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What Is a Hydraulic Press?

Blaise Pascal, a mathematician and physician, established Pascal's law.
Pascal's law explains how pressure works in a closed system.
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  • Written By: Carol Francois
  • Edited By: Heather Bailey
  • Last Modified Date: 08 July 2014
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A hydraulic press is a mechanical machine used for lifting or compressing large items. The force is generated through the use of hydraulics to increase the power of a standard mechanical level. This type of machine is typically found in a manufacturing environment.

Invented in 1795 by Joseph Bramah, the hydraulic press is also known as the Bramah press. He used his knowledge of fluid mechanics and motion to develop this device. This invention significantly increased the compression power available, expanding the product groups and options available to other inventors. By applying hydraulics to a press, an entire class of machines was invented. There is a wide range of different hydraulic press machines, ranging from small table top units for hobbyists to huge machines used to create metal parts.

The primary concept used to provide power to the hydraulic press is that the level of pressure in a closed system is constant. This type of press has pistons with a fluid inside that is displaced by the pistons' inward movement. The fluid forces its way back into the space by moving the piston outward. The additional power is created through the movement of the fluid, which is confined to the system.

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Pascal's law states that the pressure of a fluid within a closed system does not diminish, but instead acts with equal force on equal areas. In addition, this force will move at right angles to the walls of the container. It is important to ensure the hydraulic press is designed to withstand the pressure within the system and transfer that energy onto the press itself, and away from the structure.

When selecting a hydraulic press, it is important to realize that the amount of force generated is based on the size of the pistons, both in terms of piston head diameter and distance of movement. The amount of fluid moved by the piston is proportional to the ratio of piston head areas. This means a small piston would have to move a large distance to create enough force to displace the large piston any significant distance. To calculate the distance the large piston will move, divide the ratio of the piston head area by the distance the small piston is moved.

Remember that work is force multiplied by distance. As force increases on the larger piston, the distance the smaller piston travels must be decreased. This application of the core physics principle created the hydraulic press and resulted in significant developments in the manufacturing sector.

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croydon
Post 3

@Iluviaporos - I've actually seen a few schematics online for making printing hydraulic presses, which I'd be more interested in than just something to crush stuff.

I don't think they make nearly as much pressure, but it would be enough for the purposes.

I've also seen small, manual hydraulic presses in a museum I went to recently.

They were operated by a handle, and if you stuck a piece of paper under the press it would press a pattern into it, usually something related to the display you were looking at.

They were something for the kids to collect (although I enjoyed making them as well!).

lluviaporos
Post 2

@Mor - If you really want to scare yourself, you could try making your own hydraulic press.

I actually think the one you were thinking of on the Letterman show was more like 80 tons, rather than 20. And there are tutorials online that show you how to make one that's up to around 30 tons, which is quite enough for anything most people would need it for!

They aren't automated of course and they are quite bulky, so the project wouldn't be for everyone.

Alternatively you can get a used hydraulic press. As it says in the article they are available in desk top models.

Just in case you want to relive that childhood trauma up close and personal!

Mor
Post 1

I know it's a bit childish, but talking about a hydraulic press really makes me think about the old David Letterman segment where he would find new ways to crush things. I think he used a steam roller at first, but that wasn't crazy enough.

Then, they found a 20 ton hydraulic press and started crushing things in there.

I know it was meant to be funny, and it was (you can still watch it online) but I actually found it quite scary as a kid. It seemed so inevitable, and unstoppable.

Watching it as an adult it still gives me the creeps a little bit, but I still feel like cheering when they crush the bowling ball!

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