KEVOS® MAKEOS · Hydraulics
Cylinder Cushion Check (Kinetic Energy, Deceleration, Cushion Pressure, Largest Speed)
When a hydraulic cylinder decelerates a moving load in its end cushion, how high does the trapped cushion pressure rise, and what is the fastest speed the cushion can stop it from?
Check of the end cushion of a hydraulic cylinder stopping a moving load at the rod end: the kinetic energy and the deceleration over the cushion length (as the uniform acceleration tool), the force needed to stop the mass plus the drive force still pushing on the full bore and any external load, the pressure in the trapped annulus that this needs, and the highest approach speed the cushion can take at its rated pressure, against the cushion pressure rating.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Moving mass | kg | Mass of everything moving with the rod, including the rod and piston. |
| Speed entering the cushion | m/s | Speed of the piston as it enters the cushion. |
| Cushion length | mm | Length of the cushion spear or sleeve. |
| External force pushing the same way | N | Other force in the direction of motion during cushioning, such as gravity on a falling load (negative if it opposes). |
| Cylinder | ||
| Bore | mm | Cylinder bore. |
| Rod diameter | mm | Rod diameter (the cushion traps oil in the annulus on extension). |
| Pressure still on the full bore during cushioning | bar | Pressure the pump keeps on the full bore while the cushion acts (relief setting for the worst case). |
| Cushion pressure rating | bar | Highest pressure the cylinder maker allows in the cushion. |
Method and formulas
- Deceleration a = v² ÷ 2s over the cushion length (as the uniform acceleration tool); kinetic energy ½ m v².
- Stopping force = m a + drive pressure × bore area + external force; cushion pressure = force ÷ annulus area.
- Largest speed = √(2s (rating × annulus − drive force − external force) ÷ m).
- Example: 25 J stopped in 20 mm raises the cushion to 154.44 bar; up to 2.0645 m/s is safe.
Limitations
- Uniform deceleration over the cushion; real cushions peak at the start unless they are profiled.
- Rigid oil; oil compressibility and hose swell soften the peak a little.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a cylinder stopping a heavy slide
- Find the fastest safe speed into the cushion
- Decide whether external shock absorbers are needed
Who it is for
- Hydraulic engineers
- Machine designers
- Maintenance engineers
What you get
- Kinetic energy and deceleration
- Force to stop and cushion pressure
- Largest speed for the cushion rating
Interpreting the result
- Pump pressure on the full bore often adds more cushion pressure than the load itself: dropping the pressure during cushioning helps most.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 175–181, 281–286. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
