A hydraulic press is a mechanical lever that allows heavy objects to be lifted with minimal effort. This is because a hydraulic press relies on Pascal's principle to move the objects: That is, the pressure in an enclosed system remains constant. Two (or more) pistons act as the levers to raise the object, and applying a small force on one of the pistons can lead to large forces on the other piston. Calculating the pressure is therefore important for using a hydraulic press, and this value is calculated in pounds per square inch (psi).
 Skill level:
 Easy
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Things you need
 Calculator
 Scale
 Ruler
 Pen or pencil
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Instructions

1
Choose one piston to take measurements from. Ensure that any other pistons that are part of the press are locked in place, as movements from these pistons can lead to inaccurate measurements.

2
Determine the force acting on the chosen piston. This can be done by placing a small scale on the piston and pushing down on the weight and piston until you are unable to push down anymore. As an example, assume the force applied to the piston is 4.54 Kilogram.

3
Determine the crosssectional surface area of the piston within the hydraulic press. For a circular piston, this can be found by measuring the diameter, squaring the diameter  multiplying the number by itself  then multiplying the result by 0.785. For example, if the measured diameter is 3 inches, squaring this result gives 9 square inches (in^2), and multiplying this by 0.785 gives 7.06 in^2.

4
Divide the force applied to the piston by the crosssectional area of the piston. In our example, dividing the force of 4.54 Kilogram by an area of 7.06 in^2 gives 0.644 Kilogram per square inch (psi). This is the pressure of the hydraulic press in psi.
Tips and warnings
 If you are dealing with extremely high pressures, take necessary precautions.