Industrial shock absorber selection starts with moving mass, actual impact speed, continuing drive force, usable deceleration stroke and cycle rate—not the thread diameter. A unit that fits the mounting hole can still leave a hard impact, fail to extend before the next cycle, or run beyond its hourly energy rating. This guide takes production engineers at factories in Thailand from the first measurement through calculation, quotation, FAT/SAT and maintenance. The numerical example is illustrative; final model approval must use the current manufacturer’s data for the exact installation.
Define the motion before opening a catalogue
An industrial shock absorber slows a moving body over a finite stroke and dissipates energy. Typical applications include a pneumatic slide at the end of travel, a conveyor pallet entering a stop station, or a rotary arm at its end position. Draw the moving mass, actuator, guide, absorber and positive stop on the same sketch. Decide whether the plunger is hit squarely and whether the actuator keeps pushing while the plunger retracts. Do not assume the absorber itself defines the final position or provides a safety stop. Those functions depend on the selected model and machine design.
Eight values to collect on the shop floor
Collect eight inputs: (1) the moving mass including fixtures, grippers and pallets; (2) measured velocity immediately before impact, at minimum and maximum loads; (3) usable absorber stroke after tolerances; (4) drive, gravity and any downstream pushing force during that stroke; (5) impacts per hour and continuous running time; (6) impact angle and side load; (7) local temperature, coolant, chips, dust and washdown; and (8) permitted rebound, noise and final-position variation. Write down which inputs are measured and which are design estimates. A motor setpoint is not an impact-speed measurement. Likewise, a nominal 20 mm of free space is not necessarily 20 mm of usable stroke after structural deflection and stop adjustment.
A simple horizontal slide and a descending load do not have identical energy inputs. Gravity adds work during the stroke of a descending load. Rotary systems require moment of inertia, angular velocity and impact-point radius. Conveyor loads may receive a push from following products. ACE’s calculation basis separates these applications and the concept of effective mass. Select the correct application method instead of reusing a horizontal-slide equation for every axis.
Absorber, rubber stop or cylinder cushion?
A rubber bumper is mechanically simple but its rebound and deformation characteristics differ. A cylinder’s built-in cushion may be enough within its permitted mass, speed and cycle conditions. An external hydraulic absorber deserves consideration when impact noise, rebound, component damage or stop stability remains unacceptable. Within absorber families, self-compensating, adjustable, short-stroke and environment-resistant products serve different operating ranges. The SMC RB series page and SMC USA shock absorber overview distinguish product types such as standard, coolant-resistant and short variants. Choose by actual mass and speed spread, space, environment and the ability of maintenance staff to preserve adjustments.
Calculate energy per impact and per hour
For a simple horizontal translation, kinetic energy is E_k = 1/2 × m × v², where mass is in kg, impact speed in m/s and energy in J. If the actuator keeps pushing through the absorption stroke, add its work: E_p = F × s, where axial force is in N and usable stroke in m. The first estimate is E_cycle = E_k + E_p. Multiply by impacts per hour c for E_hour = E_cycle × c. ACE identifies kinetic, propelling-force, per-cycle and per-hour energy separately; none should be silently omitted.
Assume one absorber stops a 20 kg horizontal slide at 1.0 m/s. The drive continues to apply 100 N through 20 mm, or 0.020 m, of usable stroke. Kinetic energy is 0.5 × 20 × 1.0² = 10 J. Drive work is 100 × 0.020 = 2 J. The total is 12 J per impact. At 600 impacts per hour, the load is 7,200 J/h. These are stated assumptions, not a recommendation for a particular model. Actual thrust, friction, velocity variation and load cases must be checked with the maker’s current selection data or engineering support.
A speed error cannot be repaired by adjusting mass
Velocity matters disproportionately: kinetic energy varies with velocity squared. With the same 20 kg slide, raising impact speed from 1.0 to 1.2 m/s increases kinetic energy from 10 to 14.4 J. If the assumed 100 N thrust continues through 20 mm, the combined result becomes 16.4 J per impact. Measure the fastest real operating case, including an empty carrier if it accelerates faster than a loaded one. Decelerating earlier in the motion profile may reduce the end-stop load, but evaluate its effect on takt time and positioning. For electric axes, see our electric cylinder selection guide.
