How To Calculate Piston Force

A piston is the working component of engines, compressors and pumps and is housed inside a cylinder. The purpose of the piston varies depending on the system of which it is part. For example, in an engine, such as a car engine, the piston transfers force from expanding gas in the cylinder via the piston rod to the crankshaft. Calculating the force of a piston is crucial when deciding how the component will work, what practical uses it will have and how the resulting engine or compressor will function. The calculation is straightforward, provided the units remain equivalent and the correct values are input accurately.

Step 1

Measure and record the gauge pressure (p) in newtons per meter squared (N/m2). The N/m2 unit of measurement is also called the pascal (Pa). For the output stroke, the pressure will be equivalent to normal atmospheric pressure, which is standard at 100 kPa.

Step 2

Measure the full bore piston diameter (d) in meters (m) using a measuring tape or ruler, depending on the size of your piston bore setup, and record the result.

Step 3

Use the full bore piston diameter to calculate the full bore area (A) in meters squared (m2) by substituting the value you obtained from your diameter measurement into the equation A = π d2/4. π, or pi, is a constant value used in mathematics. It denotes the ratio of any circle's circumference to its diameter in space and is always equal to approximately 3.142. So, when calculating your piston area, use this value as the value of π in the equation. To do this, take the measurement of your piston diameter and square it using a calculator. A working example would be a diameter of 2.5 meters. This gives a diameter squared of 6.25 square meters; there is a button on all graphical calculators which has x2 written on it. Type your diameter into the calculator, then use this button to find the squared value. Divide the resulting value by 4. In our example, it is 6.25, so the result in our case is 1.563. Multiply this by the value of π, 3.142, and the answer is 4.909 m2. This is the bore area (A).

Step 4

Record the resulting area of your piston setup.

Step 5

Input the values obtained from each of these measurements and calculations into the main equation F = pA, where F is the piston force (F) in newtons (N), p is the gauge pressure and A is the full bore area. So, in our example, a single acting cylinder at atmospheric pressure, working on the output stroke, would require the following calculation to ascertain piston force (F): 100,000 multiplied by 4.909, which equals 490900 N.