If you run forklifts in a dusty yard, precast plant, quarry, brickworks or timber yard, it is common to see hydraulic oil weeping down a cylinder rod earlier in a machine’s life than you would expect.
A heavy impact on the rod is one possible cause, but it is not the usual one. In many cases the wear comes from fine dust settling on the rod while the cylinder sits extended, which then gets dragged back through the wiper seal each time the cylinder retracts.
A cylinder rod normally has at least two seals working together at the gland. An outer wiper, sometimes called a scraper or dust seal, is there to clean the rod as it comes back in. Behind it sits the rod seal, which is the one holding pressure. Higher pressure cylinders often carry a buffer seal as well, sitting inboard of the rod seal on the pressure side, and the exact arrangement varies by manufacturer and by cylinder type. There is normally a guide bush or wear ring in the gland as well, which keeps the rod centred as it moves.
Yard dust is often finer and harder than a standard wiper is designed to handle. Silica sand and stone fines are generally as hard as hard chrome plating or harder, so they can mark the rod surface. Cement dust is softer than the plating, so on its own it tends to abrade the seal material and cake on the rod rather than cut the chrome. It also hydrates once it picks up moisture, so a soft film left on a rod overnight can set into something much harder by morning. In most yards it arrives mixed with the harder fines rather than on its own.
Particles that get past the wiper lip can embed in the seal material, which is soft enough to hold them. At that point the seal stops working the way it should and starts behaving like an abrasive ring wrapped around a moving rod.
Once particles are held in the seal face, they can cut into the chrome plating as the rod passes. After the plating is scored the damage tends to run the other way as well, because a scored rod wears through new seals faster than a smooth one does.
Wear often starts on the inside of the seal rather than on the visible surface of the rod. By the time a score line is visible on the chrome, the seal behind it has usually been deteriorating for some time.
That is worth knowing on site. A cylinder that has just started weeping is not necessarily at the start of the problem. It may be at the point where the seal has finally given up.
The condition of the rod surface also affects how long a reseal lasts. If the rod is still smooth, new seals have a reasonable chance of holding. If the plating is scored or pitted, new seals can wear at a similar rate to the old ones and the leak may return sooner than expected.
Look for a ring of caked dust at the gland where the rod enters the cylinder. That can indicate the wiper is no longer clearing the rod, and it often appears before any oil does.
Watch for a darkened, damp film that comes back within a day of wiping the rod clean. A light film of clean oil on a rod is normal lubrication. Oil that carries dust colour with it is more likely to be coming from behind the wiper.
Check the gland face for a split or curled wiper lip. A damaged wiper generally means the rod seal behind it is taking more of the dust load.
None of these signs is conclusive on its own. Similar symptoms can come from other causes, so it is worth having a qualified technician confirm what is happening before work is booked.
It can, and there are two separate reasons. The first is mechanical. Slurry carries the same fines that dust does, and it dries hard on the rod, so the next retraction can drag a set, gritty film through the wiper.
The second is corrosion. Hard chrome plating contains fine cracks as a normal feature of the coating, and water sitting on the rod can reach the steel underneath. Corrosion below the plating can lift or break away small areas of chrome, and the pitting that leaves behind can affect seals in much the same way a score line does. Concrete slurry is also strongly alkaline. Some seal materials do not cope well with alkaline water left on the rod, which is another reason to clean slurry off rather than leave it to dry.
Directing a pressure washer at the gland can force water and fines past the wiper, which is the path you are trying to keep closed. Follow the washing instructions in the machine’s operator manual, and where the manual allows it, keep the lance away from cylinder ends.
Park with the cylinders retracted wherever the machine’s shutdown procedure allows it. Lowering the mast fully and setting the forks down at the end of a shift keeps lift cylinder rods inside the barrel overnight instead of sitting exposed. This costs nothing and is one of the more useful habits on a dusty site.
Wipe exposed rods with a clean rag as part of the daily check, using a rag that has not been sitting around collecting the same dust you are trying to remove. Where slurry or dust has dried onto the rod, soften it with a damp cloth first rather than dragging it along the surface with a dry cloth, then go over the rod again with a dry cloth so no water is left sitting on it.