Vertical, rotary and angled impacts require a different application calculation
A descending axis receives additional work from gravity throughout the deceleration stroke; for an ascending axis the direction of gravity is reversed. For a rotary arm, determine kinetic energy from angular velocity and moment of inertia, then check tangential speed at the actual contact radius. On a conveyor, slipping between the pallet and workpiece or a push from following pieces changes the force history. An angled strike can generate damaging side load even if the axial energy seems acceptable. ACE and SMC separate these applications for a reason. Use their application-specific equations or sizing assistance, and keep the simple horizontal-slide calculation only for the case it describes.
Compare seven ratings on the exact model
A catalogue maximum energy larger than 12 J alone does not establish suitability. Festo’s YSRW technical data lists size-specific absorption energy and stroke specifications. For each candidate, check these seven items against the worst credible case:
- Energy per stroke: confirm the rated maximum covers the calculated impact energy.
- Energy per hour or permissible cycle rate: repeated impacts generate heat even when each individual impact is allowed.
- Effective mass and impact velocity range: the damping characteristic must match both heavy and light production variants.
- Absorption stroke: the available machine travel must allow the model’s required effective stroke.
- Stop force, drive thrust and positive-stop requirement: check the workpiece, bracket, bolts and supporting structure as well as the absorber.
- Mounting, alignment and side loading: guide the moving mass so the plunger carries primarily axial load.
- Temperature, fluid exposure and return: check whether the plunger fully extends before the next impact in the actual environment.
Festo’s YSRW technical data lists maximum energy per stroke and per hour separately for different sizes. The listed values apply to those models and conditions, not to every absorber. Obtain the current data sheet for the exact part number, revision and accessories before purchase. If the application is vertical, rotary or angled, use the relevant manufacturer’s application calculation rather than the simple example above.
Two absorbers do not automatically share energy equally
A wide pallet may use an absorber on each side, but slight skew, guide clearance or bracket tolerance can make one side touch first. The SMC RB catalogue cautions that parallel absorbers need not receive equal energy. Assess the worst one-sided case. If you plan to credit equal sharing, specify a mechanism and a test that actually ensure simultaneous contact, then confirm the assumption with the supplier.
Select the mechanism and environment specification
First filter by maximum per-stroke and per-hour energy. Next test both ends of the mass and speed range against effective-mass and velocity limits. If operating conditions are narrow, a self-compensating unit can simplify maintenance. A broad product mix may call for an adjustable unit, different models for different products, or a changed speed profile. Adjustable does not mean automatically flexible: operators need documented settings by product and a way to detect accidental changes.
Then review the installation. Chips and coolant near machine tools, washdown on food lines, chemical exposure, weld spatter and heat can affect seals and service life. A coolant-resistant variant does not mean resistance to every liquid. Check materials and sealing against the actual fluid, concentration and cleaning method. In a Thai factory, measure the temperature at the absorber during production, particularly on high-cycle equipment, rather than copying a nominal room-temperature assumption.
Finally compare local supply and replacement. A dimensionally similar substitute can have a different velocity range, rebound or return behavior. Ask quotations to separate the absorber, brackets, positive stop, spares, installation and local technical support. Set stock quantities from the line’s allowable downtime and procurement lead time. Unit price alone is a poor comparison if one choice forces frequent replacement or a long wait for imported parts.
Design the mount and the stop together
Keep the impact face square to the absorber axis. Put lateral force and moment into the guide structure, not the plunger. Size brackets and bolts for repeated impact and verify that they do not shift during continuous operation. Record thread engagement, locknut position, bracket flatness and alignment on the assembly drawing. Determine whether the selected model has an integrated stop or needs a separate positive stop. Festo’s data sheets contain model-specific notes about stop force and external stops; follow the selected model’s dimensions rather than a general shop-floor rule.
On pneumatic equipment, pressure, speed controller settings, pipe length and valve flow change the real impact speed. Our pneumatic solenoid valve selection guide covers that circuit context. Recheck absorber sizing whenever speed or pressure is changed. For retrofits, film the motion to communicate the problem but also log mass, speed, force and cycle count. Inspect existing guide play and stop-plate looseness; damping noise alone will not correct a side-load problem.
Retrofit work needs measured logs as well as video
A retrofit request often begins with noise, a worn stopper or a workpiece that bounces. Video documents the symptom, but it cannot provide the energy calculation by itself. Retrieve encoder speed immediately before impact when possible. Otherwise measure travel and time by a safe method agreed for the machine. Weigh the heaviest and lightest product variants. For a pneumatic cylinder, pressure setting and bore can help establish a thrust bound, but computed thrust is not the same as measured thrust because pressure and friction change. Inspect guide play, stop plate looseness and sensor alignment at the same time. Replacing only the absorber may hide an increase in impact load or side load.
