Hydraulic Boom Cylinder for Mini Excavator

The boom cylinder sits between the machine frame and the boom, and it is the component that lifts the entire upper structure of the excavator. On a mini excavator the boom ram works through a shorter stroke than a full-size machine but at a high duty cycle, often thousands of cycles a day on municipal, landscaping and farm work. That combination — short stroke, high cycle count, dusty environment — is what the specification needs to answer, rather than raw force alone.

Raydafon produces this cylinder in its own factory in Ningbo, China, for both machine builders and the aftermarket. Standard bore diameters run from 50 mm to 125 mm with rod diameters from 25 mm to 75 mm, stroke up to 1000 mm and maximum thrust of 361 kN, with a working temperature range of −20 °C to +70 °C. Related cylinders from the same factory include the wider excavator hydraulic cylinder range, the hydraulic bucket cylinder for small excavator that works with it on the same machine, and the hydraulic cylinder catalogue covering other mobile machinery.

• Product nameHydraulic boom cylinder for mini excavator
• Bore diameter50 mm – 125 mm
• Rod diameter25 mm – 75 mm
• Stroke≤ 1000 mm
• Maximum thrust361 kN
• Maximum pressure29.4 MPa
• Working temperature−20 °C to +70 °C
• Barrel materialHigh-strength alloy steel forging, precision ground bore
• SealingDouble sealing structure with wear-resistant imported rubber
• Surface treatmentAnti-corrosion treated rod and barrel exterior
• MountingTo machine drawing — pin, clevis or flange arrangement
• CustomisationBore, rod, stroke, mounting centres, port position, paint colour

How thrust and bore relate: the 361 kN maximum thrust applies to the largest bore in the range at 29.4 MPa. A smaller bore produces proportionally less force at the same pressure — a 50 mm bore at 29.4 MPa gives roughly 57.7 kN, a 63 mm bore about 91.6 kN, and an 80 mm bore about 147.8 kN. Always specify the bore together with the system pressure, because the thrust your machine needs is what decides the bore, not the other way round.

Photographs and reference views of the boom cylinder we produce for mini excavators.

Forged barrel and ground bore

The barrel is forged from high-strength alloy material rather than machined from tube stock, which gives a more uniform grain structure and better fatigue resistance at the threaded and welded ends. The bore is then precision ground so the piston seal runs against a consistent surface finish; that finish is what keeps the internal friction coefficient low — around 30% lower than an unground bore in our comparison testing — and it is why the boom can still be inched accurately when the machine is working in a tight space where centimetres matter.

Double sealing for dusty sites

Each cylinder uses a built-in double sealing structure with wear-resistant imported rubber. The inner seal holds hydraulic pressure while the outer wiper keeps dust and moisture away from the sealing lip, which is the arrangement that matters on site work: a single seal that is allowed to run contaminated is what produces the slow weep that eventually becomes a leak. In service this construction extends cylinder life by more than 40% compared with a single-seal arrangement and reduces how often the machine has to come out of work for maintenance.

Made to your machine's geometry

Bore, rod, stroke, mounting centres and port positions are produced to drawing. For a replacement cylinder this is the critical part — the mounting centres and pin diameters have to match the machine's boom and frame exactly, so send the original drawing, the machine model or the measured dimensions of the failed cylinder and we will match the interface before quoting. Different stroke and pressure configurations are available across the range to suit municipal, landscaping and agricultural duties.

This boom cylinder is supplied for mini excavators in the roughly 1 to 8 tonne class, where bore diameters in the 50–125 mm range are standard. It is fitted both as original equipment and as a replacement on machines from the following brands, among others:

• Kubota
• Yanmar
• Takeuchi
• Bobcat
• Caterpillar
• Komatsu
• Hitachi
• Volvo
• JCB
• Doosan
• Sany
• XCMG

Please note: brand names are listed only to indicate the machine classes this cylinder is commonly fitted to. Raydafon is an independent manufacturer and is not affiliated with, authorised by or an original equipment supplier to these brands. Always confirm the mounting drawing of your specific model before ordering.

