Topic
Systems and control
Power elements and the loads they drive: matching, speed control, closed circuits, damping and the numbers that decide whether a drive lasts.
Articles in this topic (10)
Every article below is written from catalogue data, from the training material and from repair cases we handle.
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.
Swing, travel and the four quadrants: why a motor is not a cylinder
Technical Guide
A motor is symmetric, so speed and flow behave simply - but it works in four quadrants, and in two of them the load is in charge.
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.
Travel and swing drives: three numbers that decide whether a hydrostatic drive lasts
Technical Guide
Charge pressure, case drain flow and control response - measured hot - tell you whether a pump-controlled drive is healthy.
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.
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.
Flow gain, pressure gain and load matching: why a bigger pump is not faster
Technical Guide
Flow gain and pressure gain set sensitivity, stiffness and heat. How to read a valve pressure-flow curve, match a pump to the work it does…
Throttling or displacement control: where hydraulic energy becomes heat
Technical Guide
A valve-controlled system peaks near 38.5% efficiency with a fixed-displacement supply and about 66.7% with load sensing.
Closed-circuit hydrostatic drives: why travel and swing use pump control
Technical Guide
How a closed-circuit hydrostatic drive works: variable pump, motor, relief valves and charge pump; why it wastes less energy than a…
Four flow controls on one screen: negative, positive, LS and LUDV
Technical Guide
The same machine class can be built with four different pump-control philosophies, and they feel completely different at the levers when…
Diagnosis guides for this topic (10)
When the principle is clear, these are the checklists that start from the symptom.
Swing slow, weak or drifting to one side
Swing, travel and drive assemblies
Slewing feels sluggish or refuses to hold a load. Nine times out of ten it is not the whole swing assembly - this is the order to check…
Tracks weak, one side not moving
Swing, travel and drive assemblies
A travel fault looks expensive, but the checks are cheap. Work through them in this order before ordering a travel drive assembly.
No pressure / no power at the pump
Pump and pressure supply
No pressure is rarely the pump alone. Use this checklist to separate pump wear from control, suction and relief problems in under an hour.
Noise, vibration and rising oil temperature
Pump and pressure supply
Noise plus heat usually means air, starvation or internal leakage. Which one you have changes what you order.
Engine stalls or smokes under load
Pump and pressure supply
When the engine pulls down, the pump is usually asking for more torque than the engine can deliver.
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…
Case drain flow above specification
Pump and pressure supply
Case drain flow shows how worn a pump or motor is without removing it. Here is how to measure it so the number actually means something.
Final drive noisy or metal in gear oil
Swing, travel and drive assemblies
Noise from a travel reduction gear, or metal on the drain plug, has three usual sources.
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.
Units we supply for this topic (5)
Catalogue-verified units whose internals are the ones described above.
K3V112DTP
20–25 t hydraulic excavator
112 mL/r (per pump) · 34.3 MPa
K5V200DTH
40–45 t hydraulic excavator
200 mL/r (per pump) · 34.3 MPa
K3V280SH
large open-circuit equipment
280 mL/r · 34.3 MPa
M5X180CHB
20–25 t hydraulic excavator
148.5 / 169.4 / 180.1 cm³ (motor variants) · 34.3 MPa
FDNB08
5–6 t excavator
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 topics
Components and valves
Spools, pilot stages, windows and flow forces: why a valve behaves the way it does - and why two valves that look the…
Field diagnosis and maintenance
What to measure, when to measure it, and what the reading proves.
Industry, selection and buying
Where the technology came from, what the industry is betting on, and how to specify a replacement unit so that the part…