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How to calculate ISO pneumatic actuator force
Siłowniki dobrane przez pracowników CPP PREMA

Due to their reliability, simple design, availability and installation cost, pneumatic actuators are often the first choice for many drive systems. For maximum performance and safety, it is important to calculate the proper actuator force. In this tutorial, we will discuss how to properly calculate the force of an ISO pneumatic actuator, taking into account actuator parameters such as piston diameter, piston rod diameter, air pressure and η factor.

Determine the required force for a specific application

To calculate the pushing or pulling force of a pneumatic actuator, you must first determine its parameters. It is necessary to consider whether the actuator can withstand the assumed loads and how they will be distributed at the beginning, at the end or over the entire length of the piston rod. What range of motion (stroke) is needed? It is also worth considering the speed of the piston rod stroke and the duration of the work cycle.

In addition, factors such as environmental conditions should be checked (such as temperature and humidity). It is important to remember that additional mechanical loads, such as friction in seals, are generated during operation.

After considering all of the above factors, determine the exact required force that will be needed to move the loaded piston. Too much force when choosing an ISO pneumatic actuator can be uneconomical and lead to higher energy requirements and damage to the system component. Too little force, on the other hand, will make its use in the installation ineffective, and the actuator itself will fail.

Air pressures as a factor in proper selection of pneumatics

The ratio of the force that air exerts on a surface is its pressure. In pneumatic actuators, this gas is used as a power source to move the actuator.

In practice, the air pressure in the actuator is controlled by using a pressure control valve. It allows you to precisely set the required value that is needed to achieve the desired force.

For ISO double-acting pneumatic actuators with a single-sided piston rod, a pressure range of 3 to 10 bar (0.3 to 1 MPa) is recommended, depending, of course, on the specific model and operating conditions.

Careful monitoring and adjustments of the pressure to the required levels will avoid the costs associated with inefficient operation of the system. It will also protect users from the used equipment’s failures or replacement of pneumatics.

ISO pneumatic actuator force formula

The theoretical pushing or pulling force of a pneumatic actuator is calculated taking into account the diameter of the piston, the piston rod and the working area (stroke length, piston extension and return).

The first step in selecting the force is to choose the approximate air consumption that will be needed to perform one cycle of actuator movement. This calculation requires knowledge of the piston diameter and stroke length.

The next step is to adjust the gas pressure supplied to the actuator. This can be done by adjusting the pressure control valve.

We calculate the force of the pneumatic actuator from the following formula:

theoretical force = pressure * active area of the piston

To calculate the active area of a piston, there are two formulas depending on the type of force (pushing or pulling).

usable force = pressure * active area of the piston * η factor

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It is worth remembering that the discussed η factor may vary depending on the specific model and usage conditions. Additional information on the efficiency of a particular actuator can be obtained from the manufacturer’s technical documentation.

Calculation of ISO pneumatic actuator force - Table

Theoretical pushing force on the piston rod of double-acting actuators with single-sided piston rod

Air pressure (MPa)
Theoretical pushing force (daN)(kG)
∅ piston (mm) ∅ piston rod (mm) 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0
D12 6 3.9 4.52 5.65 6.79 7.92 9.05 10.18 11.31
D16 6 6.03 8.04 10.05 12.06 14.07 16.09 18.10 20.11
D20 8 9.42 12.56 15.7 18.85 21.99 25.13 28.27 31.42
D25 10 14.72 19.63 24.54 29.42 34.36 39.27 44.17 49.09
D32 12 24.12 32.17 40.21 48.25 56.29 64.34 72.38 80.42
D40 16 37.7 50.2 62.8 75.4 88 100.5 113 125.7
D50 20 59 78.5 98 117 137 157 176 196
D63 20 93.5 124 155 187 218 249 280 311
D80 25 150 201 251 301 351 402 452 502
D100 25 235 314 392 471 549 628 706 785
D125 32 368 490 613 736 859 981 1104 1227
D160 40 603 804 1005 1206 1407 1608 1810 2011
D200 40 942 1257 1571 1885 2199 2513 2827 3142
D250 50 1473 1963 2454 2945 3436 3927 4418 4909
D320 63 2413 3217 4021 4825 5629 6433 7238 8042

The value of the η factor depending on the actuator's work method

The actual force on an actuator’s piston rod depends on the pressure changes during the filling and emptying of the actuator chambers, as well as changes in the frictional force in the seals. In practice, it is advantageous to use the η factor, expressing the ratio of the useful Fu force to the theoretical Ft force. The table above states recommended values for the η factor.
Work method η factor's value
Slow movement, weight acting at the end of a stroke 0.8
Fast movement, weight acting at the end of a stroke or slow movement, weight acting over the entire stroke 0.75
Fast movement, weight acting approximately over the entire stroke 0.65

Approximate air consumption per cycle of a double-acting actuator with a single-sided piston rod

Approximate air consumption at 0.63 MPa (normalne dm3)
Actuator diameter Usage for 100 strokes (mm) Incremental consumption per additional 100 (mm)
D12 0.165 0.144
D16 0.293 0.272
D20 0.459 0.401
D25 0.716 0.659
D32 1.174 1.117
D40 1.835 1.649
D50 2.867 2.681
D63 4,551 4,274
D80 7.339 7.061
D100 11.47 10.88
D125 17.92 17.33
D160 29.36 28.44
D200 45.87 44.95
D250 71.67 70.23

Summary

When calculating the force of an ISO pneumatic actuator, special attention must be paid to determining the input data of the actuator, taking into account the load and stroke range. It is recommended to use a pressure range of 3 to 10 bar. In the case of double-acting actuators with a single-sided piston rod, it is worth taking into account both the diameter of the piston and piston rod, as well as the η factor in the range of 0.65 to 0.8.

It is worth remembering that if you have any doubts, our staff at CPP “PREMA” S.A. can help you select an actuator with the appropriate force and parameters you need.

Thanks to Mrs. Beata Sobolak, Constructor in the Construction and Technology Department of CPP “PREMA” S.A. for her assistance in preparing this guide.