Accurately calculating the stroke length of an air spring is essential for ensuring optimal performance in various industrial applications. Whether used in vibration isolation, load leveling, or actuator systems, air springs must be carefully selected to match the required dynamic range and operating conditions. In this guide, we provide a comprehensive method to calculate the stroke length, ensuring maximum efficiency, longevity, and performance stability. Air springs typically have stroke lengths ranging from 20 mm to 400 mm, depending on the design type and operating pressure.
Understanding Stroke Length in Air Springs
The stroke length refers to the total vertical movement an air spring can achieve between its fully compressed and fully extended states. The key factors influencing this measurement include:
- Initial installation height
- Maximum and minimum compressed height
- Internal air pressure
- Load capacity
- Material composition and reinforcement layers
For example, an 8-inch diameter air bellow typically has a stroke length of 150 mm, while a 16-inch diameter model can reach up to 350 mm. Choosing the right stroke length ensures that the air spring can handle the necessary displacement range without compromising stability or structural integrity.
Key Parameters for Stroke Length Calculation
When calculating the stroke length, consider the following key parameters:
1. Minimum and Maximum Operating Heights
Each air spring has a defined minimum compressed height and maximum extended height. This information is essential for determining the usable stroke range. The standard compressed height for air springs varies between 40 mm and 150 mm, depending on the model.
2. Load at Various Heights
The load-bearing capacity of an air spring changes with height. Understanding these variations ensures proper selection for dynamic applications. For example, a 12-inch air spring operating at 6 bar can handle up to 40 kN in force.
3. Air Pressure Influence
The internal pressure significantly affects the stroke length. Higher air pressure extends the stroke, while lower pressure limits it. At standard operating pressures of 6-8 bar, the stroke range remains optimal.
4. End Fittings and Mounting Constraints
The mounting configuration determines the available vertical space and affects the overall motion range of the air spring. Different mounting plate designs can increase or decrease the effective stroke length.
Step-by-Step Stroke Length Calculation
Step 1: Identify Air Spring Specifications
Retrieve the technical datasheet of the selected air spring. Identify:
- Nominal diameter
- Max compression height
- Max extension height
- Maximum force output at rated pressure
For example, a 10-inch diameter double-convoluted air spring may have a maximum stroke length of 250 mm with a load capacity of 30 kN at 7 bar.
Step 2: Determine Load and Pressure Requirements
- Calculate the required force at various heights.
- Use the formula:
(F = P \times A)
where: - (F) is the applied force (N or kN)
- (P) is the internal pressure (bar or psi)
- (A) is the effective cross-sectional area (cm² or in²)
Step 3: Calculate Stroke Length
Use the formula:
(S = H_{max} – H_{min})
where:
- (S) is the stroke length (mm or in.)
- (H_{max}) is the maximum extended height (mm or in.)
- (H_{min}) is the minimum compressed height (mm or in.)
For example, an air spring with a minimum height of 50 mm and a maximum height of 250 mm has a stroke length of 200 mm.
Step 4: Consider Safety Margins
To ensure reliable operation, maintain a safety margin by selecting an air spring with a stroke length 10-20% greater than the calculated requirement. A stroke length buffer prevents premature failure due to overextension.
Application-Based Stroke Length Selection
1. Vibration Isolation Systems
- Required stroke length: 20-50 mm
- Operates at low pressure (2-5 bar) to maximize shock absorption
- Designed for continuous motion applications
2. Industrial Actuators
- Stroke length range: 50-300 mm
- Requires precise height control
- High-pressure operation ensures rigid structural support
3. Load Leveling Systems
- Stroke length varies between 40-150 mm
- Automatically adjusts based on real-time weight distribution
- Uses sensor-based height adjustment mechanisms
Common Mistakes to Avoid in Stroke Length Calculation
1. Ignoring Load Variability
Failing to account for changing load conditions can lead to incorrect stroke calculations, resulting in poor performance. Some air springs exhibit up to 20% force variation based on height.
2. Overestimating Air Pressure Efficiency
While higher air pressure increases the stroke, exceeding the rated design limits can cause premature wear. The recommended limit is 8 bar, beyond which rubber materials degrade faster.
3. Neglecting Material Expansion and Compression Rates
Rubber and composite materials exhibit elastic deformation over time, influencing the real-world stroke length. Over 3-5 years, the stroke range can decrease by 5-10%.
Calculating the stroke length of an air spring involves precise measurement of its compressed and extended heights, along with consideration of load capacity, air pressure, and mounting conditions. By following the outlined steps, engineers and designers can ensure optimal selection, maximizing durability and efficiency in air spring applications. Selecting the right stroke length improves reliability, reduces wear, and enhances system efficiency.