When a hydraulic cylinder bangs at the end of its stroke or hesitates when it reverses, the first suspect is often the hydraulic circuit or the valves. In many cases, though, the cause is the cylinder's own end cushioning. This article explains what cushioning does, the four most common symptoms, the operating conditions it needs, and what to ask before choosing a cylinder.
1. What end cushioning does
As the piston approaches the end cap, the cushion gradually restricts the oil leaving the cylinder, so the piston slows down before it reaches the cap. Ideally, pressure in the cushion chamber stays close to constant over the whole cushioning stroke, which means smooth, even deceleration. Any pressure spike is felt on the machine as a surge or a bang.
2. Four symptoms of poor cushioning
- Hesitation at start: the cylinder pauses before moving away from the end position. Common cause: the return-flow path is too small, so oil cannot refill the cushion chamber quickly.
- Rough entry: sticking or rubbing as the piston enters the cushion. Common cause: the cushion parts are not concentric with their bore.
- Surge: a sudden jolt partway through the cushion. Common cause: the throttling area changes abruptly, creating a pressure spike.
- End-of-stroke bang: the piston still hits the end cap. Common cause: too little throttling at the very end, so residual speed reaches the cap.
3. Operating conditions (common industry practice)
- Speed window: without cushioning, a hydraulic cylinder should run at roughly 50 mm/s or less to avoid metal-to-metal impact. Above that, choose a cushioned cylinder or add an external stop. At speeds below about 80 mm/s, cushioning becomes less effective.
- Run to the end: if the mechanism stops 3 to 5 mm before the end of stroke, the cushion has no chance to work.
- Do not combine with shock absorbers: cushions and external shock absorbers behave differently. Used together, the inertia load ends up concentrated on one of them.
- Four common reasons cushioning fails: extremely low speed; extremely high speed combined with overload; the cushion adjusting valve left fully open; the check element not operating.
- Adjusting: start at low speed and increase gradually. Over-tightening creates abnormal pressure spikes that can damage the cylinder or the machine.
- Lower force at start is not always a fault: when the piston starts from tight against the end cap, output force drops briefly because of the smaller effective pressure area.
4. Where cushioning matters most
- Auxiliary mechanisms on forging and hydraulic presses: feeding, stripping, positioning and safety stops run to the end at high cycle rates, and every impact is transmitted to dies and frames.
- Press brakes and equipment maintenance: when worn cylinders are replaced, there is not always an experienced technician on site, and a poorly set cushion means banging or slow motion.
- Automation equipment and fixtures: impacts during clamping, pushing and lifting cause positioning drift, loosened fasteners and noise.
- Injection molding peripherals: in take-out, pushing and guard-door motions, jolts slow the cycle and increase wear.
5. Five questions before you choose
- What is the piston speed? This single question rules out most cushioning problems.
- How heavy is the load, and are there external forces? The more kinetic energy, the more important it is to confirm the cushion can absorb it.
- Does the cylinder run to the end of stroke every time? If not, the cushion never engages.
- Which end needs cushioning? Extend, retract, or both. HINAKA 15B and 5H series are currently available with adjustable cushioning at both ends, front only, or rear only.
- Is there room to reach the adjusting valve? Make sure a tool can reach it after installation.
6. HINAKA floating cushion (patent pending)
To address the two most common complaints, hesitation at start and end-of-stroke impact, HINAKA has developed a new floating cushion design, now patent pending. What it delivers:
- Smooth restart from the end position, without the piston sticking before it moves
- Less jolting, vibration and noise during cushioning
- Less need for repeated on-site adjustment
- Less impact wear on components, for longer service life
Contact HINAKA through Contact Us for available specifications.
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