Not sure which bore and stroke your machine needs? Send the excavator model, the existing cylinder's bore and rod diameter, its pin-to-pin length and the system pressure, and we will confirm the configuration.

Mini excavators are bought because they fit where full-size machines cannot, and that is exactly where the boom cylinder's control matters most.

• Factory-direct supplyThe cylinder is forged, machined, assembled and tested in Raydafon's own factory, so there is no trading margin between you and production, and drawings plus spare seals remain available for the life of the machine.
• Lower internal frictionPrecision ground bore and matched piston seal clearance reduce internal friction, which shows up as smoother low-speed control and less heat generated in the hydraulic oil during long shifts.
• Sealing built for site conditionsDouble sealing with an external wiper is specified for dust and moisture rather than for a clean workshop, which is what extends service life by more than 40% and cuts unplanned downtime.
• Range of strokes and pressuresBore, rod, stroke and pressure configuration can be matched to the machine rather than forcing the nearest catalogue size, which matters when replacing a cylinder on a discontinued model.
• Anti-corrosion surface treatmentThe rod and barrel exterior are treated against corrosion, so the cylinder survives rain, mud and wash-down without the surface pitting that destroys seals.
• Drawing-based replacementSend the original drawing, machine model or measured dimensions and the replacement is produced to that interface, so pins, ports and mounting centres fit without modification on site.

Thrust, seal life and service interval all depend on the bore selected, the system pressure, the duty cycle and how well the machine's hydraulic oil is filtered. Give us the excavator model and the working pressure, and we will confirm the bore and stroke against the load the cylinder will actually carry.

• What bore, stroke and pressure does this mini excavator boom cylinder cover?Bore diameters from 50 mm to 125 mm, rod diameters from 25 mm to 75 mm, stroke up to 1000 mm and maximum pressure of 29.4 MPa. Maximum thrust is 361 kN at the largest bore; smaller bores produce proportionally less force at the same pressure, so the bore should be selected from the thrust your machine needs.
• Can you make a replacement for my specific excavator model?Yes. Send the machine model, the original drawing, or the measured bore, rod diameter, stroke, pin-to-pin length and mounting details of the failed cylinder. We confirm the interface and produce the cylinder to match, which avoids the fitting problems that come from using a generic size.
• What is the difference between maximum thrust and pressure?Pressure is the hydraulic pressure the cylinder is rated for, in this case 29.4 MPa. Thrust is the force that pressure produces on the piston area, which is why it changes with bore diameter — 361 kN at 125 mm bore, but only about 57.7 kN at 50 mm bore at the same pressure.
• What temperature range can the cylinder work in?The standard working range is −20 °C to +70 °C. For machines operating outside that range, or with hydraulic oil that runs hotter, tell us the continuous oil temperature and we will confirm the seal material and specification that suit it.
• How is the cylinder protected against dust and water?It uses a double sealing structure with wear-resistant imported rubber and an external wiper, so the sealing lip is protected from dust and moisture. That arrangement is specified for site conditions rather than a clean environment and is what extends service life by more than 40%.
• What information do you need to quote, and can spare seals be supplied?Machine model, bore and rod diameter, stroke, working pressure, mounting type and quantity — the more of these you send, the faster we confirm the design. Seal kits and replacement components are available separately so a machine can be returned to service after a seal failure without replacing the whole cylinder. Quotation is normally within 24 hours.

• Excavator hydraulic cylinder — the full range of boom, arm and bucket cylinders for excavators.
• Hydraulic bucket cylinder for small excavator — the matching bucket ram for the same machine class.
• Hydraulic cylinder — the complete catalogue, including cylinders for other mobile machinery.
• Hydraulic lift cylinder — lifting cylinders for agricultural and municipal equipment.