Forestry Machinery
Hydraulic Lift Cylinders
Harvester · Forwarder · Grapple

DELIMBER
ARM

4–8 double-acting lift cylinders that hold the delimbing knives against the tree trunk during the feed cycle. Each knife carrier is spring-loaded open and hydraulically closed — the lift cylinder maintains constant pressure against the tree surface as the feed rollers advance the tree. Bore: 40–63 mm. Stroke: short (80–200 mm). The delimber arm cylinders accumulate 200–500 full cycles per hour during normal production — 2 000–4 000 cycles per working day. HVOF rod coating and PU seals are mandatory at this cycle rate in the bark-particle environment.

FEED
ROLLER

2–4 double-acting lift cylinders that move the feed rollers to grip and advance the tree trunk through the head. The feed roller cylinder experiences the highest shock loads in the head — particularly when the tree hits a branch stub or knot that momentarily resists the feed force, then suddenly gives way. These impact events generate pressure spikes 3–5× the normal working pressure that must be absorbed by the system’s pressure relief valve without damaging the cylinder end-cap welds. Bore: 50–80 mm. Heavy-duty end-cap weld specification with NDT verification is required for machines working in high-knot-density softwood stands.

SAW BAR /
BUTT PLATE

The saw bar lift cylinder advances the chainsaw bar through the tree during the cross-cut stroke. Very short stroke (60–120 mm), high speed, extremely high pressure at the moment of cut initiation — the saw bar must accelerate rapidly from rest to full cutting speed. The butt plate lift cylinder aligns the cut log end against a measuring stop. Both positions are contaminated with sawdust, chain oil, and bark particles — comprehensive wiper specifications are essential on both lift cylinders.

Q01

Our harvester head delimber lift cylinders are leaking after only 3–4 weeks of summer operation — is HVOF rod coating really necessary?

Yes — 3–4 week seal life on delimber arm lift cylinders with standard chrome rods is the expected result in high-production summer softwood forestry. The bark particle contamination in a Norwegian or Swedish spruce stand during summer months is extremely abrasive — the bark scales are siliceous, with Mohs hardness of 5–6, well above the hardness of the chrome oxide layer on a hard chrome rod (approximately Mohs 4–5). The result is that the bark particles embed into the chrome surface within a few weeks, effectively converting the rod into a lapping tool that destroys the rod seal on every stroke. HVOF tungsten carbide at Mohs hardness 8–9 is harder than the bark particles and does not embed them — the particles are rejected by the hard, dense coating surface. Forestry OEMs who have switched their delimber lift cylinder specification to HVOF universally report a 4–8× increase in seal change interval, which fully justifies the 2–3× higher rod cost within a single season.

Q02

The regulations in the forests where we operate require biodegradable hydraulic fluid — which type is compatible with standard hydraulic lift cylinder seals?

HEES (synthetic ester) biodegradable fluids are the most commonly specified type for European forestry machinery under regulations such as the German Blue Angel standard and the Nordic Swan ecolabel. HEES fluids are incompatible with standard NBR seals — they cause swelling and softening of NBR elastomers that leads to seal extrusion within weeks of fluid change. The compatible seal materials for lift cylinder HEES operation are: EPDM (excellent — purpose-designed for ester compatibility), PTFE (excellent — chemically inert to all fluid types), and FKM/Viton (good in most HEES formulations, but verify with the specific fluid manufacturer as some ester-FKM combinations show minor swelling). Before converting from mineral oil to HEES, all NBR seals in the system must be replaced with EPDM equivalents. The conversion process: drain mineral oil, flush with a small volume of HEES, drain flush volume, refill with HEES, and monitor closely during the first 50 production hours for any evidence of seal weeping that may indicate incomplete seal replacement.

Q03

We operate in northern Canada at temperatures as low as −40°C in January — what do we need to change about our lift cylinder specification?

For −40°C operation, the standard specification requires changes to both the seal material and the hydraulic fluid. Standard PU seals begin to harden at −30°C and become brittle at −40°C — cold cracking during the first pressurisation of the day can cause immediate rod seal failure. Arctic-rated PU seals with low-temperature plasticisers rated to −50°C are the correct specification for sub-Arctic forestry lift cylinders. Alternatively, EPDM seals have better low-temperature flexibility than PU and maintain seal integrity to −55°C — ideal for the Canadian boreal forest winter season. For the hydraulic fluid: ISO 32 HV with a pour point below −45°C is the minimum specification for −40°C operation. Arctic synthetic hydraulic fluids with pour points below −60°C are available for the most extreme conditions. Even with the correct fluid specification, a 15-minute warm-up period at low engine speed before starting production operation is mandatory at temperatures below −25°C to allow the fluid to reach sufficient fluidity for the lift cylinder seals to function without the risk of dynamic seal damage from viscous fluid drag.

Q04

Can we source replacement harvester head delimber lift cylinders that are interchangeable with original OEM parts but with an upgraded HVOF rod specification?

Yes — aftermarket replacement delimber lift cylinders with HVOF rod coating and upgraded seal specifications are available as direct replacements for all major brands including John Deere, Komatsu Forest, Ponsse, and Logset. The bore, stroke, port positions, and collapsed/extended length are matched to the OEM drawing — the upgrades are internal rather than dimensional changes. When ordering, provide the harvester head model, the cylinder position (delimber arm, feed roller, or saw bar), and whether the machine uses mineral oil or HEES fluid. For machines being converted to HEES at the same time as the lift cylinder replacement, the upgrades should be ordered with EPDM seals and the conversion performed simultaneously to avoid running mismatched seal materials during the transition period.