The jack is composed of a casing, a large piston, a small piston, a wrench, a fuel tank and the like. The working principle is that the wrench moves upwards to drive the small piston upwards. The oil in the oil tank is sucked into the lower part of the small piston through the oil pipe and the one-way valve. When the wrench is pressed down, the small piston is driven downward, and the oil tank and the small piston lower oil passage are the one-way valve. Plugged, the oil in the lower part of the small piston is pressed into the lower part of the large piston through the internal oil passage and the one-way valve. The pressure in the lower part of the small piston is increased by several tens of times due to the leverage, and the area of the large piston is several tens of times the area of the small piston. The manually generated oil pressure is squeezed into the large piston, and the Pascal principle knows that the size of the piston area is the same as the pressure ratio. In this way, the force on the hand is increased by more than ten times through the wrench to the small piston (temporarily pressed 15 times), the small piston to the large piston force is increased by more than ten times (temporarily pressed 15 times), to the large piston ( The part of the activity that protrudes from the top of the car) strength = 15X15 = 225 times the power, if the hand uses every 20 kilograms of force, it can produce 20X225 = 4500 kg (4.5 tons) of strength. This is how it works. When it is used up, there is a valve that is normally closed and opened manually. The oil is pushed back to the tank by the weight of the car.