Crane End Stops and Track Buffers: How the Last Line of Protection Works

End stop, buffer, stopper: what the names mean

The end stop is the fixed steel stop at the end of a runway or trolley rail. The buffer is the energy absorber between the moving crane and the stop: it takes the crane's kinetic energy and limits the force on both. Engineers and catalogues use many names for the two parts: crane end stop, end stopper, rail stop, runway end stop and crane stopper for the stop; crane buffer, track buffer, rail buffer and crane bumper for the buffer.

Where end stops and buffers go

• At both ends of the crane runway, for the bridge or gantry travel.
• At both ends of the trolley rails on the bridge, for the trolley travel.
• Between two cranes on the same runway, so that they can meet without damage.
• At the ends of outdoor gantry rails in ports, yards and shipyards, where long travel and high speeds make the impact energy high.

On every axis both sides must stop together. If one end stop is set back or one buffer is missing, one side of the crane takes the whole impact and the crane skews on its rails.

Buffer on the crane or on the end stop

Buffers are usually fitted to the crane's end carriages and strike a plate on the end stop. The crane then carries its protection with it, and the same buffers also work against a second crane on the runway. In the other arrangement the buffers sit on the end stops and the crane carries a striker plate; it is used where there is no room for the buffer on the end carriage.

Either way the buffer's axis must meet the plate at the right height and squarely. Our hydraulic buffers come with front-mount (FM) or rear-mount (RM) flanges, and our spring buffers have base flanges from 150x150 to 260x260 mm with matching hole patterns, so the end stop plate can be drilled to suit.

Hydraulic, spring or polyurethane track buffers

• Hydraulic buffers (HB series): four sizes, 063, 080, 100 and 125, each with strokes from 100 to 800 mm in 50 mm steps. They absorb 15 to 435 kJ per stroke at buffering forces up to 670 kN, with almost no rebound: the choice for heavy and fast cranes, port and steel-mill cranes.
• Spring buffers (SB0250 to SB7500): 250 to 7,500 J per stroke, strokes of 80 to 180 mm and end forces from 5 to 85 kN. Simple and durable; the spring gives most of the energy back, so the crane rebounds.
• Polyurethane buffers: light, compact and maintenance-free cellular elastomer buffers for light and medium duty, such as indoor overhead cranes and trolleys at modest speeds.

How to work out the impact energy and pick a hydraulic buffer is shown step by step in our hydraulic buffer sizing guide.

• Hydraulic Crane Buffer Sizing: Impact Energy, Stroke and Force →

The force the end stop must carry

A buffer limits the force but does not remove it: the end stop carries the buffer's end force at every impact. The end stop, its bolts or welds and the runway beam or rail behind it must therefore be designed for the buffer's maximum end force, acting at the height of the buffer axis, plus the factors the crane design standard requires, for example EN 13001.

An example from our tables: an HB 100 buffer with a 300 mm stroke absorbs up to 115 kJ and pushes with up to 420 kN. A crane with one such buffer on each side of the runway needs two end stops, each designed for at least 420 kN at the buffer height, before the design factors. A spring buffer SB2000 absorbs 2,000 J at an end force of 40 kN: a tenth of that load, but also a small fraction of the energy.

Because the end stop carries the buffer's force, we design and supply the two together: the stop is sized for the buffer, and its plate and hole pattern match the buffer flange.

Alignment and contact

• Both buffers of an axis touch their stops at the same moment; check this after any change to the runway or the rails.
• The buffer axis meets the centre of the stop plate, not its edge, and runs parallel to the rail.
• The end stop sits beyond the last point the crane needs to reach, with room for the full buffer stroke.
• Travel limit switches slow and stop the crane before it reaches the buffers; the buffers are for the case where they do not.

Inspection and replacement

Check end stops and buffers at every periodic crane inspection and after any hard impact:

• Hydraulic buffers: oil leaks, damage or corrosion on the piston rod, and whether the rod returns fully after compression.
• Spring buffers: broken or cracked coils and loose fixings.
• Polyurethane buffers: cracks, missing pieces and permanent compression.
• End stops: bent plates, cracked welds, loose or missing bolts and movement on the rail or the beam.

A buffer that has taken a hard impact, leaks or does not return must be replaced. When you replace buffers on an existing crane, send us the flange dimensions and hole pattern of the old buffer and of the end stop together with the crane data; we match the new buffer to them.

What to send us

• Crane type and the number of cranes on the runway.
• Moving mass: crane, trolley, and whether the load hangs free.
• Travel speed at impact.
• Space available for the buffer and the end stop; drawings or photos of the existing stops.
• Environment: indoor or outdoor, normal or aggressive.
• Whether you need buffers, end stops or both.

Frequently asked questions