Hydraulic Press System Description
A hydraulic press is a simple machine with many uses. It is used to lift heavy objects like cars and machine parts up in the air. It is used to compress hay, cotton, cardboard and other materials into bales for easy transportation and storage. It is used to shape metal parts for various industrial uses.
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Parts of a Hydraulic Press System
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A hydraulic press is basically composed of two cylinders, a tank and three pipes. The large main cylinder contains hydraulic fluid and a wide piston poised to exert its force upwards out of the cylinder. This hydraulic fluid is usually some kind of oil, because oil is incompressible and transmits any changes in pressure throughout itself without loss. The main cylinder is connected by a pipe to a pumping cylinder, which is smaller. It contains a smaller piston that moves up and down within the cylinder. Both the main cylinder and the pump are connected to a hydraulic fluid reservoir by pipes. Valves cover all three pipes.
Pascal's Principle
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The hydraulic press works because of Pascal's principle. This principle states that any pressure applied to a completely enclosed fluid is distributed evenly throughout that fluid. This is why a small amount of force can be applied to the pump and used to lift very heavy objects. Pressure is the ratio of how much force is applied to the area it is applied over. Pascal's principle tells us that the pressure in an enclosed liquid must be the same everywhere. Because the piston in the main cylinder is larger than the piston in the pump, it must exert more force in total to produce the same pressure. However, the hydraulic fluid has to spread out farther to cover the larger piston, so while the lifting piston produces more force than the pumping piston, it doesn't move as far. A hydraulic press takes long, low-force piston movements and converts them into short, high-force piston movements.
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On the Downstroke
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When the piston in the pump cylinder moves downwards, the valve from the pump to the reservoir is closed, as is the valve from the main cylinder to the reservoir. The valve from the pump to the main cylinder is open. The hydraulic fluid is forced from the pump cylinder to the main cylinder, providing lift in the case of jacks and lifts or crushing force in other applications.
On the Upstroke
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When the piston in the pump moves upwards, the valve from the main cylinder to the pump is closed, the valve from the main cylinder to the reservoir is closed and the valve from the pump to the reservoir is open. As the piston moves up, the hydraulic fluid flows into a larger space and is spread out farther. This causes the pressure at the mouth of the pipe to the reservoir to be lower than the pressure in the reservoir. This pushes more hydraulic fluid into the pump cylinder.
Afterward
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After the lifting or crushing is done, then the valves from the main cylinder to the pump and the pump to the reservoir close. The valve from the main cylinder to the reservoir opens and the hydraulic fluid drains from the main cylinder back into the reservoir.
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References
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- Photo Credit hydraulic lock mechanism image by green308 from Fotolia.com
