# How to calculate hydraulic system pressure

Written by jenny roberts
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Hydraulic systems provide a way of controlling a range of components by transmitting a force through a fluid that is confined in a sealed system. The fact that hydraulics can produce high pressure quickly and accurately through lightweight pipes of any size or shape, make them the best choice for providing powerful force in vehicle braking systems and aircraft flying controls. The principle behind any hydraulic system according to Pascal’s law is “the pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions, with the force acting at right angles to any surface in contact with the fluid.” Calculating the system pressure will enable you to determine the safe working load of the hydraulic system.

Skill level:
Moderately Challenging

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## Instructions

1. 1

Calculate the force in newtons (f). You can calculate (f) in newtons by calculating the work done by the force acting on the piston in newton metres and divide that by the piston stroke -- the distance the piston moves -- in metres. If you need to use imperial measurements, use a calculator to convert the values.

2. 2

Calculate the surface area of any piston in square metres (a). Area can be calculated using the following; if a square or rectangular piston then, width multiplied by length will give the value (a), if a circular piston then "pi" (3.142) times the radius squared will give value (a).

3. 3

Use the values from the calculations to determine system pressure, for (n) newtons per square metre, divide the value (f) by (a) for example if (f) = 100 and (a) = 25, the calculation would be 100/25 = 4 nm pressure or force.

#### Tips and warnings

• Useful conversion factors; 1 newton metre = 1.355 foot pounds, 1 litre = 0.22 UK gallons or 0.26 US gallon, 1 cm3 = 0.061 cubic inch, 1 kW = 1.34 hp 1 bar = 14.5 psi.
• Make sure you use the same values in the calculations, metric or imperial, not a combination of both as this will give false results.

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