Send a comparable request for quotation
Give each supplier the same application sketch and operating range: moving mass with fixture breakdown, measured impact-speed range and measurement method, continuing force, usable stroke and positive-stop position, impacts per minute and hour, peak continuous run, environment, accepted rebound and final-position variation, and maintenance constraints. Ask the supplier to return the checked per-stroke and per-hour energy, effective mass, speed range, stroke, stop force, environmental rating and mounting parts for its proposed part number. Compare quotations only after confirming their assumptions match.
| Item | Specify in the RFQ | If unknown |
|---|---|---|
| Application drawing | Relationship among moving body, drive, absorber, guide and positive stop | Attach photographs and a simple section sketch |
| Moving mass | Maximum and minimum masses, broken down into workpiece and fixture | Weigh the components separately |
| Impact speed | Maximum and minimum speed immediately before contact and how it was measured | Request a measurement under a stated test condition |
| Continuing force | Drive thrust, gravity component and push from following products during the stroke | Provide control conditions and the basis of the estimate |
| Usable stroke | Actual travel, fixed-stop position and adjustment range | Recalculate including drawing and assembly tolerances |
| Duty | Impacts per minute and hour, operating time and peak duty | Supply takt records and utilization |
| Environment | Temperature, liquid, dust, chips, washdown and corrosion | Inspect the actual mounting location |
| Stop quality | Permitted final-position error, rebound, noise and product damage | Agree acceptance criteria before choosing the part |
| Maintenance | Replacement time, spares, local availability and replacement trigger | Avoid assuming one fixed replacement interval |
Compare total cost before choosing the cheapest unit
Total cost includes brackets, machining, guide reinforcement, sensors, commissioning time, spares, replacement labor and the cost of lost production. An oversized model can also perform poorly at low-energy conditions, so buying the physically largest unit is not a reliable margin strategy. If service-life estimates are offered, record the supplier’s test conditions and compare them with actual temperature, dirt and duty cycle before using them in a payback calculation.
FAT/SAT: test the worst and the lightest cases
At FAT, test maximum mass and maximum speed together, the light-load condition, and representative continuous running. Check final position, rebound, abnormal noise, leakage, return before the next impact and movement of the mounting bracket. Increase speed in controlled steps with a safe dummy workpiece when product damage is possible. Keep a video and measured speed, displacement or position repeatability wherever practical.
At SAT, repeat the checks with the plant’s actual pressure, piping, conveyor load and temperature. A short FAT may miss the hourly energy limit, so run at peak takt for a duration agreed for the selected model and application. Do not infer one universal test duration from the illustrative 7,200 J/h calculation. Record model and serial number, adjustment, installed dimensions, initial stop position, speed and pressure settings, temperature and cycle count. Give local maintenance staff a clear inspection and replacement sheet. Confirm guarding, emergency stop and interlocks for a failed absorber as part of the whole machine.
Maintenance: what to record before failure
Inspect for oil leaks, damage, changed stopping point, increasing rebound or noise, slower plunger return and loose mounting hardware. When performance changes, record speed setting, pressure, workpiece mass and guide condition before replacing a unit. Use the maker’s instructions and plant data to set inspection and preventive replacement rules; avoid a universal cycle-life claim detached from the application. After replacement, recheck speed and positive-stop position rather than relying only on the old thread position.
Before freezing the specification, ask: Which combination of product mass and speed is most demanding for this model, including the light-load case? What exact dimension should separate the plunger and positive stop across mounting tolerances? Which settings and measurements must be recorded so maintenance can restore the same stopping behavior after replacement? Answering those questions makes the purchased component maintainable, not merely dimensionally compatible.
Three questions to ask the manufacturer before the specification is final
First ask which combination of mass and speed is most demanding for the proposed model. The heaviest product at maximum speed is not automatically the only critical case: a light product may sit outside the effective-mass range or use too little stroke. Send the whole product matrix and have the supplier confirm each operating point.
Second ask for the exact drawing dimension between plunger and positive stop. Check the deepest and shallowest positions after bracket tolerances, plate deflection, cap wear and stop adjustment. Do not leave this to an undocumented commissioning adjustment; bottoming out and failing to use enough stroke are different failure modes.
