Mobile Crane Cylinder

Mobile Crane Outrigger Cylinder

Four legs. Four cylinders. The entire crane — 50 tonnes of machine plus 100 tonnes of suspended load — stands on four outrigger pads pushed into the ground by four hydraulic cylinders. If one loses pressure, the crane tips. Short stroke, maximum force, zero tolerance for drift.

70–360mmBore Range

≤800mmStroke

42 MPaPressure

×4Per Crane

The Foundation of Every Lift — Why the Crane Leaves the Ground

A mobile crane cannot lift from its wheels. Tyres are compliant — they compress, deform, and shift under load. If the crane lifted while resting on tyres, the suspension would compress unevenly as the boom swings, tilting the crane and making precise load placement impossible. Worse, the overturning moment from a load at the boom tip would roll the crane onto two wheels — then onto its side.

The outrigger cylinders solve this by creating a rigid, wide-footprint support base. The four cylinders extend downward, pressing steel pads firmly into the ground. As the pads take the weight, the crane's wheels lift off the surface. The crane now stands on four solid points — spaced wider than the wheel track — providing a stable platform that resists the overturning moment from any boom angle and any load within the crane's rated capacity.

Korea Ever-Power manufactures outrigger cylinders as the stability foundation of the mobile machinery hydraulic cylinder range. Each outrigger cylinder is paired with an outrigger expansion cylinder (#21) that extends the beam horizontally before the outrigger cylinder pushes down.

Technical Specifications

Parameter	Specification
Product	Mobile Crane Outrigger Cylinder
Function	Support the weight of the entire crane during lifting operations
Bore Diameter	70 mm – 360 mm
Rod Diameter	45 mm – 320 mm
Stroke	≤ 800 mm
Working Pressure	Maximum 42 MPa
Application	Mobile Crane (all types)
Certification	ISO 9001 · 100% hydrostatic tested · load-holding verified

The Tipping Edge — Why Outrigger Failure Is the Number-One Crane Accident Cause

Crane tip-overs account for the majority of fatal crane accidents worldwide. The root cause in most cases is outrigger failure — not the outrigger cylinder itself, but the ground beneath the pad sinking under the concentrated load. However, the outrigger cylinder plays a critical role in preventing and detecting ground failure:

Load-holding valve — zero drift

Each outrigger cylinder has a pilot-operated check valve that locks the oil in the cylinder. Once the outrigger is set, the cylinder holds its position indefinitely — the pad does not creep downward even if the pump is shut off. This zero-drift performance is verified during factory testing: the cylinder is loaded to full rated force, the pump is disconnected, and the position is monitored for a defined hold period.

Level monitoring — detecting ground settlement

Modern cranes monitor the outrigger cylinder stroke position continuously. If one outrigger cylinder extends further than the others (indicating the ground beneath that pad is settling), the crane's safety system alerts the operator and may restrict the load chart. The outrigger cylinder's stroke sensor provides this critical feedback — making the cylinder a sensor as well as an actuator.

Overturning moment — the reaction force path

When the crane lifts a load at the boom tip, the overturning moment tries to tip the crane toward the load. The two outrigger cylinders on the load side resist this moment — their compressive force pushes down on the pads, and the ground pushes back up. The cylinder must sustain this compressive load without yielding, buckling, or leaking. Contact the Korea Ever-Power engineering team for outrigger cylinder force calculations.

Outrigger cylinder pad on ground — bearing pressure distribution

Short Stroke, Maximum Force — Why 800 mm Is Enough

The luffing cylinder (#17) needs 5,000 mm of stroke to swing the boom through its full angle range. The telescopic cylinder (#18) needs 22,000 mm to extend the boom sections. The outrigger cylinder needs only 800 mm — just enough to push the pad from its stowed position (tucked under the crane chassis) to the ground surface and slightly beyond (to lift the crane's wheels clear of the ground).

The travel distance from the stowed pad to the ground is 300–700 mm on most cranes. The remaining 100–500 mm of stroke provides adjustment for uneven ground — one outrigger may need to extend further than the others to level the crane on a sloped surface. The 800 mm maximum stroke accommodates the steepest ground slope that a crane can safely set up on (typically 1–3° from level, depending on crane model).

Manufacturing Process

Korea Ever-Power outrigger cylinder production

The outrigger cylinder barrel is thick-walled — designed for the full 42 MPa working pressure plus a safety factor for dynamic loads (the crane chassis experiences shock loading from wind gusts and sudden load releases). The bore is honed to Ra 0.2–0.4 µm. The rod end pad-mount is forged or welded with full-penetration welds — ultrasonically inspected, because the rod end carries the entire ground reaction force.

Chrome plating is 50–80 µm (outdoor service with direct ground contact splash). Seals are polyurethane with NBR wipers rated for -30 °C to +80 °C. Every outrigger cylinder is hydrostatic tested at 1.5× rated pressure (63 MPa) and load-holding tested — verifying zero measurable drift under full rated load for a defined hold period.

Outrigger cylinders are ordered in sets of 4 — Korea Ever-Power manufactures all 4 from the same bore batch to ensure matched force output across all four corners of the crane.

OEM & ODM

What You Provide

Crane model and maximum lifting capacity, outrigger span (distance between pads), maximum ground reaction per outrigger, stroke, bore/rod (or Korea Ever-Power calculates from force requirement), mounting geometry, load-holding valve specification, stroke sensor provision, and the outrigger beam assembly drawing.

What the Factory Delivers

Matched set of 4 cylinders with engineering drawing, load-holding valve port provisions, stroke sensor mounting, seal specification, chrome plating detail, and mounting dimensions. Hydrostatic + load-holding test certificate. Seal kits. Browse the industrial engineering cylinders and the complete Korea Ever-Power catalogue.

Korea Ever-Power hydraulic cylinder workshop

FAQ

How does the outrigger cylinder work with the outrigger expansion cylinder?

The outrigger expansion cylinder (#21) first extends the outrigger beam horizontally — sliding it outward from the crane chassis to maximise the support footprint. Then the outrigger cylinder (#19) extends vertically downward from the end of that beam, pushing the pad to the ground. The expansion cylinder provides width; the outrigger cylinder provides force. Both must be deployed before the crane can lift.

What force does each outrigger cylinder carry?

It depends on the boom position and load. When the boom points directly over one outrigger, that outrigger carries the majority of the overturning moment — potentially 60–80% of the crane's total weight plus the load. At 42 MPa with a 360 mm bore, the outrigger cylinder can produce over 4,000 KN of force — enough for cranes up to 500 tonnes lifting capacity.

Can the crane operate with outriggers partially extended?

Yes — but at reduced capacity. The crane's load chart has separate columns for fully extended, partially extended, and retracted outrigger positions. Partial extension reduces the support footprint, which reduces the crane's resistance to overturning — so the permitted load decreases. The outrigger cylinder's stroke sensor reports the actual extension to the crane's safety system, which automatically selects the correct load chart column. Browse telescopic cylinders and forklift cylinders for other stabilisation applications.