When choosing the appropriate size of the hydraulic cylinder, evaluating whether the system can meet the working requirements, or comparing the performance of different hydraulic cylinders, understanding how to calculate the tonnage of the hydraulic cylinder accurately is a fundamental step.
Through this article, you can learn how to calculate the tonnage of hydraulic cylinders and help you make the most suitable choice.
Parameters Related to the Tonnage of the 
Before calculating the tonnage of the hydraulic cylinder, you need to measure these parameters related to the tonnage of the hydraulic cylinder.
Piston Diameter
The diameter of the piston determines the size of the force area on the hydraulic cylinder. Its numerical value directly affects the magnitude of tonnage output. The force area of a circular piston is proportional to the square of its diameter.
A slight increase in diameter will lead to a significant increase in tonnage. You need to use a ruler to measure the diameter of the piston accurately.
Diameter of Piston Rod
The diameter of the piston rod is only used for calculating the tonnage of the hydraulic cylinder retraction stroke. It has no effect on the tonnage when the hydraulic cylinder is extended.
The piston rod will occupy some of the force space of the piston. When calculating the tonnage corresponding to the return tension, you need to subtract the cross-sectional area of the piston rod from the total force area of the piston.
The diameter of the piston rod should be kept in a reasonable proportion to the diameter of the piston. This can make sure the thrust requirement during retraction and also maintain the stability of structural operation.
Hydraulic System Working Pressure
The system pressure is the primary source of power for the hydraulic cylinder to generate push-pull action. It is determined by the rated performance of components such as hydraulic pumps and relief valves. When conducting the calculation, you must use the rated working pressure specified for the equipment.
How to Calculate the Tonnage of a Hydraulic Cylinder?
After obtaining all the parameters required for the calculation of the hydraulic cylinder tonnage, you can perform the calculation according to the corresponding formula. The units of the metric system and the imperial system have significant differences, and their arithmetic logic and conversion relationships are also different.
Steps for Calculating the Tonnage of Imperial Hydraulic Cylinders
Step 1. Calculate the Area of the Piston
The cross-section of the piston is circular. You can calculate the piston area based on the piston diameter and this formula.
$A=\frac{\pi D^{2}}{4}$
The unit of piston diameter $D$ is $in$.
The unit of the piston area $A$ is $in^{2}$.
$\pi≈3.14$
Example:
If the piston diameter $D=10\, in$ , substitute it into the formula and calculate:
$A=\frac{\pi D^{2}}{4}=\frac{3.14\times 10^{2}}{4}=78.5\,in^{2}$
Step 2. Calculate Thrust
At this step, you need to calculate the thrust $F$ by multiplying the working pressure $P$ by the piston area $A$.
$F=P\times A$
The unit of work pressure $P$ is $psi$ .
The unit of thrust $F$ is pound force $lbf$.
Example:
If the work pressure $P=1000\, psi$, then at this point:
$F=P\times A=1000\times78.5=78500\, lbf$
Step 3. Convert Pound Force to Tons
The commonly used $ton$ in the imperial system is the $short\;ton$.
Their conversion ratio is $1\, short\; ton = 2000 \, lbf$.
So, $T=\frac{F}{2000}$
Example:
$T=\frac{F}{2000}=\frac{78500}{2000}=39.25\,tons$
The tonnage of this hydraulic cylinder is 39.25 tons.
Metric Hydraulic Cylinder Tonnage Calculation Steps
Step 1. Calculate the Area of the Piston
$A=\frac{\pi D^{2}}{4}$
In the metric system, the unit for the piston diameter $D$ is $mm$.
The unit of piston area $A$ is $mm^2$. You can convert it to $m^2$.
$1\,mm^{2}=1.0\times 10^{-6}m^{2}$
Example:
If the piston diameter $D=100\,mm$, substitute it into the formula and calculate:
$A=\frac{\pi D^{2}}{4}=\frac{3.14\times 100^{2}}{4}=7850\, mm^{2}=0.00785\,m^{2}$
Step 2. Calculate Thrust
$F=P\times A$
In the metric system, the unit for pressure $P$ is $Pa$ or $MPa$.
The unit of thrust is $N$ or $kN$.
Example:
If the system working pressure $P=16,000,000\,Pa$, then at this point
$F=P\times A=16,000,000\times0.00785=125,600 \,N$
Step 3. Convert Newtons to Tons
The commonly used $ton$ in the metric system is the $metric\;ton$.
Their conversion relationship is:
$1metric\;ton=1000kg\times 9.81m/s^{2}=9810N$
So, $T=\frac{F}{9810}$
Example:
$T=\frac{F}{9810}=\frac{125,600}{9810}≈12.80\,tons$
Therefore, the tonnage of this hydraulic cylinder is 12.80 tons.
Notes for Calculation
Tensile Force Calculation
If your hydraulic cylinder is a double acting hydraulic cylinder or has a piston rod that requires tension calculation, you can also follow the above steps. However, you must subtract the cross-sectional area of the piston rod from the total area of the piston. Then use the resulting circular area for the calculation.
Unit
Before making the calculation, you need to standardize the units of all the parameters. This can avoid deviations in area and thrust calculations caused by unit confusion, which can affect the final tonnage results. The metric system and the imperial system must never be mixed for calculations.
Safety Margin
The result obtained from the formula is the theoretical value of the hydraulic cylinder tonnage under ideal conditions. The theoretically calculated tonnage requires a safety margin of 1.2 to 1.5 times.
This is used to offset uncertain factors in actual working conditions such as impact loads and friction losses. Avoid selecting hydraulic cylinders based on theoretical values that may cause long-term overload operation and reduce the risk of equipment failure.
