to control the flow direction of hydraulic oil, thereby changing the direction of movement of the hydraulic cylinder.

—From ‘Hydraulics for Everyone’

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