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A Jack of All Trades

My buddy’s car has been acting up lately so I went with him to the hardware store to buy a car jack. The plan was, he was going to lift his car up, crawl underneath and figure out what was wrong. Unlike me he actually knows a few things about cars. Well, we picked up a cheap jack and went back home to try it out. I still don’t know what was wrong with the car but he fixed it and is driving it around again.

Today, most car jacks are hydraulic opposed to the traditional screw jacks because they are much easier to operate. Small hydraulic cylinder manufacturers provide the main cylinder for a hydraulic jack. There are six parts in all; a reservoir, pump, main cylinder, check valve, piston and release valve.

Hydraulic fluid is held in the reservoir. To start the jack, a pump draws fluid up from the reservoir and pushes it through the check valve. The check valve is in place to allow the fluid passage from the reservoir to the main cylinder. Once in the main cylinder, a piston is forced up as the cylinder fills with fluid. To lower the jack, the release valve is opened. This releases the pressure and allows the piston to return to its original position.

Hydraulic jacks work on Pascal’s Principle, which states pressure is the same at all points inside a closed container. If two cylinders are connected, applied force to one cylinder will result in the same amount of force on the other. This is how the small hydraulic cylinder inside a car jack is able to lift a car. The greater the size difference between cylinders, the greater the increase in force.