Third ask what must be recorded to restore performance after replacement. Candidate records include adjustment dial position, thread and locknut positions, stop position, speed and pressure settings and serial number. Put the answer into the maintenance sheet. A technically compatible unit is difficult to maintain if each replacement changes the stopping behavior.
Five signs to pause the purchase decision
A calculated energy value below a candidate’s rating does not always justify an order. First, pause when impact speed has not been measured and only a controller setpoint is known. Energy depends on velocity squared, so a small speed error can materially change the answer. Measure speed just before contact using a suitable encoder or a safe distance-and-time method, or agree on a conservative design value with the supplier. An informal statement that the axis “probably stays below 1 m/s” is not an adequate RFQ assumption.
Second, pause when the mounting geometry puts lateral load into the absorber rod. An off-center pallet, guide clearance or worn impact plate can make the contact angle change over time. Correct the guide and strike face so the absorber handles axial load. Choosing a larger absorber does not fix rod bending. Include both new and worn contact conditions in inspection.
Third, pause when the machine relies on the absorber alone for its final process position or safety limit. A separate positive stop or locking mechanism may be needed for repeatable machining or assembly. Even models with an integrated stop have model-specific allowable force and position conditions. Show where the moving body can travel if the absorber fails or detaches, and address the hazard with the machine’s guard and interlock design.
Fourth, pause when the thermal duty is unknown. A few dozen commissioning cycles can look normal while peak production exceeds hourly energy or cycle limits. Identify the busiest hour and its continuous duration instead of using only average takt. Measure temperature at the installed location; enclosure ventilation and nearby equipment heat matter as well as the heat generated by repeated impacts.
Fifth, pause when a same-size substitute is treated as a drop-in without revalidation. Internal damping, return force and velocity limits can differ despite similar external dimensions. Recalculate, verify mounting and repeat the relevant FAT/SAT criteria after a model change. Update the drawing, spare-part label and maintenance record so old and new models do not silently mix.
Feed commissioning evidence back into purchasing specifications
After the first machine is commissioned, put measured impact speed, pressure, workpiece mass, cycle rate, stop position and model settings into the next machine’s RFQ. If the measured speed differs from the design assumption, recalculate energy rather than merely noting that an adjustment was made. Keep drawings, PLC settings and maintenance sheets on the same revision. When new products are added, check their mass, approach speed, contact point and continuing force. A lighter product can run faster, so lower mass alone does not prove lower energy. Give technicians photographs or short videos of leaks, incomplete plunger return, changed stop position and abnormal noise, along with the plant’s stop-and-escalate rule. Whether production can continue while a spare is obtained requires a machine-level risk assessment, not an absorber-only judgment.
FAQ on industrial shock absorber selection
Can I select by thread size?
No. Thread size is a final mounting check. Determine energy, speed, effective mass, stroke, stop force, cycle rate and environment first. Same-size replacements can have different internal damping behavior.
Is a per-stroke energy rating above my calculation enough?
No. Check the hourly energy or cycle rating, effective-mass and speed ranges, return time, stop force, temperature and mounting. In the example, both 12 J per impact and 7,200 J/h require separate verification.
Can two units each be rated for half the energy?
Only if the design and test substantiate that load sharing. One absorber may contact before the other and take more than half. Review the worst asymmetry with the manufacturer.
When is a cylinder’s built-in cushion sufficient?
When the actual mass, speed and frequency fall within its ratings and measured stop quality is acceptable. If rebound, vibration, wear or noise remains, review speed control and an external absorber together.
What drives price and replacement cost?
Capacity, stroke, adjustability, environmental specification, brackets and supply conditions affect quoted price. Compare installed cost, spares, replacement labor and downtime. Prices depend on the final specification and purchasing terms in Thailand, so a generic price would mislead.
Can I replace a failed unit with a same-size model from another maker?
Not without rechecking. Identical outside dimensions do not establish equal per-stroke and hourly energy, speed range, effective mass, stroke, return behavior, stop force, temperature or mounting limits. Confirm final position and machine safety limits during recommissioning.
Summary
For industrial shock absorber selection, calculate kinetic energy from moving mass and impact speed, add drive work during the stroke, and verify both per-impact and hourly energy. Check effective mass, speed, stroke, force, alignment, environment and return for the exact model. Give suppliers the same assumptions, then test heavy, light and continuous cases during FAT/SAT and record stop quality in operation.
Discuss your application: If a new line or retrofit still needs impact-speed measurements, force assumptions or a comparable RFQ, contact TOMAS TECH. We can help organize the machine drawing and operating conditions before a model is selected.