Why is the Tonnage of the Hydraulic Cylinder Important?
Determine the Capacity of the Equipment
The tonnage of a hydraulic cylinder directly determines the maximum mechanical force it can output. It is the key factor for you when choosing a hydraulic cylinder.
If the tonnage of the hydraulic cylinder is insufficient, the equipment will be unable to drive the target load. Excessive tonnage of hydraulic cylinders will lead to a waste of resources.
Avoid Safety Risks
The inappropriate tonnage of the hydraulic cylinder is one of the main causes of hydraulic system accidents. Insufficient hydraulic cylinder tonnage can cause the system to operate under overpressure. This is likely to cause the cylinder body to deform, the seals to fail, and even rupture.
The mismatch between the tonnage of the hydraulic cylinder and the installation conditions may also lead to force imbalance. This can cause the piston rod to bend and the transmission components to be damaged, posing a threat to the safety of equipment and operators.
Affects the Performance of Hydraulic Cylinders
The appropriate tonnage can make the hydraulic cylinder operate stably under rated conditions, and keep stable thrust output and precise action. Insufficient tonnage of hydraulic cylinders can lead to a decrease in operating speed, delayed response, and even inability to complete the movement.
If the tonnage of the hydraulic cylinder is too large, it may cause vibration and an increase in impact loads. This will also increase energy consumption and system heating.
Affecting the Lifespan of the Hydraulic Cylinder
If the hydraulic cylinder operates for a long time under conditions close to its maximum load, it will accelerate the wear rate of components such as seals and piston rods, thereby shortening the service life of the equipment.
Selecting hydraulic cylinders of the appropriate tonnage that match the actual requirements can reduce equipment failures and also lower the maintenance costs in the long run.
Factors Affecting the Tonnage of Hydraulic Cylinders
Internal Losses of the System
The sealing components between the piston and the cylinder wall, as well as between the piston rod and the guide sleeve, will generate continuous sliding friction during movement. This frictional resistance will consume the useful work generated by the system pressure.
Furthermore, during the process of transmitting hydraulic oil from the power source to the actuator, there will be a pressure attenuation.
The resistance along the pipeline, the throttling loss of the control valve, and the obstruction of components such as filters, all these factors will cause the actual pressure at the inlet of the cylinder to be lower than the output pressure of the pump. Then the actual output tonnage of the hydraulic cylinder decreased.
The Influence of Hydraulic Oil and Environmental Temperature
If the viscosity of the hydraulic oil does not meet the requirements of the working conditions, it will increase the pressure loss. Insufficient cleanliness of hydraulic oil can easily cause valve blockage and seal wear, leading to a decrease in the actual working pressure of the system and a reduction in effective tonnage.
The environmental temperature can affect the physical properties of the oil. Under high-temperature conditions, the oil will become thinner and the leakage increases. In low-temperature environments, the viscosity of the oil increases and the friction resistance also rises.
Both of these situations will interfere with the stable transmission of pressure, resulting in fluctuations in the actual output tonnage.
Installation Accuracy
The installation angle, alignment status, and coaxiality deviation of hydraulic cylinders jointly affect the transmission path of force. If your equipment is subjected to lateral forces, misalignment during installation, or has excessive coaxiality deviations, it will encounter additional resistance and uneven loads.
This will weaken the transmission of the pulling and pushing forces and reduce the actual tonnage of the load that the hydraulic cylinder can drive. It will also exacerbate the wear of components such as piston rods and seals, further weakening the tonnage carrying capacity of the equipment.
FAQs
How to Calculate the Tonnage of Telescopic Hydraulic Cylinders?
The tonnage calculation of multi-stage telescopic hydraulic cylinders should be based on the effective force-bearing area of each piston. Each section of the cylinder body has an independent piston diameter. The maximum output tonnage during calculation is determined by the telescopic piston with the largest effective force area.
You cannot calculate the tonnage of the entire hydraulic cylinder based solely on the diameter of one telescopic piston. You need to calculate the actual tonnage of each level separately according to the operational requirements.
Will the Installation Method of the Hydraulic Cylinder Affect the Calculation Result of the Tonnage?
No. Theoretical tonnage is only related to working pressure and effective piston area. But different installation methods will affect the actual output of the effective tonnage.
For example, a hinged installation may generate lateral forces during operation. This will result in uneven force on the piston rod, thereby reducing the actual available tonnage of the hydraulic cylinder.
So there is no need to consider the installation method during the calculation. But when selecting a tonnage and reserving a safety margin, you must consider the impact of installation methods.
Is there any Connection between the Stroke Length and Tonnage Calculation of Hydraulic Cylinders?
No. As long as the diameter and pressure parameters are the same, the theoretical tonnage remains consistent regardless of the stroke length.
For long stroke hydraulic cylinders, you need to pay attention to the stability of the piston rod during operation. An excessively long stroke may cause the piston rod to bend under heavy loads and affect the actual tonnage output indirectly.
Can the Hydraulic Cylinder Tonnage be Increased by Infinitely Increasing the Hydraulic System Pressure?
No. The maximum working pressure of a hydraulic cylinder is limited by the material strength of components such as the cylinder barrel and piston rod, as well as the pressure resistance level of the seals.
Exceeding the rated pressure cannot increase the effective tonnage. It can also cause cylinder deformation, seal damage, and even lead to safety accidents.
Final Thoughts
The tonnage of a hydraulic cylinder determines its ability to drive loads and its stability during operation. By accurately calculating the tonnage of the hydraulic cylinder, you can choose more suitable hydraulic equipment and reduce the risk of later debugging.
If you have any questions about hydraulic cylinder tonnage or other aspects, please feel free to contact us.
