The short answer
Trace the hoses and controls rather than counting couplers. Confirm whether flow is one-way or reversible, whether a low-pressure case drain returns independently to tank, and whether two attachment functions can operate at the same time. Then verify the result against the machine manual and a functional test.
Procedure
Complete the work in this order
- 01
Read the machine configuration
Use the model and serial number to obtain the correct hydraulic schematic or option list. Excavators of the same model can leave the factory with different auxiliary packages, and dealer-installed plumbing may not match the brochure for the base machine.
- 02
Trace each line
Follow the boom and stick plumbing from the valve area to the couplers. Identify supply, return, drain and any second auxiliary pair. A small line is not automatically a case drain, and a capped line is not proof that its valve and controls are installed.
- 03
Test direction and control
With a competent operator and safe connection, confirm which pedal, joystick button or monitor mode activates each port. Establish whether the circuit latches, reverses and proportions flow. Record whether another function can be used simultaneously.
- 04
Verify the drain path
A case drain should provide a low-restriction path to tank within the attachment manufacturer’s back-pressure limit. Confirm where it terminates and measure pressure if a piston motor depends on it. Never assume the normal return line performs the same function.
- 05
Create a circuit schedule
Write one page listing each port, coupler, control, direction, flow setting, pressure setting and drain limit. Give it to attachment suppliers with the carrier data so quotations are based on the installed machine rather than a generic tonne class.
The four arrangements buyers encounter
A one-way hammer circuit powers tools that require pressure in one direction and return oil in the other. A double-acting circuit reverses supply and return for cylinders or bidirectional motors. A case drain is a separate low-pressure leakage path for some motors. A dual auxiliary setup provides independent control for functions such as grip, saw and rotation.
Coupler count can mislead. A machine may have two large couplers for one reversible circuit, a small drain, and electrical controls that change behaviour by monitor mode. Conversely, hoses may be fitted along the boom without the valve section or software required to operate them. Function, not appearance, defines the circuit.
Translate attachment functions into circuits
List every action the head performs and which must occur together. A basic shear may need one double-acting function. A grinder may need a supply, unrestricted return and case drain. A grapple saw can require independent grip, saw and rotation so the operator maintains control of a section while cutting and placing it.
If functions are combined through diverter valves, ask what the operator loses during switching and how the safe state is maintained. A technically operable installation can still produce a slow or awkward cycle. The correct match covers simultaneous control, return limits and cooling as well as nominal litres per minute.
Common mistakes
Counting hoses
Hose quantity does not reveal direction, valve control or the path back to tank.
Calling every small line a drain
Pilot, leakage and auxiliary lines serve different purposes and pressure ratings.
Ignoring simultaneous functions
A diverter may make every function possible but prevent the productive sequence.
Trusting the model brochure
Optional and dealer-installed circuits vary within the same excavator model.
Continue the job
Measure auxiliary flow
Put verified numbers against the identified circuit.
Set up a case drain
Protect motors that require an independent drain path.
Grapple saw guide
See why multi-function heads expose circuit limitations.
