Product Overview

What this kit covers

A hydraulic cylinder on a mobile crane spends its working life under load, and the seals are the parts that hold oil on the pressure side of the piston. This set is the rubber seal kit for one cylinder on the QY50K: rod seal, wiper and piston seal, supplied together so a reseal does not stall halfway through because one ring is missing. Seals are also the smallest item in the repair — the rod, barrel and gland are normally reused when a cylinder is opened up.

Matched to the cylinder you are resealing

Cylinders on the same machine do not all carry the same set. A boom cylinder, an outrigger cylinder and a steering cylinder work at different pressures and take different rod sizes, so the kit is matched to the cylinder you name rather than sent as a generic assortment for the workshop to sort out. The three details we ask for are always the same: the machine, the cylinder, and the numbers from the parts coming off.

Where the seals come from

The kits are held by a crane parts supplier working with XCMG mobile cranes, and each set is checked against the cylinder you name before it goes into the carton. Nothing here is pulled from a mixed bin of loose rings.

Kit Contents & Seal Functions

• Rod seal. Sits in the gland and holds system pressure against the moving rod. Once it hardens, nicks or takes a set, it stops doing its job and oil starts passing the rod.
• Wiper (dust) seal. The outer lip that scrapes dust, grit and water off the rod before any of it reaches the gland. On machines working in dust or mud it is usually the first part of the set to wear.
• Piston seal. Seals the piston against the bore and keeps the two chambers separated, so internal bypass shows up as a cylinder that moves unevenly rather than as oil on the ground.
• One cylinder per kit. The set is made up for a single cylinder, not a whole machine, so count the cylinders in the job before you order.
• Handled as one set. The rings arrive coiled in a sealed bag as a matched group for one cylinder, which keeps every profile together on the bench and makes it easy to see that nothing is missing before the cylinder is opened.
• Low-cost wear items. A reseal reuses the rod, barrel and gland and replaces only the parts designed to wear, which is why a seal kit is a small line on a heavy equipment parts order next to the cost of the cylinder it protects.
• Part of a wider range. These seals sit inside our construction machinery spare parts range, which also covers crawler crane parts alongside the hydraulic, undercarriage and engine items a rebuild can turn up.

Specifications

Confirming the Right Kit

1. Note the machine and the cylinder. Write down the model from the machine plate and say which cylinder you are resealing — boom, outrigger, steering or hoist. It is the same information we need for crawler crane parts, so a mixed fleet is no problem.
2. Check the numbers on the parts you take off. Numbers stamped or printed on the old seals, or on the cylinder gland and barrel, are the quickest way to match the variant.
3. Photograph the old seals in the order they came off. Take the picture before you clean them, while the profiles and any markings are still visible.
4. Tell us how many cylinders are in the job. Give the positions and the count rather than one number for the whole machine.
5. Send the details for a check before you order. We compare them against the kit we hold and confirm the match, or tell you what we can supply from our range of crane parts instead.
6. Flag anything unusual. A repaired rod, a non-standard gland or seals that do not match the drawing are all worth mentioning — it is better to hear about them before the parcel ships than after the cylinder is open.

Rubber Seals & Build Quality

Why the material matters

The seals here are made from rubber — flexible enough to follow the rod through every stroke, firm enough to hold at the lip. That balance is what the compound is chosen for, and it is why a seal that has hardened or taken a set is worth nothing: it passes oil from the first cycle and puts the cylinder back on the bench. Every set supplied is new, never refurbished, and it comes out of the same stock as the rest of our crane spare parts.

What to look for in the parts themselves

Run a finger along the sealing lip. It should be smooth and even, with no mould flash, trimming marks, cuts or nicks, because any break in the lip is exactly where oil will find a way out. The rings should flex without creasing; rubber that has stiffened or gone shiny on the surface has aged and does not belong near a cylinder that has to hold a load. Keep the seals away from sharp edges on the bench and from contact with solvents while you are working, and check the set against the cylinder before it goes on. Every set is gone over before it is packed — that is the least a crane parts supplier can do for a workshop that has already stripped a cylinder.

The failure pattern

Wear parts like these do not fail only on mobile cranes. The same sealing principles apply right across heavy equipment parts wherever a cylinder works under pressure, so the habits that protect a seal here — a clean bench, a blunt tool, no solvents — are worth keeping on every rebuild.

Fitting & Commissioning Notes

1. Work clean. Wipe the cylinder down before it is opened and keep the bench free of swarf, grit and old oil. Contamination is the most common reason a fresh set of seals fails early.
2. Lay the new parts out in the order they will be fitted. Having everything in sequence before you start is what stops a seal being picked up the wrong way round under time pressure.
3. Lubricate the seals with clean hydraulic oil from the machine before assembly. Dry rubber drags on the rod, and a lip that rolls during fitting will leak.
4. Seat each seal square in its groove. Press evenly with your fingers or a blunt tool — never drive a lip over a sharp edge or lever it in with a screwdriver.
5. Reassemble the gland and end cap to the manufacturer's torque figures, tightening evenly so the seal is not pinched to one side.
6. Bleed the circuit before the machine goes back to work. Cycle the cylinder slowly through its full stroke a few times with no load on it, then check the oil level.
7. Look at the gland after the first working cycles. A dry gland and a steady rod are what you want; a persistent drip means something in the assembly needs a second look before the crane goes back on full duty.

Ordering & Delivery

Model & Fluid Compatibility

• Built for one machine and one cylinder. The set is matched to the QY50K cylinder you name, not to the QY50K as a whole. Two cranes of the same model can carry different glands after years of repair, so the machine plate on its own does not settle the question.
• Not a cross-model kit. Seal size follows bore, rod diameter and groove profile, so a cylinder on another XCMG mobile crane — or on any other crane in the yard — will not take this set just because the machine is similar in capacity. Send the model and the cylinder position and we check it before it ships; a set that is close but wrong puts the crane straight back in the workshop.
• Counted by cylinder position. Boom, outrigger, steering and hoist cylinders on one crane are different sizes and take different sets. Order by position and number, and do not open a second cylinder just because the first kit went in cleanly.
• Confirm from the old parts. Numbers stamped or printed on the seals coming out, and the numbers on the gland and barrel, are the fastest way to pin down the variant. Photograph them before cleaning, while the markings are still legible.
• Tell us what the crane actually runs. These seals are supplied for the hydraulic oil the cylinders normally use. If the machine has been converted to another fluid type, or your site runs a fluid you are unsure about, say so when you enquire and we will confirm what suits the system before you commit to the order.
• Deal with contaminated oil at the same time. A seal failure that follows a pump or motor failure is usually a debris problem. Flush the circuit, change the filters and check the oil before the new kit goes in, or the same failure returns within weeks. Filters and repair kits for the same machine can travel on the same crane spare parts order.
• Keep the set together. Do not drop in a ring from a mixed box of loose seals or from another kit to get a machine back on hire. A profile that is nearly right still leaks, and it takes the cylinder off the machine a second time.
• What to send for a quick answer. Machine model, cylinder position, the numbers off the old seals and the fluid in use. We compare that against the kit we hold and come back with a straight answer, or with what else we can supply from our range instead.

Discontinued & Hard-to-Find Parts

When a machine is out of production but still working, the part number matters more than ever. If the number you have is discontinued or hard to trace, send us the machine model together with that number: we search our supplier network, confirm what is genuinely available, and give you a straight answer before you commit. Where the original is no longer made, we set out the alternatives we can actually supply, or an upgrade path, and coordinate samples, inspection and made-to-order work with the suppliers we buy from. Sourcing, consolidation and export handling stay with us.

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