Cushioning and a mechanical end stop solve related but different problems. Cushioning slows the piston near the end of travel by restricting flow. A stop defines the permitted final position and must withstand the remaining load. One should not be assumed to perform the other’s job.
Energy and position are different requirements
A moving mass carries kinetic energy proportional to the square of speed. Doubling approach speed therefore gives four times the kinetic energy before considering gravity or other external work. Cushioning slows the piston over a short end zone by throttling oil; the available deceleration distance, flow path and pressure limit determine what it can absorb. A mechanical stop fixes the final machine position and carries the residual static or impact load. If the machine requires an exact parked geometry, that stop should be identified on the assembly drawing.
Parker’s application engineering guide asks the designer to review cushioning where piston speed and end-of-stroke contact matter. Actual absorbed energy depends on moving mass, speed, load direction and valve timing, not speed alone. Some machines need an external stop that is reached before a cylinder bottoms internally; others use a cylinder end position as part of the intended arrangement. The chosen sequence should be shown on the machine drawing and tested at the most severe operating load. Check whether the circuit can generate pressure spikes during rapid deceleration.
Watch the complete load path at the stroke end
An external stop reached before cylinder bottoming may protect the piston from contact, but it can leave the actuator still pressurized against the machine frame. An internal piston stop may set travel, but only if its design and load rating were agreed for that role. A cushion adjustment that gives a gentle stop with an empty machine may behave differently with a full load or an overrunning direction. Record pressure at both cylinder ports during the end approach and verify there is no excessive peak or unstable reverse motion.
A press-ram example
A heavy press ram approaches the bottom of its travel quickly, then slows as the cylinder cushion begins to restrict flow. The die set still needs a defined final position. If the machine stop contacts too early, the actuator may keep forcing the frame while the cushion has not completed its job; if the piston bottoms first, the cylinder may absorb a load intended for the frame. Plot position, speed and both port pressures during the final movement under representative load. The acceptance criteria should name the intended contact order, final position and permitted pressure peak, not merely whether the operator hears an impact.
Commission with a defined acceptance condition
Specify target approach speed, load, stopping position and acceptable shock or pressure trace. Test both ends independently at representative oil temperatures. If the mechanism needs a separate structural stop, show its contact surface and clearance from the cylinder’s internal limit. If it uses the cylinder end position, obtain the cylinder maker’s approval for the expected force and cycle rate. A vague instruction to “adjust cushion until smooth” gives the commissioning team no measurable pass condition.
Checks to put on the drawing or test plan
- Estimate moving mass and speed immediately before the end zone.
- Show which component provides the final travel limit in each direction.
- Verify stop and cushion behavior at full load and operating temperature.
Failure mode to avoid: Increasing cushion restriction until impact disappears can create excessive pressure or unstable motion if the load is overrunning.
Information to request before approval
- Load and speed profile near both stroke ends.
- Machine stop geometry and available overtravel.
- Required acceptance measurements.
For a related explanation, see what cylinder cushioning does.
Technical references: Parker Application Engineering Guide. The cited manuals and product data describe their makers’ equipment; this article is independent engineering guidance and does not assign their ratings to Yongjian products.