Hydraulic Crane Buffer Sizing: Impact Energy, Stroke and Force
Updated:
A hydraulic crane buffer has one job: to stop a travelling crane or trolley at the end of its runway without damaging the crane, the end stop or the building. Choosing one comes down to three numbers: how much energy the buffer must absorb, how long a stroke you can fit, and how much force the structure can take. This guide shows the calculation step by step, with worked examples based on the KRANHAUSS HB series.
How a hydraulic buffer works
When the crane hits the buffer, the piston rod pushes oil through calibrated orifices. The resistance of the oil turns the crane's kinetic energy into heat, and a return spring pushes the rod back out once the crane has stopped. In most industrial hydraulic buffers the orifice area shrinks as the piston moves in, so the braking force stays close to constant over the whole stroke.
That near-constant force is the main difference from spring and polyurethane buffers, whose force rises as they are compressed. For the same energy and stroke, a hydraulic buffer gives the lowest peak force on the crane and the end stop, and it returns almost none of the energy as rebound.
Step 1: Collect the input data
You need four values before any calculation:
- Moving mass m: the self-weight of the crane or trolley, plus the payload where it moves with the crane. A rigidly guided load counts in full; how a freely hanging load is treated depends on your design code. If you are unsure, include it: the result is on the safe side.
- Impact speed v: the travel speed at the moment of impact. Some design rules allow a reduced value, often 70 % of the rated speed, when the crane has automatic slow-down or end-limit switches. Without them, use the full rated speed.
- Number of buffers n that take the impact at the same time, usually two per runway end (one per rail).
- Space and structure: the length available for the buffer, and the force the end stop and the crane structure can carry.
Step 2: Calculate the impact energy
The energy to absorb is the kinetic energy of the moving mass: E = ½ · m · v². With m in kg and v in m/s, E is in joules; divide by 1,000 for kJ. Convert speeds in m/min to m/s by dividing by 60.
The buffers that take the impact share this energy, so each must absorb E / n. Where the mass is not centred, for example a bridge crane with its trolley at one end, one side carries more of it: size the buffers for the heavier side.
Speed matters most, because energy grows with the square of speed. Reducing the impact speed to 70 % cuts the energy to 49 %.
Worked examples
50 t at 60 m/min, 2 buffers
Total energy 25 kJ, 12.5 kJ per buffer
| Model | Capacity W | Stroke | Force F |
|---|---|---|---|
| HB 063 100 | 15 kJ | 100 mm | 170 kN |
| HB 080 100 | 23 kJ | 100 mm | 260 kN |
| HB 063 150 | 23 kJ | 150 mm | 170 kN |
200 t at 40 m/min, 2 buffers
Total energy 44.4 kJ, 22.2 kJ per buffer
| Model | Capacity W | Stroke | Force F |
|---|---|---|---|
| HB 080 100 | 23 kJ | 100 mm | 260 kN |
| HB 063 150 | 23 kJ | 150 mm | 170 kN |
| HB 063 200 | 30 kJ | 200 mm | 170 kN |
The examples use the full rated speed and no extra design factors. The figures come from the HB data table; the calculator on the product page does the same for your own values.
Step 3: Choose capacity, stroke and force
Pick a buffer whose energy capacity W is at least the energy per buffer. Every HB size comes in strokes from 100 to 800 mm, and for the same energy you can trade stroke against force: a longer stroke stops the crane more gently and loads the end stop less.
Then check the buffering force F against what the end stop and the crane can carry. The deceleration of the crane is roughly F divided by the mass behind each buffer; keeping it low protects the crane, the load and the operator.
If your design code adds factors, such as dynamic factors, safety margins or a drive force that keeps pushing during the stroke, apply them to the energy before you compare it with W.
HB series at a glance
| Size | Strokes | Energy capacity W | Buffering force F |
|---|---|---|---|
| HB 063 | 100–800 mm | 15–60 kJ | 70–170 kN |
| HB 080 | 100–800 mm | 23–109 kJ | 150–260 kN |
| HB 100 | 100–800 mm | 38–240 kJ | 330–420 kN |
| HB 125 | 100–800 mm | 60–435 kJ | 590–670 kN |
Step 4: Mounting and operating conditions
- Mounting: HB buffers come with front mount (FM) or rear mount (RM) flanges; choose the one that fits your end carriage or end stop.
- Environment: tell us whether the crane works indoors or outdoors, in normal or aggressive conditions such as dust, humidity, salt air or heat. This decides the sealing and the coating.
- Colour: the housing can be painted to your colour; red, blue, yellow, green, black and white are standard.
- Counterpart: the buffer must meet a flat striker plate or another buffer squarely. Misalignment loads the piston rod sideways.
Hydraulic, spring or polyurethane?
- Hydraulic buffers: the most energy for their length, a nearly constant force and almost no rebound. The usual choice for heavy or fast cranes.
- Spring buffers: store the energy and give most of it back, so the crane rebounds; the force rises steadily as the spring is compressed. Suited to lighter, slower cranes.
- Polyurethane (elastomer) buffers: compact and economical for low energies; their force rises sharply near the end of a short stroke.
KRANHAUSS offers all three types; the crane buffers page compares them.
Crane Buffers →Frequently asked questions
How do I calculate the energy a crane buffer must absorb?
Use E = ½ · m · v² with the moving mass in kg and the impact speed in m/s, then divide by the number of buffers that take the impact. For example, 50 t at 60 m/min (1 m/s) gives 25 kJ, or 12.5 kJ per buffer with two buffers.
Should the payload be included in the buffer calculation?
A load that is guided and moves rigidly with the crane counts in full. How a freely hanging load is treated depends on the design code you work to. Including it gives a conservative result.
Which travel speed should I use?
The speed at impact. Some design rules allow a reduced impact speed, often 70 % of the rated speed, when automatic slow-down or end-limit switches are fitted; otherwise use the rated speed.
Why choose a hydraulic buffer instead of a spring buffer?
A hydraulic buffer absorbs more energy for its length, keeps the braking force nearly constant and has almost no rebound, so the crane and the end stop see lower peak forces.
What do you need from me for a quotation?
The moving mass, travel speed, number of buffers, the installation length available, the mounting type and the operating environment. The quote form on the hydraulic buffer page has a field for each of them.
Size your buffer
Enter your crane's mass and speed in the calculator on the HB page, download the datasheet, or send us your data for a written offer.