Diagnosis area
Boom, arm and cylinder functions
The working functions: drift, creep, jerky movement and every-function-at-once complaints.
Guides in this area (3)
Each guide lists the checks in the order a workshop should work through them, what each result means, and which parts usually solve it.
All functions slow
Boom, arm and cylinder functions
When travel, swing, boom and bucket are all slow, the fault sits upstream of the individual circuits.
Cylinder drifts down under load
Boom, arm and cylinder functions
Drift is a leakage question. These checks tell you whether oil is passing the piston seal, the control spool or the holding valve before…
Movement stutters or crawls when the lever is barely open
Boom, arm and cylinder functions
A function that moves smoothly at speed but stutters when the lever is barely open is fighting friction or air, not power.
The principle behind these symptoms (6)
Reading the mechanism first usually shortens the checklist.
Why extend and retract are not the same: valve control of a differential cylinder
Technical Guide
A single-rod cylinder is asymmetric, so speed and force differ in each direction.
Force against speed: matching the power element to the load, and why oversizing cooks the oil
Technical Guide
Matching means pressure times flow on the hydraulic side equals force times speed on the load side.
Why a hydraulic function overshoots and hunts: damping, correction and what you can change
Technical Guide
Every hydraulic loop needs correcting: gain buys speed but costs stability, and the damping ratio moves with temperature and air.
Same valve, different speed: what "the current controls the opening" really means
Technical Guide
A proportional valve controls an opening, not a flow. That one fact explains speed droop, why identical machines differ, and what to…
Speed droop, travel drift and run-away: what a velocity loop changes on a machine
Technical Guide
Open-loop throttle control droops with load and can run away downhill.
Spool valve lap and metering: why the same valve body feels different on two machines
Technical Guide
Lands, working edges, lap and metering area: how the geometry inside a spool valve decides whether a machine feels crisp, sluggish or will…
Units we supply for this topic (4)
Catalogue-verified units whose internals are the ones described above.
K3V112DTP
20–25 t hydraulic excavator
112 mL/r (per pump) · 34.3 MPa
K3V140S
industrial open circuits
140 mL/r · 34.3 MPa
K5V140DTP
27–33 t hydraulic excavator
140 mL/r (per pump) · 34.3 MPa
M5X180CHB
20–25 t hydraulic excavator
148.5 / 169.4 / 180.1 cm³ (motor variants) · 34.3 MPa
Parts that solve this (6)
Catalogue part lines from the same families. Search the full library by part number from the parts library.
3853802464
PISTON ASS'Y · pos. 011
2924530-0424
PISTON ASS'Y · pos. 011
29245300460
PISTON ASS'Y · pos. 011
29245300462
PISTON ASS'Y · pos. 011
2924530-0735
PISTON ASS'Y · pos. 011
2924530-0462
PISTON ASS'Y · pos. 011
Machines this applies to (6)
Machine pages that list the units above as fitment, model by model. See every machine →
SANY SY215
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
SANY SY225
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
VOLVO EC210B
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
VOLVO EC210D
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
DOOSAN DH220-5
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
HYUNDAI R220-5
Machine page
Pump, swing motor and travel assembly options for this machine, with the fitment list.
Other diagnosis areas
Pump and pressure supply
Pressure, delivery, wear and the pump-engine match: the guides that start at the source of the oil.
Swing, travel and drive assemblies
Motor and reduction-gear complaints: slow swing, weak travel, run-away, noise and metal in the gear oil.
Valve and pilot control
Spools, pilot pressure, proportional solenoids and pressure transients: the control layer between lever and load.
Oil, filtration and the system as a whole
Oil condition, water and air, cleanliness, climate and the system-level decisions that follow.