Do that wiping only with the machine shut down, the park brake applied and the operator’s own site procedure followed. Reach the rods from outside the mast, and never put any part of your body between the mast channels or under a raised carriage or load. If a rod cannot be reached safely from the ground, leave it for scheduled service rather than working around the restriction.
Standard parking procedure on most trucks has the mast tilted forward until the fork tips rest on the ground, and in that position the tilt cylinder rods are extended. Tilting back is not a substitute for correct parking, so tilt rods spend time exposed on most sites regardless of what else you do. That is one reason they often show a leak before the lift cylinders do.
Have the wiper lips inspected at each scheduled service. Replacing a wiper usually means removing the gland, so in practice it is done as part of a full seal kit rather than on its own. Finding a split lip early is still useful, because it gives you the chance to book the work before the rod is scored rather than after.
Opening a hydraulic cylinder is work for a qualified technician. Hydraulic systems can hold pressure after shutdown, and fluid escaping under pressure can cause serious injury, including injection injuries that require immediate medical attention.
Ask for the mast and carriage side rollers to be checked at the same service. Worn rollers can let the mast rack slightly under load, and a racked mast can side load the lift cylinder rods, which puts uneven pressure on the seals. A worn guide bush inside the cylinder can have a similar effect, so it is worth asking about that at the same time.
On sites where this keeps happening, ask your dealer whether a different wiper or seal specification is available for that cylinder.
Running a fingernail along the rod is a rough field check. If it catches on a score line, a reseal on its own is less likely to hold. Do this under the same conditions as the daily wipe, with the machine shut down, the park brake applied, your own site procedure followed and the rod reached from outside the mast. Lifted or flaking chrome can leave a sharp edge, so wear gloves and do not run a bare finger along a rod you already know is damaged. The fingernail check is an indication rather than a measurement, and a technician will assess the rod condition properly before a decision is made.
Where the rod is damaged, the usual options are rechroming or replacement. On forklift cylinders the rods are relatively small and replacement rods are often not expensive, so a new rod can work out cheaper than grinding and replating the old one. On some lift cylinders the rod is not supplied as a separate part, and in that case the cylinder is replaced as a unit. Which way it goes depends on the machine, on parts availability and on the quotes involved.
Where the surface is still smooth and the leak is recent, a reseal is more likely to be worthwhile, and doing it sooner reduces the time the rod spends running against a failing seal.
Cylinders that have been leaking for a while are worth checking for contamination as well. When the wiper and the rod seal have both lost their sealing function, the gland can become a two way path, and dust and water can be drawn in as the rod retracts. Checking the hydraulic fluid and the return filter at that point is sensible. On a dusty site the tank breather is worth checking too, since it can be a larger source of contamination than the cylinder gland and costs very little to inspect.
Look at the yard fleet in the morning and note which trucks were parked with the mast raised, leaving the lift cylinder rods sitting out overnight. Changing that habit is a conversation with operators rather than a maintenance spend, which makes it one of the cheaper changes available on most dusty sites.
If a rod already has a score line and you are not sure whether it needs a reseal, a rechrome or a replacement, that call is easier to make early. That assessment is work for a qualified technician rather than something to judge from the ground. Hyundai Forklifts Australia technicians can assess rod condition through the dealer network, and your local dealer can advise on what is available in your area.
This article is general reference material about how cylinder seals wear in dusty conditions. It is not a maintenance instruction for any particular machine and it does not replace the operator and service manuals for your equipment. Any work on a hydraulic cylinder should be carried out by a qualified technician. Before repair work is booked, check with your dealer whether it is covered by the manufacturer’s warranty, since work done outside the approved process may affect what the manufacturer’s warranty covers.
Behind the dealer network sits a technical team at our head office with many years of hands on experience in forklifts. In the next article we will look at how that support works in practice, what the training covers, and how a site can get head office involved when a machine is not behaving the way it should.
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