Cylinder-assisted shock absorber sizing must combine impact kinetic energy, ½mv², with drive work, F×S, because the actuator continues adding energy during deceleration.
A complete selection uses four inputs: effective mass in kg, impact velocity in m/s, cylinder propelling force in N, and cycles per hour, followed by checks against stroke, force, energy, and thermal capacity [S1][S2].
Separate Impact Energy from Cylinder Work
For a horizontal moving mass, kinetic energy is Eₖ = ½mv². A 90 kg load reaching 2.05 m/s therefore presents 190 J per impact, using joules, newton-metres, and kilogram-metre-per-second-squared as equivalent energy units [S1].
Propelling-force work is Eᵥ = F×S, where F is the cylinder force in N and S is the shock absorber stroke in m. With a 110 N cylinder force and a 0.025 m stroke, the cylinder adds 2.75 J per event, bringing the combined input to 192.75 J per cycle [S1].
The distinction matters because a drive force can remain present while the piston moves through its stroke. A catalog sized only for 190 J would omit the 2.75 J supplied by the cylinder and the 300 impacts per hour associated with the worked example [S1].
Calculate Pneumatic Cylinder Force
For a pneumatic cylinder, propelling force is derived from operating pressure multiplied by piston area, with backpressure included where it opposes cylinder extension: F = P×A for ideal single-acting extension, and F = ΔP×A when both sides of the piston contain pressure [S2].
Use pressure in Pa and bore area in m² to obtain force in N. For bore diameter d in metres, A = πd²/4. A 50 mm bore at 500 kPa gauge provides an ideal extension force of about 981 N before subtracting return-side pressure or accounting for actual losses [S2].
Do not substitute nominal supply pressure for the effective pressure at the cylinder, and do not omit rod-side loading in double-acting cylinders. The selected absorber must also tolerate the maximum propelling force listed for that model; if the calculated force exceeds the rating, the model or stroke must be changed and the work calculation repeated [S5].
Account for Gravity and Vertical Motion
A vertically falling load cannot be sized from horizontal impact energy alone. For release through height h, gravitational potential energy is Eₖ = mgh, using g = 9.81 m/s². A 90 kg mass released through 0.5 m supplies 441 J before adding any cylinder work [S1].
Gravity can also act as the propelling force. On an incline, the component parallel to travel is F = mg sin θ, and its work over the selected stroke is added to the other work inputs. The shock absorber still converts mechanical energy into heat rather than storing it for rebound [S3][S4].
Compare Main Energy-Input Methods
The principal sizing methods differ in what they include and where they can fail. The kinetic-energy-only method captures impact speed but misses an actuator that continues pushing; the drive-work-only method captures cylinder force but misses stored motion; the combined method uses E_total = ½mv² + F×S and is the appropriate baseline for an actively driven horizontal load [S1][S2][S6].
The same combined method applies to industrial shock absorbers, but the final choice still depends on available stroke, mounting space, permissible reaction force, cycle rate, and unit cost rather than energy alone [S3].
Check Per-Cycle and Hourly Capacity
Select a model whose maximum absorbed energy per cycle is at least the combined input. In the worked example, 192.75 J per cycle becomes 57,825 J per hour at 300 cycles per hour, calculated as E_hour = E_cycle×300 [S1].
The selected example unit, with a 0.025 m stroke and a rated hourly capacity of 111,400 Nm per hour, exceeds the calculated 57,825 J per hour, while its per-cycle recommendation includes a minimum 5% margin against maximum rated energy [S1]. Use the manufacturer’s actual duty-cycle and margin rules for the final model rather than transferring those figures between products.
Per-cycle adequacy does not guarantee thermal acceptability. A unit that handles one impact may overheat during high-frequency operation because the absorbed mechanical energy becomes heat. If hourly capacity is insufficient, increase unit size, recalculate work using the new stroke, or add an oil reservoir or cooling provision [S2][S5].
Validate Force, Stroke, and Deceleration
The candidate unit must meet three independent limits: maximum energy per cycle, maximum propelling force, and stroke. Energy capacity protects the internal fluid and structure, force capacity protects the piston and mounting interface, and stroke determines both the F×S work term and the distance available for controlled deceleration [S1][S5].
Impact velocity must be the velocity at contact, not the average actuator velocity. Taylor Devices gives impact-velocity factors of 2 for an air cylinder and 1.5 for a hydraulic cylinder when average cylinder velocity is used [S3]. A 1 m/s speed error changes the kinetic term by 2.1 J for a 90 kg mass, while the error grows in proportion to the square of velocity.
Industrial shock absorbers meter fluid through openings arranged to dissipate energy progressively and produce nearly linear deceleration. Air must be bled from the fluid because entrained air can cause spongy or erratic action, and hydraulic fluid viscosity changes with temperature can alter the deceleration profile [S2][S4].
Size for the Correct Audience and Duty
The combined energy method is intended for moving linear loads driven by cylinders, motors, gravity, or another force source. It is not a complete design for rotary mechanisms with complex linkages unless the rotary input is first converted to equivalent linear mass, impact speed, and force at the contact point [S2][S3].
Effective mass should include the payload, tooling, grippers, fixtures, and moving drive components such as a cylinder rod or linear carriage. Rotary systems may require conversion to equivalent linear mass acting at the impact point, while complex inputs such as explosions, seismic events, and weapons effects fall outside ordinary industrial sizing guidance [S2][S3].
For a broader equipment-specific treatment, shock absorber sizing for pulp and paper covers roll stops, conveyors, and oscillating screens. The shared rule remains the same: calculate the force-assisted work with the selected stroke, then validate energy and thermal capacity before release.
Track four values on the final calculation sheet: combined energy per cycle in J, cylinder force in N, selected stroke in m, and absorbed energy per hour in J/h. If any value changes after installation, recalculate F×S and repeat the capacity checks.